I'm investigating the possibility of deriving power from solid fuels. Just burning something. There's boilers and steam engines, but steam engines require a lot of maintenance, super heated steam is preferred and boilers are dangerous. At the hight of the steam age in the late 1800s and early 1900s something like 50,000 people per year were killed in or because of boiler explosions. Besides all that I would be looking at a cost of a few thousand dollars for at most a few horsepower with no guarantee on how long it would last before it breaks or blows up. Also running a steam engine would be an active involved process, almost like a steam locomotive engineer and fireman. I already work with saturated steam coming from three 1,200hp boilers. So I'm well aware of how dangerous steam is. But using thermo electric generators for some degree of off grid or backup power is looking much more appealing. There are no moving parts aside from pumps for circulating hot and cold fluids. They work at much lower temperatures than steam engines. They have the potential to work with an air cooled cold side, but this would generate less power than a liquid cooled cold side, at least in theory. They are about as expensive as solar panels just to buy the thermoelectric cells. Then you have to come up with a way to heat and cool them. That's where all the money goes. So they end up costing at least several dollars per watt. To get the most power out of these units they should probably use a MPPT charge controller. That way the battery isn't over charged and the voltage can be handled efficiency across the wide voltage range these things develop. To get the most efficiency a variable speed hot water pump controlled by voltage would and an air cooled cold side seem like the way to go, in theory. My money would be on building and running them getting the most power out of them. Applications. I'm considering that thermoelectric generators could be used on their own or with a liquid cooled engine. Let's say I use a diesel engine to generate power to bulk charge batteries. You don't really need or want to run an engine to float charge batteries because they draw hardly any power during float compared to bulk charging. But while bulk charging the engine could be heating a hot water tank full of coolant, then that coolant could be used to heat a thermoelectric generator. A thermoelectric generation unit and mppt could float charge the batteries. Or build a fire and heat a tank of water and use that to generate some power. There is also a 3rd possibly. ThermoElectric from solar but I have already established these things are definitely going to produce power at a cost a lot higher than solar panels. The only thing that would be appealing is the ability to store hot water till night and create some power after the sun is down. Or produce power from excess solar heated water.