Category: solar

Ok so January is OVER. Woohoo. This means I have a full month where my solar farm was actually operating at full capacity (well not quite…we have not replaced the missing 10 panels from the storm damage, and I suspect some strings may be turned off as a result, but its fairly minimal). Because we had our farm switched on in the middle of a month, and then had the storm damage, and also had some brief downtime for meter related stuff, there have not been long periods of uninterrupted operation so that I can analyze the data. Hopefully this is almost over and we can get to the point where the generation is steady and predictable… Anyway for those new to this blog, this is a 1.23kwp solar farm, kind of near the midlands UK. Commissioned in October 2024. here are the details: (first the Solis inverter combined data)

You can see just how variable the generation is. There have been some really wet days and plenty of cloudy ones. It is January after all, so this is to be expected. Ignore the GBP scale, its not accurate, but the kwh is. I have no idea why they bother showing it as ‘full load hours’. Who cares? Its a crazy metric. We know the theoretical full load, but how does that help us. You can’t even remove the line! Anyway, the real figure that matters is 38,216kwh. In the same period the solar in my garden generated 41kkwh. This is disproportionately low. Thats 10kwh per kwp for my home solar. The farm is 30.7kwh per kwp, so 10x the output, despite being the EXACT same panels. Why? Because we have really bad winter-shading on our home panels and the farm has zero shading by design. Shading is everything!

Now time for the meter-level (Orsis) data:

You will notice the monthly data is lower, a difference of 743kwh or 1.9% of generated output. Why? Line losses basically. We generate more power at the inverter level but by the time it goes from DC to AC and then through the ten cables to the switchgear box and gets read by the meter, we have lost 1.9%. This is higher than I would like, and I do find myself wondering how its possible to lose 743kwh just by heat. Thats running an electric heater on full blast for 10 days over the course of a month. The trouble is when you translate in your head from domestic level numbers to grid scale it all starts to seem ludicrous :D.

Of course what I REALLY want to know is how my farm is operating with regards to expectations. The Orsis UI will even show you this…but I have issues with it:

At first glance this looks AMAZING. OMG My solar farm is generating at double the expectations. Time to select the best interior/exterior color combos on a Maserati EV. But actually I think this is just WRONG. The numbers used to generate these expectations are just numbers that I think the installers entered in the Orsis UI, and I *think* they are wrong, and my best guess is that this sort of generation curve predates advances in solar panel performance. These days solar panels (especially the latest monocrystaline ones) are really good at coping with scattered cloud. 10 years ago, some cloud on a single panel would be bad news, but panels now have bypass diodes and other tricks to ensure that really bad performing areas of a single panel can be temporarily ‘switched off’ so that you can still get maximum power from the rest. The result, I *think* is that the power generation curve over time is less pronounced.

To put that another way, I think that this chart should be flatter, and will be once I have a full years data. I am not celebrating yet, and will not be able to draw real conclusions until the end of December. Obviously that will not stop me extrapolating like crazy in blog posts every month :D.

But wait! This is not the only news. I have also sent off my final response to the UK REGO scheme regulator(ofgem) about my REGO application. For anyone new to this blog, let em explain what the hell I am talking about first:

REGOs are Renewable Energy Guarantee of Origin certificates. When you own a solar/wind/geothermal/wave energy plant and generate a megawatt-hour of power (1,000kwh) then you get a REGO certificate, that proves it was renewable energy. You can then SELL these, to people like retail energy providers, or companies who want to be able to prove their power is renewable. This is not a subsidy, but a free market, and for solar farms you tend to lump in the REGOs with the sale of the power. In my case we sell the power to OVO, and they buy each REGO at a fixed price. Once I have them…

The first time I applied for REGOs I was told it couldn’t be approv4ed because the site was not finished, and when I said can be put my application on hold, they said no, we have to delete it ,and in future you cannot re-use the name, so you need a new one.

Yes, words fail me too.

Anyway, my second application was responded to with a huge bunch of requests for extra data. You would not believe what they question or want clarified or what level of detail they want. It reminds me of the planning permission system, where it is 100% clear that this is not actually a process, but a game, where their success criteria is that they get to reject you. There is zero attempt at ‘good faith’ evaluation of whether or not its a solar farm, and 100% focus on looking for any minor reason to reject the application. It is awful.

I have replied with a lot of detail, and screenshots of settings, and forms and charts and so on. They seem to want evidence that the farms output is limited to 900kw (it is) but the only evidence of this is that the inverters are set to only output this amount. There is literally no other way I can prove this, and I expect yet more arguments. Its totally ridiculous, because we are basically arguing with bureaucrats, who are absolutely unaffected by how much power we export. The DNO (the distribution company ) IS happy with our inverter limits, and its their substations, transformers and cables that will explode if we are lying, so if its good enough for them… you would think this was a done deal…

I will be very happy with this ridiculous procedure is completed and we actually are being paid the correct amount for each MWH. Luckily you can back-date REGOs, so we are not actually losing out. In the meantime, this generates a ton of work for bureaucrats to argue about forms which achieves absolutely nothing. BTW this is all extra costs on your energy bill.

Expect a super upbeat blog post if it gets approved though!

My solar farm got hit by a big storm. The storm was pretty bad, lots of property damage across the UK. For the whole of my life, I have never worried about such things as long as my house is ok and no trees fall on us. What else would I have to worry about? Its not like I have had a huge number of very expensive to install sheets of silicon and glass standing on a hilltop is it? Wait…

One text message you don’t really want to get is one from the landowner your solar farm is on telling you that panels have been ripped off their frames by high winds. This is scary news, especially before you see pictures. At that point, you worry how many have been destroyed? 100? 500? And how much will it cost to fix? and how much other damage is done.

As it happens, it was not too bad. The total damage is about £8k. Annoyingly thats the cost to actually fix and replace things, not the actual material cost of new panels, because we happen to have 30 spare ones on site anyway. This seems super expensive to me, but I have not personally visited the site to look at the damage. Its not just that ‘some’ panels are destroyed, others would have been scratched by flying debris, and also actual metal supporting beams were twisted and broken by the force of the winds. Yup, it was super windy. It looks like among the other costs we need…

• 25x M12 fixing sets (wholesale about £10 each, so about £250)
• 50x M8 fixing sets (not sure, about £2 each? so about £100)

Which means a lot of it is going to be labour, and no doubt travel expenses. Its a REAL PAIN that the site is so far away. Also of course all of this is through 3rd parties. I pay a construction company who pay contractors. Those 2 extra profit margins add up. If I was younger and more ambitious I’d hire a bunch of people and build my own solar farms with my own employees, which would be much more efficient…

The storm was bad enough that the power was down in that area anyway. The farm got shut off, and for reasons that are not clear, was switched off for a long period before people got up there and switched everything back on. At one point, the farm was briefly reconnected but not transmitting data, so in the chaos that ensued it was not clear if even switching it back on worked. This was very very stressful for me. I would have liked to go a year before I had any major bills for anything relating to this project, but there you go… As a result, the power output chart looks like this:

Thats quite a gap. The site did actually come back on and generated on the 19th as I can see from the pure meter stats instead of the inverter reported stats:

But even so, we had just under 2 weeks of downtime with zero generation. By absolute luck, this was in December, the lowest point in the year for generation. If this had been mid summer it would have a been a catastrophe.

There are other solar farms that were massively damaged and half destroyed by the same storm, so I actually think we got off lightly. Also it seems like the damage was to a specific strip of the farm on the very crest of the hill, so its likely that this is just ‘the weakest point’. We are looking at strengthening some bits on those areas given that we now have real world data that this is the part of the farm most at risk.

Mounting systems for solar panels are rated for certain windspeeds, but although ‘the windspeed’ on a certain day might only be 60mph, there may be specific small pockets where it will hit much higher. The only real defense against this sort of thing is going to be accepting some occasional storm damage and factoring it into the budget :(.

Of course the real kicker in all this is that the climate emergency is meaning extreme weather events like this will get worse and worse and worse unless we take drastic action. I have made a 25 year investment, and who knows how bad the peak storms will be in 2050 unless we actually do something. Of course this is not just a renewable energy problem. Roads, railway lines, power lines, and all infrastructure gets very vulnerable once rain, wind and temperature levels move outside the normal boundaries. The UK almost lost its marbles when we had some 40 degree days a few years back, but sadly thats likely to become the norm.

It really is about time people started giving a damn, but recent ‘drill baby drill’ rhetoric from the USA suggests that we are rapidly heading in the wrong direction. This is insane :(.

On the positive side, £8k damage on a £1.5m installation is not the end of the world. Its a pain, but hopefully a one-off. We shall see. I am looking forward to the power output of the site creeping up in the coming months. I am also close to getting certification for REGOs, which will boost the income a bit. You would not believe the detailed forms and paperwork required just to prove I own a solar farm.

Just over two years ago, I took the plunge and added a lithium-ion storage battery to my home. It went in the cellar. Its been doing its job faithfully ever since, and has been pretty cool. I reckon 85% of our energy usage has been either free or off-peak electricity since we got it installed. Here is a pic:

The original blog post is all the way back here. Anyway, today we had someone come to the house to talk about doubling it, and having not 9.5kwh of storage, but 19kwh, by sticking another one right next to it. Cunningly I had forward-planned this, by asking them to make that big wooden backboard big enough for two batteries during the initial install.

At the time, I was not sure what the right size of battery would be. We nearly got a Tesla powerwall, but they were hard to get hold of. They had a 13kwh capacity at the time, so we ended up with slightly less at 9.5kw. It also has a separate inverter (some modern batteries have the inverter in the same box now) and the inverter is limited to just 3kw input/output. So that means if at any point we draw more than 3kw by cooking/heating/whatever, then we pull power from the grid EVEN IF the battery has tons of charge in it. Now with our solar panels, its a bit different because if they are producing at their peak (about 4kw), we can in theory use 7kw of power and still not touch the grid, but that involves being very organised :D.

I mention the 3kw limit because that is not changing. We could in theory get another inverter but thats a lot more hassle. With a second identical battery its just attached to the wall and then connected with a phat cable and thats it. So we will then have 19kwh of storage, that we can use 3kw per hour. This is not ideal, but we are doing it anyway. Why?

We are likely going to get a heat pump soon, probably this year. Heat pumps are very environmentally friendly, but they do increase the amount of electricity you use. In our case it will mean getting rid of an expensive and emissions-heavy oil boiler and oil tank, so its definitely a win, but our actual electricity usage will rise a fair bit. Right now, we have everything balanced perfectly. In a dark cold winter, we get almost nothing from solar (0.67kwh today), and we use about 11kw. So we can buy 10kw overnight at cheap rates, and combined with some solar, we can still just about get through the day without using peak electricity.

The heat pump will change this. We will have a higher average daily electricity consumption, so in order to have the same fully off-peak strategy, we need more storage, and its cheap enough (£3,900 supply+fit) that we may as well double it. I think we don’t NEED double, but I’d rather have 2 identical batteries for compatibility reasons and would rather be too big than too small. We should get the battery fitted soon, way before we get the heat pump. If you wonder about charging the EV… thats done entirely during off-peak times, so its never a problem.

In an ideal world, we would also have re-wired the entire house to survive a power-cut and run off the battery. In practice this is REALLY hard to do. Its not the kwh that is the problem, but the kw and the amps. Houses can draw up to 100amps in the UK, and no, no home battery is going to provide that. What SOME home battery installs do is wire ‘some circuits’ so they work in a power-cut. So basically you can have all the sockets in one room, or all the lighting. Thats likely low amps and low power. However it does involve running extra cables and a new fusebox in the cellar, and when we looked at what fuses were behind what sockets… it all turned into a bit of a nightmare. So we went for a bit of a bodge…

We are going to (pending the quote) have 2 sockets fitted next to the battery in the cellar on a separate battery circuit. In a power-cut, they will still work. So we can charge up a laptop or phone quite happily down there, although its a cold 1650s brick cellar with a well in it, more suited to a lord-of-the-rings re-enactment than leisure time, so no, we won’t be living down there. On the plus side, thats still better than having NO power in a power cut. We had power out for 6 hours a few months ago, so its a thing here. I also think that given climate change and extreme weather, this will be more likely. All our power cables here are overground on poles, so vulnerable…

It might sound ‘not very resilient’ but we have two log-burning stoves here, so not short of heat, and actually we can always charge phones in the car anyway (even watch netflix and disney and apple tv in the car), so we are not totally bereft :D.

BTW if you follow me on X and saw THAT POST about the solar farm, I have not forgotten to blog about it…I just need more information…

Ok, the sun is still in the sky, but its late enough that I am going to declare November over now, and blog about my generation from my solar farm. First here is the exciting main chart thing:

So thats 34.2 MWh, or to put it in rooftop-solar or home-energy terms, 34,248kwh of lovely renewable green solar power! Not bad I think for a pretty wet, cloudy November in the UK. June in the Sahara desert would be different…

A crude extrapolation to 12 month would give 410MWh which is obviously way too low. I am expecting more like 1,000-1,200 MWh for the whole year. If I can get 1,200 that would be nice, and I would not worry too much about the business case for the whole thing. However that depends on the ongoing costs. I am still comparing quotes and discussing ways to cut that. The actual annual sums for each individual component always seem reasonable, until you multiply them by 25 years…

I do have some other software that analyses the output and gives an estimate of how good or bad you generation has been. That software suggests that November output for me has been noticeably better than expected, but you shouldn’t get too excited extrapolating from a single data point. Lets not forget the panels are new(ish) and clean(ish), and that will not always be the case. The real reckoning will come after a full years generation and operations.

In other news, I got paid! So its only for part of October (we had some downtime, and also did not switch on until the 4th) but the money turned up in my account on time and the right amount, which is never something a small business can take for granted. If you are a UK residential electricity customer of OVO, then I am providing some of your power :D. I get paid for the power plus VAT (sales tax in UK of 20%) so I have to pay that tax to the government (useless busywork!). It definitely feels good to have even just this ONE entry in the company accounts that is green instead of red!

OMG its actually happened, I have been sent an invoice (well a statement really I guess) for the sale of my solar power for the first time. The spoiler is that its about what I expected, but that doesn’t stop me breaking it down in extreme detail! If you are googling for the details of what a power purchase agreement (PPA) for a solar farm is, and how its calculated and how much you actually get paid etc, then you have probably found the right blog :D.

So firstly, lets have some disclaimers. The farm was only energized on October 4th, and this payment is for October, so we already lost 4 days (we didn’t switch on at 8am :D). We also had to turn everything off for two days later in the month so that we could fill in some earthworks around some high voltage cabling, and they wouldn’t do that while they were live. TBH they were only 400v I think, and this seemed a bit overkill to me, but then I don’t drive a digging machine :D.

Also be aware that this was OCTOBER, so not exactly peak sunshine roughly half way up the west side of the UK, so do not extrapolate this in a linear sense to be a typical month because it was not. So how much is the total paid?

Roughly £5,300

To break it down in more detail, the amount is calculated like this:

• Electricity output £4,400
• REGO Certificates £0
• DUoS benefits £945
• DUoS costs -£12
• Triad benefits £0
• Admin fees -£25

All figures are slightly approximated as I’m not sure what I can / cannot be explicit about and don’t want to be told off :D. Anyway to break it down…

Electricity output is the amount I can see that many MWH of power for. More on that later.

REGO certificates are things I do not have yet due to stupid insane *are you kidding me* levels of bureaucratic BS, but I WILL get them, and they will be backdated. I need to collect a ton of paperwork and then sit and wait for months for the awarding government body to try their hardest to find a missing comma or i without a dot. I wish I was joking.

DUoS. Well this is a whole world of insane complexity. The acronym stands for ‘Distribution Use of System’. Its the bewildering network of charges and fees and credits that are calculated depending where you are in the national network of distribution power lines. Basically if you generating power next door to a substation, and the re is an aluminum smelter next door to that, then all of the power you generate will stay local, and not flow out onto the wider ‘national grid’, so you are not heaping pressure on the big pylon networks. Thats the ideal situation. Amazingly, you can get both charges and benefits from the exact same system. My solar farm is fairly remote, but small enough that our energy will only ever go to the nearest town. So we got charged £12 for being so remote and using some local pylons, but credited £945 because we are remote enough that us powering that town a bit more means LESS pressure on the big power lines heading from elsewhere to that town.

Think of it as toll road charges.

Triad benefits: This is something very weird and arcane that makes DUoS look simple. Here is the googled explanation.

The Distribution Network Operators (DNO) pay what you might call a standing charge to National Grid (NG). This charge is set according to the amount of electricity being drawn by the DNO when the UK as a whole is using the most. More specifically, it is the average MW being drawn during the three highest half-hour periods (subject to being a minimum of 10 days apart) of UK electricity consumption between 1st November and 28th February inclusive. The cost incurred by the DNO is then passed on to energy suppliers who in turn charge it to their customers. (from:https://www.nowthenenergy.co.uk/news/triads2021 )

If you think ‘WTF? why do they choose three? and why those months? and why half hour? Yup : welcome to the UK energy market. You thought C++ was complex? Ha! Anyway, looks like we are unaffected which is good?

Now actually I will get paid MORE than this, because I get paid VAT (sales tax) but I then have to pay that to the government anyway, so its just a bureaucratic waste of time and doesn’t figure into the calculations.

But Wait! There is more! The ‘Electricity output’ figure is more involved. My actual PPA did not start until November 1st. From that point I get a fixed price per MWH for the next year, but up until then, the price was ‘floating’. I got paid the ‘market ‘system sell price’ price each half hour. (The whole UK commercial energy sector works on half hour billing). They send you a handy spreadsheet showing what the price was every half hour for the whole month. Do you think it was relatively stable? Ha. Behold:

Well I guess two things stand out right? Firstly what the hell was that spike? and secondly WTF does it go negative? To answer the second part first, YES, at times I was being charged actual money to generate power. When its super-windy and super-sunny, and mild, and the Uk has too much energy and we cannot cope with any more, the wholesale energy price goes negative. It happened a few times that month, but as you can see its very short lived. With a solar plant, you can’t easily switch it off (and you wouldnt want to keep turning it off and on again), but if you are burning physical fuel like gas, coal or oil, or even wood, then that price signal tells you to stop imemdiately, which is why I think it recover.s

But hey-ho check out settlement half hour #564, when I was paid a whopping £669 per MWH. Oh yes. Sadly there were only a few brief periods of this.It seems to have happened on the 11th October about 75% through the day (so 6pm) Lets look at country wide stats. Seemingly no explanation here:

But in a sense… it doesn’t matter, because annoyingly its October and solar output at 6PM on 11th October was likely pitiful, if not zero. I checked…, and it was 4.89kw at that time. So the super high price only earned me £3.27 per hour. Actually less, because the power trailed off and the price dropped off too.

FWIW this is why in some cases lithium-ion grid-scale batteries can make sense. If I had one (I ran the numbers and couldn’t justify it for such a small site), I could have stored 1 MWH in it from earlier in the day, then let it flow out at 6PM and pocketed a handy £669. The trouble is I would need about £200,000 to install that battery, and you need to be sure you are going to get enough of a return on those occasional spikes to make it worthwhile. Plus other people are doing the same thing, so as more grid scale storage is rolled out, that chart is going to look a lot less spiky. Especially over the lifetime of the farm (25+ years). Note you can also do ‘peak shaving’ which improves the economics. I blogged about that previously.

Anyway, all very exciting to see actual payments heading my way. 10 days until the money is transferred. It will be WEIRD to see money flow INTO this company. Its been an absolute money pit until now :D.