Investment: varies significantly with buffer type and capacity. Request an indicative budget via the pilot partner programme.

PRODUCT RANGE

Caldum thermal storage

Caldum stores heat from the sun in summer and makes it available year-round. Four to six times more compact than a water tank, with operating life of over 50 years and no degradation. Two configurations: salt-based for individual homes, ore-based for larger complexes and district heating.

WHY CALDUM

Compact, durable, fossil-free

Existing solutions are either too bulky, too expensive in operation, or rely on materials with limited lifetime. Caldum solves all three at once.

HOW IT WORKS

Three phases across the seasons

TWO CONFIGURATIONS

Caldum 1 and Caldum 2

	Caldum 1	Caldum 2
Primary application	Homes, commercial buildings, small collective systems	Larger buildings, industry, district heating
Temperature range	80 – 225 °C	80 – 450 °C
Energy density	approx. 260 – 320 kWh/m³	approx. 320 – 460 kWh/m³
Heat output	Adjustable 30 – 95 °C	Adjustable 30 – 95 °C or higher
Storage mass lifespan	At least 50 years	At least 50 years
Electricity generation	Not the primary function	Possible as secondary application

COMPACTNESS IN PERSPECTIVE

Why not just use water?

Water is the most obvious storage medium — but for seasonal storage at residential scale, the volume quickly becomes impractical. The comparison below is fair: both buffers deliver 1,800 kWh, both usable down to 40 °C output.

Two configurations for different scales, sharing the same operating principle.

CALDUM VS BATTERY

Why heat storage outperforms electrical storage for heating

For heating applications, storing heat directly is fundamentally more efficient than storing electricity and converting it twice.

	Caldum	Lithium-ion battery
Energy density	260–320 kWh/m³	around 200 kWh/m³
Operating life	50+ years, no degradation	10–15 years, degrades each cycle
Materials	Salts and ore minerals	Lithium, cobalt, rare earths
End-of-life	Recyclable, no toxic waste	Complex recycling, limited recovery
Fire risk	None	Real, requires fire safety provisions
Best use	Heating and hot water	Electrical loads

APPLICATIONS

Where Caldum fits

Also under exploration: affordable heat storage at smaller scale

Alongside Caldum 1 and Caldum 2 — both designed for seasonal storage with high energy density — DEI Thermal Solutions is also investigating demand for smaller-scale, affordable heat storage.

The rationale is straightforward: many owners of solar PV systems generate more electricity in summer than they consume themselves, while heat demand peaks in autumn and winter. A well-insulated heat buffer of 500, 1000 or several thousand litres can convert that surplus electricity into usable heat for domestic hot water and space heating, substantially increasing PV self-consumption.

Two directions we are exploring

• Water as storage medium — proven, low-cost and straightforward to scale. Working range up to 90–95 °C. At this temperature, a 1000-litre buffer delivers around 60–65 kWh of usable heat — enough for several days of domestic hot water or a substantial contribution to space heating.
• PCM (phase change materials) — a medium with a targeted phase transition around 58 °C, chargeable up to around 80 °C. Energy density in the practically usable temperature range is roughly one and a half times that of water. More important in many applications: discharge temperature stays stable around the phase transition point for longer, and the lower required charging temperature pairs well with heat pumps. Interesting where space is constrained or where discharge comfort matters.

Who is this relevant for?

• Owners of homes or small buildings with substantial PV installations who want to increase self-consumption.
• Small commercial buildings and SMEs whose heat demand does not align with their own generation peaks.
• Parties with a limited or expensive grid connection who need storage without the scale of Caldum 1 or 2.

Status: exploratory. We are currently gauging market interest and technical constraints. Do you have a concrete situation in mind? Get in touch — your input helps us decide whether and how to develop this line further.