Storage boiler technology

Unlike traditional boilers that rely on fossil fuels, Storage Boilers uses straightforward electric elements. With no combustion and few moving parts, the technology is designed to deliver the reliability needed at factories and hospitals. This simplicity also means servicing requirements are kept to a minimum. The modularity of the system means it is suitable for a wide range of applications.

Facts & figures

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Fast charge in 4 hours
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Output power up to 32 MW
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Storage capacity 4 to 100 MWh
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Standby heat loss 6.5% per day
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Design life of multiple decades
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Ideal for retrofit
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No combustion, no hazardous materials
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Zero operational emissions

Inside a heat cell

The heat cell is the enabling innovation in every Caldera Storage Boiler, allowing intermittent renewable energy to be converted into on-demand heat. Assembled rapidly on site, blocks of Caldera’s patented thermal storage material are enclosed in a vacuum-insulated chamber.

The suite of patented and patent-pending technologies required to create a heat cell took years to develop, yet the principles behind it are surprisingly simple.

Conductive core

Every heat cell contains blocks of Caldera’s proprietary composite of recycled aluminium and volcanic rocks. This ‘supermaterial’ has a high energy density and is conductive, durable, and affordable. Heat cell cores are heated using standard electric elements. Thanks to their high conductivity, heat spreads evenly throughout the core.

Vacuum insulation

Each core is encased in a double-walled vessel, essentially a vacuum flask. The vacuum prevents conduction and convection of heat, while an additional material prevents radiative losses. This proprietary system provides lasting performance over years without maintenance, though the vacuum can be ‘topped up’ during servicing if necessary.

Heat extraction

A closed steam loop runs through each heat cell to maintain ultra-high purity and prevent eventual degradation from the build-up of solids. A small quantity of water is passed through a coil within the core where it turns to steam. This steam extracts stored energy from the heat cell, and varying the volume of water controls the power output.

Balance of plant

Alongside each heat cell is the equipment needed to enable it to charge and discharge. These are supplied together as a turnkey Storage Boiler, able to replace or reduce the use of any existing fuel-burning boiler or steam generator.

Compact substation

This factory-assembled package houses the MV switchgear, transformer, and LV switchgear to take power from the site’s 11kV ring-main and manage the 690V load to each Heat Cell.

Steam plant

A standard packaged heat exchanger uses steam generated from the Heat Cell to heat feedwater from the site hotwell and generate plant steam to be fed into the site’s steam header.

Additional content


Download 'Storage Boiler data sheet' PDF


Read 'Why Caldera chose vacuum insulation for energy storage'


Read 'Choosing steam for Caldera's energy storage'


Read 'Storing Energy in Volcanic Rock and Scrap Metal'

Get in touch

Whether you are interested in a site suitability assessment, partnering, or anything else, we look forward to hearing from you.