The estimated lifetime of a PV module is 30 years. Furthermore, the modules' performance is very high providing over 80% of the initial power after 25 years which makes photovoltaic a very reliable technology in the long term.

Most manufacturers in general propose performance guarantees on the modules after 20 years of 80% of the initial output power. On the electronic components and accessories (inverters), the guarantee usually does not exceed 10 years.

But this doesn't mean that PV systems don't produce energy after 20/25 years. Most PV systems installed more than 25 years ago, still produce energy today!

The electricity production of a PV system depends on external (environmental conditions) and internal (technology, layout of the system) parameters.
 
The efficiency of the PV module depends on:

• The size of the PV system and its technology
• The orientation of the PV module towards the sun. The optimal orientation for locations above the Ecuador is the south. 
• The tilt angle or inclination of the roof. For European countries, the average optima inclination is 30-35 degrees
• The irradiance value on site
• The climate zone.

Shadows on the modules (also if they appear only at certain times of day) reduce significantly the gain of the whole system and should be avoided.

To determine the PV electricity generation potential for a particular site, it is important to assess the average total solar energy received over the year.

PV cells are made from layers of semi-conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced.  Groups of cells are mounted together in panels or modules that can be mounted on your roof.

The power of a PV cell is measured in kilowatts peak (kWp). That's the rate at which it generates energy at peak performance in full direct sunlight during the summer. PV cells come in a variety of shapes and sizes. Most PV systems are made up of panels that fit on top of an existing roof, but you can also fit solar tiles.

Solar tiles and slates

Solar tiles are designed to be used in place of ordinary roof tiles. A system made up of solar tiles will typically cost around twice as much as an equivalent panel system, although you will save the money you would have spent on roof tiles or slates. Solar tile systems are not normally as cost-effective as panel systems, and are usually only considered where panels are not considered appropriate for aesthetic or planning reasons.