Heat storage without degradation sounds like a marketing claim. It’s a direct consequence of the technology involved: a lithium battery returns less energy after ten years than on day one. A PCM that has melted and solidified hundreds of times loses part of its capacity to subcooling and phase segregation. A salt buffer that’s heated and cooled for fifty years performs on day eighteen thousand exactly as it did on day one. Most storage comparisons pay little attention to that difference, even though it can flip the business case over a long period.
What exactly is degradation?
Degradation is the gradual loss of storage capacity through use. In a lithium battery this happens through chemical side reactions with every charge and discharge cycle: the electrodes wear, internal resistance rises, and manufacturers therefore often guarantee only around 70-80% of original capacity after eight to ten years. Phase change materials (PCM) involve a different mechanism: after hundreds of melt and solidify cycles, subcooling occurs — the material cools below its freezing point before it actually solidifies — along with phase segregation, where the components of the mixture separate. The result is that the effective latent heat decreases, usually visible as a gradual decline in how much heat the material can still release per cycle.
Why doesn’t a salt buffer degrade?
Caldum stores heat: the material — a salt mixture or ore, depending on the version — gets warmer or colder without melting or solidifying and without a chemical reaction. There’s no electrode to corrode, no electrolyte to dry out, and the material’s solid form stays intact even after thousands of cycles. Heating and cooling a solid mass is a purely physical process: as long as the material doesn’t melt, decompose, or the vessel corrode, storage capacity stays constant. That’s also the basis for the 50+ year lifetime Caldum maintains without degradation.
What does degradation cost you in practice?
With batteries and PCM systems, degradation is rarely included in the initial payback calculation, even though it can significantly change the real business case. A system that stores 100 kWh on day one but only 75 kWh after ten years means you have to oversize from the start to still meet demand at the end of its life — or replace or add capacity partway through. With thermal storage using a salt buffer, that’s not an issue: the sizing you settle on day one is the sizing you keep, with no correction needed for capacity loss over the years.
So is there no wear at all?
The storage medium itself doesn’t wear out. But a buffer consists of more than just salt or ore. The insulation around the vessel and the heat exchangers are exposed to large temperature swings for decades, which calls for careful design — something we cover in more depth in our article on sizing a thermal buffer correctly. The difference with a battery or PCM system: maintenance here concerns the construction. The storage medium itself doesn’t slowly burn itself out. An insulation panel can be replaced if needed; the core of the system doesn’t have to be.
Who does this matter to?
This weighs heaviest for investments with a long horizon: housing corporations planning in decades, commercial buildings with a depreciation period of 20 to 30 years, and private owners who don’t want to buy a new system in ten years. The longer the investment horizon, the more degradation counts toward the real cost per kWh stored. When comparing quotes, it therefore pays to ask how much capacity a system is expected to still have at the end of its depreciation period. The price per kWh on day one only tells half the story. For a salt buffer, the answer to that question is simple and unambiguous: the same as on day one, regardless of how many years the system has been running.
What the absence of degradation means for service life, depreciation and the business case is covered in Fifty years without degradation: what service life really means.