Game Design, Programming and running a one-man games business…

Bad news for consumerism: Everything’s good enough.

Posted on January 17, 2023

I am well aware of the history of the term ‘640k is enough for everyone’, so hold your horses in your excitement to post it as a ‘gotcha’ response. I would like to lay out a case for a big slowdown in consumer spending, and put it to you, the reader, that although often we are wrong when we predict such things, this is not always the case. We have not all rushed out and bought 3D TVs, as predicted. We did not all buy VR headsets. I have still only seen a single folding phone in the wild…

I’m in the economically enviable position of having some spare cash which, in previous years I would probably have put towards buying some new thing that I coveted. Maybe a new TV, or phone, or gaming PC or laptop, or whatever. However, I am definitely noticing that this is slowing down, at least for me. Maybe this is an age thing? but maybe not…

I’ve had a bunch of mobile phones over the years, right back to the first actually practical ones, which were given to me at work when I was in IT. They were big, they were dumbphones (no apps or games or internet access), they were heavy, they sucked.

The first phone I had which was a smartphone was a revelation. Then, the next one was much thinner, much lighter, and much more powerful. The last one I bought was a samsung S8. Its amazing. It has bluetooth/wifi it has a fingerprint reader, it has GPS, it has a nice big screen that does face recognition, takes amazing pictures, and videos, can post-process them, and can play games. I use it to control my car, my drone, my lights, my TV, to talk to my solar panels and home battery, to surf the net, and to pay for everything. It charges wirelessly. I record my weight on it, and my steps. I take it everywhere.

I’ve had it years now, and there is basically no reason I can think of to get a new one. At least not yet. I’m not just ‘skipping a generation’, I think I’m at the end. It would be *nice* if the phone battery lasted longer, or if it was a bit thinner or lighter, but its not exactly a hardship now. It charges wirelessly in my car anyway, and its hardly heavy or bulky. It fits easily in a pocket, but its not too small to lose track of. Its thin, but not so thin I can break it.

To get me to buy a new phone, you need to REALLY go nuts on the few things that would improve it. Make the battery last 10x as long, and make it 1/5th the thickness (but same strength) and yeah…MAYBE I would pay the money to buy a brand new phone. I don’t anticipate this being possible in the next 5 years though.

My TV is a 43″ TV. I cant go bigger, because it fits in a small alcove. We sit far enough away from it that a 4K resolution would be pointless. The streaming apps *are* a tad slow on it, but can I really be bothered to set up a new TV, and recycle the old one, and tell alexa about the new one… just for a minor speedup in streaming UI? Not really. If a new TV was FREE, and had a slicker, faster UI, then *maybe* I’d bother. But my current TV does the job well enough.

Its not just these two things.

We bought a toaster years ago that seems indestructible and will probably last as long as me. My gaming PC has ridiculous power, and plays 60FPS Battlefield 2042 even on a 5120 res monitor. This laptop is fairly new, and amazing, and frankly…I am not sure if there is any improvement that is worth paying for. If you gave me a voucher for consumer electronics that I had to spend RIGHT NOW, I honestly struggle to think of anything I’d upgrade. Home theater system is fine and will last forever, alexa works fine…err…don’t bother with bluray player any more. No radios, everything is streamed. Nothing needs upgrading. Nothing.

Now obviously this is not the end of consumerism because a) I’m clearly well-off enough to have bought all this, and many people are not and b) I don’t know what crazy tech may come out soon, but I am definitely noticing a change…

chatgpt is amazing. midjourney is amazing, but these two amazing discoveries don’t require me to buy ANYTHING. The most exciting tech breakthroughs right now seem to be software, not hardware. When I see headlines about CES (Consumer electronics show), it just seems laughable. They are running out of ideas now. I really don’t need a phone that I can fold. I don’t need a 3D TV, I cant be bothered to wear a VR headset to be entertained.

The trouble is, our entire societal model of economics seems to be focused on selling new shiny gadgets to the wealthiest 25%. Thats how the system works. Bored wealthy people buy expensive cool cars which in 10 years time end up in the hands of ordinary people. The trouble is, we have run out of ways to get those wealthy people to trade in their current stuff. Its good enough. People now want ‘experiences’ not a slightly thinner, slightly faster phone.

And yet… there is a ton of work for society to do. So many people do not own a refrigerator, let alone a drone or a VR headset. We need to be addressing that huge swathe of people without the basics of western consumerist culture, not working harder and harder to make VR and the metaverse a thing. To be blunt: we need cheap fridges, not AR goggles.

In theory you can fix this with a lot of high taxes and high welfare, taxing those AR goggles like crazy to fund purchases of ‘my first fridge’. In practice, I think we do need to do that, but ALSO we need a shift in thinking in modern technology companies. For the last 30 years or more, it seems that the assumption in ‘tech’ is that the goal is always to produce some new, amazing cool thing that wows the CEO and impresses everyone in the boardroom. The problem is, everyone in the boardroom is rich.

The future may not be ‘look at these AR goggles, they are phenomenal’, but in fact be ‘look at this ordinary fridge. It was made for $30’. Thats what we NEED, but its not what we are getting. Companies are more excited about new features and functionality, but never about low cost. Tech companies want the specs on new tech to always be higher bigger, better. Hardly anybody talks about affordability, or how cheap something is to run.

I don’t know how the politics of the future will work out. We may end up with UBI and a crazy high tax rate on a super-wealthy 0.1% of the population. Who knows? What I do hope for is a future where technologists and industrialists care more about what the bottom 25% cannot yet afford, rather than what the top 0.1% might buy if you can make something 1% faster.

What about you? do you have a big long wishlist of stuff you wish you could afford on amazon? or are you quite happily reading this on a 3 year old phone or 4 year old laptop?

Solar farm battery storage business case calculations

Posted on January 15, 2023

I’m currently in the throes of building a 1.2MW solar farm somewhere in England. Its an adventure, to put it mildly :D. So far the planning process and bureaucracy has taken just under 2 years. In that time a lot has changed.

Originally the plan was for a 1.2mwp solar farm, and a battery of either 256kwh or 512kwh. The current situation is that I’m evaluating a 583kwh battery (they can basically pack a bunch more cells in there now), but the economics have got a bit trickier and it may not actually be viable. This does not mean the project itself is not viable, the farm likely still is profitable (I hope!).

First things first, I’ll explain why any of this would make any sense. You cannot just rent a field, fill it with solar panels (assuming the farmer lets you, and planning permission is granted), and make a pile of money. Its not that simple. (And trust me: none of that is simple). The main problem you face is the grid connection. Basically solar farms go in fields, so we are already limited to relatively rural locations. This means that the land is large enough, and also its not going to upset too many people. Our site is surrounded by fields and hills and generally…nothing, so there were zero objections. This is all good news..

…but it also means you are on the edges of the power grid. If you are REALLY lucky, you find a site that has a field to rent, thats rural, but also just-so-happens to be a site where a major grid connection cable runs right through it. This is super ideal, and no, there no sites left like this any more in the UK because all the canny early developers have already snapped them up :(

So…we end up with a perfect field, planning permission, and a happy landowner, but we are basically connected to the rest of the grid by what amounts to a thin USB cable (not really). This is the point at which you ask the grid to upgrade that line and send you the bill, they do, then you laugh at how they accidentally added a few zeroes to the bill, and then you start to cry. Basically upgrading a power line is a nightmare. They cant just add heavier cable and be done. That cable may then sag too much in summer, or be too heavy, so you need new pylons, and then the ground under the pylons is too weak so you need foundations and omg expenseahontas.

In practice, that means that the local DNO (power company) has told us ‘you can generate 900kw at any moment from here but no more’, and thats AFTER we pay for a major grid upgrade. This sounds nuts, but when you think about it, if a power cable was only ever built to supply 2 farm houses, its not ever expecting a power flow of more than about 40kw total maximum. Then suddenly we arrive on the scene with 3,000 solar panels and want to push 20x as much power through those cables…

What does this have to do with batteries?

You might have noticed the difference between our 1,200kw solar farm and the 900kw limit on export. Well spotted. Its quite glaring isn’t it? Actually, this is exactly what most people do, and if you have solar panels at home, you do it too. Its called inverter under sizing.

The inverter is the box that converts DC to AC, and is the device that determines the maximum power that can come from your solar panels. In many cases, its rated BELOW the maximum output of your panels. This must seem insane…because surely that means at peak sunshine some of your power is just wasted right? YES. This is exactly what happens, and its normally because the bigger inverters are very expensive, and the PEAK output of your solar panels only triggers quite rarely, maybe for just 1 or 2 weeks in summer around midday. This means that the extra spend on the ‘bigger’ inverter might not be worth it.

Example: You have a choice of a 2kw inverter or 2.5kw inverter. The difference is $1,000. You have 2.5kwp of solar panels. Which do you choose? Well its actually hellishly complex. You need to model the output of your panels for every hour for every day in a typical year, and then ‘clip off’ the top portion where output would have been above 2kw. You then need to value that power at whatever you get paid to sell it, or what it would have cost you to buy it. You do that for the lifetime of the inverter, then work out if its a good deal.

I’m currently basically doing a similar thing, except the limitation for me is export limits, not inverter sizing. Our site will have 10 inverters anyway, and the bigger you get, the more granular you can be with how many you have. (For those curious, yes, thats like 300 panels per inverter, but each inverter supports a bunch of strings).

What does this have to do with batteries?

Well batteries let you cheat the system! They can do it in home installs, with what they call DC-coupled batteries, and you can do it at the grid/utility scale with batteries the size of shipping containers. (I’m evaluating a 20ft long one). Before I get into this, I need to list the different ways the battery might make sense in our solar farm. The battery would generate revenue basically 3 ways:

Frequency support services:

This is where the national grid basically pays you to act as a sort of ‘cache’ or ‘buffer’ for the grid. If they suddenly have slightly too much power, then dump it on you, then grab it back a bit later (maybe even a few seconds or minutes). They do this to keep the electricity grid at 50hz, to prevent every transformer in the country going bananas and maybe even failing. This is a constant battle, fought every second of every day. Here is a chart of the last 36 hours of it:

You can make money from these services, just by having a battery connected to the grid, and being registered to rent out your battery to act as a local buffer.

Time-based arbitrage stuff

You might think the price of electricity is fixed for your current contract term. Ha. Yes, at the consumer level it is, but behind the scenes, the wholesale price of electricity fluctuates like crazy, not only each month, or each day, but each 15 minutes. And it fluctuates a LOT. You can decide to ‘keep’ some of that solar power you generated at midday and sell it later. In fact in theory this can be hugely profitable, based on the current volatility. Again, here is a price chart the last 36 hours:

In that chart, the price gyrated between negative £70 (They pay YOU to use power) to positive £200 for a MWH. In theory, if you could buffer the whole farms output, and only sell it at the peaks, you would make decent money

Peak-Shaving

This is a system where you take that extra power that you are not allowed to export, you buffer it in the battery, and trickle it out later. This transforms the usual bell curve of solar output into a different shape:

We fill the battery with the ‘red’ energy, then trickle it out later to extend the peak output duration of the site. This energy would otherwise be totally lost, and we would not earn a penny for it!

Ok, so these are three ways storage can make money alongside your solar farm. What the problem? The problem is two-fold. Firstly, there has been a HUGE increase in the amount of grid-connected storage in the UK, which means lots of batteries bidding for the same grid services regarding frequency and price arbitrage. That means that naturally, the profits from these mechanisms have dropped. There are a lot of VERY big companies doing this now, and tons more on the way. Plus, there are other technologies that you compete against. The main one would be hydro (basically a gravity-water battery), but also there are experimental things like gravitricity, and companies working with flywheels and other tech. Its VERY volatile.

Secondly, the price of the battery has gone fucking nuts. In 2 years, the price has gone up 50%. Thats crazy. This may partly be due to the EV revolution, which is scooping up all those lithium ion batteries I was hoping to pack my shipping container with. It might also be related to components shortages for power electronics (lots of chips in a stationary battery), and general inflation for stuff like shipping and labour to install a concrete base and so on…

So right now, with the first two potential battery income streams kinda poor, we have to think whether the basic and most obvious one (peak shaving) is actually worth it. It looks right now that a 583kwh battery cost is about a quarter the total cost of the entire project.

That MIGHT mean its just not worth doing. Sure, being curtailed at peak output for a few weeks each summer may suck, but the big question is how much? I don’t have access to the data yet, and do not have software that accurately measures it, nor is it likely worth the hassle of buying any. I am digging further.

The maths I need is pretty simple, IF you have the modeled data: Given the output each day, for 25 years, what amount of KWH is curtailed on the site given a 900kw power limitation. I then need to guess the market price for this and compare it to the battery install and maintenance cost for 25 years. (I know, its optimistic to expect the electronics to last 25 years, but hey).

Hopefully it DOES make a convincing case, because if not, I basically have to scrap the idea of a battery, or at least wait and see if prices fall. I can still install the solar farm in the meantime.

Why the discovery of behavioral economics means you need to uninstall tiktok.

Posted on January 9, 2023

I studied pure economics at the London School Of Economics. At least, thats what I tell people when I am trying to sound clever. Technically its a true statement. What I tend to leave out, is that I pretty much lost interest in the topic after year one, and was mostly coasting in years 2 and 3. I went to the pub a LOT, I drunk a LOT of vodka and whiskey. I played the guitar a lot, I listened to a lot of heavy metal. This was all unexpected, because I was super-good at economics A-level, and was destined to be good at degree level. The problem? I suddenly realised I found economics beyond a certain level boring, and too maths-focused.

Annoyingly, the solution to my interest-failure would soon be at hand, because 2 clever people eventually discovered an entirely new field of economics called behavioral economics, which, to my mind, was 1000% more interesting, and absolutely was the sort of thing I would be interested in, had it been an option. But no, the LSE still taught ‘classical’ economics, which focuses on interest rates. Other things matter, but you would be amazed how much of classical macroeconomics is focused on interest rates. I studied it for 3 years. I still don’t know whether rates should go up or down. This stuff is complex as fuck.

Why are you reading this?

The significant thing here is how those clever people suddenly were motivated to invent behavioral economics. I’ll give you the short version, and tie it in to the title soon. Are you excited?

Classical economics models rational behavior. In classical economics, every ‘agent’ in the system has perfect information and is perfectly rational. All data is available, and all decisions make sense. If offered 2 products, an agent will evaluate all of the properties of each of these products, giving this decision their 100% attention. They then make an absolutely perfect choice, based on the cost/benefit analysis of each choice. There is no regret in classical economics, no buyers remorse.

Classical economists were not idiots. They were extremely clever people, and they knew that is not entirely how people work, and that we all make the odd silly decision, but at the macro level, across large populations, its pretty clear that rationality wins out. The best product, taking into account the best offer in terms of features/price will always win. In the long run, rationality rules.

These economists were at a dinner party (presumably where they would while away an evening arguing about interest rates), and the host was cooking the main course, while the guests enjoyed some small nibbles. The guests were enjoying the nibbles, and suddenly one of them concluded, with the agreement of all present, that they should ‘put these nibbles away so we stop eating them’, presumably because they were concerned they might spoil their appetite for the main course.

So far, so middle class dinner party.

But hold on. One of these clever economists suddenly pointed out that this was irrational. At the moment, everyone present has a choice: Eat a nibble, or wait for the main course. This was a simple choice between instant satisfaction or a potentially better option if they wait. They were all adults, they could all make that decision. But WAIT. Everyone agreed that in fact, they would be better off if this choice was removed. They would actually be better off with LESS choice.

On the surface of it, this is not exactly earth shattering, but actually, its a revelation. In the word of classical economics, more choice is ALWAYS good. The idea that en-masse, intelligent adults with full knowledge of the available choices, would be better off if they removed some choice, is a complete refutation of everything that classical economics tells us about the world. It was the beginning of an entirely new science of behavioral economics, which would make its inventors widely read, respected and famous, and change economics forever. It would lead to studies of the special nature of ‘free’ as a magical price, and a staggering amount of research and publication. Behavioral economics is awesome.

Ok, but so what?

What this massive upheaval of literally hundreds of years of analysis shows us, is that human beings are incredibly irrational. We are extremely good at backwards-justification, where we pretend our choices make sense, but if you actually look at how we make decisions its an absolute car-crash. We are massively irrational, and so far from the happiness-maximizing creatures that classical economists imagined. Even given really, really simple choices such as ‘eat these nibbles now… or more of the main course in 15 minutes’, our brains completely and utterly collapse with the stress. Only PHYSICALLY removing the nibbles from our immediate vicinity enables us to make what we think is the ‘correct’ choice.

Social media is the nibbles.

You probably spotted that early. I’m not Agatha Christie here, but I hope the point rings true. Deep down, we are all aware that the amount of time we spend doom-scrolling on twitter is not maximizing our happiness. We know that having twitter and tiktok on our phones is just leading us to waste endless time getting into arguments, or just mindlessly scrolling for a tiny tiny serotonin hit…

About two years ago I uninstalled twitter from my phone. I also don’t have a facebook or reddit app on there. I’ve never used tiktok or instagram. A few years before that I quit an online community that just sucked me into arguments and flamewars. I was aware for a good time that these things were ‘bad’ for my mental health, but they were the tray of nibbles in front of me, so I kept nibbling.

I still have a twitter account, but the fact that I have to go to a laptop or desktop PC to use it means I’m wasting less time there. This is, for me at least, a good thing. I know a bunch of people who tweet at least 50 times a day, always political, always angry, always distressed. This is *not good*.

The best economists in the world went decades without realizing just how irrational we are, and just how out-of-touch their model of human behavior was. We are THAT delusional about our ability to make choices in our healthy interest. Its incredibly hard to take this lesson to heart and actually do something about it, but once you do it, its pretty amazing.

You should delete all the social media apps from your phone.

2022: A year spent trying to build a solar farm

Posted on December 31, 2022

The year is almost over, so I thought I would recap. For those unaware, as a side-project (yes its a big side project), I started an energy company called Positech Energy, and decided to build a solar farm. This is an epic tale of frustration and expense, that seems to be endless,, but here is what happened during 2022 for this project!

The first blog update of the year was this one, where I talked about the solar panels. I ordered them way in advance, before we actually had planning permission, because I was hoping to slap them in during summer of this year and start generating actual income. This proved to be both a mistake, and a genius move, depending on your POV.

This was during a time of climate emergency, a global supply chain collapse, and pandemic shutdowns, so it was obvious that lead times on panels would be long, so I ordered them anyway. That means I ended up with over 3,000 410 watt QCells solar panels. They did show up! But by the time we got them… we had no planning permission because it got refused. Oh dear…

I initially decided to forget the whole enterprise at that point, and was quite depressed about it. I tried phoning round wholesalers to sell my panels before they even hit the UK but basically got nowhere. I think people can tell you need to shift them, and offered me a pretty bad price. The company that is managing the project for me did offer to buy them off me at the price I paid, as and when they needed more panels. This was good, and put a floor under my losses, but the trouble is all 70 tons of panels needed storing…

To date I have paid out £15,000 in storage costs for these solar panels. Yup, I PAID £15,000 to keep SOLAR panels in a warehouse during summer. However annoying that sounds to you, it sounds worse to me, but there was no other option. Its still costing me about £600 a week to do this…

Luckily, the price of those panels went up, and I am currently still ahead of the game on this. Assuming they get taken out of storage on schedule (hopefully April), I wont have actually lost out anything except the transport costs for the panels to the site. (Originally that was included, but they needed to be left at a port warehouse instead.

So what else happened?

Well hey we WON planning permission in October, which was a very stressful process, not to mention expensive. In fact the whole process has so far cost me £541,568.94, including buying the panels themselves. Yes, this is a stupid amount of money.

The rough breakdown is:

£50,000 grid connection deposit

£424,000 solar panels

£6,795 for pull-out tests to pick the ground mount system

£3,750 in rent to the farmer for the field so far

..and the rest is planning application and legal bullshit.

Of course the good news is that once you have planning permission…you have it. We cannot get blocked now. The ONLY things standing between us and total conquest of the galaxy is the grid connection and the actual build-out of the site. That means waiting for decent weather, because its in a muddy field near the English/Welsh border, and frankly taking dozens of trucks up a single track lane on very hilly ground when its raining would be a nightmare. Luckily, the UK is so situated that solar output at this time of year is farcically low anyway, so its actually no massive loss.

So where are we left? We are hopefully about a week away from a final, committed quote for the build-out of the farm, and then at that point, the developer will buy the ground mount kit, and order the inverters and other electrical stuff, like the substation. Apparently the first thing that will happen will be putting up a ‘deer fence’ around the whole site as security. Eventually we will have either real or fake CCTV cameras, depending what insurers say.

The aim is to get building in April-ish time. We have mentioned MANY TIMES to the DNO that will put in our grid connection that we really, really want to get connected this year, in Q1 or Q2 if at all possible. These is no free-market for this, and its basically a state-granted private monopoly that does what it likes, so we just have to grin and put up with this.

Also, the cost of the grid connection is likely to go up even more, which is insane. For the love of god, can we nationalize this bit of the grid, and just pay the army to go round the country doing grid upgrades as an urgent matter of national security?

Anyway… a mixed year because we DID get planning permission, but there has not been any real progress on the physical build. I’ll feel a bit more optimistic once I actually see people on site putting up a deer fence. I’ll fill much more optimistic when we see the mounting kit installed and work starts on the grid connection.

Hopefully next years update will be full of amazing progress!

My experience of having a 9.5kwh home battery in the UK for about a month

Posted on December 12, 2022

Recently, we got a 9.5kwh givenergy battery fitted in our cellar. I was very excited about it, and keen to dive into the stats, and wrote a blog post about it here.

I’ve now had it for about a month and thought it was worth typing up the inevitable impressions having got used to the thing! So here goes…

First, some context. This is in a 2.5 bedroom (attic doesn’t count really) detached house, thats very old (pre napoleonic), but has been insulated to the best of our ability. 2 people working from home, in the southwest UK. Also be aware that this was during November/December, and a pretty cold December. As I type this, there is snow everywhere…

I had some initial confusion when the battery was first set up. Day 1, they calibrate it, by basically filling it with grid energy and then discharging it, which feels horrible when you see the first thing your battery does is suck up some prime-time expensive power! Luckily this is a one off thing :D. Once that first day is out of the way, you can then choose your settings and.. to be honest then completely forget about it! My settings, because I have cheap power (75% off!) from 12.30am – 4,30am, is for the battery to fill to 96% during that time and then be in ‘eco mode’ for the rest of each day.

GivEnergy’s eco mode is basically a maximise self-consumption, minimize grid import system. So if you have solar panels, and are producing more power than you are using (fat chance for here in December), the excess gets diverted into the battery. Any power load during the day gets sourced from the battery, so you see the battery state of charge slowly trickle down through the day as its used to power the house:

On the far left is the battery filling up (purple below the line) and my car charging. Combined, the battery charge and car charger hit 9,000w! You will see a few spikes during the day which are basically kettles and coffee machines, and cooking. It looks like breakfast was a big spike load on the grid! and then later mini spikes (below 3,000w) are handled entirely by the battery, slowly draining down to about 8% by midnight. That sustained power draw from 4pm-6pm is a gaming PC and huge monitor playing battlefield V :D.

The thing is… once you have watched these charts a few times, you kind of get the hang of it, and then never really need to look at them, or go near the battery ever again. Its just a magic box somewhere in your house that cuts your energy bill by 75%. The only tweak I have made is that now its even colder, and we are cooking more and for longer, I’ve adjusted it to fill to 96% instead of my original 90%, because we need a bit more energy each day (and if I can possibly avoid any prime-time energy consumption…I will!).

So this is all very well, but what have I learned that might be relevant for people who are considering installing a battery?

Firstly, you really need to get the size of the battery right. I kind of lucked-out a bit, and ended up with the perfect size, but nearly didn’t. At one point, we were going to get an 8.2kwh battery, then a 9.5kwh, then maybe 2x 9.5kwh ones, and even had a board installed on the cellar wall to support a 2nd one, but we ended up with a single 9.5kwh which feels right. Obviously, when you think about it, all you need to do is check your energy bill for how many kwh you use on average each day… and thats the size of the battery you want!

Its a bit more complex if you have solar, because if you have a decent solar array, there may be days where you are generating more than your daily usage, and want to store some in case its cloudy/raining the next day, to maximise your usage. Remember, the goal is to NEVER export any energy to the grid, because they pay you a pittance. So there are circumstances where you might need to oversize things…

For example, if your daily usage is 10kwh, but your solar array in June/July regularly produces 20kwh, then you will be using 10kwh, and sticking 10kwh in the battery for tomorrow. If you dips in solar power are fairly sparse, you will be often faced with surplus solar power and a full battery. IF you have an electric car too, and are bothered enough to trickle-charge it with the excess, then you can of course do this. There are setups and systems that can automate this BTW, that involve cables running to the EV charger from your battery/inverter, but I found it to be prohibitively complex, especially with our EV charger about 100ft from the fuse box.

I reckon for the vast majority of people, whether you have solar or not, you probably should stick to a simple format of just buying a battery that can hold 100-150% of your average daily usage. Its not like you can precisely pick a size anyway, as our options were basically 8.2kwh or 9.5kwh or some multiple.

Something that IS worth paying attention to is the inverter. You need an inverter coupled with your battery, or batteries. Its the thing that converts the stored power (DC) back to AC so the house appliances can use it. We have a first generation GivEnergy inverter, that runs at 3kw, and the ones run at 5kw. If at all possible get the higher output one. Get the highest output inverter you can. Why is this?

Its important to understand the difference between kw (kilowatts, thousands of watts) and kwh (kilowatt hours). The first is a measurement of power as in, the amount of oomph that is running down a cable to a thing, and the second is a measurement of stored energy, ie: the amount of oomph multiplied by how many hours you can provide it, before you run out. Or think of kw as your salary and kwh as your savings :D,

In my case, we have a 9.5kwh battery, fed by a 3kwh inverter. That means that even if the battery is FULL, if I plug in some theoretical device that wants to draw power at 9,000 watts… the battery can only squeeze out 3,000. The rest will get imported from the grid. Why does this matter? It matters because British homes have kettles! and also sometimes electric heaters! In an ideal world your day to day current draw will never exceed the power of your inverter. Every time it does, you will draw the excess from the grid.

With something like charging an EV, you need to just admit defeat. Most EV chargers at home are about 7kw, and you are not going to power your home AND an EV charger with a simple domestic battery and inverter. You need to schedule any EV charging for off peak anyway. The real culprits for going over 3kw are stuff like a kettle, a power-shower, or multiple induction hobs going at once. You might think 3,000 watts is a lot, but boil the kettle and fry some bacon while someone is in the shower and you zip right over that, no problem.

So… I’d suggest a 5kw or better inverter, and probably a 9.5kwh battery, or if you use slightly more energy than me, maybe a 13.5kwh Tesla powerwall. If you have a 4 bedroom house and power-hungry kids, and can afford it, maybe you have a good case for getting 2 9.5kwh givenergy’s or 2 powerwalls, especially if you also have solar.

So there ya go. I’m a total home-battery geek, and look at my stats every day, but if you arent that into it, but just want cheap electricity, then you can just go for it, set it up once, and then never look at it again! Ours is in the cellar and I only even see it if I go down to the cellar to get something out of the freezer :D. Batteries come with apps that will soon ping you if there is an error, so you can comfortably just ignore them.

I worked out on the basis of our first month that payback time for us was 5.7 years. That will fall a LOT in march when our fixed price tariff comes to an end, and fall AGAIN in summer when we get the advantage of saving up our surplus solar power during the day. (At the moment the only financial benefit for us is to buy cheap power overnight and use it during the day). I think in the long run the payback time for us will be maybe 3-3.5 years. Thats crazy good.

PLUS! We did it as a retrofit to existing solar. Right now the govt charges zero VAT on new solar, and batteries can be included, so if you can get solar+battery right now, its an even better deal. I highly recommend it!