Electrical self-sufficiency in a city flat: batteries and 400 kWh

Electrical self-sufficiency in a flat: 400 kWh and 50-kilo batteries

A city flat, a battery setup weighing about 50 kilos and monthly consumption of around 350-400 kWh. With those three pieces, a domestic electrical self-sufficiency system has been put together without its own solar panels and without a terrace, right in the heart of the capital. The stated goal is not to live off-grid, but two more modest things: that a long blackout doesn’t ruin the frozen food and that the bill stops bleeding money every month. The first serious test came at a Christmas Eve dinner that stretched into the early hours. The battery never dropped below 35% charge, above the 30% set as a safety margin. It passed the test. What is less clear is whether it can stand up to the maths.

How much do home batteries cut your bill?

The figures being tossed around vary widely and should be taken with a pinch of salt. A bill of €13 for eight days, extrapolated to a month, comes to close to €50. The previous month, without the setup, the bill had been €82. And with another company, that same bill would have been around €51. Translation: the real saving depends less on the battery than on the tariff you’re on, and its owner has been hopping from one supplier to another — from a big utility to a small one, and from there to another with the kilowatt at €0.05 — until he found one that works for him. Anyone who has wrestled with a utility bill knows that’s half the battle.

The total cost and the fine print no one factors in

The stumbling block that reappears every time is TCO, the total cost of ownership. It’s not enough to look at what the equipment costs: you have to add the degradation of the panels and batteries and the losses in every charge and discharge. Some argue those losses are around 20%, which would leave the whole thing with negative returns for a home. The owner counters with his own measurement: he stored 9,906 kWh according to his plug-in meter, and the utility billed him for 10,000 kWh, a difference of -0.94%. Two figures that clash head-on, even though they measure different things. The disagreement isn’t about the result, but about what is being measured. Some also point out that buying the battery, inverter and charger separately makes installation cheaper and repairs easier, though a compact format is the only option in a flat with no workshop space.

How much backup does the battery give a flat?

Usage has been fine-tuned through trial and error. Now it charges to 95%, leaves a 20-25% reserve, and the biggest power hogs — a lit indoor garden and a distiller — are plugged in at night, during off-peak hours, while the battery charges. The technical service says that range is best for the equipment to last at least 10 years. The problem is consumption: between the grain mill, bread maker, distiller and garden lighting, the battery barely made it to midnight with only 10% reserve. Its owner admits that spending has shot up “because I kept adding electrical appliances without any real control.” He has already swapped fluorescents for LEDs and plans to turn off three garden lamps.

City or countryside: where do you ride out a long blackout better?

That’s where consensus breaks down completely. Some argue that a petrol generator on a terrace beats any battery, while others point out that a flat without a terrace can’t use that solution. Against the argument that the countryside, with a well and a garden, can hold out for years, comes the opposite: in a flat you can grow vegetables year-round in planters and don’t have to go out to buy food. And on security, the most debated point: some warn that a home showing light during a blackout becomes a target. The answer is to leave only an oil lamp visible while fridges, chest freezers and the washing machine keep running silently, with a reinforced door and no need to go out. Nobody settles the matter, because ultimately it depends on how long the outage lasts.

And if the grid doesn’t go down, is it worth it?

Here the analysis gets stuck. The owner admits he probably won’t recoup the investment, and justifies it with another calculation: fiat money loses value every day and the system lowers his bill in the meantime. His critics respond that an expensive installation to save a few dozen euros a month doesn’t add up. With chest freezers at -24°C storing food and medicine, and kerosene lamps in the cupboard just in case, the decision is more insurance policy than investment. The problem is that no one has yet put an exact price on that annual premium.