absolutsnwbrdr wrote:Trying to run any size electric heater from an inverter while boondocking is not really a reasonable expectation...Without a massive power bank, you're going to be very disappointed, even with the "little" 100W heater...
Exactly. People use the words "power" and "energy" interchangeably but they are very different ideas to an engineer or scientist.
Energy is an amount. Power is a rate.
Batteries are great for power. Whatever energy is in them can get out fast, at a very high rate. But there really is not much energy in them, so you can end up with a dead battery quickly if you try get out a large amount of energy.
Let's use a Duracell marine deep discharge battery, model SLI31MDC for this example.
(105) amp hours x (12) volt = 1,260 watt hour
We can convert watt hours of energy to BTU directly, because energy is energy in all units. BTUs are handy for comparison, because chemical fuels like propane and gasoline are usually measured in BTUs. One watt hour equals 3.4 BTU. Let's convert the battery energy to BTU:
(1260) watt hour x (3.4) BTU per watt hour = 4,284 BTU. So we have 4,284 BTU in that battery.
A standard gas grill propane bottle is 20 pounds, and propane has a lower heating value of 20,990 BTU per pound.
(20) pounds x (20,990) BTU per pound = 419,800 BTU. So we have about 419,800 BTU in a bottle of propane.
This allows us to directly compare the energy in batteries with the energy in a bottle of propane.
4,284 BTU in a marine battery
419,800 BTU in a bottle of propane.
It would take about 100 marine batteries to equal the energy in a 20 pound bottle of propane. It's actually worse than that, because you lose energy in the inverter and in the charge/discharge of the battery. But you get the point.
A nice toasty warm heater is a heater that delivers a lot of energy. If you want a toasty warm heater, use propane or some other chemical fuel.
I think we are not aware of the difference because our portable electrical devices use only tiny amounts of power and energy, and our heavy electrical devices are connected to the grid. Things like charging a phone, or running a stereo or a laptop or a few LED lights are all small energy and small power. But space heating or heating water or running an air conditioner is heavy lifting, and you want to use either a chemical fuel like propane or be connected to the grid where some machine burning natural gas or coal somewhere is sending you gobs of energy.