In this episode of the Physics World Weekly podcast, we meet Markku Ylönen, who is co-founder and chief technology officer of the Finnish company Polar Night Energy. The firm has created a “sand battery” that stores excess renewable energy as heat, and can be used to smooth out variations in supply that occur when the Sun isn’t shining and the wind isn’t blowing.

Ylönen is in conversation with Physics World’s Margaret Harris, who has also written a feature article about how installing a heat pump and solar panels can reduce domestic energy consumption from mains sources. In this podcast she talks about the economics of these technologies and what governments can do to encourage their uptake.