Storage systems for residential photovoltaic installations

If you have a photovoltaic installation on the roof of your house, you have surely thought of buying an energy storage system.

In this article we try to solve this problem, trying to highlight the most important aspects.


Use of the energy produced by a photovoltaic system.

Although the use of photovoltaic energy is widespread, the operation of the system and the use of the energy produced are not always clear. But understanding it is key to assessing the usefulness of a battery.

During the day, if there is sunshine, our photovoltaic system constantly generates electricity. This energy can have two possible destinations: our home or the commercial power grid.

The energy we produce can be consumed immediately at home, ie at the same time as the system produces it (“self-consumption” simultaneously with production); or that it is not consumed inside our home and, therefore, is discharged into the electricity grid, to be consumed, for example, in the homes of our neighbors.

The destination depends on the demand for electricity compared to the instantaneous production.

A good use of the photovoltaic system is to maximize daytime consumption. Even through changes in habits or home automation systems, it is almost always possible to increase daytime consumption: for example, programming the use of the washing machine, dishwasher, dryer, etc.

But, nevertheless, it is not possible to transfer all consumption to daylight hours because there is a “basic” consumption that we have always had, composed, for example, of refrigerators and freezers, lights, all standby that is not turned off, etc.

As the subscribed power is limited, the various devices must not be used at the same time so as not to exceed the power available according to the contract. For this reason, in the residential sector, assuming correct sizing of the system and in the absence of a storage battery, a percentage of approximately 30% of the energy produced is generally “self-consumed”.

Usefulness and operation of a self-consumption battery.

The battery can be used to self-consume a higher percentage of the energy produced. If I don’t need to immediately consume all the energy I have produced, instead of sending it directly to the grid, I can accumulate some or all of it in a battery. From there I can use it at night or in any case in the absence of sun (there is no production) but always during the day.

This means an increase in the percentage of self-consumed energy compared to the total energy produced; Depending on the size of the installation, in principle, 100% of the energy produced daily can be used. More realistically, residential systems with storage can be considered to inject between 40% and 10% of the energy produced into the network.

During the winter months, the production of our system may not be sufficient to cover daily needs; even in summer there are cloudy days and therefore they are not productive. In general, over a year, thanks to the storage system, up to 90% electrical autonomy can be achieved. A portion of the energy, however small, will still be purchased (taken from the grid).

Should I install a solar battery?

Assessing the convenience or otherwise of a storage system is complex.

Leaving aside the economic aspects (which include the cost of batteries, tax deductions, the cost of electricity, etc.), we try here to shed some light on the aspects related to electricity consumption.

The storage system must be sized according to consumption in the evening and at night.

The essential things to know are: our consumption profile, our annual consumption, the amount of energy produced annually by our photovoltaic system, our percentage of self-consumption and energy independence in the absence of a battery.

In my opinion, it is better to consult a professional.

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