We're part of a real-time pricing program with our electric utility company, and a good strategy for offsetting electricity use during peak demand times is to pre-cool the house. The more thermal mass that our house has, the more effective the pre-cooling will be.
I've read about phase-change materials and the promise of Thermal Core PCM drywall, but it seems like the development into a commercial product isn't going to happen any time soon. I've seen various vessels filled with room-temperature PCMs for sale, but I have no idea how much I would have to buy in order to make a noticeable difference in thermal mass of a house.
Is there a practical way to add thermal mass to my house? I've heard of people suggesting adding large drums of water, though I'd be leery about doing so due to the possibility of structural damage and/or leakage. I also considered loading up our side crawl with bricks, but I'm not sure how much I could safely add without again running into structural concerns.