How many solar panels per 1kW? How much electricity does a solar panel produce?

Information on the amount of electricity produced by the photovoltaic panel can be found on the nameplate. The panel’s Power Rating determines its performance under STC (Standard Test Conditions). What are these conditions? Temperature 25°C, insolation 1000W/m2, wind speed not higher than 1m/s. 

How many solar panels per 1kW? How much electricity does a solar panel produce?

The number that we see on the nameplate tells us how much energy the panel will generate in calm conditions during one hour of exposure to maximum solar radiation. In Polish conditions, due to the specificity of the climate, it is not always possible to operate the panel in the same conditions as the test ones, therefore its efficiency may be slightly lower. For this reason, it is best to entrust specialists with the calculation of the energy demand of our property and the determination of the number of photovoltaic panels necessary to cover it.

The main factor that decides  how much electricity a photovoltaic panel will generate is  :

• climatic conditions  , including the intensity of solar radiation (the power of solar radiation covers one square meter for one second of radiation) and insolation (the number of hours per year during which the sun’s rays fall on the ground) – the largest increase in energy is generated by photovoltaic panels in May, and the smallest from December to February.

• the degree of shading of the panels and their arrangement relative to each other  – if the panels are mounted in series, it is enough that one of the panels is shaded, for example, 30% more than the rest, and then the entire series of panels panels it is 30% less efficient.

• the angle of inclination, the location and the size of the ceiling on which the panels are mounted  : on a well-lit ceiling with south exposure (south-east and south-west), the power of the installation resulting from the calculations will correspond to the energy demand of the building , but a different orientation of the cover can make it 10% -15% smaller than the optimal configuration and it is necessary to increase the power of the installation, that is, add one more panel.

• type of inverter installed  – two photovoltaic installations of the same power can differ in price by up to 20-30% due to the fact that they are equipped with two completely different inverters, but it is a good inverter that makes each module work individually while achieving its maximum efficiency.

The efficiency of a photovoltaic panel, that is, how much electricity it will produce under standard conditions, is defined in the unit kWp – kilowatt-pic. This performance is called Peak Panel Power. It is estimated that  a household  (family with two children)  consumes between 4,000 and 6,000 kWh per year  . For such a farm, an installation that generates electricity with a maximum power of 4 to 6 kW is sufficient. 

Modern photovoltaic panels available on the Polish market generate an average of 290-400 W of energy. Let’s do a simulation, taking as an example a 335W panel, which will work for one hour at maximum power. The performance will then be approximately 335 Wh of energy. If we want to get 1kWh of energy, we need 3 panels running for one hour. If we assume that the annual electricity demand is, for example, 4,500 kWh, then this value must be divided by the annual yield (4,500: 335)  , which will give us 14 (13.4) photovoltaic panels.

 The power of the installation is calculated using the formula:

• 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 grid [%]
• 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 power installed by the photovoltaic installation [kWh]

It should also be remembered that depending on the type of cells (monocrystalline or polycrystalline), the performance of the panels will vary significantly. Polycrystalline panels have power in the range of 270 Wp-290 Wp. If 1 kWp is equivalent to 1 kW of power, for 1 kWp of installation there are 3.5 polycrystalline modules. On the other hand, monocrystalline panels are found in the power ranges of 300 Wp-360 Wp, therefore, 1 kWp of a photovoltaic installation is from 2.7 to 3.3 modules.

The size of the photovoltaic plant depends on the number and size of the panels. A standard photovoltaic panel measures on average 1 m wide and 1.7 m long (1.7 m2). So,  to install 4 solar panels of this size, we will need 6.8 m2 of free space on the roof  . If the roof is too small, you can opt for a solar installation on the ground.

Gaining insight into how much electricity a PV panel produces and how many panels are therefore needed  to meet the energy demand of a specific property always requires an on-site PV audit of the planned investment.Therefore, all data and calculations in this article should be treated as an estimate, and if you have already made the decision to invest in PV, please contact a professional PV system designer and supplier who will make the calculations for your specific investment. .