Every installer will show you a payback figure. Not every installer will show you where it comes from. A solar and battery system earns its money back through four distinct streams, and understanding them is the best defence against a quote that flatters to deceive.
Stream one: solar you use directly
Every unit of electricity your panels generate and your home uses on the spot is a unit you don’t buy from your supplier. Because it replaces electricity at the full price you pay, this is usually the most valuable stream. How much you get depends on the size of the array, the direction and pitch of your roof, any shading, and how much you use while the sun is up.
Stream two: solar you store
Without a battery, surplus generation goes to the grid for an export payment that is usually lower than the price you pay to import. With one, that surplus charges the battery and powers your home in the evening instead, so more of your generation replaces electricity you would otherwise have bought.
Stream three: cheap-rate charging
On a time-of-use tariff, a battery can charge when electricity is cheap and power your home when it is expensive, including in the darker months when the panels produce less. What this is worth depends entirely on your tariff and how your household uses energy.
Stream four: export income
Whatever still goes to the grid earns a Smart Export Guarantee payment from your supplier. It is usually the smallest stream, and the rate varies between suppliers and tariffs.
So what decides your payback?
There is no single typical answer, which is why we don’t quote one here. Payback depends on what the system costs, how much it generates on your roof, how much of that you use yourself, the tariffs you import and export on, and what happens to energy prices. Homes that use more of what they generate tend to see a quicker return. A smart tariff and a battery that manages it well, such as SigenStor, can help too.
The useful question for any quote is not “how fast?” but “based on what?”. Ask to see each assumption, and check it against your own bills.
The traps to watch
- Inflated self-use assumptions. Assuming you’ll use nearly all your generation without a battery is storytelling.
- Silent price-inflation assumptions. Aggressive energy-price growth flatters any payback number.
- Brochure generation figures applied to a shaded, east-facing roof.
- Ignoring the export limit your DNO may apply (see our G98 and G99 guide).
Our savings calculator lists every assumption beside its estimate, and your full proposal is modelled on your actual roof and usage. If the numbers don’t stack up for your home, we’ll say so.
This guide is general information, not advice for your specific property. Every Powergy proposal is modelled on your actual roof, usage and tariff.