No number the engine did not produce
The website performs no arithmetic of its own. If the engine cannot be reached, we show nothing rather than an approximation. An honest blank beats a plausible wrong figure.
Why we built this
Because the honest answer is worth more than the flattering one, and nobody else in this market is selling it.
Households with solar want to know one thing: what it earns them. The market has answered with the number that sells best rather than the one that is true. Comparison sites publish a single flattering figure with no indication of how firm it is, because a range converts worse than a promise does.
We think that gets it backwards. A figure with no stated uncertainty is not more useful than a range. It is a range with the uncertainty hidden, which is worse, because you cannot plan against it and you cannot check it.
So we publish both: what we expect, and the level we stay above in nine out of ten simulated years. The second number is the one to plan with, and it is the one an installer can put in front of a customer and defend.
The same logic produces the part that costs us money. For a lot of households a home battery will not earn its cost back inside its warranty. We say so, in plain language, on the result page. A site that only ever says yes has told you nothing.
What that commits us to
Every figure carries its date
Tariffs and regulation move. Each supplier and each article shows when its numbers were last checked, so you can judge whether to trust them.
We publish what we have not proven
Our one validation of the physics against a real site did not meet the threshold we set. That is on the method page rather than buried, because you should weigh it.