You don’t need physics to own solar, but knowing roughly what’s happening on your roof makes every other decision easier, from panel choice to reading your generation graph. Here’s the whole journey, from photon to kettle.
Light in, electrons loose
A solar cell is a thin sandwich of silicon treated so that one layer wants to give up electrons and the other wants to receive them. When light hits the cell, photons knock electrons free, and the cell’s built-in electric field sweeps them in one direction. Free electrons flowing in one direction is, quite literally, an electric current. No moving parts, no fuel, no noise. Light in, direct current out.
A panel is simply dozens of these cells wired together behind glass. The premium, back-contact designs we fit move the wiring to the rear face of the cell, so no silver lines shade the silicon. That’s a chunk of why they lead independent efficiency tests, and why the front of the panel is a clean, uninterrupted black.
DC to AC: the inverter’s job
Your home runs on alternating current, so the panel’s direct current needs converting. That’s the inverter. In the systems we install it’s built into the battery unit itself: Powerwall 3 and SigenStor both integrate a hybrid inverter, which means solar can also flow straight into storage as DC without an extra conversion round trip.
kWp and kWh, untangled
Panels are rated in kilowatts peak (kWp): output under standardised test conditions. Your bill is measured in kilowatt hours (kWh): energy over time. The bridge between them is your location, roof pitch and orientation. As a UK rule of thumb, each kWp installed generates roughly 950kWh per year on a decent roof. A 5kWp array, then, produces in the region of 4,750kWh annually, close to a typical home’s entire consumption.
Cloudy days, short days
Panels respond to irradiance, the intensity of light reaching them. Clouds reduce it but don’t eliminate it: overcast British skies typically yield 10 to 25% of full output rather than zero. Winter’s real cost is shorter days and a lower sun, which is exactly why batteries and smart tariffs carry the December load while solar dominates from March to October.
How panels age
Modern premium panels degrade slowly and predictably, typically guaranteed to hold around 87 to 90% of their original output after 25 years, with warranties to match. The first year sees a small settling-in drop, then the curve flattens to a fraction of a percent annually. The panels we fit will almost certainly outlive the roof fixings, the inverter and quite possibly your ownership of the house.
Curious what your specific roof could produce? The savings calculator gives you a two-minute estimate, and a full proposal models it properly from satellite imagery and your actual usage.
This guide is general information, not advice for your specific property. Every Powergy proposal is modelled on your actual roof, usage and tariff.