What is active power?

The active power is the one called "useful" power, and it is the one consumed by the electrical equipment of the installation, the amount of power in kW that they really use to carry out the work. When making an installation, it is necessary to calculate how much power is going to be necessary for the consumption of all the appliances in the house at peak times and the energy needs based on the usual daily consumption (kW/h), and then  the batteries, solar panels, solar inverters, etc., that are necessary are sized.

What is the recommended active power?

But if it is an isolated solar photovoltaic installation, from Techno Sun we recommend that the minimum nominal active power in inverter is at least 2kW higher than the previous calculation. If for a house we need 3kW, the ideal would be to make an installation not less than 5kW (22A). The photovoltaic system and the accumulators must be sized according to this power, the usual consumption indicated above and the expected autonomy.

This is due to the fact that we must leave a power margin for possible start-up peaks or start-up of inductive loads that will produce reactive power. These must be taken into account when calculating the active power that we are going to need.

Continuing with the hypothetical case of a house that regularly consumes an active power of 3kW. In the case, for example, that during half an hour a day we connect a 600W drill, although the sum between the active power and the power of the drill is 3600W, we must suppose that we will have a reactive power that could be 700W, this would take us to that the sum of the active power plus the reactive power gives us 4400W + Wr. This total is closer to the recommended 5000W.

Otherwise, the maximum power that the inverter can deliver would be exceeded, and if this happens, the supply would be cut off immediately due to an overload. If the inverter is oversized, as well as the PV system and batteries, it will withstand the necessary power peaks and there will be no problem.

How is the active power calculated?

The active power to be provided by the electromotive force source (EMF) is determined by the useful work generated by a resistive load or resistance (R) when connected to an alternating current circuit. The active power is represented by the letter (P) and its unit of measurement is the watt (W).

The mathematical formula to find the active power consumed by any electrical equipment when connected to a single-phase alternating current circuit is:

P = I * U cos Ø

where:

V = Voltage of the current, expressed in volt

I = Intensity of electric current, expressed in ampere (A)

cos Ø = cos of the angle or power factor