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Have you costed solar slates? I think that would let you cover most of the south facing roof, except for those that are actually cut.

I say you start to get your money back the day you buy anything renewable as in no matter how much income you're on you have more money in your pocket, im retired and its taken me since 2015 to be almost off grid, i have had my gas meter removed so that's over £100 a year thats is mine to spend on something i like rather than need . im now waiting for my 2nd Powerwall to be installed and i will be set for this winter .

Thanks Tim. Great info video and now I’m convinced to switched from basic Flux to intelligent flux. A couple questions, now and again the battery and inverter have software upgrades available, does Octopus take charge of that too ? or do I still take control of the process?, I also have a GivEnergy EV charger which I set to only draw from solar when when the sunshines as I do a small mileage in my Zoe (5,000 miles per year), so do I have full control of me EV charger? I think answer will be yes. And by the way I now have 3x 9.5kW batteries and hybrid 5kW inverter and solar all on the latest software. I’ll be interested to hear your comments. And thanks again for all you do. My wife and I are into our 70’s and it would be great not to keep adjusting things ourselves particularly if my wife was left on her own as I am the one that does the technology stuff around the home. Hopefully I’ve still got a few more years left in me yet.

Another Pro is it costs much less even without the Government grant , my system with the pump and 3 cassette were less than £5000 and only took a day .

Alto strata days are very good too. (High clouds), cool and bright.

New changes to Cosy tariff coming. New video? 😉 My own spreadsheet takes my use and calculates my total use in each of the 48 half hour time periods and applies the tariff rates to estimate a cost (or uses the average half hourly tariff rates for Agile).

We have a 6kWp system, almost south facing, but have been seeing 7.5kW at times, a whole 25% over specified capacity.

Hi, I have solar but no battery, I store it in the car. What are my tariff options if I don't have a smart meter? It's not an option where I live.

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

Your observation 'reflects' our experience.....

Okay, so what is the best method to control the clouds? 😂

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.

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.

Hi Tim, thanks as always for your informative videos. I’m interested in switching from octopus Flux which I’ve been on for a year, to intelligent octopus flux. I currently enjoy exporting to the grid and have all GivEnergy products, 5wK hybrid inverter, qty3 9.5kW batteries and GivEnergy EV charger for My Renault Zoe GT EV (50kW with rapid charge option) . I’m finding it difficult to decide to switch to intelligent Flux . I notice on their FAQ that they say they on support 1 battery, do you think that applies to me as my 3 batteries are all linked together? I would value your opinion.

I notice that my NE facing panels don't produce much power in winter but if there are clouds in the north and broken cloud in the south then the NE panels will produce, even if the Sun is on the SW side of the house and the NE panels are shaded.

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.

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.

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.

First day on Intelligent flux - yipeee- - I hope it is a learning tariff as this example shows the issue; - it pre-filled the 20kwh battery this morning.. but it was a very sunny day (been a while!).. so when the solar panels met and exceeded the 5kw export rate (5kw inverter) almost 3kw of excess solar had nowhere to go as the battery was still full(the panels were generating 8kw !) That energy was clipped / discarded for several hours. Filling the battery only half full on forecast sunny days makes more sense with this house. It still manages a full 5 kw of export for 4 to 7pm but a half full battery can be partly on standby able to swallow excess solar which can then be exported later instead of clipping it. So as I say it’s day 1 - it’ll be interesting to see if the tariff handles tomorrows sunny weather any differently now that it has noticed it clipped (discarded) so much power today. Will post results!

Another thought: PVs produce power from certain wavelengths. Is more light from these wavelengths reaching your panels when scattered clouds are around?

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?

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.

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

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.

Interesting thoughts and observations, thanks for sharing

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.

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.

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.

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.

Temperature I'd say.

I have noticed the exact same. However, I've chalked it down to cooler panels, getting shade from the relentless sun.

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.

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

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.

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.

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.

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 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 .

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'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.

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.

Clouds are good for interaction with your viewers! 😂

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.

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.

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?

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 😊

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.😂

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!

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.