[oceanplexian]

> It will always take at least 4190 Joules to heat 1 kg of water by 1°C. Even with perfect efficiency, you can never beat that number.

You can. A great example of technology that produces greater than 100% efficiency is a heat pump. You can actually buy commercial heat pump tank water heaters that are much greater than 100% efficient at turning electricity into hot water. The energy comes from the ambient air, but the Earth has no shortage of heat energy that can be recovered to do useful work.