>I'm not sure what the solution to the latter problem is Heat batteries - basically, a bunch of insulated sand/rocks that you heat up, and then later you use t

>I'm not sure what the solution to the latter problem is Heat batteries - basically, a bunch of insulated sand/rocks that you heat up, and then later you use the heat directly for heating. To be crystal clear: I am NOT talking about batteries that output electricity. Heat batteries are literally dirt-cheap, and you can dump excess midday summer solar into them and they'll keep for months. The only problem is that heat is hard to transport and heat batteries are necessarily large (due to the cube-square law) which makes it hard to build them hyper-local. For residential buildings that means you'll want district heating. Heat batteries aren't a good choice for everything or everyone, but reducing grid load is a numbers game so they don't need to be - they just need to load-shift most heating, and everyone else can use heat pumps.