Energy self-consumption is defined as the use of energy generated by oneself through an installation – for example a photovoltaic one – for own consumption.
Photovoltaic solar energy installations are usually divided into two types: installations connected to the grid and isolated installations (without connection to the grid). Although technically both can be self-consumption, since they can serve to cover, partially or totally, our electricity consumption, we usually call self-consumption installations to those connected to the grid that serve to reduce our electricity bill.
In Spain there are some charges on self-consumed energy that we know as “sun tax”. This tax only affects facilities connected to the network. The isolated photovoltaic installations of the network do not have any type of tax or charge.
Self-consumption installations connected to the grid are connected inside a consumer electrical installation (the electrical installation of our facility, home, office or warehouse).
Normally we will not use energy storage by batteries in this type of installations, since it is possible to take electricity from the electrical grid in the cases of low or no generation of energy by solar panels.
Batteries can be used to store part, or all, of the energy coming from the solar installation during the day and use it afterwards when the the sun has gone. This will happen when our electricity needs during sun hours are covered and the solar installation is able to supply us with more energy. With this we will be able to increase the percentage of our demand covered with solar energy, with respect to a battery-free installation, although the overall economic profitability of the project, taking into account the costs of current batteries, will decrease.
Self-consumption is regulated in Spain by Royal Decree 900/2015. This RD distinguishes two types of self-consumption: