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Photovoltaic: what installation capacity will cover my needs?

Photovoltaic solar energy has become very popular in recent years, this is because year after year the price of electricity increases and also because there are many power outages. One solution to these problems is the installation of solar panels in your home.

Before proceeding with the installation of the photovoltaic installation, the most important thing is the correct selection of the power of the system. In the case of households, the photovoltaic power must be selected in such a way that the energy produced during the year does not exceed the annual consumption. 

Photovoltaic: what installation capacity will cover my needs?

How to choose the correct power for a photovoltaic installation: this is usually what the company that installs the installation will help you with, but it is worth knowing what determines the size of the solar power plant. What is  photovoltaics  and how to choose its size correctly?

What is photovoltaic energy?

The word  photovoltaic  (often incorrectly referred to as photovoltaic) is a combination of two expressions: the Greek word phōs for light and the unit of measurement for voltage, volt. Therefore, it  is  easy to conclude that  photovoltaic energy 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 by Alexander Becquerel in 1839, direct current is generated in them. The electricity generated by the panels then goes to the inverter, where it is transformed into alternating current and uses cables to power your refrigerator, television or dishwasher, thanks to the higher voltage that displaces the electrical network of the house. The electricity that is not used daily goes to the network and begins to supply all the houses in the area. 

This surplus, legally, can be received again directly from the network (80% or 70% depending on the capacity of the installation). Usually by generating an overproduction in the summer months, you can easily use it to power your home in winter as well. When doing calculations, remember that despite being at work,

                                                                Photovoltaic (left) and solar collectors (right)

Photovoltaic panels themselves are most often confused with solar collectors used to heat water. The installed photovoltaic installation does not require periodic technical inspections, services or, for example, glycol replacement, as is the case with collectors, which makes solar energy one of the simplest and easiest to obtain.

The average cost of a photovoltaic installation in the home is 7000 to 10,000 collars and depends directly on the amount of electricity we use. It should be mentioned that the cost of a photovoltaic installation is significantly reduced by subsidies (the My Electricity program in the amount of 5,000 PLN), as well as tax breaks (the so-called thermo-modernization relief allows you to deduct the cost of investing in photovoltaics from the tax base ).

How much energy does the house consume?

The most important aspect when  selecting the power of  a photovoltaic installation  is determining how much electricity we use at home during the year. The size of the photovoltaic installation and the payback period will depend directly on this parameter; Most of the time, the larger the installation, the faster it pays for itself. For this purpose, electricity bills should be used, preferably summarizing all the previous year or the last months. Based on them, we can choose the approximate power of the installation so that it is neither too small nor oversized. 

At this stage, the possible increase in demand must also be taken into account, that is, if we are going to change the heating method to electric in the near future (for example, install a heat pump) or buy devices that consume energy (dishwasher, larger refrigerator). , air-conditioning). Each of these factors that we take into account will help us to better plan the photovoltaic installation.

From the analysis of the invoices received from the energy company, taking into account the principles of energy billing in the form of discounts, we can determine the approximate power of the photovoltaic panels that will be suitable for the home. According to the discount system for installations with a capacity of up to 10 kW per 1 kWh supplied to the grid, the prosumer can charge 0.8 kWh, in the case of installations with a capacity of 10-50 kW, the settlement is made in the ratio quantitative from 1 to 0.7 kWh.

How to determine the power of the installation if I am only building a house?

For existing buildings, determining the power of the installation is easier because it is compared to the average amount of electricity bills from the last year. In the case of new buildings, the electricity consumption should be estimated on the basis of the planned consumption and therefore the number and type of energy consuming devices and the number of household members should be determined. When the installation turns out to be too small during operation, it is always possible to expand the system, for example with the use of microinverters.

How to determine the power of the installation if I am only building a house?

Selection of photovoltaic energy and the location of the house and the size of the roof.

Before starting the installation work, it is necessary to determine the installation options, including the ceiling / floor surface, the surface exposure to the sun, the angle of the roof slope, and the possibility of shading. It is also important to evaluate the roof truss and covering. If conditions are not favorable, for example the roof to the east and west, it may be necessary to select a larger installation capacity to cover the farm’s total electricity demand.

                                                                                          Photovoltaic on the roof

                                                                                          Photovoltaic on the roof

Why is ceiling size important? A question that investors frequently ask is: ”  How many photovoltaic panels per 1kW?” . Approximately 3 panels are needed for this size of installation. The area that an installation of this type will occupy is approximately 4.5 m2.
In the case of 4kW it will be greater than 18 m2, and in the case of 10kW – 45m2. If the ceiling has insufficient surface area, installation on the floor should be considered.

Photovoltaic on the ground

Photovoltaics and the production of electricity by installation on the ground is as efficient as by a set located in the building. Mounting photovoltaic panels on the ground provides a great opportunity. Although the plot is large and has no shade, it is much easier than on the roof to position the structure at the optimal angle and in the correct direction towards the sun. A photovoltaic installation on the ground or in an outbuilding (for example, a garage) has the same VAT as in the house: 8%. However, PV installation costs can vary due to the need to erect the structure and make additional cuts.

                                                                              Photovoltaic on the ground

                                                                              Photovoltaic on the ground

Too low or too high power of a photovoltaic installation, which is better?

Opinions on photovoltaic energy and system energy are different. It is better if the installation is selected in a way that fully meets the needs of the farm, but is not always successful. Installing less power only results in lower savings on electricity bills. If the solar park does not fully cover the demand for electricity in our home, in addition to the fixed charges, there will also be small charges for energy consumption in the electricity bills. The payback period for the smaller PV plant will remain at a level similar to that for a full coverage plant.

Too high installation power means higher investment costs and a long payback period. The savings are not greater because excess energy is lost.
Oversizing the facility without justification is not profitable.

Photovoltaic: is it possible to increase the power of the installation?

If we do not plan to increase consumption in the near future, it is not advisable to oversize the installation, because there is always the possibility of expanding it with new modules.
In the case of a slight increase in power consumption, when it is enough to add 1 or 2 panels, it is often possible without replacing the inverter. However, when expansion is significant, it is a good idea to use microinverters. This photovoltaic installation will work independently of the original system, it is not necessary to replace the inverter and it is possible to choose panels of any technology or power.

If our electricity demand has been low so far, but, for example, we plan to change the heating system to an electric one, install a heat pump or purchase an electric car, it is best to immediately inform the consultant responsible for selecting the power of the system in this regard. Based on this information, the specialist will design the installation in such a way that the installation fully satisfies the household’s consumption, taking into account the new needs.

How to correctly calculate the power of the installation?

When choosing the power of the installation, one can take into account the fact that in Polish solar conditions, 1.25 kWp of the power of the photovoltaic installation is selected for every 1000 kWh of energy consumed annually.

  • Ek: amount of energy consumed annually [kWh]
  • a – percentage of current own consumption [%]
  • b – percentage of the amount of energy injected into the network [%]
  • discount: 0.8 per 1 kWh for installations up to 10 kW per 1 kWh, 0.7 kWh for installations with a capacity of 10-50 kW.
  • a + b = 100%
  • Yield: annual energy production from 1 kWp of installed power by the photovoltaic installation [kWh]

Own consumption

To calculate the power of the installation for a house, it is necessary to take into account not only the amount of energy consumed annually, but also the estimated part of own consumption, that is, the amount of energy produced that will be used continuously. . The higher the self-consumption, the better, because we use 100% of the energy produced. When we give a large amount of energy to the network, it must be taken into account that part of it (20 or 30% depending on the power of the system) will be lost. If our current consumption is low, and we use the energy produced by solar panels mainly in the afternoon or at night, it may turn out that to use only free energy, we need a slightly higher installation power.

Not the photovoltaic energy itself …

To maximize the power of the photovoltaic panels, it is important to correctly select the power of the inverter. The efficiency of the entire system depends on the inverter. Inverters achieve higher efficiency with a slight overload, an inverter with a low load will result in lower returns. The power of the inverter must match the power of the set of photovoltaic panels, but also with the manufacturer’s recommendations, the sunlight conditions in a certain region or the orientation of the panels towards the directions of the world.

The power of the photovoltaic installation and energy storage

In a standard photovoltaic installation, the energy storage is the public grid. The prosumer stores there the surplus energy produced and not used during the day, which can be collected at night, when the installation is not operating. In this case, the “charge” for energy storage is between 20 and 30% of the electricity produced. When selecting the power of the installation, it must be taken into account.

If we plan a hybrid installation, that is, with energy storage, we become largely independent of the grid. The electricity supplied by the RES facility to the batteries is stored in the form of a chemical substance, then transformed again and returned in the form of electricity. After unloading, the warehouses can be reloaded. In this way, a home can achieve up to 90% energy self-sufficiency. Energy storage They are a good solution for people who do not consume much energy during the day, when its production is highest, but use it, for example, at night and want to use it 100% for their own needs. 

Thanks to increased self-consumption during the day, we do not lose the energy produced irretrievably. This is especially important in the case of larger installations> 10kWp, where for 1 kWh we can receive 0.7 kWh from the grid. Thanks to the hybrid installation, the percentage of current self-consumption increases and the percentage of the amount of energy that is injected into the grid decreases. This affects the final power of the installation that we will need to fully cover the electrical demand of our home.

Although you can find many photovoltaic calculators on the Internet that can count the power of a photovoltaic installation without leaving your home, we encourage you to consult our energy advisor for free. The specialist, based on consumption, mounting possibilities, technical design and parameters of the photovoltaic panels, will accurately assess which size of the system will be the most advantageous. 

Why is it so important? The power of the photovoltaics installed on your roof is influenced not only by total energy consumption, but also by technical aspects: the angle of the roof, its orientation or even your lifestyle. These are factors that even the best solar calculator will often miss. The precise selection of power determines the profitability of photovoltaic energy, so it is better to entrust it to