This is a follow-up on my previous post about home energy, providing advice and experience after owning a solar PV and battery storage system for a while. The numbers are in for 2022 and we have a whole calendar year of data.
I’m not trying to cause a big sensation, just helping you to decide if you should get solar too (tl;dr, yes you should).
Here are the rough headline numbers for 2022:
- 2.5 MWh generated (at the panels)
- 0.8 MWh exported and sold back to the grid
- 5.5 MWh consumed (average of 15 kWh per day)
- 3.9 MWh bought (mostly during off-peak hours, ~11 kWh per day)
The numbers don’t quite add up due to losses at the inverter and in the battery charge / discharge cycles. I’ve rounded everything to reflect the inaccuracy and always towards the worse value. Configurations, weather, prices and inflation vary so this is only a rough guide with some big error margins. Ours is a very typical small system of ten panels (< 3.7 kW export) and not a perfect aspect (east / west split with shading).
This might look like a lot of consumed energy but we have electric vehicles a (small) heat pump and an induction hob. If you don’t need to own a car and have a modern, well-insulated house then solar generation could probably cover your entire usage. Compared to the 7.0 MWh of gas we used for heating (which includes none at all for over half of the year) it doesn’t seem that high.
We’re planning to get off of gas completely and hence will use more electricity. More on this in another post but I’d expect our electric consumption to go up by another couple of MWh per year.
This is why solar PV is only part of the solution. You could cover every home in panels and still not have enough energy when you need it. We need to build more wind, including more local onshore.
We’re on the Intelligent Octopus tariff and smart-charge our cars overnight to make the most of the cheap energy blowin’ in the wind. That’s the answer.
The price differential between peak and off-peak rates is now over 30p/kWh, which leads to these savings:
- ~£300 a year for charging the batteries off-peak (~5.5 kWh daily cycle)
- ~£600 a year for solar generation (peak rate minus low export rate)
- ~£30 a year for export (export rates suck so we minimise export)
Let’s call it ~£900 a year, which means it will take about 8 or 9 years to pay back the investment at current prices. Obviously, prices can and do change, as they have done with the recent dramatic rises. If local “nodal” pricing comes in (as National Grid would like) then energy will get more expensive in the south unless we get on it building local onshore wind and solar farms, and more transmission (e.g. overland high voltage direct current overhead lines)1.
Our solar system came in at £7,600 (inc. VAT and bird deterrent wire). The batteries make up £3,000 of that but are crucial and help in summer too to buffer generation and demand.
The batteries are rated at over 6000 cycles, which is over fifteen years of use. They should be going strong well after we are back in (the) black.
One decision you need to make is whether your battery storage system is AC or DC coupled. Ours is DC, which means that the batteries are directly connected to the solar inverter and wired to the same low voltage DC bus as the panels.
This keeps things simple but you can also have an AC coupled system, where the battery has a separate inverter and is wired in to the mains separately. AC can be useful if you are adding a battery to an existing solar installation, have multiple solar systems or if the systems need to be far apart.
For example, if you don’t have space near the solar inverter for batteries you could place them at a different site. Long runs of low voltage cable incur heavy losses so the distance between panels / batteries and the inverter should be kept as short as possible.
If you are siting the batteries elsewhere then be aware that some models don’t tolerate low temperatures. AC coupling can also help with metering things separately but this is not a big concern if the inverter is smart enough.
Generation varies, as you might expect, sinusoidally. This awesome wave means that some months we generate over 400 kWh but some less than 20.
In summer we have more than we need and in the winter we don’t generate anywhere near enough. You’ll need to be on-grid but can shift consumption and charging to off-peak.
The battery helps with this and it’s important to size it correctly. Ours doesn’t quite cover a day in the depths of winter but you don’t want to pay for capacity you won’t use.
The big expenses of a solar PV install are fixed (scaffolding, labour, inverter) so go large. Squeeze as many panels up there as you possibly can and get bird deterrent fitted from the start. It is expensive to retrofit anything later.
Get a solar battery inverter that is smart and can be controlled remotely. This gives you more flexibility for load shifting, particularly if you also have (or plan to get) other low carbon tech such as a heat pump and electric vehicles.
Unless you have frequent power cuts then I wouldn’t bother with a backup mode. This adds more cost and requires re-wiring the house (not all circuits can be put on a backup due to output limits).
We didn’t get a backup installed but then we have a battery with over ten times the capacity and a greater output sat on the drive (that could run the house for a week if required). More on this another time.
The trick to making solar work economically these days is to maximise self-consumption and minimise grid import / export. This is because mostly you pay a lot more to buy energy that you can get by selling it.
You can get solar matching kit that will heat a tank of hot water with energy that would be exported or top up your electric vehicle with a trickle charge. However, these are only to make the most of the sun, you will still need to do most of you charging from the grid.
This is why we need lots more cheap green electricity that we can simply get by building many more wind turbines, both offshore and onshore near where there are consumers of the energy. This may be intermittent but is perfect generation for smart flexible loads that can make the most of when it is windy nearby and hence cheap.
If you can’t see a wind turbine out of your window then that’s part of the reason that your energy bill is so high
Burning anything is bad. Some things may be worse to burn than others but we need to simply stop burning stuff at all. The key to transitioning heating and transport away from gas / wood / petrol / diesel quickly is cheap electricity.
We need to start thinking about tomorrow and we are in a race. Onshore wind and solar are the cheapest and quickest forms of generation to deploy. It’s a very simple solution but it’s not easy, and the reasons behind this are planning restriction rules. Hard to believe, given the national security and cost of living crisis implications of the last year.
A government consultation on planning rule changes for wind turbines closed last week. They should be treated the same as any other infrastructure project but there has been an effective ban since 2015. Hopefully the petitions and open letters have been effective. A change of government will be needed if not.
Local elections are coming this May. Make wind an issue, tell your candidates. If they canvas at your door then ask them why we are not building more wind to improve air quality, reduce carbon emissions, increase energy security and decrease costs for everyone.
You may get an uninformed something, something, birds, something back. Yet birds fly into windows all the time and we haven’t banned putting windows on buildings.
Let’s get more green power to the people.
- More info on wind curtailment and why we should buy local energy. ↩