3 juni 2026
The increasing use of renewable energy creates a persistent mismatch between when power is produced and when it is actually needed. Excess generation during off-peak hours cannot always be used immediately, and without a way to store it, that energy is simply wasted. Converting electricity into heat and storing it for later use is one of the most straightforward ways to solve this problem.
Sand was chosen as the storage medium because it holds heat for a long time and has desirable thermal properties. The drum itself is a standard 55-gallon steel oil drum, which costs less on second-hand platforms than the dry weight of the materials. Inside it, eight Nichrome resistance wire coils are wound around brick beams and heat the sand when electricity is supplied, and the heat slowly spreads outward through the material. A copper pipe spirals down through the sand carrying sunflower oil, which picks up heat and delivers it to a heat exchanger outside the drum. The outside is wrapped in rockwool to keep the surface temperature safe. The entire prototype costs less than 500 €.
The system charges overnight and around midday when electricity prices are low, and releases heat during morning and evening peak hours. A microcontroller handles the scheduling, reads three thermocouples inside the drum, and adjusts the operational state of the prototype accordingly. An interesting aspect of this design is that the rate of discharge is not software controlled. Heat diffuses through the sand slowly and predictably, so the system releases energy at a rate determined by the physical properties of the materials and the geometry of the components.
The thermal energy storage prototype is a nice proof of concept, but the real potential of this solution sits at a much larger scale of adoption. Thousands of these systems distributed across homes and neighbourhoods would collectively represent an enormous thermal storage buffer; Excess renewable energy generated during off-peak hours would be absorbed and held until demand picks up, instead of being wasted. That constant realignment of supply and demand throughout the day would naturally flatten the price fluctuations and improve the competitiveness of renewable energy technologies.
A blog by: Danail Valov, fourth year student of Mechanical Engineering
Participated in the Learning Community Future Heat Heroes
