Category: solar

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.

You might think that collecting data on how much energy your solar farm has generated would be a simple matter, where you have an app on your phone, or a website, with a single figure that was just easy to rely on and so on… Ha no. Obviously not. Everything is a billion times more complex when you go from the rooftop kilowatt-hour level to the grid-scale megawatt level.

There are THREE systems (oh yes) that are reporting the output data from the farm. We can call them the Solis, Orsis and Meter systems. Right now, I have data from two of them (although patchy) and the third one remains a mystery that I think I get access to through a third party, or maybe they just show up in the final invoices I get when I get the payment for the energy. Why are there three systems? surely its all one level right?

There are ten inverters on the site, each with up to 20 strings of solar panels. They are all made by Solis, but are different capacities, ranging from 80kw to 110kw in output. All of these inverters report their data, which as I recall is connected by actual physical cabling, running alongside the actual power cables, and all of that then gets connected to the big old wide interwebs using a router thats in our switchgear building. This means I can log into a portal either on my phone or a webpage on my desktop and read off the output of the whole site, or each inverter. The basic view looks like this:

This is the data so far today, which is actually looking pretty good. Total output today is 1.154MWH. For those not familiar with the terms, that’s 1,154kwh. For perspective, a high-end electric car has a battery size of 80 kwh. You probably use between 10 and 20 kwh a day in a house this time of year in the UK, assuming no EV or heat pump. Late October in the UK is bad weather, and very far below peak output, so seeing these numbers is encouraging. We have been connected for about 3 weeks, but have had 2 days complete downtime, and a lot of rain, so 40.7MWH in that time is fairly good I think. You can look at stuff in much more technical detail:

The yield figures differ for each inverter mostly because their capacities are different. I know people imagine a nice flat square field full of panels with a nice round 200 panels per inverter, all of which are identical…and oh how I wish this was the case for my farm too, but pretty much everything is slightly unusual about this site. (I was told by the developer that this was the hardest site they had done in ten years…just my luck!). Anyway, if you want to waste even more hours of your life, you can stare at stats for each inverter, which is pretty much there for fault-finding purposes but also kinda cool:

This is the screen where my geeky interest runs into the brick wall of me not being an electrician, but luckily other people also check this stuff, and the system will trigger alarms if something unusual happens, which would represent a cable breaking or a connector failing, or worst case, an inverter actually failing. Obviously right now it all works great :D.

Anyway…all of that is the inverter-level reporting, but thats not the ‘real’ output figure. There is also a site reporting system through a different portal (orsis) that is as far as I know, oblivious to the individual inverters and just looks at the combined power flowing out of the system. Thats also got a web portal. It might have an app too, I have not searched for that yet. Already most of my phone home screen is various solar/battery/farm/ev reporting apps :D. Here is the basic orsis view:

In comparison this reporting seems kinda rubbish, and it seems to not show the current day at all. It relies on a modem (WTF is a modem these days?) to send out data. TBH the whole UI for this system has a sort of ‘coded in 1990’ vibe to it. Maybe they need to hire a game designer with extensive experience of flashy data-visualization to do a new front end :D.

But hold on, I mentioned three systems right? Well there is a meter on the site that is remotely read by a special company, which is called a meter operator. It might seem ridiculous to need yet another service to just read a simple string of digits, but its worse. You also need to have a data collector and a data aggregator. These three different names for basically the same thing (reading about 1k of data a day) are how the insane fees that get charged are justified. In a sane world, some big tech company like Microsoft or Google would handle this sort of thing for a flat fee of $9.99 a year. Unfortunately this is not the case…

So anyway, as I understand it, that meter gets read remotely and the data from it passed by the Meter Operator (MO)/Data Collector(DC)/Data Aggregator(DA) to the buyer set out in the Power Purchase Agreement (PPA), and then I get sent some money.

Eventually.

Hopefully.

If I had £1 for every energy company acronym I have encountered I wouldn’t need a solar farm. There is then all the excitement of applying for, and getting accredited for the REGOs (Renewable Energy Guarantee of Origin), which always takes MONTHS and has a level of bureaucracy that would make a Tax collector blush. I hope to have all the information I need to finalize my application for that within a few weeks at most. Obviously you cannot pre-apply, because that would be efficient.

Anyway, I am currently in solar-stats-heaven. I was musing about buying some nano-leaf programmable RGB light blocks for my office wall to connect to the solar output from the farm. It seems like an SDK for the blocks is all very easy, but I would need to learn how to code some system to log into the web portals and periodically scrape the data. I probably cannot be bothered :D.

So yesterday was the big day and we finally switched on our solar farm! The site is not 100% finished, with a lot of tidying up to do, but for the first time ever, the 3,024 solar panels on the site are finally generating power and feeding it into the national grid. Overall, it will provide power for 300 homes, which is pretty good. That might sound a lot if you are reading this in the US, but UK per-household electricity consumption is actually quite low. Yesterday was a big big milestone, but not the total end of the project. We do not have the monitoring logins set up yet (but the power is being logged by the meter), and we do not have the final construction bill, soi I cannot tell you if/how profitable it might be yet. But here are the switch-on day details:

Annoyingly, I live hundreds of miles away from the site, so we have a four hour drive to get there (including a short breakfast/coffee stop where I recharge the EV). Because switch-on was booked in for 9.30AM, that meant a very early start, and then a long drive in darkness and eventual sunrise. That did mean that the project manager was onsite at sunrise and got some really nice pictures:

Because you have to arrange someone from the distribution network operator (DNO) to come and ‘witness’ the site energization, you have a hard deadline, because they are busy and not flexible. My wife had to come back from holiday a day early to make the date. It also meant that this was a HARD deadline, and everything had to be ready. I had assumed we would comfortably meet that, but when we arrived on site there were about 9 vans and a bunch of people still running cables and connecting stuff. This was pretty scary because the DNO will not wait all day, and there is every chance some initial test fails, or something is wrong. There was a lot of pacing up and down. Also the site manager was beyond stressed. Obviously a good time to just take photos :D.

Because everything was being tested, it was a good time to poke around and look at how everything works. The DNO substation was open and being worked on, which is a rare chance to see inside it. We will probably never see inside this box again, as it is owned by the DNO, and is their responsibility, and only they have the key! The insides are basically some big fuses and switching stuff and a transformer. This is where the power gets converted from about 400v to 11,000 volts to go out into the grid. This box is also where the (now underground) cable that connects the farm comes into the site. You can see that a lot of cabling goes down through the floor and then runs underground out to where it eventually goes back up above ground onto power poles away from the site. There is other, much thicker cabling on the LHS that goes to our big green switchgear box.

Here is the big green box I’m talking about with both doors open:

The left hand door goes into the main room that has all the switchgear and is where all of the phat cables from the inverters enter (from under the floor into that concrete trench, yet to be filled in with earth. Thats the bit that has the fire suppression system in it, and the big cooper bars which are live when energized (see previous blog post). The room on the right hand side is basically the meter and CCTV room. Its got the incoming supply meter (to measure how much power we have imported to site overnight to power minor stuff like CCTV etc) and the outgoing meter, which is the one I care about, and is remotely read to work out how much power we are generating. It also has the wifi router for the CCTV and other CCTV related equipment. Here is the meter stuff:

As I recall LHS is the power supply (import) meter, middle bit is CCTV related and RHS is the important export-tracking meter. I guess what most people are interested in, including me, is where is the big button with ACTIVATE SOLAR FARM written on it, with klaxons and so on. The answer to this seemed pretty vague, and thats in part because we connect each of our inverters through to the DNO substation, rather than there being a single cable or a single switch. The closest we get to it seems to be this button, and ironically this isn’t even my finger, its the project manager pointing at it :D

Also you would imagine there is some big ceremonial ‘moment’ when its activated, but I think such things are only really staged for TV. Basically each inverter got switched on, and then the DNO people check that nothing trips or goes wrong, and then they switch everything on, then switch the power TO the site off, just to check that when that happens, the site correctly switches itself off in reaction (just like home inverters do).

In practice this means there is a lot of nervous pacing while DNO people and ‘my’ people switch things on and off and then give the thumbs up to each other, and then eventually they come over and get you to sign a piece of paper, and declare that its all approved and energized. Any disappointment at the lack of champagne and fireworks is just matched by relief that it happened.

What I do NOT have yet is live (or indeed delayed) monitoring of the site. That should be set up at the start of next week, at which point I will exhaustively investigate all the options and data and write long blog posts about it :D. I definitely felt extremely relieved at the point at which everything was declared live, although frankly the site manager seemed even more relieved than me. I thought he might feint/explode. It was also cool that the landowners were taking a break from looking after their 1,200 sheep (OMG) to come witness the final energization of the site.

It feels almost surreal that its connected. There is other stuff to do, but no matter what, I now own (entirely! no financing!) my own solar farm. It has a peak output of 1,243 kwh (output capped at 900kw), will supply 300 houses, and has over three thousand solar panels. It is the ultimate geek toy. My stupid-ass DJI drone failed me (software awfulness for which I blame google 100%) on the day, so no decent drone pics, but it was untidy and a bit cloudy anyway. As a result I may well frame one of the sunrise pictures to sit above my monitor in my office :D.

I hope you enjoyed following this epic saga of many years. Its not 100% over yet, but this is a huge milestone. I celebrated after the 4 hour drive home with a glass of bubbly, and luckily my celebration-purchase (a chunky watch) arrived as I was typing this blog post. I feel much less stressed, but the true smugness of owning a solar farm has not kicked in yet :D.