Awesome and very simple. There is a small community of eco housing that uses this system, in Boekel. They use solar panels in summer to heat the battery which l

Awesome and very simple. There is a small community of eco housing that uses this system, in Boekel. They use solar panels in summer to heat the battery which lasts all winter. On a diy scale, there is also this system for passive greenhouse called a climate battery which uses the same principle, storing heat underground and using it in winter. With almost zero energy we can use it to grow bananas in a greenhouse in the Netherlands.