This is going to be a very unemotional, numbers-based blog post. I've rounded the figures to make it more readable. And I've put some pictures in to make it slightly more interesting.
We have 5kWp of solar panels on our roof.
The panels generate about 4,200kWh per year. Mostly in summer, but a decent amount in winter.
Over a year, we export about 2,800kWh. That is what we sell back to the grid.
We get paid an average of about £0.22 for every kWh we export. That's about £600 per year in tax free income.
We use about 1,400 kWh directly from our panels. When the sun is shining, we don't buy electricity. Assuming electricity prices of £0.30 per kWh, that's a saving of £400.
We earn £600 and save £400. That's a total yearly "income" of £1,000.
The average installation of domestic solar panels is - very roughly - £5,000 to £8,000. You might find a group-buy scheme which does it for less, or you may have a really awkward roof and find it costs much more.
So, at the current prices solar panels will pay for themselves in ~5-8 years.
If electricity prices rise, and export prices also rise, that timescale will drop.
If electricity prices fall, it will take longer to pay back.
If the price of solar installation continues to drop, it becomes a no-brainer to get solar installed.
Given another 20 years of generation, that could turn a healthy return on investment.
There are no on-going maintenance costs with solar panels. The panels are usually guaranteed for 25 years. It is possible that the inverter needs replacing (usually guaranteed for 10 years. Cost of a few hundred). And, like any electrical installation, things can break.
I should note that we have 2kWh of batteries. That will affect the ratio of how much electricity we use and export. It also adds to the cost of installation.
We use Octopus Energy for Solar Export (join and we both get £50). Their "Agile Export" pays a variable amount depending on electricity demand. It is worth shopping around to see if anyone offers a higher payment for export, or a lower price for import.
Solar has high upfront capital costs. Not everyone has £6,000 laying around. But if you can afford panels, they can dramatically reduce the amount of money you pay for electricity.