When building a photovoltaic installation, especially an isolated one, it is very important to calculate the electricity consumption, to ensure that there will never be a lack of energy supplied by the solar panels for the solar installation and to adjust the economic cost of the same.

The correct dimensioning of the installation is perhaps one of the most important aspects when we are going to install photovoltaic solar energy. For this sizing it will be essential to know what is the electricity consumption.

What is power consumption?

Electricity consumption is defined as the amount of energy (kW) that has been used at a supply point during a specific period of time, such as an hour or a day, for example.

This means the sum of all the consumption generated by the different appliances connected to the home or business network.

How much is the electrical consumption of my home/business?

When calculating the amount of consumption, the two types of energy consumed by electricity must be taken into account:

• Active energy. It is the energy consumed directly.

• Reactive energy. Some devices convert energy into electromagnetic fields that have a storage cost and consume energy, even if it is not useful.

Normally, reactive energy will be included in the active energy consumption indicated for each appliance, so when calculating the amount of kW consumed, the following factors should be taken into account:

• Characteristics and dimensions of the house.

• Electrical appliances in the building.

• Supply location.
  

• Number of users.

• Time of consumption.

With these factors in mind, we should make a list of all electrical appliances and items that consume electricity (such as light bulbs) and indicate the hours of daily use, or the approximate monthly average.

As a reference, in an average household, it is estimated that electricity consumption is distributed as follows:

• Household Appliances 55.2%.

• Lighting 11,7%.

• Cooking 9,3%

• Hot water 7.5%

• Heating 7.4% 

• Standby 6.6%

• Refrigeration 2.3%

Below is a list of the consumptions for some of the most common appliances. These consumptions are indicative, since they vary according to their efficiency and with the passage of time they have to consume more energy. For greater precision, it would be best to go to each appliance and check the exact consumption in the manual. From this list it would be necessary to choose the appliances that we have and how many hours they are used per day.

Once all the consumptions have been added up, we have the average daily consumption. Multiplied by 30, the monthly, and by 356 the daily. As an example, let's imagine that we have a daily consumption of 9 kW per day.

To this amount we must apply an installation performance of 75%, this means that we must take into account that the installation will not always perform at 100%, in fact usually due to the different hours of sunshine, possible clouds and other aspects, the performance of the installation will be somewhat lower. In order to apply this yield, we will have to divide the previous amount by 0.75. In our previous example, for the consumption of 9 kW, the result would be 6.75 kW per day.

In this way we have been able to calculate the approximate electricity consumption of our home or business.