Do you have room for a battery?

Image caption 1: Even manufacturers of electric cars are entering the market of home energy storage. (Photo source: Tesla)

Image caption 2: A combination of an inverter and a 2 kWh battery storage. (Photo source: Power-one)

Let’s have a closer look at the future of the home’s electric system. In the upcoming years, the network feeding our homes with electricity will increasingly be under pressure. The reason is the expected increase of the number of electric vehicles and heat pumps, combined with a higher penetration of electrical solar panels for homes. Solar panels pose a problem in that the energy they produce during the day when there’s ample sunshine, needs to be used at the same time it is generated. Storing energy at home would offer an attractive solution to this issue. Storing that energy would enable us to use that same energy in the evening or at night, reducing the amount of unutilized energy that is put on the public power grid. Let’s take a peek at what the future could have in store for us all.

AC/DC

The subtitle has nothing to do with the Australian rock band, but rather with the types of tension and current. Alternating Current (AC) is the sinusoid tension with a 50 Hz frequency that is currently found in most countries or the 60 Hz used in the US and parts of Asia. The current in a closed current circuit changes direction 50 or 60 times per second. The power grid to which our homes are connected supplies such a tension.

Direct Current (DC) always flows in the same direction. There is a polarity indicated with ‘+’ and ‘-’. Such tension is generally used in car batteries. Solar panels also supply DC tension. In order to use the latter in an AC home environment, an inverter needs to transform the DC into AC.

Storing energy: the benefits

Storing energy is only meaningful when energy is produced at home, for instance via solar panels. Solar panels only produce energy during daylight hours. For many families, this is the time when they are off to work. Hence, a large part of the produced energy is not used, but put on the distribution grid out in the street. However, if we could store this unutilized energy at home, we could use it at times when the panels are not producing any energy because it is dark or the sun is not shining. It will obviously help us reduce our energy bills.

It will also reduce our dependency of fluctuating energy prices due to the grid’s load, or general price increases for power consumption. During power outages—which occur far more frequently in some countries—we will be less dependent upon our energy supplier, and we can carry on as we were prior to the outage. Some people even go to great lengths by making the energy storage capacity large enough so that they can be fully detached from the distribution grid.

A battery

The solar panels’ self-generated energy is stored in a battery, larger than the battery in your car. For 3 to 4 kW solar panels for home use there are batteries of 2 to 4.5 kWh. The current standard seems to be 2 kWh. Not all generated energy needs to be stored, because you also consume energy when it is produced.

Current batteries are Li-Ion models. They have a lifespan of about 3000 charge cycles, or 8 years in case of daily charging. Purchase prices are currently rather high (about 1500 €/kWh), but it is expected that prices will drop in the coming years to a level that attracts a broader market.

And the battery for your electric car?

An electric car already has a decent battery. In the near future it will become possible to use the residual energy of this battery for other domestic applications. However, if the car is out all day, you will not be able to charge its battery with the energy coming from your solar panels. A second, small electric car that is only used occasionally could use this cheap, self-generated green power.