Is DIY Solar Worth It? (UPDATE)
It’s been almost exactly three years since I built my own off grid DIY solar power system, and my god a lot has changed since then, so I thought this would be a perfect time to look back at my setup, see what’s changed over the years, how much power I’ve generated and cost I’ve saved, and if DIYing a solar power system is worth it. Let’s dive in, starting with my setup.
In 2022 I bought three Trina Solar 400W panels, a Renogy 60A MPPT charge controller, eight FOGSTAR LiFePo4 cells, a 150 amp Daly BMS, and a 3KW pure sine wave inverter. All of that was something like two and a half grand, with the majority of that being the battery. I’ve done my best to track at least the energy used with a Samsung SmartThings Zigbee plug, and it has recorded over 2 megawatt hours of energy use exclusively from solar. The back-of-the-napkin maths says that’s about £700 worth of energy at the varying energy prices over the years I’ve not had to spend. That does mean the return on investment time is like a decade, although I’ll talk more about that in a moment. For now I should also add that I’ve actually had to replace the inverter because I was an idiot and accidentally connect the grid to the inverter’s output (through multiple circuit breakers, I might add) which blew it. The new one was another £300 or so, and while I was in there I added a battery isolator switch and pre-charge resistor, and I’ve put the whole thing in an enclosed and partially insulated box where especially for winter the inverter’s heat output helps keep the batteries warm. I’ve spent maybe £500 on improvements over the years, which I’m well aware is basically the majority of the savings I’ve made.
There are plenty of changes I’d make to the system now, having experienced it for years. The biggest one is more solar panels. Three 400W panels only offer a maximum of 1.2KW, in summer, for an hour or two a day. The maximum this system can output is around 6KWh per day – I think one day was like 7KWh but that was one time. That’s obviously a decent chunk of power, and I do make use of it, but it isn’t enough to both run all my systems AND charge the battery fully. That means switching loads on and off (which is why I blew the inverter, I made an automatic switchover box) which is a little annoying. I’m planning on building a bit of decking with a slanted roof attached to the back of the house, so I’m considering adding another two or three panels on that and another charge controller so I can actually make use of the energy every day – and I might have some chance of using at least my displays over winter.
The battery capacity is actually fine, the thing I’d change is the BMS and monitoring so I can better track exactly how much energy is in the batteries, because right now I have to go off of the battery voltage, which obviously changes under load, and for LiFePo4 cells the voltage is remarkably flat with sharp changes at either extreme, so it’s pretty hard to know exactly. More info is definitely more better in this case. That would help me make better use of the energy I’m capturing. I would also love even a small wind turbine to supplement the energy production, but that’s a different story. I’d also consider running a five core armoured cable to the shed instead of the tri-core I have, so I can run mains power out to the battery and have a mains powered charger connected to the battery so even if I can’t fill the battery full, I can keep using everything connector to it. That also means I could potentially swap to a cheap nighttime tariff and fill the battery at night with the cheaper electricity to then use throughout the day.
To be fair to the system, there have actually been a couple of power outages that the system has helped tide me over. That self-reliance is something I value quite a lot, so having the ability to at least run the essentials even if the grid is out is really nice. That helps offset the slower-than-expected returns for sure. It’s also just been a fun project. If I were to build this again today, the biggest change has to be the batteries. The same pack that cost me like two grand would now set you back just £500. Seriously. That’s how much these LiFePo4 packs have come down in price, it’s mental. Stuff like the inverters are the same price, although the solar panels have always been remarkably cheap, but they’ve even come down more. I found 450W panels for £66 per panel – new! £66 for 450W for 30 years. That’s an absolute steal!
So, is it worth building your own DIY solar power system? Well, it’s pretty hard to give a definitive answer, but to be honest I think it’s more worth it now than it was three years ago when I built mine. It’s way cheaper, you can build basically the same system as me for £1500, or for a touch more build something even more useful. It depends a lot on your current energy supply and how much space you’ve got available. If, like me, you’ve only got space for a couple of panels then its usefulness is perhaps a little limited, and how I actually use the power is still a bit janky, but if you’re looking to power a cabin or something that wouldn’t otherwise have power and just want enough for lights, maybe a little media centre, this sort of thing with a couple panels on the roof would be great! Considering the dramatically cheaper costs involved now, this is an amazing way to be at least partially self-sufficient, save money and do something really cool. Of course, those are my thoughts, but I’d love to hear yours in the comments below.
