Updated June 2017
Where solar can realistically be used depends on the need and motives, but generally it is in temperate areas and at latitudes lower than 38-40 degrees.
The map below gives you a general guide. Technically it just becomes feasible for you where there is at least 2.5 Peak Sun Hours (PSH) a day. That, for example, is typical for a sunny Tasmanian/New Zealand/Spanish mid-winter. Solar really comes into its own from 3.5 PSH onward. That is typical across much of Australia, Europe and the USA excepting mid-winter. It’s more or less anywhere that’s not light yellow on the map.
This map shows typical average yearly daily input in PSH. Technically 1 PSH is an irradiation of 1000 watts per square metre. Map: original source unknown.
Where solar can realistically be used
Apart from mid-winter months, most of central Australia, and central America and India has about 6.5 PSH a day. Solar modules (in 2017) are 14%-21.0% efficient in turning sunlight into electricity. About 1000 watts of solar modules in such area will thus produce 140-205 watts. That gives you about 910 – 1335 watt/hours a day.
You can find the Peak Sun Hours, for almost anywhere. Google the name of the closest big town plus Peak Sun Hours. You can also obtain it from meteorological offices worldwide.
Our books Solar Success and Solar That Really Works! show Peak Sun Hours for Australia’s mid summer and mid winter. Solar Success covers every aspect of designing, installing and using solar in homes and properties. Solar That Really Works! does likewise for boats, cabins and RVs. Both will assist you in building a successful solar system.
These too will assist you.