How accurate is Sun Hours, really?
Geographic and seasonal monitoring
I don’t just claim my forecast is accurate — I publish the real numbers, straight from opted-in users comparing my forecast to what their panels actually made. I’m still on v1, and this trend line is how I hold myself to it.
New here? What is a solar forecast, exactly?
All-time average
71.3%
Across every forecast checked
Best month
81.4%
Jul 2026
This month
62.1%
Oct 2026 so far
The trend, month by month
From Jul 2026 — the earliest month with enough contributors to publish responsibly — to today.
| Month | Average accuracy | Contributors |
|---|---|---|
| Jul 2026 | 81.4% | 10 |
| Aug 2026 | 80.1% | 17 |
| Sept 2026 | 72% | 36 |
| Oct 2026 | 62.1% | 48 |
63
users are sharing their real generation data with me right now
Every one of them opted in, for free, so I — and everyone else using Sun Hours — can see exactly how well the forecast is working. Thank you.
Want to help? Turn on the Accuracy card on your Home screen. Anonymous, opt-in, delete anytime.
How I calculate this
Method updated September 2026: readings are checked for valid dates, units and setup information. Poor forecast accuracy alone is never a reason to remove someone. Historical months shown here use these same checks, so changes from previously published scores do not by themselves demonstrate a better forecast.
This page currently measures saved daily forecasts. The separate morning-only planning benchmark is being collected and is not yet substituted into this chart.
Each day, opted-in users’ apps report what their panels actually generated. I compare that to the forecast I gave for the same day, and turn the difference into an accuracy percentage — 100% minus the size of the miss. I group every comparison by calendar month and publish the average.
Any month with fewer than three contributing users isn’t published, so a quiet month can never be read as one or two individuals’ actual generation figures. Sharing is opt-in, uses a random installation identifier, and uses only a coarse (roughly 11km) location — see my privacy policy for details.
Honestly
I’m still on v1
I’m not a professional developer — just someone who got fed up not being able to see, simply, when it was worth using my own solar panels, without wading through ads to do it. I built Sun Hours to fix that for myself, and I’m still the only one working on it. This page is how I hold myself accountable — the trend line is the truth, whichever direction it points.
See what I’m building next →Questions
How accurate are Sun Hours' solar forecasts?+
Averaging 71.3% accuracy across all opted-in users as of Oct 2026, calculated from real predicted-vs-actual daily generation data. See the full monthly trend and methodology on this page.
How is Sun Hours' forecast accuracy measured?+
Opted-in users' apps report what their panels actually generated each day. We compare that to the forecast we gave for the same day, expressed as 100% minus the size of the miss, then average it by month.
How many users share forecast accuracy data with Sun Hours?+
63 users have shared forecast accuracy data in the last 90 days. It's entirely opt-in, free, and uses a random installation identifier — no account required.
Is my data private if I share my forecast accuracy?+
Yes. Sharing is opt-in and uses a random installation identifier rather than an account. Your location is only ever stored rounded to roughly 11km, never your exact address, and you can turn it off and delete your shared data at any time from the Accuracy card on your Home screen.
Why don't all months appear on the accuracy chart?+
Any month with data from fewer than three contributing users is withheld from this page, so a quiet month can never be traced back to one or two individuals' actual generation figures.
How often is this accuracy data updated?+
Automatically, once a day — there's no manual step on our end. As more users opt in and more days pass, the trend updates itself.
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