Approx cost to fit?
Ballpark of £1K per kWp installed for a basic system. More if you need optimisers/get a battery/want big brand panels/have a complicated roof.
We had 3.9kWp installed in December with optimisers on each panel and a 5.2kWh battery. £8,140.
Are they worth it?
In purely financial terms, yes, eventually, so long as you are not paying interest on the money to pay for them. Payback period will depend on how close to ideal your installation is, your usage profile and electricity prices. The more of your generation you can use, and the higher electricity prices are, the quicker you will recoup your expenditure in bill savings. It will be measured in years at least, almost certainly more than 5 years, hopefully less than 10.
How does it work? I don't know much about them and due to move to a south facing garden so wondering if it's worth looking into.
Light on the panels is converted into electrical potential, then a piece of kit called an inverter converts that into AC electricity, the same as you draw from the national grid. If the amount you are generating is less than your house is using, you get the difference from the grid. If you are generating more than you’re using, the extra is exported to the grid.
Once things are set up right, you can get paid for what you export, though not very much - most SEG (smart export guarantee) rates are about 5p/kWh. But you don’t have to use the same supplier that you buy your electricity from, so shop around.
One extra to consider is a battery. Although these are expensive, it means you can hang on to more of what you generate and use it later, rather than export it for buttons and have to buy back at full rate later. If you are on a split rate tariff you can also charge the battery on the lower rate and use it during the expensive period.
A few general points. I referred to kWp - this stands for kilowatt peak, and is the maximum amount which panels will produce in ideal conditions. However, much of the time conditions are not ideal. My system is 3.9kWp and I have seen it produce that (and slightly more) on a nice sunny day, but today it is grey and raining and the best I’ve had is 700W. It’s currently less than 100 W.
The amount you generate varies massively from day to day and throughout the year. Some days it will provide all you need and you will be exporting hand over fist. Other days it will help significantly, some days it barely makes a dent (mainly in winter). That’s a big factor in why I went for a battery, because even on days when there’s not much generation, I save by filling the battery at a cheap rate overnight and using it the next day. (I have an EV so am on a tariff with 4 hours very cheap each night)
It will help if you get your head round a few concepts.
Power (measured in watts or kW) is how quickly you are using energy, e.g. an old fashioned lightbulb was 60W or 100W, a kettle typically uses 3kW.
Background load: the power your house uses when there’s nothing much going on, so it’s just devices on standby,the fridge freezer and your router, for example.
Energy (measured in kWh, sometimes referred to as ‘units’) - this is what you are billed for at so many pence per kWh. If you consume a constant 1kW for exactly 1 hour, you have used 1kWh. 500W for an hour is 0.5kWh, 2kW for 3 hours is 6kWh etc.
A typical house will use about 3,000kWh per year, less than 10kWh per day. Some use an awful lot more.
If you get a solar quote, they should give you an estimate of the number of kWh which the system will generate in a year. Multiply that by the price you are paying per unit, and that is the maximum amount you could save in year, if you can use every single kWh you produce. But you will never do that, because there will be lots of times when you are producing more than you can use, and others when you’re not producing enough. Without a battery, consuming 20-30% of what you produce is the best most people will get.