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

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

Unless a battery is connected to it, a domestic solar power plant cannot replace the moment the electricity is cut off from the network. During a blackout, you will therefore lose electricity, even if you have photovoltaic panels on your roof. If the situation seems unreasonable, it is explained by the last 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 have one may also think they are safe from total power cuts. However, photovoltaic panels can only replace the network if they are connected to a battery. A configuration that is still rare in France, because it is very expensive.

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Automatic shutdown in case of power failure

Most of the photovoltaic power plants installed in private homes are for self-consumption: they inject their production into the domestic network, then the public if there is an excess. The two networks are ultimately not that different: the electrical wires of a house form the end of a large public network.

Therefore, during a total loss, the production of solar panels installed there is interrupted in the same way as other power stations located in the affected area. This is a legal obligation. Shutdown occurs automatically thanks to the decoupling relay built into the inverter.

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A security matter

This is primarily a security measure. This avoids the presence of current in the lines, where the agents tend to intervene. Interruption of production also prevents risks associated with unbalancing network loads.

During an outage, the photovoltaic panels that continue to inject their production will give irregular voltage and intensity, because they are not synchronized with the demand. There is therefore a risk of equipment damage, overheating of conductors and therefore fire.

In addition, the “network inverters”, which convert the direct current produced by the panels into alternating current intended only for injection into the network (public or domestic), can only work when they detect the a voltage on the latter. They are designed to deliver a current that fully conforms to the specifications of the public network and thus stops when it is not working or desynchronized.

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How can solar panels become autonomous?

To be autonomous once the photovoltaic panels are cut, the only solution is to install a battery and a “hybrid” or “off-grid” inverter. The system automatically takes over during interruptions and injects only the power required for the operation of your electrical devices, without sending current to the public network.

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

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

Domestic battery: expensive but useful

Purchased alone, a battery capable of supplying a fridge-freezer, a computer and a 150-liter water heater for 24 hours without another power source, costs about €5,000 (10 kWh).

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Photovoltaic installations able to be independent during power outages therefore more expensive. However, it can be interesting if you live in an area with frequent interruptions or if you really can’t do without electricity, even for a few hours a year.

Investing is not only beneficial 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 cheap electricity (currently only €100/MWh) into the public network.

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