When humans produce energy, we do it very inefficiently. Usually what happens is that we make something very hot (like a car engine), use a tiny bit of that energy to do work, and then spend even more energy getting rid of all the waste heat. Panasonic has developed a new thermoelectric material that can get a chunk of that energy back.
A thermoelectric material is something that can convert heat directly into electricity. It's not a new thing, but generally it's so inefficient that anyone who's serious about capturing electricity through heat instead uses some sort of steam generator. Where thermoelectrics have potential is in microgenerators, where you're just looking for a little bit of power to take the edge off of your electricity bill.
Panasonic's new thermoelectric material can suck 2.5 watts of electricity out of hot water running through a 10 centimeter section of pipe. Four pipes put together gets you about 10 watts, which is enough to power a light bulb. Nothing is free, of course, and this material is really just harvesting energy from whatever energy source you used to heat up your water in the first place. But losing energy from hot water is something that happens anyway, and the difference here is that instead of losing that energy out into the environment, it's being reclaimed (to some extent) by the thermoelectric material instead. It's also important to keep in mind that this stuff doesn't just require a source of hot water; since it operates based on a temperature differential, it needs cold water as well, along with (long term) a pump to keep the cold water circulating.
Even with these restrictions, technology like this is a promising way to help make nearly everything more efficient, from power plants to water heaters to car engines. Panasonic has to figure out a way to make it cheaply and efficiently, but when it does, you can expect it to start showing up all over the place.