The best route you could go is with Solar heating of 30 gallons with on demand heating at each location. This way there is no energy used to heat the water during non use, and no running of water waiting for the hot water to get to the faucet.

The next best option would be using high efficient water heaters in many different forms. The best would likely be if you had radiant floor heating that also heated a water tanks from ground source heating.

Lastly for a more economical approach would be wrapping your hot water heater and using a system to turn the heater on and off during the day to meet the occasional demands of the home. Home Automation systems can control electric hot water systems based on occupancy, and turn the heater off altogether when no one is home. Today\’s Hot water heaters are efficient to maintain water temperature for a day or so. Example our last power outages, around the 24 hour mark with no power I opened the hot water tap and got rather hot water.