Choosing Steam for Caldera's Energy Storage

Caldera is committed to decarbonising industrial heat. Our proprietary heat cells use renewable energy when available, storing it as heat for later use. Each heat cell employs three innovations: a composite core material, steam-based energy extraction, and vacuum insulation. The core material was previously covered here. This post explains how we heat the cells and later extract that heat.

Caldera’s heat cells are charged using electrical elements embedded in the core. Due to the high thermal conductivity of the aluminium/rock material, heat quickly spreads through the core. This allows the heat cells to rapidly charge from solar or wind whenever the power is available. It also requires no pipework at all, making it simple, reliable, and cost-effective.

There are various design options for extracting the heat from a thermal store: water, air, thermal oil, molten salts, and steam. Our heat cells operate at temperatures up to 500°C. Water is unsuitable due to its low boiling point, and thermal oils break down at these temperatures. ?Molten salts are not an attractive option as they need to be kept liquid; if the unit cools down you are likely to get freezing, which carries the risk of bursting the pipes.

If the thermal store needs to work at very high temperatures (>1,000°C) then air is the only viable option. However, the downside is that when you heat air its density falls – even at 500°C it is a third of the normal density. Combining this effect with the relatively low heat capacity of air it becomes apparent that you need very large pipes to carry significant energy flows. Large pipes at high temperatures mean lots of insulation and, as we will cover in a future post, insulation is expensive and takes up lots of space. ?

Caldera's solution targets industries requiring clean, flexible heat up to around 200°C, such as food & beverage, textiles, and pharmaceuticals. Therefore, we can avoid the drawbacks of using air as the working fluid by flashing water to steam instead.

To extract heat rapidly we use a very useful property of water as it changes state into steam. Water, when in contact with a very hot surface, instantly changes to steam by absorbing a lot of energy from the surface. Constrained in an insulated pipe, steam moves at very high speed. When it encounters a cool surface it condenses back into water, giving up all that absorbed energy. This principle, widely used in process industries, enables quick and efficient heat transfer with small, insulated pipework.

In Caldera's heat cells, a network of small pipes is embedded in the core in a closed-loop system. Water introduced into this pipework turns into steam, thus drawing energy from the core. We don't directly use this steam for heating; instead, it is used to convert process water into steam via a heat exchanger. Using separate loops is common practice and means that we can maintain ultra-high purity in our internal pipework and therefore avoid degradation over time due to build-up of solids.

To conclude, Caldera's heat cells charge quickly through simple electrical heating. Using steam gives us a compact, high-performance system where we can extract energy rapidly and on-demand.

Interested in supporting our mission to decarbonize heat? You have an opportunity to invest in us via Crowdcube. Here's the link: https://link.caldera.co.uk/v8SI2G

Risk warning: Don’t invest unless you’re prepared to lose all the money you invest. This is a high-risk investment.