electric car: charging solar power from the roof with your own charging station

Electric car being charged

How to charge my electric car at home with solar power?

To charge your electric car with solar power, you need a photovoltaic (PV) system, a charging station (wallbox) and optionally a battery storage system and an energy management system.

You should know that without a battery storage system you can use solar power only at the moment it is produced. So if you want to charge your e-car with solar power, this is most effective during the day when the sun is shining. In addition, the PV system must be sufficiently large to cover both the electricity demand in the house and to charge the electric car. E-cars are charged with at least 1.4 kW for technical reasons. This is how much power should be left after subtracting household needs. The higher the power of your solar system, the greater the amount of solar power in the e-car. If no solar power is available, your car will be charged with electricity from the grid.

Can I charge the electric car from a normal socket??

Theoretically, charging is possible at a standard household socket, but this is not recommended not recommended for safety reasons. Household sockets are not designed for hours of continuous use under high currents greater than 10 amperes and should therefore be used for charging only in case of emergency can be used for charging electric vehicles. They can overheat and become a safety hazard. You should always prefer a permanently installed charging station. In addition, charging power is low at 2.3 kilowatts (kW) and it usually takes more than 10 hours to fully charge a common e-car battery.

Why it pays to have your own charging station?

The most important link between the PV system and the electric car is the charging station, also called wallbox. Wallboxes are specially designed for charging electric vehicles. The usual charging powers are between 1.4 kW and 22 kW (for home use). This results in average charging times of 2 to 6 hours, which, however, depends not only on the power of the wallbox, but also on the charging power of the e-car.

What do I have to pay attention to when buying my own charging station??

When selecting and purchasing a wallbox, be guided by the requirements set by your e-car. Wallboxes are available in various designs: They differ in their design, charging power, plug type features and purchase costs. There are charging stations with sockets, in which the cable carried in the car is connected. Wallboxes with a permanently installed cable and plug, which is inserted into the car as when refueling at the gas pump, are now more common.

Can I connect and install a charging station myself??

No, charging stations may only be installed by a specialist electric company and must be registered with the network operator beforehand or, if necessary, be installed by an electrician. be approved. It is also best to have the existing electrical installation checked in advance. If possible, always choose a larger cable cross-section (or, if necessary, a longer cable cross-section). empty conduits) than is actually required for the current charging station. The effort for a possible later extension of the charging power is then much lower. On it you should address the specialized enterprises directly.

Where to install the charging station? What do I do if I don’t have a garage or live in a rented apartment??

In the most favorable case, a domestic charging station is installed in the immediate vicinity of your own parking space. The charging cables – some of which are installed on the wallboxes – are available in different lengths. The exact length you need must always be weighed up individually.

Consumers without a fixed parking space (also known as “lantern parkers”) are currently dependent on public charging stations, which are currently offered by various parties (municipalities, energy supply companies and automotive companies).

Tenants with a permanent parking space or underground parking space on the premises of the residential complex can now request the installation of a charging station from their landlord at their own expense. The basis for this is provided by § 554 BGB. A guide to the purchase of a domestic wallbox for tenants and owners can be found on the ADAC website.

Which charging power for the charging station is the right one?

Wallboxes are available with 11kW and 22 kW capacity. The higher the power of the charging station, the faster the vehicle battery can be charged.

A 22 kW wallbox charges twice as fast as one with 11 kW power, provided that the charging system of your e-car can also accommodate 22 kW power. The specified power of a charging station refers to a 3-phase charge. However, some e-vehicles only have a 1-phase charge controller. This means that, for example, with an 11 kW wallbox, only a maximum of 3.7 kW (with 16 amp fuse protection) can flow – i.e. one third of the rated power. This is what you should consider when choosing a car and a wallbox, especially if you want the fastest possible charge.

Wallboxes fall within the regulatory scope of the Low Voltage Connection Ordinance (NAV). There is a Obligation to register with the grid operator and from 12 kW (§19 NAV) a Permit requirement. Please note that a wallbox with 11 kW power is subject to a registration requirement, and with 22 kW also to a permit requirement with your network operator.

Are there subsidies for charging stations??

Wallboxes are currently subsidized by the Kfw development bank of the federal government from tax funds. A prerequisite to be able to apply for the subsidy: The electricity for charging must come from renewable energy sources, for example from your own PV system or from a green electricity tariff. There is a €900 subsidy per charging point (a charging station can also have several charging points). Wallboxes with an output of 11 kW that are intelligently controlled and can communicate with other components from the power grid (for example, energy management system or smart meter gateway) are subsidized. Energy management systems are also eligible for subsidies.

Note that you don’t commission any installation work – be it just for laying cables for the electronics – until after the application has been approved. Otherwise your application may be rejected.

Additional subsidies from the state, municipality or your utility company are also possible, however, these are usually not combinable with the Kfw subsidy. The subsidy landscape is constantly changing. Check your options, which subsidies are possible, which can be combined and which are suitable for you as a private household!

Do I need a second electricity meter?

In advance, the installation company should always consult with the local grid company to determine whether a charging station can be installed at your desired location and, if so, under what conditions. This is always a case-by-case decision by the grid operator.

If you have large electricity consumers such as instantaneous water heaters or night storage heaters in the house, it may be that the existing electricity meters would be overloaded with a higher load from the e-car. Therefore, especially for larger charging stations (z.B. 22 kW), for which an additional electricity contract and metering space is then required.

However, once the electricity for the e-car is billed through a separate meter, the solar power can no longer be used directly to charge the e-car. You would then have to work with your electrician to find a solution to use your own green power for the vehicle after all. One possibility could be a smaller charging station to avoid the additional electricity meter.

There are also charging stations that already have integrated electricity meters. However, these must be billable. You can also get information about this from the specialist or manufacturing company. If you have no choice but to have new meter locations installed, this will make the installation considerably more expensive.

Is it worthwhile to have a battery storage system to increase the amount of solar power when charging?

To increase the amount of solar power in your e-car, you can also purchase a battery storage system. This stores the electricity produced by the PV system during the day and also makes it usable at night.

Ecologically, a battery storage system makes sense, but as of mid-2021 it is not yet very economical.

The initial cost of a PV storage system is still too large compared to the amount of electricity it will save you.

What is the advantage of an energy management system?

For optimal use of solar power from the PV system and battery storage, it is advisable to purchase an energy management system. These controls can adjust the car’s charging speed to the PV system’s instantaneous output. If there is a lot of solar power left, the charging speed is increased, if there is little sun, it is automatically decreased. More detailed information on energy management systems can be found here.

Bidirectional charging: Using the electric car as a power source

Bi-directional charging means that e-cars can not only be charged with electricity, but also be available as a power source. A prerequisite for bidirectional charging is that the wallbox and the vehicle also support it. Combined with intelligent energy networks and management systems, renewable energies can potentially be used more effectively in the future. The technical prerequisites for bidirectional charging are available, but not yet implemented in the market. For widespread applicability, there are still many regulatory issues that need to be fundamentally clarified.

Two models that can be practically implemented in the future are V2H – Vehicle To Home and V2G – Vehicle to Grid. With V2H, e-cars can be used as a power source at home. V2G refers to linking the e-vehicle to the power grid so that it can also feed in electricity when needed. The latter, however, is not so easy to implement in practice and will possibly only play a role in the future.

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