Is deploying your battery during negative pricing a good idea?

In recent days, electricity prices have been very low and even regularly negative. Since the entry of storm Pia on 21/12, the market price for electricity has not been above 65€/MWh. There have been as many as 47 hours in recent days when the electricity price was 0 or negative.

If you know that until before storm Pia there were "only" 172 hours over the whole year that the market price dropped below 0 €/MWh, you realize the impact of one winter storm.

Now, many may be thinking, "This is the ideal time to charge the home battery when the power price is negative, to avoid grid off-take when paying for off-take later."

But is this really the case?

The story goes beyond just the price of electricity, and by this we mean not only distribution and grid fees, but also the wear and tear on your home battery. Every time your battery is deployed, it undergoes a complex chemical process that eventually leads to wear and tear. This is why manufacturers place a limit on the number of guaranteed cycles.

Moreover, there are also losses, such as the conversion from AC to DC and vice versa, which causes transformer losses. Ignoring these aspects, your battery would indeed charge when the price is negative, only to discharge when off-take is again paying. But many people do not realize that storing energy in a battery also costs money, on average about 4 cents per kWh stored.

We strongly believe that a battery should only be used if the benefit on your energy bill is greater than the wear and tear cost of the battery. We do not support an "out of one pocket into another" operation, even if that would make us look better in the savings numbers.

Let's look at 24/12 prices: they range from -5€/MWh to 10€/MWh. So local storage can save you 15€/MWh (~ 1.5 cents/kWh) on your energy bill, but consider that your battery is wearing out at 4 cents/kWh. Is this really a smart move by an Energy Management System (EMS)?

So sometimes the best action is to do nothing, and we are proud to do that on this festive day. The only action FlexiO took over Christmas was to control your monthly peak, because that does lead to savings.

On 26/12, now that storm Pia is less powerful, the difference between the prices on the electricity market is again higher, namely a difference of 85€ / MWh ( ~ 8.5 cents / kWh). So now it does pay to charge the battery when prices are lowest, so we can start using the energy stored in the battery this evening.

After all, you do save now: If you charge the battery this night between 3h00 and 8h00 you have no energy cost, only a wear and tear cost of 4 cents / kWh. From 16h this afternoon, the price is at least 7 cents and you will thus benefit by 3 cents per stored kWh.

It's not the big bucks you're going to "earn" today, but at least you're going to use the battery responsibly.

And what exactly did FlexiO do? In the same installation described above, he charged the battery from 3:00 a.m. this morning....

So, while the gourmet sets are in full swing and the dishwasher is doing its job, give your battery a break, too. You'll be better off yourself, too.