My other idea is using insulated tanks of distilled water buried in the ground for residential peak shaving. Overnight, the water is heated to 90°C using cheap excess capacity. During the morning peak, the heat pump uses it as a source of readily available heat for central heating. You can even have a fully mechanical heat pump "trickle-heating" the water during the night from a small wind turbine, since you just need to run the compressor and move the liquids around. There should be enough wind to heat up a tank of water even with a small backyard turbine.

I'm a complete dilettante in this, so I'm probably missing 99 reasons why this would be a lot more difficult.