How we score

Each product earns up to 100 points, shown as a score from 4 to 10 (4 plus 0.6 for every 10 points), so a sound product is never marked down to a harsh low score. Scores compare a product only with others in the same category (and, for power stations, the same size band). Price counts, but commission never does. Where a maker doesn't publish a figure, that part scores half marks and the page says "not published".

Power stations

Solar panels

Plug-in solar kits

Plug-in kits are only recommended once we have confirmed a Compliant listing on the ENA Type Test Register. Home solar batteries are listed without a score.

The figures we work out

1. Power-cut cover: hours a station runs a fridge-freezer (30 W average), router (15 W), two LED lamps (8 W each) and phone charging (10 W), with 85% of stored energy reaching the sockets.
2. Battery cost over its life: price divided by capacity times rated cycles.
3. Solar: 862 kWh a year per 1,000 W of panels facing south at 30° (DESNZ).
4. Savings: self-use of 62% (tilted) and 72% (upright wall) for a home with someone in during the day, from the same DESNZ table; 26.32p a kWh (Ofgem). Other directions, shade levels, "out at work" self-use, and panel watts above 800 W counted at half value are our own estimates, labelled as such.

Where the facts come from

Makers' own UK stores and big UK retailers, each with the date we read it. No Amazon prices or ratings. No hands-on testing claims. Prices are checked daily by an automatic monitor and in full every month.

Corrections

Tell us at [email protected] and we fix errors within a working day.