People who plan to install photovoltaic panels most often focus only on comparing electricity consumption. However, this is definitely not enough, because several key factors that affect the efficiency and profitability of photovoltaics should also be taken into account. Choosing the wrong set power is a mistake that can turn out to be very costly.
The proper selection of the power of a photovoltaic installation is not only a matter of savings, but also the efficiency of the entire system. Too large an installation generates unnecessary costs, and too small an installation will not cover the energy demand. Well-chosen power translates into faster return on investment and real financial benefits.
Photovoltaics step by step. How to calculate the required power of photovoltaic panels?
As explained by the Ecosynergia.pl website, the power of the installation should be adjusted to the annual energy consumption, which is best determined on the basis of invoices. It is worth remembering that the actual energy production is usually 10-20 percent. lower than the nominal power (maximum found in laboratory conditions).
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As Enerad.pl explains, the nominal power is determined at solar radiation intensity of 1000 W/sq m. and panel temperature, which does not exceed 25°C. Meanwhile, in Polish conditions, the maximum solar radiation in summer rarely exceeds 800-900 W/sq m, and photovoltaic panels – especially in summer – heat up to 50°C, and in extreme cases even to 70-80°C.
Good calculations and estimates are the basis for successful photovoltaic investments
When deciding on the type of photovoltaics, you should also adopt a basic formula that allows you to estimate energy demand. The annual energy consumption (kWh) should be divided by 1000 and the result multiplied by 1.25 due to uneven sunlight throughout the year.
For example, for a house consuming 4,000 kWh per year, the optimal installation power is approximately 5 kWp. The kWP designation is kWp (kilowatt-peak), a unit that determines the maximum peak power of a photovoltaic installation in ideal conditions. As explained by the Enerad.pl website, 1 kWp of installed power allows the production of an average of approximately 900–1000 kWh of electricity per year in Poland.
Theory is one thing, practice is another. Photovoltaics without errors
The selection of the power of photovoltaic panels depends on energy consumption, sunlight, the angle of inclination of the panels and their orientation. You should not be guided by the surface area of the house – the key is the actual electricity consumption. It is assumed that for every 1000 kWh of consumption, approximately 1200 kWh from PV is needed, i.e. for 5000 kWh per year, the installation should have approximately 6 kW.
As Enerad.pl explains, the most popular panels have a power of 400 to 700 W, although there are models exceeding 700 W. In practice, the actual power of the panels is usually lower than that declared by the manufacturer, due to operating conditions.
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It is worth avoiding overdimensioning – overproduction of energy is not always profitable. Single-family houses usually need 4-5 kWp, houses with a heat pump or an electric car – 6-10 kWp, and companies and farms even above 15 kWp. It is crucial to take into account both current and future energy demand.
As Enerad.pl reminds, in the net-billing system it is recommended to assume 1.2 kWp of power for every 1,000 kWh of consumption. Oversizing the installation is not profitable – it is better to invest in energy storage than in excess panels. In the discount system, surpluses are lost after 12 months, and in net-billing, the difference in purchase and sale prices of electricity may extend the return on investment.
