The word photovoltaics is a combination of two expressions – the Greek word phōs meaning light and the unit of measurement for voltage – volt. It is therefore easy to conclude that photovoltaics is simply electricity generated by the sun. But in what way?

The sun’s rays fall on the photovoltaic cells, and thanks to the photovoltaic effect discovered in 1839 by Alexander Becquerel, a direct current is generated in them. The electricity generated in this way by the panels then goes to the inverter, from where in the form of alternating current sent via wires, it powers your dishwasher, TV or fridge, thanks to the higher voltage displacing the mains electricity from the house. The electricity that is not used on an ongoing basis goes to the grid and starts to supply other consumers.

The most important aspect when choosing the power of a photovoltaic installation is determining how much electricity we use in a year. The size of the photovoltaic installation and directly the payback period will depend on this parameter – most often, the larger the installation, the faster it “pays back”. For this purpose, electricity bills should be used – preferably summarizing the entire last year or the last months. On their basis, we are able to select the approximate power of the installation, so that it is neither too small nor oversized. At this stage, the possible increase in demand should also be taken into account, i.e. whether we intend to change the heating method to electric in the near future (e.g. install a heat pump) or buy additional energy-intensive devices (dishwasher, larger fridge, air conditioner). Each such factor that we take into account will help us plan a photovoltaic installation better.

Based on the analysis of bills received from the energy company, taking into account the rules of energy settlement in the form of discounts, we can determine the approximate power of photovoltaic panels that will be appropriate for the house. In accordance with the system of discounts for installations with a capacity of up to 10 kW, a prosumer can collect 0.8 kWh for 1 kWh delivered to the grid, in the case of installations with a capacity of 10-50 kW, the settlement takes place in the quantitative ratio of 1 to 0.7 kWh.

For existing buildings, determining the power of the installation is easier, because it is matched to the average amount of electricity bills for the last year. In the case of new buildings, electricity consumption must be estimated on the basis of planned consumption, i.e. the number and type of energy-intensive devices and the number of household members must be determined. When the installation turns out to be too small during operation, there is always the possibility of expanding the system, e.g. with the use of microinverters.

Before commencing assembly work, it is necessary to determine the installation possibilities, including the roof / ground surface, exposure of the surface to the sun, the angle of the roof slope and the possibility of shading. It is also important to evaluate the roof truss and coverage. If the conditions are unfavorable, e.g. a roof to the east and west, it is possible that it will be necessary to select a higher power of the installation so that it covers the total demand of the household for electricity.

Why is the size of the roof important? A question often asked by investors is – ” How many photovoltaic panels per 1kW?” . Approximately 3 panels are needed for this size of installation. The area that such an installation will take up is approx. 4.5 m2. In the case of 4kW, it will be over 18 m2, and 10kW – 45m2. If the roof has insufficient space, ground installation should be considered.

If we do not plan to increase consumption in the near future, do not oversize the installation, because there is always the possibility of expanding it with additional modules.
In the case of a small increase in energy consumption, when it is enough to add 1 or 2 panels, it is often possible without replacing the inverter. However, when the expansion is to be significant, the use of microinverters is a good solution. Such a photovoltaic installation will operate independently of the original system, there is no need to replace the inverter and it is possible to choose panels of any technology or power.