Why Caldera Chose Vacuum Insulation for Energy Storage

At Caldera we are passionate about delivering a solution to decarbonise industrial heat. The Caldera solution has at its heart a heat cell that stores energy for later use. Each heat cell uses three interlocking innovations - a composite core material, steam for energy extraction and vacuum insulation. This post focuses on insulation and explains why we felt the need to develop a proprietary alternative to conventional options.

The heat cell’s insulation is used to reduce the rate at which the stored thermal energy is lost to the environment. It is also potentially one of the more expensive parts of the system. Just consider this – if you were to fit a 20ft container with 30cm of internal insulation you have just lost 50% of the internal volume and need to buy and fit 16m3 of insulation!

Conventional insulation such as mineral wool fibre relies on trapping air within its structure – think loft insulation. It is the low thermal conductivity of static air that provides the insulation. However, using this sort of insulation at higher temperatures does not work because the hot air is not still, so heat is transferred by convection. To counter this, the mineral wool can be sealed behind fitted metal sheets which is time-consuming and expensive.

Another option is to use sealed or solid insulation such as microporous or refractory insulation. Microporous insulation combines micro pockets of air and materials that reflect infra-red radiation. Refractory insulation is heavier and cheaper, but has higher overall thermal conductivity, so needs thicker insulation for the same heat loss. In all cases additional environmental protection is also required to avoid water ingress.

Compared to these conventional options, a vacuum is between five and ten times more effective. In a Caldera heat cell the thermal core is encased in a double-walled steel vessel, effectively creating a vacuum flask. A vacuum is created which reduces conduction and convection of heat from the core. The core vessel itself is wrapped with a material which reduces radiative losses. Moreover, the outer part of the vessel automatically provides weather proofing.

Using a vacuum means that our insulation takes up much less space, keeping our unit compact. Consider the previous example of the 20ft container: if the insulation is five times better, then you only need 6cm of insulation and the amount of lost space drops from 50% of the volume to just 12%, leaving room for more thermal storage material!

Caldera believes that their vacuum system represents the cheapest and most efficient means of insulating the thermal core taking into account construction costs, insulation selection and weather proofing.

Thanks to Caldera’s three interlocking technical solutions - composite core material, using steam for energy extraction and vacuum insulation - each heat cell is small enough to enable mass production and straight-forward road transportation to site. This again drives down cost and paves the way for the mass roll out of the system.

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