Before you say "it's all down to temperature" there are a few things I'd like to point out first. Firstly, I'm specifically talking about my particular system in this video, I'm not making general statements about all systems, as the orientation of your array will change the relative importance of different factors. For example, extra illumination from clouds is likely to be more important for North facing arrays than South facing. For our E/S split array I think it's an important factor, with temperature being less important, as I'll explain below. And, yes, of course temperature plays a part in solar panel generation levels, with some panels reducing their output by 0.5% for every degree of increased temperature (some are as low as 0.3% per degree). Some have suggested that this is why my sunny day peak values are lower than my cloudy day peak values. That may be a small factor in what I'm seeing in my data but I don't believe it's the dominant effect. For what I'm seeing to be down to temperature changes alone consider how much colder it would need to be to increase the 5 kW peak generation I'm seeing on a cloudless day up to nearly 7 kW when there are clouds around. Sure, temperature plays a part, but to get a 40% increase in power output (from 5 to 7 kW) the temperature difference would need to be huge (0.5% output change per deg difference = 80 deg!). Also consider that we have an E/W split array rated at 6.8 kWp, so it should be impossible for it to generate that much even on a freezing cold Summer's day, yet I'm seeing more than that on a typically mild, slightly cloudy, day in May. A South facing 6.8 kWp array may hit nearly 7 kW on a (cool) sunny day, but an E/W split array will max out at about 5 kW due to not ever fully facing the sun, as is the case in my data. It's not so much that I'm seeing reduced generation on a sunny day, it's that I'm seeing *extra* generation when there are a few clouds in the sky. The fact that my array is E/W split also means it'll not get as hot as South facing panels in the first place, and so will not suffer so much from reduced output on a sunny day. Finally, consider the generation curve I showed for June 12th, where it was sunny all morning up until 11 am when a cloud went in front of the sun. There was clear extra generation well above the level shown in the equivalent curve for the cloudless day, with a rapid increase just before the cloud moved over the sun. This increase in generation happened before the cloud could cool the panels. The panels experienced the same level of sun before 11am as on the cloudless day, so would be at a similar temperature on both days. That extra generation could not be caused by cooler panels, it could only come from increased illumination due to the scattering of light from the clouds. Once again, yes, temperature plays a part, but the data for my particular system cannot be explained by temperature alone. In this case I believe the extra illumination from the clouds is the dominant factor, not the temperature difference, which is only a minor factor at most. And once again, this won't necessarily be the same for all systems; for a South facing array temperature may be more important than extra illumination, and for a North facing array the extra illumination is probably going to be even more important than for my E/S split array.
I was just about to be the commenter who pointed to temperature but you make some great counter points! I like your theory and I've just flicked through my data for the days you've shown and I have a similar pattern! I've also wondered about windy days being able to cool the panels considerably.
@@UpsideDownFork I reckon you might find this happening even more for your NW array, as it'll benefit relatively more from scattered diffuse light. I'd be interested to see if that's the case!
We can sit around and talk about it, but the only way to answer the question is to gather some data. Like how much is the brightness changing? And how hot are the panels getting? You've done the temperature as an increase from minimum, not a decrease from maximum. 7kW peak power at 20°C STC with a (reasonably achievable) panel temp in direct sunlight of 65°C would be a dT of 45°C, and at 0.5% efficiency drop per °C, that's a 22.5% drop. That would be 5.4kW. That is ballpark correct. But it's more likely that it's a mix of both effects. I can't find any data on how much difference the edge of cloud effect is. I don't have a solar array on my roof, so I can't do my own test to correlate temperature and brightness to power output.
@@Leo99929 but you can't explain how a 6.8 kWp E/W split array can generate more than 6.8 kW using the temperature hypothesis, without going to extreme negative temperatures. You need extra illumination, it's as simple as that. Getting 5 kW from an E/W split 6.8 kWp array under normal Summer illumination at midday is about right (4.9 kW according to PVGIS), so I think the temperature argument is a red herring. The panels are no way getting that hot, simply because they are not facing the sun, what with them being E/W split. Temperature may have a small effect, I'm sure, but it is insufficient to explain the vast majority of the data I have already shown.
For my little DIY off grid solar setup with 350 watts of panels I get around 250 watts in full sun because the panels are so hot. I never see 350 watts unless the panels are cool. On partly cloudy days the panels get a chance to cool as clouds pass and then you get a peak when the sun comes out. The diffuse and reflected light also allow you to make more than the rated power so I've seen a peak of 391 watts on a above average day and only 307 watts on my best day so far. I think you'll get the most production on days that are bright with cloud morning and evening but with full sun around the middle of the day.
I wonder if the clouds drop the temperature of the panels, which would also contribute to the better efficiency when the sun the cones out again and hits the cooler surface? That said, the final curve definitely suggests that cloud reflection also bumps ups the generation. Great video as always!
Temperature has a big impact on the panel output. Watch when a cloud passes and the output of the panels which are cool will soar as the sun hits them, then drop a bit as they heat up. We live around 600m altitude where it can be very cold in winter. The panel output on a cold but sunny day (eg -5C) in March can be near max output, whereas yesterday it was nearly 30C and very sunny and output was around 80% of max capacity even with the sun being higher and the panels being angled better for summer as for a normal roof. But a longer day and clearer sky mean the total output for the day is better. This may not be so much of an issue in the UK where the temperature fluctuations are much lower. But yes, light dispersal in the cloud has an impact too, especially in non-south facing panels. Less impact of this on south facing panels.
I'm seeing nearly 7kW peak output with clouds but only 5kW peak output on a cloudless day, so I think in my case the extra illumination is the dominant effect here, although I expect temperature makes more of a difference in other scenarios.
It would be down to temperature also, panels don’t like to be hot and are less efficient the hotter it is, generally when there is cloud around its cooler so it will be allowing the panels too cool down instead of being in direct sunlight, then you’ll get a bit of a boost on the efficiency.
I have a small array of 6 x 385w panels on a SW facing roof with no shading, 2.31kWp. On days like you have shown I have noticed the array peaks above the 2.31kWs. One of those days on April 24th I had a peak of 2.99 kW, 30% above what my max should be. It normally does this around an hour before and after the solar noon. Nice to see someone else has noticed this.
Our best monthly production figures on our original 3kw array since 2012 have always been in April or May (south facing Lincolnshire). All panels lose efficiency once over a certain temperature so I believe that answers part of the question. We obviously get more hours of daylight in June and July and you would think that would generate more but our experience shows they consistently do not. A completely cloudless day in April or May has generated more than a completely cloudless day in the summer months. However, mixed scattered cloud on summer days has generated more than a cloudless day in April or May too,probably because the scattered or hazy clouds prevent the panel temperature from rising too high. However the total “record production months “ remain April or May for us.
I think temperature will play more of a part for whole day energy production (hence your high values in April/May), but I'm seeing 7kW peak output with clouds around but only 5kW peak on a cloudless day, so I don't think that huge peak increase is just down to temperature. Lots of factors at play, of course.
Is the higher output on cloudy days not down to temperature of panels? When there’s no clouds the panels reach higher temp than their optimum and hence you get lower output. When it’s cloudy it gives them a chance to cool down.
On a partially cloudy day the temperature of the panels won't be much different to full sun. Temperature certainly doesn't explain why my panels can output 5 kW on a full sun day but nearly 7 kW when there are a few clouds around! Temperature is important, of course, but I don't think it can lead to these super high spikes.
Higher generation peaks on scattered cloud days more likely down to panel heat level Tim, with panels being less efficient as they get hotter under consistent sunshine.
The sky is definitely brighter with a few clouds around though. And temperature alone wouldn't explain why I see nearly 7kW max power when there are clouds but only 5kW on a cloudless day.
Interesting observations. My west facing array produces significantly more generation with 100% cloud cover compared to a cloudless day for the first few hours when the panels are shaded. Unless it’s so dull nothing is produced 😊
I've heard people say similar about north facing panels; they may not receive sunlight directly, but do generate more on a slightly cloudy day than on a totally cloudless day when there's lots of sunlight but nothing to reflect it back onto the panels.
Your solar panels lose heat rapidly when clouds go over the sun making them more efficient. In the morning on my south westerly facing array, if it’s sunny I get a bit of solar generation but if it’s cloudy I get a lot more using refraction. The refraction of light is the bending of light rays as they pass from one medium to another, thereby changing the path of the rays. This is the water molecules in the clouds bouncing the suns light on to my panels. On a clear day in the morning no refraction less Solar, for me a cloudy day till 10am,then the sun with no clouds much better. Enjoy the show. Cheers
I think that you're mistaken. I've got optimizers which display the panel temperatures. These don't fluctuate wildly when clouds pass over. They tend to slowly heat up and cool down over the course of a day.
Why use optimizers when an SMA inverter will do it all for you. This is why SMA has developed a superior optimization technique - SMA ShadeFix. And the best thing about this solution is that SMA ShadeFix optimization is integrated into SMA inverters at no extra cost.
One of your optimisers goes down, full scaffolding to remove solar panels to change optimizer. Job goes into 4 figures very quickly for a part not required, just like having your appendix out, a pointless piece of equipment.
I see the high peaks before the clouds go over the panels too though, so it's not a case that the panels are cooled by the clouds first. Lots of variables at play, of course. And I'm seeing nearly 7kW with clouds and 5kW without, so I doubt temperature alone could explain that.
I think it could be to do with temperature as other people have mentioned. I lost quite a lot of generation on those 40c days we had a few years ago.. it was really clear to see. With clouds it may be more subtle
I agree temperature plays a part but I doubt it'd raise my max power output from 5kW on a cloudless day to nearly 7kW with a few clouds around on an otherwise very similar day, temperature wise.
I have noticed a similar effect in winter, when I have early morning shading from a neighbour’s roof. In bright winter sunshine, and hence well defined shadows, my system performs as you would expect, ie the whole string is clipped to the performance of the panels in shadow. However, on bright days, at the same time of day, with high, wispy clouds and virtually no discernible shadows, the system performs really well. I had therefore concluded that it is the contrast between the sunlit and shadowed areas of the panels that triggers the bypass diodes whereas even ambient light does not.
Also, if your inverter doesn't have active cooling, it's very likely a good idea to add some fans to get air moving around it. Almost anything is better than having a very hot inverter because the hot air around it isn't moving as much as you thought due to simple convection.
I imagine this is most important for systems that don't point south, when diffuse light causes some generation from the side that would normally be shaded. We also have an EW array, and have noticed that our daily generation is pretty consistent as the cloud increases, and only drops if it's actually raining.
Yes, I think you're spot on. I think this is also why North facing arrays are more effective than a lot of people realise, and often generate more on cloudy days than on sunny days due to the higher diffuse light levels, as you say.
I have noticed the same thing over the last 5 years since having extra panels added to my East facing roof. On a Sunny day, the 19th May, I max around 4.2 for an hour (Total solar 40.2kWh). However on a cloudy day, 26th May, I saw a max of 5.3kWh (Total solar 21.2kWh). I think of it as an old flourescent tube, when the cloud cover is light but sufficient to block the direct sunlight, so diffusion working well.
Three consecutive days in early July, UK azimuth 242 degrees, same time 08:00, same air temperature 18 degrees Celsius. Clear blue sky 100W. Thin bright white cloud filling sky 800W. Thick cloud 100W. The panels facing away from direct sunlight appear to benefit from the scattered light arriving perpendicular to the collectors give or take an angle. Scattered blue light from clear sky versus scattered brighter white ( ROYGBIV) from certain cloud structures, the latter wins hands down IMO. On your EW split system it would be interesting to look at unusual days in terms of their individual contributions to the total. One receiving direct sunlight at a near optimal angle and the other receiving scattered bright white which adds a boost to what a clear blue sky would offer could be a winner.
Yes, I definitely see a boost in the array facing away from the sun when there are clouds about, more so than for the array facing the sun itself. I think this is why North facing arrays do much better than some people would assume, especially in the UK!
I’m a few miles from you, Tim. 2 June was my best ever production 61.5kwh. My data isn’t as granular (every 15 mins I think according to the Solar Edge app) but recorded peak was 7.5kw. On 27 May: 48.5kwh, peak 8kw. Today I observed 10.7kw in real time from my mostly east/west 9.75kwp array. I like to think recent peaks are at least partly due to recently cleaned panels.
What about panel temperature? Clouds providing partial intermittent cover reduce average panel temperature, resulting in higher peak power output when the panels are fully illuminated?
I had watched this video from "Rosie does Engineering" ruclips.net/video/-dJixtZdkU0/видео.html and was expecting at least a 10% drop off with my in roof system as it runs hotter than an on roof. This does seem to be the case but not too bothered here as we don't get that hot for long and wanted the aesthetics of in roof. So I am with you and others here it is heat.
Temperature does have an impact, for sure, but I don't think it's sufficient to explain why I see nearly 7kW peak output with some clouds around but only 5kW on a cloudless day.
@@TimAndKatsGreenWalk I see your point. Even at a panel temp of 65°C, that could be 45°C above standard test conditions. At a worse case 0.5% less power per degree. That's only 22.5% less power. Assuming 7kW peak, the lowest the max should be on the hottest day in full direct sunlight would be ~5.4kW... Maybe it's a bit of both? Knowing the panel temps might help work out how much of what? Google does suggest that if the sun is clear, but the rest of the sky is white clouds, then they can reflect some of the scattered light back down to the ground, increasing solar generation. Here's the big question though: When you integrate the curve, what proportional difference is there on a completely clear day vs a "beneficially cloudy" day?
@@Leo99929 I added some more thoughts on this to my pinned comment. The E/W split array shouldn't ever reach the 6.8 kWp it's rated at due to orientation, yet I see more than this with clouds around. It's not about reducing the output on a sunny day, it's about adding extra output on a cloudy day. I think temperature plays a minor part at best in my case, it's dominated by the extra light from the cloud scattering, I believe. I mentioned in the video that whether this will ever give an overall benefit over a full day is doubtful, but I'll be keeping my eye on the data to see if it ever happens.
Yes, I have noticed that the edges of thin clouds do cause generation to spike and I have also seen the solar is performing better than I thought it would on some cloudy days too.
I thought this too but it's not sustained at that peak rate it's only for a few seconds when the sun comes out of the cloud so it doesn't really make much difference. It is documented online - Solar electricity production can also intensify for brief moments on cloudy days due to the “edge-of-cloud” effect, which occurs when cumulus clouds pass by the sun and their edges magnify sunlight, causing more powerful sunlight beams to reach solar panel surfaces.
Also the panels are less effective when hot and they cool down when the sun goes behind a cloud which is why they peak. In 12 years of owning a 9.8kw South facing array I've never seen a cloudy day produce more than a completely clear one.
Interesting observations. I see cloud induced improvement in solar generation in the mornings with my west facing array. In unbroken sun when my west roof is shaded my generation profile follows a very smooth profile (minimal generation). 100% cloud cover significantly boosts solar generation unless it is so dull that nothing is produced. The screenshot shows 2 days the solid line being the previous day with unbroken morning sun. The following day with patchy cloud cover
Yes, that was the point I was making. Higher instantaneous generation for sure but could you get higher generation over a full day? I need more data for that one.
It's the temperature of the panels, I have two panels on my shed that I use to charge my bike and hand tools and on a sunny day I can massively increase the output by spraying a hose on them, output goes down when temperature goes up
Temperature does play a part, yes, but the sky is definitely brighter when there are clouds around. It can be as hot on a slightly cloudy day as a full sun day too, of course. Lots of factors at play. And I get nearly 7kW with clouds around but 5kW on a cloudless day, so I doubt that's just temperature.
@@TimAndKatsGreenWalk I think temperature makes the biggest difference that's why on roof panels are better than in roof as you don't get the cool air at the back of them.
Interesting observation. Another factor to consider that affects your generation is the battery SoC. On a Gen 1 hybrid for example the max DC throughput is 6500W but the inverter max AC is 5000W. So if the battery is full the most generation you’ll get is 5kW as the rest gets clipped. If the battery isn’t full then the inverter can charge the battery eg at 1500W and export 5000W. I’m turning my charge rate down to 750W to maximise my solar generation and not fill the battery too early in the day
Yes, I only see those higher peaks when the battery is not yet full, so it's not getting clipped. When the battery is full I can see the clipping happening, although thankfully it's pretty rare for us.
I’ve seem the same observation. I get 7kw generation on a clear sunny cool day in May. But when I have direct sunshine, plus fluffy clouds near to the sun, then the output gets bumped up to 8kw (regardless of whether clouds are advancing or retreating). I suspect that’s due to extra light getting scattered off the clouds. However my best output is 9.5kw., but only for no more than a minute or so. This happens “after the rain”. I suspect that a combination of evaporative cooling and possibly some micro lensing is going on with the rain droplets.
Might be worth comparing inverter temperatures on the examples offered. During long, high generation periods, the inverter may be hitting 50C+ and potentially derating? During peaks and troughs, its not working as hard and therefore cooler?
40 deg max on the sunny day, 35 on the cloudy day. Not enough to see any derating (in fact I don't think I've ever seen my inverter derate even after force exporting at full power for three hours, when it gets to about 49 deg after two hours or so).
It might seem counter-intuitive, but it really is logical. Sunlight that was headed towards the ground kilometers away from you is instead scattered by white fluffy clouds and some of it ends up hitting your panels. Kind of like a really bad solar concentrator. As long as the clouds do this better than blue sky (and don't directly block the sun) you should see a benefit. Perhaps one could plan their solar setup with nearby flight corridors in mind to take advantage of this scattering effect from contrails.
Indeed. The only problem is that those same clouds can then block the sun too. I'm not yet sure if there's a point where minor cloud cover will give an overall benefit to total generation over a day, but I'm going to continue gathering data to see if a cloudy day ever does generate more in a day than a cloudless day.
I've noticed this overshoot when there are clouds about too, although it is rarely maintained for very long. I think another aspect of a cloudless day is that they normally occur under high pressure, when there is usually a fair amount of haze, dust or pollution in the atmosphere, which will block some of the sunshine in a more uniform way. In contrast, sunny intervals are often seen in lower pressure scenarios when the clear spells contain far fewer particles. You can often see this in the colour of the sky, when a clear sunny day has a much paler blue sky than the blue between scattered clouds.
@@TimAndKatsGreenWalk What's happening in the air is way more complex than OP has suggested. For instance the picture of the clouds you showed in the video was a cumulus cloud which would have been on a high pressure day but a thermal has broken through the temperature inversion that turns a clear day into a cloudy one. These thermic day mix the air up. Warm air ascends taking all the pollutants and cool clear will descend between the clouds.
Yes some bright cloud will increase the solar output, I notice in the evening when the sun has went so far north west that the sun is shining underneath the panels ie edge on , so some big bright cloud reflecting from the sw or se helps. The big swings during the day I believe has more to do with the resistance of the individual solar cells increasing as they get hot under the sun, when suddenly the cold cells get illuminated they will have a lower resistance and hence larger current flow. My 5.1 kwp will out put over 6kw at times, and during a really sunny warm day they produce around 4.5kw so panel temperature is a factor.
I'm seeing nearly 7kW with clouds around but only 5kW on a cloudless day. I doubt efficiency changes due to temperature could explain all of that. Some, for sure, but the extra illumination is the dominant factor, I think.
Interesting data! I've noticed similar behaviour when there's sunny days with rain showers, I have a 2.7Kw array (I usually see around 2-2.5Kw output) and have seen up to around 3.1Kw~ max output during rainy days, I guess it's most likely due to the rain cooling the panels off then the sun being at max straight after.
Temperature only changes panel efficiency by 0.5% per deg, so I don't think that's sufficient to explain my 7kW peak output with clouds around (no rain) but 5kW on a cloudless day. It'll have a small impact but I think the extra illumination is dominant in my case here.
Tim I have noticed in the mornings when the sun is from the east and we have a west array, if we have cloud this defuses the solar we generate more than if a blue sky
Yes, it's surprising how effective diffuse light can be for panels that are facing away from the sun. I think that's why North facing panels are surprisingly more effective than most people realise.
Same for us. With a WSW array, think we probably get more on a cloudy but otherwise bright morning (up to 1100ish) than with a cloudless sky. But have to caution that I don't have the figures to prove it. After that time any enhancement due to cloud is really hard to measure - we fairly regularly hit or exceed our kWp maximum output, normally when the sky is cloudless.
good video Tim and I have noticed this, we have had only had two clear days so far (pathetic !!) but never reached peak generation and what I have noticed is the same as you compared to say today which is like your pic. South facing here BTW. I also noticed on perfectly clear days it is a bit hazy.
There are many factors contributing to solar generation, of course, but I thought it was interesting to mention my observations. I hope you get a few more good days over the rest of the Summer!
Another thought: PVs produce power from certain wavelengths. Is more light from these wavelengths reaching your panels when scattered clouds are around?
I had my Air 2 Air installation Monday and was all done by Tuesday afternoon, So far im really pleased with it , so simple to install ATM i have it at 30 degrees and its only pulling 1kw , The Gas meter has gone and im waiting for another Tesla Powerwall 2 . the sky here today is the same and i keep going up to 5kw , Snow can also be good for panels too .
Good to hear. I hear that snow covered ground is great for boosting the output of vertically mounted bi-facial panels. Although I'm not sure how much it'd help roof mounted panels. I'd be interested to find out though.
Snow has always been terrible for our roof mounted panels. It can be a lovely bright day when they should be generating nearly 2kw but they're actually doing less than 50 watts 😢
@philhimsworth its a shame that there isnt a heating element built-in for this scenario. I guess it wouldnt be worthwhile from a cost point of view as it would likely get little use in the UK....but would likely benefit other snow-rich countries. I wonder how Scandinavian countries deal with snow on their panels? Or is solar not a thing there?
I think panel temperature is a red herring. Your example is of a morning that had no cloud cover up to the point you took the photo/measurement, so the panel temperature should be no different to the fondant(?) day. I often see the same. Panel temperature only has a significant effect on hot days when the panels are in the sun all day. Is it maybe due to a meteorological effect? Are the clouds a symptom of water vapour being concentrated (in the clouds) making the clear skies in between clearer than on a cloudless day?
I agree temperature can't explain all of my observations, especially getting nearly 7kW max power with clouds around but only 5kW max on a cloudless day.
From Google Gemini: Cumulus clouds are a sign of generally fair weather conditions.This often means there's less dust and haze in the atmosphere, which can actually make the sky appear a clearer blue compared to a day with high humidity or pollution.
@@TimAndKatsGreenWalk If the temp in the shade that day was 28 c, the black panels would be 50-60 c. maybe even 70 in an all day long cloudless full sun day.
@@jimpilot330 look at the curve for the day I showed on the day of recording (12th June). The generation was increasing above the expected curve well before any cloud covered the panel, so the temperature of the panels would be the same as a cloudless day up to that point, yet the generation was significantly higher. And bear in mind this is the UK and our panels are E/W facing, so will never experience the extreme levels of temperature you're talking about, even on a fully sunny day.
Don't think weve seen a perfectly cloudless day in Lincolnshire this year 😢 "For every degree Celsius above 25°C (77°F), a solar panel’s efficiency typically declines by 0.3% to 0.5%" Actually if that is correct then it can't be down to temp hmm.
Quite. It'd have a small impact, for sure, but not enough to go from 5kW on a cloudless day up to nearly 7kW with some clouds around. I'm sure you'll get one or two cloudless days at some point! Hopefully!
Ideally you need diffused sun in the shading period and full sun the rest of the day. I get better generation in winter during shaded periods when it's not full sun. I think it's because the shading is not an issue when the light is defused but is pronounced when full sun hits half a panel and they shut down
Yes, any panels in the shade will certainly benefit from diffuse ambient light. I think that's why North facing panels actually do a lot better then most people would assume.
I have some panels on my garage roof, SW facing, but in the hard shade of the house until lunchtime. These panels can produce more on cloudy mornings with diffuse light, as long as the cloud cover isn't too heavy.
Tim. I've been looking for a way to make my fortune in a sustainable and ethical way. I think I've spotted how to do it. Instead of rushing out with a hose pipe to water solar panels, could you develop an integrated sprayer system to do this? One which watered the panels when they got too hot and stopped watering when they'd cooled down? Of course, it would require three people's input. Someone to work out whether it would be worth it, by trialling with a hose pipe. Right up your street. Someone to do the electrical and water stuff. There's bound to be someone reading this who could develop a prototype on a sunny Saturday morning. And Someone to come up with the idea. Me.😂
Would making the panels wet, so covered with a film of water, reduce the light they get coming through to use? May be as useful to wet the roof tiles below as they will be acting like storage heaters.
I think water cooled panels do exist, actually, with the heated water also being used too. Not sure where I saw that, possibly the Just Have A Think channel.
@@TimAndKatsGreenWalk It's both the cloud effect and the temperature of the panels. That's why you get big differences. Unfortunately for people in Canada and Scandinavia these effects can literally fry the equipment if temperature and cloud effects are not taken into account when designing the systems.
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Before you say "it's all down to temperature" there are a few things I'd like to point out first.
Firstly, I'm specifically talking about my particular system in this video, I'm not making general statements about all systems, as the orientation of your array will change the relative importance of different factors. For example, extra illumination from clouds is likely to be more important for North facing arrays than South facing. For our E/S split array I think it's an important factor, with temperature being less important, as I'll explain below.
And, yes, of course temperature plays a part in solar panel generation levels, with some panels reducing their output by 0.5% for every degree of increased temperature (some are as low as 0.3% per degree). Some have suggested that this is why my sunny day peak values are lower than my cloudy day peak values. That may be a small factor in what I'm seeing in my data but I don't believe it's the dominant effect.
For what I'm seeing to be down to temperature changes alone consider how much colder it would need to be to increase the 5 kW peak generation I'm seeing on a cloudless day up to nearly 7 kW when there are clouds around. Sure, temperature plays a part, but to get a 40% increase in power output (from 5 to 7 kW) the temperature difference would need to be huge (0.5% output change per deg difference = 80 deg!).
Also consider that we have an E/W split array rated at 6.8 kWp, so it should be impossible for it to generate that much even on a freezing cold Summer's day, yet I'm seeing more than that on a typically mild, slightly cloudy, day in May. A South facing 6.8 kWp array may hit nearly 7 kW on a (cool) sunny day, but an E/W split array will max out at about 5 kW due to not ever fully facing the sun, as is the case in my data. It's not so much that I'm seeing reduced generation on a sunny day, it's that I'm seeing *extra* generation when there are a few clouds in the sky. The fact that my array is E/W split also means it'll not get as hot as South facing panels in the first place, and so will not suffer so much from reduced output on a sunny day.
Finally, consider the generation curve I showed for June 12th, where it was sunny all morning up until 11 am when a cloud went in front of the sun. There was clear extra generation well above the level shown in the equivalent curve for the cloudless day, with a rapid increase just before the cloud moved over the sun. This increase in generation happened before the cloud could cool the panels. The panels experienced the same level of sun before 11am as on the cloudless day, so would be at a similar temperature on both days. That extra generation could not be caused by cooler panels, it could only come from increased illumination due to the scattering of light from the clouds.
Once again, yes, temperature plays a part, but the data for my particular system cannot be explained by temperature alone. In this case I believe the extra illumination from the clouds is the dominant factor, not the temperature difference, which is only a minor factor at most. And once again, this won't necessarily be the same for all systems; for a South facing array temperature may be more important than extra illumination, and for a North facing array the extra illumination is probably going to be even more important than for my E/S split array.
I was just about to be the commenter who pointed to temperature but you make some great counter points!
I like your theory and I've just flicked through my data for the days you've shown and I have a similar pattern!
I've also wondered about windy days being able to cool the panels considerably.
@@UpsideDownFork I reckon you might find this happening even more for your NW array, as it'll benefit relatively more from scattered diffuse light. I'd be interested to see if that's the case!
We can sit around and talk about it, but the only way to answer the question is to gather some data. Like how much is the brightness changing? And how hot are the panels getting?
You've done the temperature as an increase from minimum, not a decrease from maximum. 7kW peak power at 20°C STC with a (reasonably achievable) panel temp in direct sunlight of 65°C would be a dT of 45°C, and at 0.5% efficiency drop per °C, that's a 22.5% drop. That would be 5.4kW. That is ballpark correct.
But it's more likely that it's a mix of both effects.
I can't find any data on how much difference the edge of cloud effect is. I don't have a solar array on my roof, so I can't do my own test to correlate temperature and brightness to power output.
@@Leo99929 but you can't explain how a 6.8 kWp E/W split array can generate more than 6.8 kW using the temperature hypothesis, without going to extreme negative temperatures. You need extra illumination, it's as simple as that. Getting 5 kW from an E/W split 6.8 kWp array under normal Summer illumination at midday is about right (4.9 kW according to PVGIS), so I think the temperature argument is a red herring. The panels are no way getting that hot, simply because they are not facing the sun, what with them being E/W split. Temperature may have a small effect, I'm sure, but it is insufficient to explain the vast majority of the data I have already shown.
For my little DIY off grid solar setup with 350 watts of panels I get around 250 watts in full sun because the panels are so hot. I never see 350 watts unless the panels are cool. On partly cloudy days the panels get a chance to cool as clouds pass and then you get a peak when the sun comes out. The diffuse and reflected light also allow you to make more than the rated power so I've seen a peak of 391 watts on a above average day and only 307 watts on my best day so far. I think you'll get the most production on days that are bright with cloud morning and evening but with full sun around the middle of the day.
I wonder if the clouds drop the temperature of the panels, which would also contribute to the better efficiency when the sun the cones out again and hits the cooler surface? That said, the final curve definitely suggests that cloud reflection also bumps ups the generation. Great video as always!
Yup, temperature is important but I doubt the efficiency gain would account for nearly 7kW with clouds, but 5kw without. It's all very interesting!
@@TimAndKatsGreenWalk I agree, the reflection from the clouds must play an important role - who knew?! 😁
Temperature has a big impact on the panel output. Watch when a cloud passes and the output of the panels which are cool will soar as the sun hits them, then drop a bit as they heat up. We live around 600m altitude where it can be very cold in winter. The panel output on a cold but sunny day (eg -5C) in March can be near max output, whereas yesterday it was nearly 30C and very sunny and output was around 80% of max capacity even with the sun being higher and the panels being angled better for summer as for a normal roof. But a longer day and clearer sky mean the total output for the day is better. This may not be so much of an issue in the UK where the temperature fluctuations are much lower.
But yes, light dispersal in the cloud has an impact too, especially in non-south facing panels. Less impact of this on south facing panels.
I'm seeing nearly 7kW peak output with clouds but only 5kW peak output on a cloudless day, so I think in my case the extra illumination is the dominant effect here, although I expect temperature makes more of a difference in other scenarios.
Another thought-provoking video, Tim!
It would be down to temperature also, panels don’t like to be hot and are less efficient the hotter it is, generally when there is cloud around its cooler so it will be allowing the panels too cool down instead of being in direct sunlight, then you’ll get a bit of a boost on the efficiency.
Temperature is a factor, for sure, but I doubt it could explain why I see nearly 7kw max power with clouds around but only 5kW on a cloudless day.
I have a small array of 6 x 385w panels on a SW facing roof with no shading, 2.31kWp. On days like you have shown I have noticed the array peaks above the 2.31kWs. One of those days on April 24th I had a peak of 2.99 kW, 30% above what my max should be. It normally does this around an hour before and after the solar noon. Nice to see someone else has noticed this.
Ah ha! Great to see you've made the same observation.
Our best monthly production figures on our original 3kw array since 2012 have always been in April or May (south facing Lincolnshire). All panels lose efficiency once over a certain temperature so I believe that answers part of the question. We obviously get more hours of daylight in June and July and you would think that would generate more but our experience shows they consistently do not.
A completely cloudless day in April or May has generated more than a completely cloudless day in the summer months. However, mixed scattered cloud on summer days has generated more than a cloudless day in April or May too,probably because the scattered or hazy clouds prevent the panel temperature from rising too high. However the total “record production months “ remain April or May for us.
I think temperature will play more of a part for whole day energy production (hence your high values in April/May), but I'm seeing 7kW peak output with clouds around but only 5kW peak on a cloudless day, so I don't think that huge peak increase is just down to temperature. Lots of factors at play, of course.
Is the higher output on cloudy days not down to temperature of panels? When there’s no clouds the panels reach higher temp than their optimum and hence you get lower output. When it’s cloudy it gives them a chance to cool down.
On a partially cloudy day the temperature of the panels won't be much different to full sun. Temperature certainly doesn't explain why my panels can output 5 kW on a full sun day but nearly 7 kW when there are a few clouds around! Temperature is important, of course, but I don't think it can lead to these super high spikes.
Higher generation peaks on scattered cloud days more likely down to panel heat level Tim, with panels being less efficient as they get hotter under consistent sunshine.
The sky is definitely brighter with a few clouds around though. And temperature alone wouldn't explain why I see nearly 7kW max power when there are clouds but only 5kW on a cloudless day.
Interesting observations. My west facing array produces significantly more generation with 100% cloud cover compared to a cloudless day for the first few hours when the panels are shaded. Unless it’s so dull nothing is produced 😊
Same here. SW facing and shaded in the mornings.
There's got to be a sweet spot, I reckon.
I've heard people say similar about north facing panels; they may not receive sunlight directly, but do generate more on a slightly cloudy day than on a totally cloudless day when there's lots of sunlight but nothing to reflect it back onto the panels.
Yup, I think that's why North facing panels generate more than most people would assume.
Your solar panels lose heat rapidly when clouds go over the sun making them more efficient. In the morning on my south westerly facing array, if it’s sunny I get a bit of solar generation but if it’s cloudy I get a lot more using refraction. The refraction of light is the bending of light rays as they pass from one medium to another, thereby changing the path of the rays. This is the water molecules in the clouds bouncing the suns light on to my panels. On a clear day in the morning no refraction less Solar, for me a cloudy day till 10am,then the sun with no clouds much better. Enjoy the show. Cheers
I think that you're mistaken. I've got optimizers which display the panel temperatures. These don't fluctuate wildly when clouds pass over. They tend to slowly heat up and cool down over the course of a day.
Why use optimizers when an SMA inverter will do it all for you. This is why SMA has developed a superior optimization technique - SMA ShadeFix. And the best thing about this solution is that SMA ShadeFix optimization is integrated into SMA inverters at no extra cost.
One of your optimisers goes down, full scaffolding to remove solar panels to change optimizer. Job goes into 4 figures very quickly for a part not required, just like having your appendix out, a pointless piece of equipment.
I see the high peaks before the clouds go over the panels too though, so it's not a case that the panels are cooled by the clouds first. Lots of variables at play, of course. And I'm seeing nearly 7kW with clouds and 5kW without, so I doubt temperature alone could explain that.
Your observation 'reflects' our experience.....
Very good! I approve.
Alto strata days are very good too. (High clouds), cool and bright.
Yup, they sure are.
I think it could be to do with temperature as other people have mentioned. I lost quite a lot of generation on those 40c days we had a few years ago.. it was really clear to see. With clouds it may be more subtle
I agree temperature plays a part but I doubt it'd raise my max power output from 5kW on a cloudless day to nearly 7kW with a few clouds around on an otherwise very similar day, temperature wise.
I have noticed a similar effect in winter, when I have early morning shading from a neighbour’s roof. In bright winter sunshine, and hence well defined shadows, my system performs as you would expect, ie the whole string is clipped to the performance of the panels in shadow.
However, on bright days, at the same time of day, with high, wispy clouds and virtually no discernible shadows, the system performs really well. I had therefore concluded that it is the contrast between the sunlit and shadowed areas of the panels that triggers the bypass diodes whereas even ambient light does not.
Yes, quite possibly.
Also, if your inverter doesn't have active cooling, it's very likely a good idea to add some fans to get air moving around it. Almost anything is better than having a very hot inverter because the hot air around it isn't moving as much as you thought due to simple convection.
My inverter is pretty good at temperature control.
I imagine this is most important for systems that don't point south, when diffuse light causes some generation from the side that would normally be shaded. We also have an EW array, and have noticed that our daily generation is pretty consistent as the cloud increases, and only drops if it's actually raining.
Yes, I think you're spot on. I think this is also why North facing arrays are more effective than a lot of people realise, and often generate more on cloudy days than on sunny days due to the higher diffuse light levels, as you say.
I have noticed the same thing over the last 5 years since having extra panels added to my East facing roof. On a Sunny day, the 19th May, I max around 4.2 for an hour (Total solar 40.2kWh). However on a cloudy day, 26th May, I saw a max of 5.3kWh (Total solar 21.2kWh).
I think of it as an old flourescent tube, when the cloud cover is light but sufficient to block the direct sunlight, so diffusion working well.
That's a good analogy.
Three consecutive days in early July, UK azimuth 242 degrees, same time 08:00, same air temperature 18 degrees Celsius. Clear blue sky 100W. Thin bright white cloud filling sky 800W. Thick cloud 100W.
The panels facing away from direct sunlight appear to benefit from the scattered light arriving perpendicular to the collectors give or take an angle. Scattered blue light from clear sky versus scattered brighter white ( ROYGBIV) from certain cloud structures, the latter wins hands down IMO.
On your EW split system it would be interesting to look at unusual days in terms of their individual contributions to the total. One receiving direct sunlight at a near optimal angle and the other receiving scattered bright white which adds a boost to what a clear blue sky would offer could be a winner.
Yes, I definitely see a boost in the array facing away from the sun when there are clouds about, more so than for the array facing the sun itself. I think this is why North facing arrays do much better than some people would assume, especially in the UK!
I’m a few miles from you, Tim. 2 June was my best ever production 61.5kwh. My data isn’t as granular (every 15 mins I think according to the Solar Edge app) but recorded peak was 7.5kw. On 27 May: 48.5kwh, peak 8kw. Today I observed 10.7kw in real time from my mostly east/west 9.75kwp array. I like to think recent peaks are at least partly due to recently cleaned panels.
Crikey, yeah, getting over 10 kW from an E/W split 9.75 kWp array is impressive. Sounds similar to what I'm seeing. I'm sure clean panels can't hurt.
What about panel temperature? Clouds providing partial intermittent cover reduce average panel temperature, resulting in higher peak power output when the panels are fully illuminated?
I had watched this video from "Rosie does Engineering" ruclips.net/video/-dJixtZdkU0/видео.html and was expecting at least a 10% drop off with my in roof system as it runs hotter than an on roof. This does seem to be the case but not too bothered here as we don't get that hot for long and wanted the aesthetics of in roof. So I am with you and others here it is heat.
Temperature does have an impact, for sure, but I don't think it's sufficient to explain why I see nearly 7kW peak output with some clouds around but only 5kW on a cloudless day.
@@TimAndKatsGreenWalk I see your point. Even at a panel temp of 65°C, that could be 45°C above standard test conditions. At a worse case 0.5% less power per degree. That's only 22.5% less power. Assuming 7kW peak, the lowest the max should be on the hottest day in full direct sunlight would be ~5.4kW...
Maybe it's a bit of both? Knowing the panel temps might help work out how much of what?
Google does suggest that if the sun is clear, but the rest of the sky is white clouds, then they can reflect some of the scattered light back down to the ground, increasing solar generation.
Here's the big question though: When you integrate the curve, what proportional difference is there on a completely clear day vs a "beneficially cloudy" day?
@@Leo99929 I added some more thoughts on this to my pinned comment. The E/W split array shouldn't ever reach the 6.8 kWp it's rated at due to orientation, yet I see more than this with clouds around. It's not about reducing the output on a sunny day, it's about adding extra output on a cloudy day. I think temperature plays a minor part at best in my case, it's dominated by the extra light from the cloud scattering, I believe. I mentioned in the video that whether this will ever give an overall benefit over a full day is doubtful, but I'll be keeping my eye on the data to see if it ever happens.
Yes, I have noticed that the edges of thin clouds do cause generation to spike and I have also seen the solar is performing better than I thought it would on some cloudy days too.
Cool. I'm curious to see if I ever get more generation in total over a full day when there are clouds around vs a cloudless day.
I thought this too but it's not sustained at that peak rate it's only for a few seconds when the sun comes out of the cloud so it doesn't really make much difference. It is documented online -
Solar electricity production can also intensify for brief moments on cloudy days due to the “edge-of-cloud” effect, which occurs when cumulus clouds pass by the sun and their edges magnify sunlight, causing more powerful sunlight beams to reach solar panel surfaces.
Also the panels are less effective when hot and they cool down when the sun goes behind a cloud which is why they peak. In 12 years of owning a 9.8kw South facing array I've never seen a cloudy day produce more than a completely clear one.
Interesting observations. I see cloud induced improvement in solar generation in the mornings with my west facing array. In unbroken sun when my west roof is shaded my generation profile follows a very smooth profile (minimal generation). 100% cloud cover significantly boosts solar generation unless it is so dull that nothing is produced. The screenshot shows 2 days the solid line being the previous day with unbroken morning sun. The following day with patchy cloud cover
Yes, that was the point I was making. Higher instantaneous generation for sure but could you get higher generation over a full day? I need more data for that one.
It's the temperature of the panels, I have two panels on my shed that I use to charge my bike and hand tools and on a sunny day I can massively increase the output by spraying a hose on them, output goes down when temperature goes up
Temperature does play a part, yes, but the sky is definitely brighter when there are clouds around. It can be as hot on a slightly cloudy day as a full sun day too, of course. Lots of factors at play. And I get nearly 7kW with clouds around but 5kW on a cloudless day, so I doubt that's just temperature.
@@TimAndKatsGreenWalk I think temperature makes the biggest difference that's why on roof panels are better than in roof as you don't get the cool air at the back of them.
@@terrymackenzie6784 0.5% efficiency drop per deg increase in temp. Enough to go from 5kW to 7kW? That's an 80 deg difference required.
Interesting observation. Another factor to consider that affects your generation is the battery SoC. On a Gen 1 hybrid for example the max DC throughput is 6500W but the inverter max AC is 5000W. So if the battery is full the most generation you’ll get is 5kW as the rest gets clipped. If the battery isn’t full then the inverter can charge the battery eg at 1500W and export 5000W. I’m turning my charge rate down to 750W to maximise my solar generation and not fill the battery too early in the day
Yes, I only see those higher peaks when the battery is not yet full, so it's not getting clipped. When the battery is full I can see the clipping happening, although thankfully it's pretty rare for us.
Interesting thoughts and observations, thanks for sharing
No problem. I sometimes think I spend too much time looking at my data.
Yes it's always the case also the panels will be cooler that also helps but sooner have a totally sunny day.
The day can be just as hot when there are some clouds as on a fully sunny day. It's not all down to how much sun there is. Cold and sunny FTW.
I’ve seem the same observation. I get 7kw generation on a clear sunny cool day in May.
But when I have direct sunshine, plus fluffy clouds near to the sun, then the output gets bumped up to 8kw (regardless of whether clouds are advancing or retreating). I suspect that’s due to extra light getting scattered off the clouds.
However my best output is 9.5kw., but only for no more than a minute or so. This happens “after the rain”. I suspect that a combination of evaporative cooling and possibly some micro lensing is going on with the rain droplets.
Micro lensing is an interesting thought. I'll have to keep an eye out the next time we get rain to see if I get a similar effect to you.
Might be worth comparing inverter temperatures on the examples offered. During long, high generation periods, the inverter may be hitting 50C+ and potentially derating? During peaks and troughs, its not working as hard and therefore cooler?
40 deg max on the sunny day, 35 on the cloudy day. Not enough to see any derating (in fact I don't think I've ever seen my inverter derate even after force exporting at full power for three hours, when it gets to about 49 deg after two hours or so).
It might seem counter-intuitive, but it really is logical. Sunlight that was headed towards the ground kilometers away from you is instead scattered by white fluffy clouds and some of it ends up hitting your panels. Kind of like a really bad solar concentrator. As long as the clouds do this better than blue sky (and don't directly block the sun) you should see a benefit.
Perhaps one could plan their solar setup with nearby flight corridors in mind to take advantage of this scattering effect from contrails.
Indeed. The only problem is that those same clouds can then block the sun too. I'm not yet sure if there's a point where minor cloud cover will give an overall benefit to total generation over a day, but I'm going to continue gathering data to see if a cloudy day ever does generate more in a day than a cloudless day.
I've noticed this overshoot when there are clouds about too, although it is rarely maintained for very long. I think another aspect of a cloudless day is that they normally occur under high pressure, when there is usually a fair amount of haze, dust or pollution in the atmosphere, which will block some of the sunshine in a more uniform way. In contrast, sunny intervals are often seen in lower pressure scenarios when the clear spells contain far fewer particles. You can often see this in the colour of the sky, when a clear sunny day has a much paler blue sky than the blue between scattered clouds.
Yes, there are many many factors at play, for sure. It's all very interesting.
@@TimAndKatsGreenWalk What's happening in the air is way more complex than OP has suggested. For instance the picture of the clouds you showed in the video was a cumulus cloud which would have been on a high pressure day but a thermal has broken through the temperature inversion that turns a clear day into a cloudy one. These thermic day mix the air up. Warm air ascends taking all the pollutants and cool clear will descend between the clouds.
Yes some bright cloud will increase the solar output, I notice in the evening when the sun has went so far north west that the sun is shining underneath the panels ie edge on , so some big bright cloud reflecting from the sw or se helps.
The big swings during the day I believe has more to do with the resistance of the individual solar cells increasing as they get hot under the sun, when suddenly the cold cells get illuminated they will have a lower resistance and hence larger current flow.
My 5.1 kwp will out put over 6kw at times, and during a really sunny warm day they produce around 4.5kw so panel temperature is a factor.
I'm seeing nearly 7kW with clouds around but only 5kW on a cloudless day. I doubt efficiency changes due to temperature could explain all of that. Some, for sure, but the extra illumination is the dominant factor, I think.
Interesting data! I've noticed similar behaviour when there's sunny days with rain showers, I have a 2.7Kw array (I usually see around 2-2.5Kw output) and have seen up to around 3.1Kw~ max output during rainy days, I guess it's most likely due to the rain cooling the panels off then the sun being at max straight after.
Temperature only changes panel efficiency by 0.5% per deg, so I don't think that's sufficient to explain my 7kW peak output with clouds around (no rain) but 5kW on a cloudless day. It'll have a small impact but I think the extra illumination is dominant in my case here.
@@TimAndKatsGreenWalk Yeah, I agree with you 👍
Tim I have noticed in the mornings when the sun is from the east and we have a west array, if we have cloud this defuses the solar we generate more than if a blue sky
Yes, it's surprising how effective diffuse light can be for panels that are facing away from the sun. I think that's why North facing panels are surprisingly more effective than most people realise.
Same for us. With a WSW array, think we probably get more on a cloudy but otherwise bright morning (up to 1100ish) than with a cloudless sky. But have to caution that I don't have the figures to prove it. After that time any enhancement due to cloud is really hard to measure - we fairly regularly hit or exceed our kWp maximum output, normally when the sky is cloudless.
good video Tim and I have noticed this, we have had only had two clear days so far (pathetic !!) but never reached peak generation and what I have noticed is the same as you compared to say today which is like your pic. South facing here BTW. I also noticed on perfectly clear days it is a bit hazy.
There are many factors contributing to solar generation, of course, but I thought it was interesting to mention my observations. I hope you get a few more good days over the rest of the Summer!
@@TimAndKatsGreenWalk today here was my third best this year so thats something !! but 20% down on a fair estimate I had for this month !!
Another thought: PVs produce power from certain wavelengths. Is more light from these wavelengths reaching your panels when scattered clouds are around?
Possibly.
We have a 6kWp system, almost south facing, but have been seeing 7.5kW at times, a whole 25% over specified capacity.
Wow!
I had my Air 2 Air installation Monday and was all done by Tuesday afternoon, So far im really pleased with it , so simple to install ATM i have it at 30 degrees and its only pulling 1kw , The Gas meter has gone and im waiting for another Tesla Powerwall 2 .
the sky here today is the same and i keep going up to 5kw , Snow can also be good for panels too .
Good to hear. I hear that snow covered ground is great for boosting the output of vertically mounted bi-facial panels. Although I'm not sure how much it'd help roof mounted panels. I'd be interested to find out though.
@@TimAndKatsGreenWalk Snow also melts on solar panels, ive watched the other houses in my street .
Snow has always been terrible for our roof mounted panels. It can be a lovely bright day when they should be generating nearly 2kw but they're actually doing less than 50 watts 😢
@philhimsworth its a shame that there isnt a heating element built-in for this scenario.
I guess it wouldnt be worthwhile from a cost point of view as it would likely get little use in the UK....but would likely benefit other snow-rich countries.
I wonder how Scandinavian countries deal with snow on their panels? Or is solar not a thing there?
@@David-bl1bt i saw a long time ago that as soon as UV passes through the snow the panels warm up and the snow slides off the panels .
I think panel temperature is a red herring. Your example is of a morning that had no cloud cover up to the point you took the photo/measurement, so the panel temperature should be no different to the fondant(?) day.
I often see the same.
Panel temperature only has a significant effect on hot days when the panels are in the sun all day.
Is it maybe due to a meteorological effect? Are the clouds a symptom of water vapour being concentrated (in the clouds) making the clear skies in between clearer than on a cloudless day?
See my later comment from Google Gemini, stating that there's possibly less dust and haze in the atmosphere on these days.
At first I also thought it would be temperature, before I saw the same fondant-day build up to the peak he showed on the graph. I think you are right.
I agree temperature can't explain all of my observations, especially getting nearly 7kW max power with clouds around but only 5kW max on a cloudless day.
From Google Gemini:
Cumulus clouds are a sign of generally fair weather conditions.This often means there's less dust and haze in the atmosphere, which can actually make the sky appear a clearer blue compared to a day with high humidity or pollution.
Hmm, interesting. Clearly lots of variables at play!
I have noticed the exact same. However, I've chalked it down to cooler panels, getting shade from the relentless sun.
But I doubt that's enough to increase my peak power output from 5kW on a cloudless day to 7kW when there are some clouds around.
It's widely accepted that high temperatures can reduce output by 20-30%
@@heshamthearab see my pinned comment. The temperature difference would need to be 80 deg to account for my observations.
@@TimAndKatsGreenWalk If the temp in the shade that day was 28 c, the black panels would be 50-60 c. maybe even 70 in an all day long cloudless full sun day.
@@jimpilot330 look at the curve for the day I showed on the day of recording (12th June). The generation was increasing above the expected curve well before any cloud covered the panel, so the temperature of the panels would be the same as a cloudless day up to that point, yet the generation was significantly higher. And bear in mind this is the UK and our panels are E/W facing, so will never experience the extreme levels of temperature you're talking about, even on a fully sunny day.
Don't think weve seen a perfectly cloudless day in Lincolnshire this year 😢
"For every degree Celsius above 25°C (77°F), a solar panel’s efficiency typically declines by 0.3% to 0.5%"
Actually if that is correct then it can't be down to temp hmm.
Quite. It'd have a small impact, for sure, but not enough to go from 5kW on a cloudless day up to nearly 7kW with some clouds around. I'm sure you'll get one or two cloudless days at some point! Hopefully!
Ideally you need diffused sun in the shading period and full sun the rest of the day. I get better generation in winter during shaded periods when it's not full sun. I think it's because the shading is not an issue when the light is defused but is pronounced when full sun hits half a panel and they shut down
Yes, any panels in the shade will certainly benefit from diffuse ambient light. I think that's why North facing panels actually do a lot better then most people would assume.
Yes I agree, I have a massive north facing roof which is always on my mind, don't tell the wife
Haha! Same, as it happens. Although Kat does not object to the idea of a big array on there.
I have some panels on my garage roof, SW facing, but in the hard shade of the house until lunchtime. These panels can produce more on cloudy mornings with diffuse light, as long as the cloud cover isn't too heavy.
Yup, diffuse ambient light can be very handy for shaded panels, for sure.
Tim. I've been looking for a way to make my fortune in a sustainable and ethical way. I think I've spotted how to do it. Instead of rushing out with a hose pipe to water solar panels, could you develop an integrated sprayer system to do this? One which watered the panels when they got too hot and stopped watering when they'd cooled down? Of course, it would require three people's input. Someone to work out whether it would be worth it, by trialling with a hose pipe. Right up your street. Someone to do the electrical and water stuff. There's bound to be someone reading this who could develop a prototype on a sunny Saturday morning. And Someone to come up with the idea. Me.😂
Would making the panels wet, so covered with a film of water, reduce the light they get coming through to use? May be as useful to wet the roof tiles below as they will be acting like storage heaters.
I think water cooled panels do exist, actually, with the heated water also being used too. Not sure where I saw that, possibly the Just Have A Think channel.
Bother! 😊
Temperature I'd say.
Enough to change my peak output from 5kW to 7kW? I doubt temperature alone can explain all of that.
@@TimAndKatsGreenWalk It's both the cloud effect and the temperature of the panels. That's why you get big differences. Unfortunately for people in Canada and Scandinavia these effects can literally fry the equipment if temperature and cloud effects are not taken into account when designing the systems.
Clouds are good for interaction with your viewers! 😂
Let's get those algorithms pumping! 😊
Clearly!
Okay, so what is the best method to control the clouds? 😂
A very good question