Our solar and wind power systems

Over the last few months I've been asked by a few people about what we've done in terms of PV and wind turbine electricity generation, so I thought I'd lay out the basics of our systems here. I am not a qualified electrician, but I do understand electricity and the dangers associated with it, and I spend a lot of time reading datasheets and learning about how to do this stuff before starting. If you do go down this path then make sure you have a clear understanding and be careful. Having said that, in my opinion, there is nothing stopping any competent DIYer from building an effective and useful off-grid system safely and at relatively low-cost. There is lots of information out there from manufacturers of bits of kit and from enthusiasts and YouTubers.

So, what do we have?

Two systems:

1) A standalone system that we use almost exclusively for charging our cars. This system can supply 4kW max to the car charger, and can also store energy in a 24kWh (nominal) 48V lead-acid battery bank. This system is housed entirely in the shed and was the first one that I put together. It has been in use for 5 years now, and seems to be working as well as it did when first installed. We have had one failure very early on (the inverter), but the manufacturer sent new parts and it has been working without any faults ever since. The battery bank was expensive (~£2000) and being lead-acid needs regular water top-ups, especially in the summer, so is a bit of faff but seems to be holding up ok. When I installed it I estimated that it would have about 5/6 years lifespan, but it still seems to have reasonably good capacity, so I'm not thinking about changing it yet. Last year I added a manual changeover switch so that we could run the house from this setup when the cars were fully charged, but the 4kW limit was a bit irritating as we'd often forget and switch on the kettle at the same time as the washing machine and the inverter would cut out (not popular with the gamer in the household). The more normal mode of use (pre-COVID) was that the battery bank in the shed would charge up during the day and then be transferred to one of the cars in the evening. This is not a nice mode of use for lead-acids (being fully discharged daily), so I set the voltage limit very conservatively which means that we only actually use about 10kWh of the 24 available in order to improve the battery lifespan. This system has a total of 6kW of PV panels (second-hand 5 years ago) and a (fairly poorly sited) 500W wind turbine, and provides about 70% of our car charging needs throughout the year. For about 7 or 8 months of the year we use this almost exclusively, with the exceptions being when we have multiple long trips on consecutive days. We usually do one or two round-trips to town per day. A round-trip is about 25 miles and has ~1,300ft of climb. I spent a bit less than £5,000 on this when I installed it and suspect that it has paid for itself around twice over by providing electricity for about 50,000 miles of driving (probably actually a bit more than this).

About once a month in summer and a couple of times through the winter I spend a happy 20 minutes topping up the battery electrolyte (that squeezy bottle is perfect for the job).

Rather dusty bank of 16 Trojan T105s. Still going strong after a bit more than 5 years.

Very impressed with this 4kW Voltacon inverter/charger. Not very proud of the wiring job mind .

The watering kit for the Trojans is a god-send. Would be a nightmare having to do 48 individual caps by hand each time.

What it's all about.

These QUBEV chargers were very cheap and seem to work pretty well. Box is getting a bit rusty though!

2) A system for the house. This system is relatively new and has a newer model inverter that can supply up to 8kW. We have a 9kWh LiFeP04 battery bank on this which is charged from 3kW of (again second-hand) PV panels (soon to be expanded to 4.5kW). We are also considering another 500W wind turbine, in a better site than the one for the car charging system. The 8kW capacity means that we have not yet hit the limit using our normal domestic load habits, and we can run the washing machine, dishwasher and heat-pump simultaneously although this almost never happens in practice! It is on an auto-changeover switch, so when the battery runs out of juice it switches back to the mains. As this was only recently commissioned (in the middle of summer), I don't really have a feel for how much of our usage this will provide when the PV is less productive. As I type this we have been "off-grid" for about 48 hours, including one rather grey and one fairly sunny day. This includes a couple of loads of washing, a couple of dishwasher runs, the immersion heater and a batch of cupcakes (yum). My rough calculations indicate that to be completely off-grid through the winter, and using the heat-pump for heating, would need about 30kW of PV and about 20kWh of storage: probably not realistic, but we'll keep adding bits and pieces of generation and see where we get to.

Fancy new Pylontech US3000C batteries. Built-in BMS will talk directly to the inverter, so hopefully all properly managed and no more faffing with the squeezy bottle.

Fancy new 8kW inverter connects to WiFi and does all sorts of performance logging etc. Even the app (I'm a bit allergic to apps these days) works pretty well.