Home battery versus thermal buffer: the home battery has had a lot of attention in recent years. Fair enough: more homes have solar panels, feed-in tariffs keep getting less attractive, and using your own electricity in the evening saves money. For daily shifting, a battery is a logical answer to a logical question.
But a home battery and a thermal seasonal buffer don’t solve the same problem. One is about electricity in the short term. The other is about heat over the long term. Confuse the two and you buy the wrong tool for the job.
Rhythm sets the rules
Electricity has a daily rhythm. Generate during the day, use in the evening. Eight hours of storage is enough. That fits a battery that charges and discharges hundreds of times a year.
Heat has a seasonal rhythm. Almost no demand in July, plenty in January — and that winter, by the way, also raises everything else: more lighting, colder laundry runs, shorter days, more cooking at home. The distance between summer surplus and winter need isn’t eight hours — it’s closer to four months. A battery built to bridge that becomes enormous. An average home easily burns through 1,500 to 2,000 kilowatt-hours of heat in a single winter month. Cover that month electrically and you’re looking at dozens of Tesla Powerwalls stacked together — capacity you don’t use for a few hours every day, but draw on fully for a few months a year. That’s not how investments pay back.
For thermal seasonal storage, that’s not an issue. You charge slowly in the surplus season and use the heat months later. The storage has to do one thing well: hold heat until it’s needed.
Electricity is expensive if all you want is warmth
Electricity is high-grade energy. You can do almost anything with it: power a laptop, charge a car, run an induction hob. For space heating and hot water, you don’t need that versatility. The end use is low-grade: a radiator doesn’t need 230 volts, a shower doesn’t need frequency control.
Storing electricity in order to convert it back into heat means paying for flexibility you then throw away. Thermal storage holds the energy in the form it will be used. That’s a fairly dull observation, but it changes the entire calculation.
Different question, different solution
A battery answers the question: how do I use my solar power later today?
A thermal seasonal buffer answers the question: how do I use my summer energy for my winter heat?
These aren’t competing technologies. They’re answers to different questions. A home with solar panels, underfloor heating and hot-water demand benefits from both — a battery for daily electricity use, a buffer for winter heat. The mistake isn’t choosing between the two. The mistake is thinking one can replace the other.
Where does Caldum fit?
Caldum is a compact thermal buffer, charged with energy from solar panels or from the grid when supply is plentiful. It delivers heat for space heating and hot water, designed to bridge periods of weeks to months — not hours or days.
In a new installation, Caldum usually replaces the heat pump. Hybrid operation is possible: alongside a heat pump, an existing gas boiler or another heat source, for example as a back-up or in a refurbishment where the current installation still has years of life. For daily electrical shifting, a battery remains the right answer.
What does that mean for a home?
Take a house with solar panels that generates far more in summer than it uses. In winter, generation is low and heat demand is high.
Without seasonal storage, the summer surplus disappears into the grid (under less and less favourable terms), and winter heat has to come from outside. With thermal storage, part of that summer energy gets stored locally as heat. The home becomes less dependent on peak pricing, feed-in rules and external heat sources. Not automatically fully autonomous — and it doesn’t have to be — but with markedly fewer crutches.
And for blocks or districts?
With multiple homes, the difference grows. A collective battery for a neighbourhood handles electrical peaks. But the biggest winter energy demand is usually heat — not electricity. A local thermal buffer can supply heat centrally or semi-centrally, without immediately rolling out a full district heating network with all the permits, distribution losses and governance questions that brings.
For housing corporations, municipalities and developers, this gets interesting where standard solutions hit walls: insufficient grid capacity, restricted space for outdoor units, noise requirements, existing buildings, or a heat demand that doesn’t fit a single model.
Choose by function, not by belief
The energy transition is sometimes argued as a faith war. Battery versus heat pump. District heating versus individual systems. Hydrogen versus electricity. None of that helps the end user.
The sober question is what function the system has to perform. For short-term electrical storage, a battery makes sense. For heating and hot water across longer periods, a thermal buffer makes sense. In most homes, a combination is the most practical. Caldum fills the part batteries can’t handle: heat across the seasons, in a form compact enough to actually fit in a home or a building.