The first thing to consider is the direction of your House as each roof does not have the correct orientation or angle of inclination to take advantage of the Sun's energy.
Ideally non-tracking PV systems in the northern hemisphere must point toward South true, but guidelines that face in East and West directions more can work well with any efficiency.
It is also important to tilt the solar panels in an angle as close to the region's latitude as possible in order to absorb the maximum amount of energy all year round.
You can increase the level of energy production through a different orientation and/or inclination for morning or afternoon, Summer or winter.
Obviously, the modules that should never be placed in a place where they are shaded by trees nearby or buildings, no matter what time of day or time of year is to maximize production.
If you have a roof that is unshared and facing the South and then you'll need to decide the size of the system that you need; this can be a little tricky, as the production of electricity through solar means depends on the climate, which is never entirely predictable, and the demand of electricity can also vary.
However, you can troubleshoot them easily with a little help. Use meteorological data to discover the monthly average levels of sunlight for different geographical areas; this takes into account the rainy and cloudy days, as well as altitude, humidity and other more subtle factors. Design your system to the worst month, so you can have electricity enough all year round.
Along with these data and their average household demand that you can discover through your utility bill, you can easily determine the number of PV modules that you'll need.
