[count-your-change]

There’s the real use of solar, heating water and building space. Even on cloudy days solar heat is available and a well insulated building could probably use it as a sole means of heating most of the time.
Since installing solar heat isn’t complicated or difficult to install during construction I would think the payback time wouldn’t be too long.

[Minn]

Even on cloudy days solar heat is available and a well insulated building could probably use it as a sole means of heating most of the time.

You must live in the tropics.