Charge an electric car at home with solar power, possible ?
Many of our customers, who come to get a charging station for their electric car, ask us the question “Can I recharge my car directly with solar panels”? This is the question we will try to answer in this post
Before answering this question, here are a few facts that allow us to grasp the magnitude of the challenge.
The power of solar radiation is about 1000W / m2
This energy of 1000W / m2 is available only when the sun is perfectly aligned with the solar panels. With south-facing panels, this condition only occurs at noon on a sunny day (no rain, clouds or snow). So, although the days are much longer than this, we can only rely on the equivalent of about 5 hours of full sunshine per day, during the longest days of the year.
The efficiency of solar panels available on the market is about 15 to 20%
Of the 1,000 W / m2 emitted by the sun, approximately 150 to 200 W / m2 can be captured by the solar panels currently available on the market. By consulting a calculator like PV Watts, it can be seen that in Quebec, in Montreal for example, we can expect an annual solar production of about 1 200 kWh for a 1kW solar installation (4 panels of 250W).
The storage capacity of an electric car battery varies from 24 kWh to 100 kWh approximately
Although an electric car driver rarely comes home with a completely empty battery, in order to recharge it with a solar system dedicated to this purpose, it would be necessary to be able to produce between 24kWh and 100kWh during the day in order to recharge the battery. On a sunny day, a solar system of 6kW (24 solar panels of 3.5 feet x 5.5 feet) would be required to recharge the empty battery of a Nissan LEAF. It’s a lot…
The consumption of an electric car is about 150Wh per kilometer
For a car like the Nissan LEAF, for example, it is possible to travel about 6.5 km with 1 kWh of energy coming from the batteries (this figure will vary according to the type of road and the season) , which is therefore 150Wh per kilometer. So, to allow an electric car to travel, let say, 20,000km per year, with solar energy, it will be necessary to provide about 3,000 kWh of electricity. To produce such an amount of energy, a solar system with a total power of about 2.5 kW (10 solar panels of 250W) is required.
The charging of an electric car at home is done at a voltage of 240V AC
Solar panels produce direct current (typically at a voltage of about 30V for 60-cell panels). By joining several panels in series it is however possible to increase the tension. On the other hand, the charging of an electric car at home is done with alternating current, with a tension of 240V. This recharge is controlled by a charging station (level 2), which, contrary to what many might think, is not a charger. The charger is actually in the car. The role of the charging station is therefore only to control the passage of the alternating current. It is the charger of the car that makes the conversion of alternating current into direct current. All this to come to the conclusion that in a recharge scenario directly from solar panels, an inverter would be required in order to convert the DC current of the panels into AC power at a voltage of 240V.
Charging is normally done in the evening or at night when the sun is down
For most workers, charging their electric car is done in the evening or at night, when the sun is no longer present. Not to mention that at certain times of the year the sun can be more rare. In order to be able to recharge one’s vehicle directly with solar energy, one would have to think of storing energy in order to use it at the right time, which would add very significant costs. Indeed, the storage of solar energy requires batteries, which, depending on the type, have a lifetime and a very variable cost. While acid-lead batteries are the most economical, their lifetime is limited to a maximum of 8 years with very good maintenance (regular adjustment of the electrolyte level). Their lifespan will however be much lower if they are regularly discharged by more than 50%. To avoid these drawbacks must then opt for lithium batteries, much more expensive, but have a duration of 20 years without requiring maintenance. They can also be discharged regularly more than 80% without problem.
However, batteries may become more interesting if Hydro-Québec decides to offer variable rates depending on the time of day. The batteries could thus be recharged with solar energy or from the network, at the time when the rates would be the lowest. The energy stored in the batteries could then be used at a time when rates would be higher. Hydro-Québec has announced that it will soon offer, on a voluntary basis, dynamic pricing.
So what do we do ?
The simplest and most economical solution to recharge an electric car with solar energy is to produce electricity with a grid-tied solar system. This allows to produce annually a certain amount of energy that can be related to the power consumption of the car. This allow, at the end of the year, to say that the electricity used by the electric car came from X percent of solar energy. This approach also makes it possible to immediately consume the solar energy produced and return the surplus on the Hydro-Québec grid, thanks to the net metering option. Thus, the solar energy produced is not dedicated to the only charging of the car but to all appliances in the house.
This is why one of our customers, who owns a Tesla, has decided to install a 10kW solar photovoltaic system on the roof of his garage, made up of 40 270W Axitec solar panels and a 10kW Fronius Primo central inverter.
Although the idea of a residential electric car solar charging station may seem attractive, it is not the most interesting option. It is better to opt for a more global approach that maximizes the efficiency of its solar installation and its investment by not dedicating the energy produced by its solar system to the only charging of its electric car. It also ensures that you can recharge your car, regardless of the weather conditions and the power of your solar installation. We can size its solar system according to its budget and space available.
Meanwhile, some automakers, like Audi, are exploring the possibility of integrating solar panels on the roof, hood or even the doors of their electric cars. This should allow to add a few kilometers of additional autonomy to electric cars in the coming years.