The huge investments in solar energy around the world are not only about environmental concerns. An equally important reason is financial. The theoretical limit for the efficiency of photovoltaic panels exceeds 80%. And the efficiency of current models averages 20-25%. This forces engineers and scientists to constantly look for ways to increase specific productivity – and thus benefits. One of the options being researched is the installation of mirrors for solar panels.
The rationale for this attempt is obvious. The physical laws of optics make it possible to reflect and focus any number of rays at one point. An increase in insolation in it will lead to an increase in energy. However, with an equivalent increase in efficiency in such a situation, everything is not so simple.
When the combination of “solar panel and mirror” becomes profitable
In practice, the use of mirror reflectors is not always advantageous. The list of optimal conditions for this is as follows.
- For various reasons, the working surfaces of solar panels cannot be positioned at an optimal angle to the sun. Using a mirror can easily make the direction of the beam ideal.
- In a solar power plant with rigidly fixed modules, the installation quickly loses its performance when the position of the sun changes. In this case, mirrors can replace trackers, providing an increase in efficiency by 25-30%.
- In space and other systems, where financial costs are not fundamental, and the highest possible efficiency is in the first place.
- When using double-sided panels. Placed underneath, an inexpensive mirror surface will increase the overall system output by almost a third.
- In tower solar power plants, where mirrors always play the role of reflectors, and the solar battery is replaced by a heating tank.
Solar installations of various types with the use of mirrors were most widely used in the first half of the 2010s. The price of photovoltaic panels was still high then, and systems with reflectors and concentrators proved to be more profitable and efficient.
As soon as the cost of classic solar equipment fell below a certain limit, the situation was reversed. And today the idea of concentrating energy by using reflectors is used only in exceptional cases.
Is it worth installing solar mirrors under standard conditions
Experts in the field of solar energy do not recommend this choice. There are two main reasons for this.
- The system, based on the use of a large number of perfectly polished surfaces, is difficult to operate. Specular reflectors require frequent cleaning and constant repositioning. It is impossible to carry out the latter manually, and the use of automatic trackers significantly increases the cost price.
- When a large amount of energy is concentrated in a small area, it heats up to high temperatures of several hundred degrees. Silicon panels in such conditions will begin to degrade rapidly, and their efficiency will decrease.
There are two exceptions to the second option:
- the use of mirrors in installations operating in regions with prevailing low temperatures;
- replacement of conventional silicon modules with panels based on additives and materials that are insensitive to heat.
Solar panels and magnifying glass reflector
All of the above applies to large mirror surfaces. However, miniature reflective lenses of a special design have found their market niche. Among them, the most demanded are:
- mini-cells up to 1 cm2 with additional liquid cooling;
- Fresnel lenses widely known in optical physics;
- facetted mirror structures, reminiscent of the structure of the eyes of some insects.
The success of such experiments is evidenced by the technical characteristics of the following known systems on a “mirror” reflective basis.
- Amonix Inc. (USA) and IES _ & _ UPM (Spain) – facet, two working layers of absorption, efficiency 35.8%. Market value – from $ 450 per square meter.
- Sharp (Japan) – concentrating lenses, three working layers of absorption, efficiency 41.5%. Market value – from $ 550 per square meter.
- Sharp (Japan) – Fresnel lenses, 4 to 6 layers, efficiency 48.0%, designed specifically for the aerospace industry. From $ 800 per square meter.