Economical Calculation

There are two main ways of looking at this issue:

1) The cost of energy of solar origin. This approach is more suitable when the solar energy device supplies all the energy necessary for the given process (the solar collectors are not an add-on to a conventional energy device). It refers to the entire life of the solar energy device. The equation is:

the better and the less expensive device means lower cost of energy

where K is a coefficient depending on the conditions of installation of the solar device. It is around 0.9 for a good installation of the solar collector, but can be around 0.7 or even lower for a solar collector that does not face the Equator or comes under the shade of surrounding buildings or trees.

As easily observed, the cost of the energy produced is directly proportional with the price of the solar device and inversely proportional with its efficiency.

2) The payback time is an approach more suitable where the solar device replaces a previous conventional energy device or where it works in conjunction with it.

less cost and high efficiency means low payback

The denominator of this equation represents the value of the conventional energy saved each year by the solar energy device.

As expected, it results again that the price of the solar device should be small, while its efficiency should be high.