Can a house-sized sand heat store carry summer heat into winter, and how does its electricity use compare with a heat pump?
research/energy-thermal
Can a house-sized sand heat store carry summer heat into winter? A transient model: 10 MWh after 120 days needs 222 m³ (70 if lossless) and returns 26% of the electricity as heat, so a COP-4 heat pump wins unless its electricity is 15× dearer; a days-scale store at house size. Stylised.
What it found
A transient finite-volume model of a spherical sand store in mineral wool (a hot-water tank run through the same code), checked against analytic cases. A store sized to still give 10 MWh after 120 days needs 222 m3 (against 70 if lossless) and returns only 26% of the electricity put in as heat, so a COP-4 heat pump wins unless its electricity costs 15× more, before capital cost. After a day or a week the same store returns 79% and 73%: a days-scale store at house size, seasonal only near 1,000 m3 (43% left after 180 days). Stylised: assumed properties, a sphere, instant uniform charging, no pipes or ground.
A figure from its own output
Paper, code and results
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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.