How we research

We don't test products hands-on. Our product figures come from manufacturers and from independent tests published by others, and we label which is which. If that changes, we'll update this page and clearly mark any product we've measured ourselves.

Rules and regulations

• We read the rule itself where we can: the bill or statute, or the regulator's guidance, not just news reports about it.
• News coverage helps us spot changes, but we only mark a place as "allowed" once we've found the primary source.
• Each rules page shows the date we last checked it, and we re-check when a change is announced.
• We're not lawyers. Our summaries are a starting point, and your regulator, network operator or utility has the final word.

Product data

• Capacity, output, battery type and expansion options come from the manufacturer's spec sheet or manual.
• Where a published independent test measured something different, we note it and link to it.
• If we can't confirm a figure, we leave it blank and mark it "Specs being verified" rather than guess.
• Prices change constantly, so we date any price we show or link to the retailer instead.

Calculators and their assumptions

Every calculator shows its formula on the page and works in any currency. These are the defaults behind them:

• Plug-in solar output: kit AC watts × sun hours × 365 × 0.85. The85% factor allows for losses from heat, dirt, wiring and the inverter.
• Sun hours means peak sun hours: the equivalent number of hours of full sunlight a day, averaged over the year. Free tools such asPVGIS (Europe and beyond) andPVWatts (US) give a figure for your address.
• Savings: yearly output × share used at home × your electricity price. We assume you use 80% of what the kit makes, and you can change that. Power you don't use flows back to the grid, often for little or no payment, so we only count the share you use.
• Power station runtime: capacity (Wh) × 0.85 ÷ load (W). The85% factor allows for inverter and battery losses when running mains appliances.

Results are estimates. Orientation, shading, season, cold weather and appliances that cycle on and off all move real-world numbers.

Sources and updates

Guides end with a list of the sources we used and the date we last checked them. When a rule or a product changes, we update the affected pages and their dates.

Corrections

When we get something wrong, we fix it. If the fix changes a conclusion, such as whether something is allowed or which product we'd pick, we add a note to the page saying what changed and when. To report a mistake, emailhello@plugwattlab.com.

How we use AI tools

We use AI tools to help research and draft pages. Facts, figures and rules are checked against the sources listed on each page before we publish, and we decide what goes on the site.