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It runs on the sun instead of gasoline. How to use panels for cheap travel

Jan Staněk has photovoltaic panels on the roof of his family house with a maximum installed power of 10 kWp. The photovoltaic system can cover a significant part of the household’s electricity consumption, including heating. Since 2018, he has even been charging two electric cars with the electricity he produces on his roof.

It’s not obvious. The battery of an ordinary electric car needs a good amount of electricity to be charged. “It logically follows that the car needs to be charged when the sun is shining and our photovoltaic system is producing at full capacity,” says Jan Staněk at the very beginning of the tenth part of the Home Photovoltaics series.

You cannot charge the car from the battery

While the batteries that we normally buy for the home as part of a photovoltaic system have an average capacity of 10 to 12 kWh, cars powered by an electric motor usually carry a battery with a capacity of around 75 kWh. Therefore, charging the car in the evening from the home battery, from which we want to “feed” the household at the same time, is not a good idea.

However, the Staňkas use the battery in the house to cover fluctuations in the power of the photovoltaics during the day.

So charge only on weekends? That does not make sense. “And from November to January, you simply won’t charge the car. The little that you make on the roof will be consumed by the household,” says Staněk flatly. To sum it all up, the cooperation of domestic PV and electric cars will make sense for those who can work at home office or simply charge their car during the weekday.

ElectroDad for the Message List

  • Jan Stanek is a well-known supporter of electromobility and sustainable energy in a broader context. The Brno BUT graduate previously worked for eBanka, worked as an IT consultant at Deloitte, and later represented Moravia IT in China.
  • Today, he heads Purple Ventures, a company focused on investing in startups. His video channel ElectroDad, through which he describes the issue of household transition to sustainable energy in an entertaining and informative way, is watched by more than 25 thousand subscribers on YouTube and Stream.cz.
  • Exclusively for Seznam Zprávy, independently of Seznam’s business partners, he produced a series of ten videos on the topic of Home Photovoltaics.

If your PV system is not producing as much electricity as you need at any given moment, it is time to consider priorities. What do I want to charge, what do I want to use the produced electricity for.

“This happened to us at the moment when we switched to heating the house with a heat pump. At the edges of the photovoltaic season, by which I mean, for example, March, when the panels are not yet producing as much and, moreover, we still need to heat them, we have to make a choice. Charging from car overflows, or heating,” says Staněk. The priority is probably clear, so at the end and beginning of winter, the electric car will lose its taste for electricity from the roof. Then the solution is to charge the battery with electricity from the distribution network in times of cheap tariffs.

Modern electric cars have a battery large enough to cover several days of basic appliances at home, at the cottage or at the campsite.

Jan Stanek

The technical side of things

In order for an electric car to be meaningfully charged with a photovoltaic system, the system must work in three phases. This is possible if we have a three-phase distribution system in the house (for example, a 3x 25 A circuit breaker). And, logically, the charging of the electric car is ideally carried out equally in three phases, that is already the standard today. When each of the phases supplies a current of 16 amps, the total power of the charger reaches 11 kW.

An important feature of today’s electric cars is the ability to regulate the charging power as needed, i.e. according to the source that currently provides us with energy.

“In the summer, your roof will give you maybe 7 kW immediately when the sun is shining. But the car would like eleven. Therefore, it is necessary to adapt the charging, to reduce the required power. Otherwise, you would buy the rest from the network. And you don’t want that,” explains Staněk.

The charging power can also be regulated through the wallbox, which should, in cooperation with the inverter (you already have it at home, it is part of every photovoltaic system), be able to charge the car, similar to how an inverter and a boiler heat water, only if you have surplus energy.

Video series about home photovoltaics

In general, it can be said that charging an electric car with electricity produced at home is possible. In the summer, on a sunny day, you can certainly charge an electric car for a range of 50 to 100 km. However, regular or at least frequent charging requires quite a lot of “care”, which mainly consists in the organization of time. It’s not for everyone.

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