Category: solar

A few days ago I got the latest invoice/statement showing how much I was paid for the solar farm, generation in January. The grand total is…

£3,716 + VAT

For those from other countries, VAT is basically sales tax. I get paid the VAT by the people buying my energy (OVO) and then I have to pay it to the government each quarter. Its all quite tedious. Interestingly, the VAT is 20%, which is different to the rate for home power purchasing. Its irrelevant anyway, because I basically just earn interest on it for 3 months before I give it to the government, so I tend to just ignore it in any calculations. Any interest earned will be in my awful cater-allen company account which has an interest rate that is comically low. UK business banking is one giant rip-off.

Anyway, lets dig into that payment a bit more because to break it down. The full details are as follows:

Electricity output:	£2,540
DUoS Benefit:	£667
DUoS Costs:	£-13
Transmission Loss Passthrough	£28
Distribution Loss Passthrough	£511
Admin Fees	£-24
Before VAT	£3,716
VAT	£743
Total for January:	£4,459

Its a complex mess isn’t it? Also it has not included REGOs yet, because I am STILL going back and forth over the minutiae of my application with ofgem. I kid myself this latest batch of questions they have will be the last and that I will finally get them. Plus the ofgem REGO website is about to be completely re-implemented, and I have ZERO faith that they will not just ‘accidentally’ delete my application so far in the inevitable chaos.

Frankly the whole system should take a tenth of the people and the time, but here we are :(

Worryingly, I have no idea how precisely the four entries under ‘electricity output’ get calculated. I assume this is fixed based on where my site is on the distribution (DNO) and transmission (National Grid) system, but I am not sure. My power is almost certainly just used very locally, so I probably don’t use the transmission network at all (hence the £28 rebate?). I likely use very little of the distribution network either, hence the £511. My best guess is that if I was an offshore windfarm 100 miles from the nearest town, that Distribution loss would be actually negative?

The DUoS stuff is a complete minefield of complexity. Best explanation from grok as to how DUoS can be a benefit to me:

Triad Avoidance: By generating during peak demand periods, you help reduce transmission network charges (TNUoS), which benefits suppliers and can result in payments or incentives for you.
Avoided DUoS Costs: If your generation offsets local demand, it reduces the DUoS charges that suppliers would otherwise pay, potentially increasing the value of your electricity in Power Purchase Agreements (PPAs).

Triad avoidance? Hold on, was that not a sci fi kids TV show? How are the triads an issue? Or is it Japanese mafia? Whats going on? Its actually even more complex:

Triads are the three half-hour periods of highest electricity demand on the transmission network each year, typically occurring between November and February.

You will be thrilled to know that my ‘Triad avoidance benefit’ for January was £0, which is why it was not included. Confused yet? You should be. I am, and I literally own an energy company. Anyway, out of interest the DUoS benefit in January was 17.9% of my total(pre-VAT) payment. I just checked December’s statement and it was 16.69%, so its not even fixed. Are they really calculating the flows in and out of each part of the distribution network on a daily basis and adding up how much ‘my’ power used it? Interesting…

In other news we finally got our second home battery installed! we now have 19kwh of home storage. In winter this does not make a vast amount of difference, because our 9.5kwh one already covered mots of our peak usage, so we could load-shift to off peak (the car charges off peak anyway). However in summer this means that on those crazy days where we generate 20kwh of power we can store all of it, even if we are away or not using any power that day.

The last summer we did actually end up with *too much* power, and had to fiddle with car charging to avoid exporting it to the grid (which we do not get a marginal export fee for, as we are on the old feed in tariff). Also we did it because I like the idea of being as resilient as possible.

We also managed to get a cable running from the battery upstairs to the living room and a new double socket installed there, amusingly next to a triple socket, so it looks like we are addicted to power sockets :D. Anyway, those two sockets are the ONLY ones that will work in a power-cut. We couldn’t power the whole house because our inverter is only 3kw, and this was the next best thing.

Its not exactly off-grid living, but being able to charge laptops and phones in a power-cut, or with an extension lead, still run the router and TV and a coffee machine will be nice :D. We paid £3,900 to have the second battery installed and the sockets fitted.

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!