Your father's idea is a good one. Here is a thermal heat pit which is being used to store heat for the winter: https://stateofgreen.com/en/partners/ramboll/so

Your father's idea is a good one. Here is a thermal heat pit which is being used to store heat for the winter: https://stateofgreen.com/en/partners/ramboll/solutions/world-largest-thermal-pit-storage-in-vojens/ https://stateofgreen.com/en/partners/ramboll/solutions/world...