A British-built domestic heat battery could help decarbonise millions of UK homes. Caldera has invented a hyper-efficient thermal store which automatically heats up when renewable electricity costs are lowest. This funding will accelerate the rollout of pilot schemes this year.

  • Nationwide rollout could create gigawatts of energy storage.
  • Simple, low-cost system made from recycled and natural materials.
  • Est £3.5 bn total annual addressable EU market.
  • Cornerstone investor König Metall leading the current round.


In Britain, we have ambitious goals to decarbonise our economy by 2050.

Caldera takes renewable energy when it is low cost (using a flexible green tariff with prices as low as 5p/kWh) and stores it as heat, providing carbon-free hot water and heating.

Our patented breakthrough WarmstoneTM heat battery can store enough heat (100kWh) for a standard home for 24 hours.

The idea is the brainchild of engineers James Macnaghten and Guy Winstanley. After a decade working on thermal storage, our founders saw the potential of an ultra-efficient vacuum insulated heat battery.

To date we have:

  • Raised over £1.5 million through grants and investment;
  • Installed our first pilot Warmstone product in a family home;
  • Established a manufacturing and R&D base;
  • Been supported by the Energy Systems Catapult;

We intend to build and sell Warmstone units via a range of approved UK installers. In the EU; we work with manufacturing partners like König Metall and our intention for the rest of the world is to license the technology.

We also plan to install a small number of pilot units in trial homes this year, prior to a full commercial rollout in 2022.

Caldera have developed an easily adopted technology which can help reduce CO2 emissions in every home it is used. Your investment will enable us to begin changing the way our homes are heated forever, saving millions of tonnes of CO2 worldwide.


James Macnaghten, CEO and co-founder

Whilst at Cambridge studying Engineering James left to start his first business, experienced CEO, entrepreneur and engineer with 15 years' of engineering experience in energy research.

Guy Winstanley, COO and co-founder

Guy has 30 years of operational, project and engineering experience. His career has encompassed R&D, manufacturing processes and operations management, including international experience in UK and Germany.

Mark Lee, Non-Executive Director

Mark is a Senior Banker with experience working with industrial clients across Europe.

Andrew Brown, Non-Executive Director

Andrew has more than ten years’ experience leading the corporate affairs functions for global listed firms including the UK’s largest generator of renewable electricity, Drax Group Plc.

Ranulf Slee, Chief Engineer

Ranulf is a senior research and development Scientist/Engineer. He has a successful track record in delivering ground-breaking research projects including cutting edge batteries and fuel cells through his work with DERA, QinetiQ and Ceres Power.

James Hutchinson, Senior Design Engineer

James is an experienced Design Engineer with over a decade of experience in thermal energy storage systems and automotive manufacturing.