Why won’t your solar panels save you from a blackout?

Why won't your solar panels save you from a blackout?

Illustration: Energy Revolution, image: David Trebosc – Flickr CC.

Unless a battery is associated with it, a domestic solar power plant cannot take over in the event of a power cut from the network. During a blackout, you will therefore be without electricity, whether or not you have photovoltaic panels on your roof. If the situation seems absurd, it is explained by ultimately logical technical and safety rules. Explanations.

The fear of a blackout next winter may encourage some people to equip themselves with a solar power plant. Individuals who already own one may also think they are safe from general power outages. However, photovoltaic panels are only able to replace the network when they are associated with a battery. A configuration that is still rare in France, because it is very expensive.

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Automatic shutdown in the event of a power failure

The vast majority of photovoltaic power plants installed in private homes are in self-consumption : they inject their production into the domestic network, then the public one in the event of a surplus. The two networks are ultimately not so distinct: the electrical wires of a house constitute the end of the large public network.

Thus, during a general outage, the production of the solar panels installed there is interrupted in the same way as the other power stations located in the affected area. It is a legal obligation. Shutdown takes place automatically thanks to the decoupling relay built into the inverter.

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A matter of security

This is primarily a security measure. This avoids the presence of current on the lines, where agents are likely to occur. The interruption of production also prevents risks linked to an imbalance of loads on the network.

During an outage, photovoltaic panels that would continue to inject their production would deliver an irregular voltage and intensity, because they were not synchronized with demand. There is therefore a risk of deterioration of the devices, overheating of the conductors and therefore fire.

In addition, the “network inverters”, which convert the direct current produced by the panels into alternating current only intended for injection into the network (public or domestic), can only operate when they detect a voltage on the latter. They are designed to deliver a current perfectly in line with the specifications of the public network and thus stop when it is inoperative or desynchronised.

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How to be autonomous with solar panels?

To be autonomous in the event of a cut with photovoltaic panels, the only solution is to install a battery and a “hybrid” or “off-grid” inverter. The system will automatically take over during the interruption and will only inject the power necessary for the operation of your electrical devices, without sending current into the public network.

The set is often marketed as “anti-cut solar kit” on online shops specializing in photovoltaic equipment. It generally includes a hybrid inverter, one or more batteries (lead or lithium), the cables and devices necessary for the connection and sometimes includes the panels.

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These kits are marketed between 1,3000 and almost 10,000 € depending on the battery capacity and the power delivered. Please note that it is essential to have irreproachable skills as an electrician or call a professional to install it at home. These kits should not be confused with the “ready-to-connect self-consumption kits”.

Domestic battery: expensive but useful

Purchased alone, a battery capable of supplying a fridge-freezer, a computer and a 150-litre water heater over 24 hours without any other power source, costs around €5,000 (10 kWh).

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Photovoltaic installations able to be independent during a power outage are therefore particularly expensive. However, this can be interesting if you live in an area subject to regular interruptions or if you absolutely cannot do without electricity, even for a few hours a year.

The investment is not only useful for compensate for power cuts. The rest of the time, the battery will allow you to maximize your self-consumption rate and to avoid injecting free or very low-cost electricity (currently only €100/MWh) into the public network.

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