Home battery and mining on surplus solar

Sunny afternoons increasingly bring so much electricity that the wholesale price drops below zero. Anything you export to the grid at those times earns little or nothing. A home battery and a small miner can both soak up that surplus. Here is what a battery stores, what a miner uses and why mining on surplus solar earns little.

What is changing

The Netherlands ends net metering on 1 January 2027. In Germany, new installations get no payment for power fed in while the price is negative, with temporary exceptions for small systems. In France, new installations have received only 1.1 cents per kWh for their surplus since June 2026.
Using the power yourself therefore matters more than exporting it: in your home, in a battery or in a miner.
The rules differ by country and by contract. Ask your energy supplier or grid operator what applies to you.

How often were power prices negative?

With plenty of sun and wind, there is sometimes more electricity than demand, and the wholesale price drops below zero. This is how often that happened in 2025:

Country	Hours with a negative price in 2025
NetherlandsSource: TenneT	584
GermanySource: Bundesnetzagentur	573
FranceSource: CRE	513

For the Netherlands, 584 hours is about 7% of the year. In France, the count had already reached 568 hours by 8 October 2026, more than in the whole of 2025.

What a home battery stores

A plug-in battery is one you plug into a wall socket yourself; a fixed home battery is connected by an installer. Plug-in batteries start small and can be expanded:

EcoFlow STREAM Ultra

One unit: 1.92 kWh
Expandable to: 11.52 kWh

Manufacturer specifications, accessed 23 October 2026. We do not have a home battery ourselves and have not measured these models.

What a miner uses

Multiply the power in watts by the number of hours and divide by 1,000 to get the consumption in kWh. A 140-watt miner running day and night: 140 × 24 = 3,360 Wh, or 3.36 kWh a day.

15 W, a small miner

Per day: 0.36 kWh
Per year: 131 kWh
At 500 negative-price hours a year (NL, DE and FR had more in 2025): 7.5 kWh
On a full 2.7 kWh battery: 180 hours

40 W, such as the Braiins Mini Miner

Per day: 0.96 kWh
Per year: 350 kWh
At 500 negative-price hours a year (NL, DE and FR had more in 2025): 20 kWh
On a full 2.7 kWh battery: 67 hours

140 W, such as the Avalon Nano 3

Per day: 3.36 kWh
Per year: 1,226 kWh
At 500 negative-price hours a year (NL, DE and FR had more in 2025): 70 kWh
On a full 2.7 kWh battery: 19 hours

The battery times leave out conversion losses; in practice the battery runs flat sooner. To find out what your miner really draws, measure it with a plug-in power meter.

Work it out yourself

In what order

Use surplus power yourself first: the washing, the dishwasher, charging the car. That saves you the full electricity price, including tax.
Then charge the battery, for the evening and the night.
Only what is still left over after that, plus the hours with a negative price, goes to the miner.
Switch the miner on and off with a smart plug that you control through an app or home automation. With a dynamic contract, you can make that depend on the electricity price.

Honestly: the drawbacks

Payback is uncertain

Whether a home battery earns back its cost depends on what it costs, what you pay for electricity and what you get for the power you export. Those figures differ by country and by contract, and in several countries the rules are changing, so future prices and export payments are not yet known.

Mining on surplus solar earns little

A 15- to 140-watt miner earns little. If it runs only when the price is negative, at 500 such hours a year it stands idle 94% of the time. And surplus power is not free: what you do not export, you do not get paid for either. Check the numbers with the mining calculator; we make no promises about earnings.

Heat and noise

A miner turns almost all of the electricity it uses into heat. Surplus solar comes mainly in spring and summer, when you do not need that heat. The miner also makes noise: according to the manufacturer, the Braiins Mini Miner produces 40 dB.

Safety of a plug-in battery

The Dutch fire service advises: put the battery in a dry, well-ventilated room, not in an escape route or under the stairs. Plug it directly into an earthed socket, without an extension lead or multi-socket adaptor, and not on the same circuit as the washing machine. Fit a smoke alarm in the same room.

Frequently asked questions

Can I run a miner on my home battery?

You can, but it is rarely a good idea. A 140-watt miner uses 3.36 kWh a day, more than a 2.7 kWh plug-in battery stores. Whatever the miner takes out of the battery, you often end up buying back from the grid in the evening. It is better to run the miner only on surplus power that the battery can no longer absorb.

Do I get paid if I use electricity when the price is negative?

Not automatically. A negative wholesale price is not the same as a negative price on your bill: even with a dynamic contract, you still pay network charges and taxes on what you use. Exporting at such times, on the other hand, earns little or nothing and, depending on your contract, can even cost you money. Using the power yourself is then the better choice: in your home, in a battery or in a miner.

Why are electricity prices sometimes negative?

In sunny and windy hours, there is sometimes more electricity than demand. According to the grid operator TenneT, renewable generators are increasingly responding by scaling back production. Whatever is still exported at those times earns little or nothing.