Selection of the power of a photovoltaic installation

The most important issue when purchasing a photovoltaic installation is selecting its power. Poor selection has a number of bad consequences in the future and remains an expensive issue to repair. The photovoltaic installation should not exceed the annual electricity demand. Therefore, the selection of the power of the photovoltaic installation should be entrusted to specialists, e.g. ecoABM. Specialists are able to perform a preliminary simulation of the operation of the installation, including designing the location of PV modules on the roof or ground.

The basic element of a photovoltaic power plant are photovoltaic modules (popularly called solar panels). Photovoltaic panels consist of semiconductor elements that convert solar energy into electricity as a result of the photovoltaic phenomenon. The cell is composed of two layers of semiconductor – n-type and p-type and connected electrodes – upper and lower. As a result of the impact of sunlight on photovoltaic cells, electrons are knocked out by photons. As a result of knocking out, a potential difference is created, followed by a direct current.

When planning a micro-installation, you should first answer the question about the current annual electricity consumption and forecasts for the coming years (will there be new devices, will the family grow, will someone in the household retire). If in the near future we plan to install air conditioning, a heat pump, a water heater or purchase an electric stove, dishwasher, etc., such comments should be reported to the consultant.

The basic element of a photovoltaic power plant are photovoltaic modules (popularly called solar panels). Photovoltaic panels consist of semiconductor elements that convert solar energy into electricity as a result of the photovoltaic phenomenon. The cell is composed of two layers of semiconductor – n-type and p-type and connected electrodes – upper and lower. As a result of the impact of sunlight on photovoltaic cells, electrons are knocked out by photons. As a result of knocking out, a potential difference is created, followed by a direct current.

Below is a table showing the average electricity consumption in single-family houses in Poland.

When answering the question about what power our photovoltaic installation should have, we should know that under sunlight conditions in Poland, 1 kWp will give us about 1000 kWh of electricity. Therefore, a 5kW installation will produce approximately 5,000 kWh per year, which should cover the electricity needs of a standard 4-person family.

However, if we do not plan to increase energy consumption from the grid in the future, based on the annual energy consumption from previous years and the building predispositions to install the installation (deviation from the south, deviation from 35 degrees, etc.), we can estimate the power of the installation so that it is properly balanced.

With good design of the photovoltaic installation, location options and sunny years – our electricity bills will be reduced only to fixed fees, i.e. approximately PLN 20 per month – approximately PLN 240 per year.

Once you know the power of the micro-installation that should be installed on a given farm, the next step is to select the appropriate number of photovoltaic panels with a given power. Please remember that there is a huge range of power on the market and you will find both polycrystalline panels with a power of 280W and monocrystalline modules with a power of 380W, both in a standard size of approx. 1 m x 1.7 m.

Depending on the availability of space on the roof, the installation can be performed more or less economically (the fewer panels with higher power, the higher the installation price).

A common mistake is purchasing too large photovoltaic installations. Not only will the cost of such an installation be much higher and the payback will be longer, but the surplus electricity will not be able to be used anyway. Therefore, there is no point in installing a power plant that is too large, as the surplus electricity will simply be wasted, or too small, as we will still receive electricity bills higher than the fixed charges.

However, if the photovoltaic installation turns out to be too small due to the purchase of new electrical devices or a reduction in the scale of savings – there are several ways to do it. First, check whether the current inverter still has enough power to add modules (inverters like to be oversized and then operate with better efficiency). If several photovoltaic modules can be added to a given inverter, this operation will be very simple and low-cost. However, if the inverter is already overloaded by 20% and the roof slope faces south, expanding the micro-installation will be expensive. After analyzing the current offer on the market, you can decide to use microinverters for added modules or simply replace the inverter with a larger one (or add another inverter). All of the above possibilities should be analyzed by an experienced team of consultants, because they are influenced by a huge number of factors.

The first step in selecting panels is to determine the size of the roof/ground, exposure in relation to the direction of sunlight, the angle of the roof and possible shading. If the roof slope does not face south, an east-west installation can be used. In this case, panels are most often placed symmetrically on two surfaces. However, please remember that this type of installation must be approximately 20% larger than an installation facing south in order to achieve the same parameters.

A common question from customers is how many solar panels per 1kW. Assuming that we plan to make the installation using standard size panels, i.e. approx. 1 m x 1.7 m, it can be assumed that we need approx. 1.8 m2 of area for one 310 W panel.

Example:

For an installation of 10 kW = 10,000 W, we need 33 panels with a power of 310 W (10,000/310 = 33 pcs.). Therefore, the roof area we need to install 33 photovoltaic modules on a sloping roof is approximately 60 m2. You can manipulate the number of panels – if we have a smaller area than 60 m2 and we want to achieve 10 kW, we can use, for example, monocrystalline panels with a power of 380 W. On the other hand – if we are not limited by the area and the main goal of the installation is to return it as quickly as possible, we can use more polycrystalline panels with a power of 280 W.

It can therefore be concluded that:

The electricity consumption of 1,000 kWh per year assumes approximately 1.25 kWp of photovoltaic installation power.

And

For every PLN 100 of the monthly electricity bill, 2.75 kWp of PV installation power is assumed.

You can also use a pattern

Where,

• Ek – amount of energy consumed annually [kWh]
• a – percentage share of current own consumption [%]
• b – percentage share of the amount of energy fed into the network [%]
• discount – up to 10 kW 0.8 above 0.7
• a+b = 100%
• Yield – annual energy production from 1 kWp of installed power by the PV installation [kWh]

Please remember that these are only general assumptions. In order to correctly select the installation power, it is also necessary to analyze the simulation of the location of the photovoltaic system depending on the angle of inclination and deviation from the south. It is also necessary to analyze potential shading.

The installation of a photovoltaic installation should be treated in the same way as the installation of solar collectors. Free-standing structures that are no more than 3 meters high do not need to be reported to the relevant authorities. This results from Art. 29 section 2 point 15 in connection with Joke. 30 section 1 of the Construction Law. However, if the structure exceeds 3 meters in height, such an installation must be reported. If the installation of the power plant will be carried out on a building and will involve the reconstruction or expansion of the property, this fact should be reported as an extension or superstructure of the building.