Predicting Sun Hours in the UK: The 8-Second Check (and When You Need Something More)

People are searching for this more than ever

Spring 2026 was one of the sunniest on record, with most UK regions seeing 5–25% more sunshine than average. It's no surprise more people are typing some version of "prediction of sun hours in the UK" into Google — whether they've just got panels, are thinking about getting them, or just want to know if today's worth hanging the washing out.

We've started showing up well for that search. So has Solcast, and so has a genuinely useful Reddit thread on r/SolarUK where their free tool gets recommended repeatedly. That's worth addressing directly, because we think both can be right answers — just for different questions.

What "predicting sun hours" actually means

A sun hour isn't clock time. It's a measure of energy — one sun hour is the equivalent of your panels receiving peak-intensity sunlight (1,000 W/m²) for a full hour. A UK winter day might only deliver 1 sun hour's worth of energy across 8 hours of daylight. A clear June day can deliver 5 or 6.

Predicting it means forecasting how much of that peak-equivalent energy is going to land on your specific patch of roof, sky, or balcony on a given day — which comes down to three things: your latitude, the time of year, and how much cloud is forecast to get in the way.

Two different questions people are actually asking

Dig into the searches and the Reddit threads, and there are really two separate needs hiding under one search term:

"Is today good for solar, and when's my best window?" — This is the vast majority of people. Panel owners deciding when to run the dishwasher, EV owners timing a charge, plug-in solar owners wondering if it's worth pegging the washing out. They want an answer in seconds, not a login.

"I need accurate, site-specific irradiance data for a project" — Installers sizing a system, developers building something on top of forecast data, anyone who needs panel-tilt-and-azimuth-level precision or an API. This is a smaller, more technical audience with genuinely different requirements.

We built Sun Hours for the first group. Solcast, from what we've seen, is genuinely excellent for the second.

The Sun Hours version: two questions, eight seconds

No inverter login. No account. No system specs to look up. Just your postcode and the best single-day kWh figure your panels have ever produced — a number most people can find on their inverter app in a few taps.

From those two answers, Sun Hours builds a personalised 7-day, hour-by-hour forecast calibrated to your actual system, using live UK weather data rather than historical averages. Open the app, see today's number, know your peak window. That's the whole job it's trying to do.

When Solcast is the better call

We're not going to pretend a two-question app is the right tool for every job, because it isn't. If you're an installer quoting a system, a developer who needs an API to pull irradiance data into your own product, or you want panel-tilt-specific modelling rather than a postcode-level estimate — that's a genuinely different level of precision than Sun Hours is built to give.

Solcast's free rooftop solar forecasting tool is built exactly for that. It's the tool Reddit's r/SolarUK keeps pointing people to for a reason, and if bespoke, technical-grade data is what you actually need, it's worth going straight there rather than trying to force a quick-check app to do a job it isn't designed for.

How to decide in ten seconds

• Want to know if today's good for solar, with zero setup? Sun Hours.
• Want to know your best window this week for the dishwasher or EV charge? Sun Hours.
• Sizing a system, quoting a job, or need site-specific accuracy? Solcast.
• Building something that needs an irradiance API? Solcast.

Both are free to start. Neither is trying to be the other.

The bit that ties back to plug-in solar

If you've landed here because you're weighing up plug-in solar rather than a full rooftop system, the forecast question matters slightly differently — you're less concerned with system design and more with simply knowing when to use the electricity you're already generating. That's squarely the quick-check use case. Our UK plug-in solar guide → covers current pricing, the rules, and a savings calculator, alongside the forecast.