The Five Most Important Performance Specifications You Need For The Evaluation Of A Solar Panel System

The Five Most Important Performance Specifications You Need For The Evaluation Of A Solar Panel System 1
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The Five Most Important Performance Specifications You Need For The Evaluation Of A Solar Panel System


An essential selection and quality criterion for the solar PV systems (or rather solar PV panels) is the yield obtained from the solar panel system. When comparing different quotes, you inevitably come across specifications, which are essential for the evaluation of a solar PV system.

The performance evaluation depends on the particular perspective: Is it the matter of the rated power of the Solar panel system, the solar panel efficiency, the total efficiency of the solar PV system or the ecological balance?

1. Peak output/ Kilowatt peak

Watt peak or kilowatt peak is the unit of power of the solar PV system, and it is also a characterization of a solar panel system, which delivers xy kilowatt peak output.

The so-called peak output is defined as the nominal output of solar PV panels under the Standard Test Conditions (STC). These are based on the following conditions: a global solar radiation of 1000W/m², solar cell temperature of 25°, and air mass of AM=1.5. In reality, the Standard Test Conditions can rarely be achieved.

The peak output of the solar panel system depends on two things:

  1. The nominal power of the installed solar PV panels, and
  2. the size of the solar panel system (the number of solar PV modules).

The peak output can rarely be achieved. Therefore, the informative value of the Watt peak is limited. It serves as actual information. However, there are cases, in which the reference to Watt peak (Wp) / kilowatt peak (kWp) is useful:

  • The expression of nominal power in Watt peak is also interesting to determinate the area needed to install a certain solar capacity on a limited roof surface.
  • For price comparison between the different solar panel types. Then, it is possible to make a quick estimation whether the solar panel system will be cost effective or not.

Tip: It should be compared only solar PV panels, which use the same solar photovoltaic cells, so not for example, monocrystalline with thin-film solar cells.

When comparing, the temperature coefficient (this describes the solar cell efficiency’s behavior when warming) and the absorption capacity of diffused light (weak light behavior) must also be considered.

  • Moreover, finally, the selection of the solar power inverter is based on the peak output as well as on the current and voltage range, in which the solar PV system can operate.

2. Efficiency of a solar PV system

The effectiveness of a solar PV system is decisively influenced by two factors:

  • Solar panel efficiency
  • Solar inverter efficiency

The solar inverter efficiency is more the important out of the two. A solar power inverter with low efficiency can nullify the best efficiency of solar PV panels.

3. Solar panel efficiency

Solar panel efficiency is defined as the ratio between the energy output and the irradiated solar energy. It gives the answer to question: How much available solar energy is converted into solar current?

The Solar panel efficiency depends on the used solar cell technology in the modules.

The following chart shows an overview of the efficiencies of the different solar cell types.

Solar cell typesSolar cell efficiency
Monocrystalline solar cell18 % bis 21 %
Polycrystalline solar cell13 % bis 16 %
Amorphous silicon cell6 % bis 7 %
Tandem cell10 %
Thin-film cell (CIS)10 % bis 12 %
Thin-film cell gallium arsenide20 % bis 25 %
Thin-film cell cadmium telluride11 %
Dye cell "Grätzel cell"2 %

4. Energy amortization time


The Five Most Important Performance Specifications You Need For The Evaluation Of A Solar Panel System 3

The energy amortization time indicates the time in years, from which a solar panel system begins to produce more energy than the energy used during its manufacture. The shorter is the energy amortization period of the solar PV system, the better.

The energy amortization time is also important for the ecological assessment of the solar panel systems.

The energy amortization time depends on the location of the solar panel system. It is shorter in southern countries than in northern countries and bad weather regions, because the energy amortization time can be rapidly reached in the regions with high global solar radiation.

5. The ecological balance of solar panel systems


The Five Most Important Performance Specifications You Need For The Evaluation Of A Solar Panel System 5


You hear many good things about solar panel systems: they are profitable, they have a good CO2 balance, their resource consumption is comparatively low etc.

Although these are important aspects, which play a role in the establishment of an ecological balance, but it lacks for a correct life cycle assessment a lot of other things.

Ecological balance considers the solar PV system from the extraction of raw materials (the production of silicon from quartz sand) until the disposal of the worn-out solar PV panels. The focus here is the environmental impact at each stage.

An establishment of the ecological balance is not a simple task, because especially in the use phase of the solar PV panels, various parameters interact. This makes the evaluation very difficult.

Investigations carried out at the Fraunhofer Institute for Building Physics have demonstrated that the ecological balance of solar panel systems is constantly improving and that it is clearly better than the ecological balance of the fossil fuel plants.

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