Steam engines as they are typically thought of are those in locomotives. All the engines that we think of require high output for heavy tasks such as mowing your lawn, driving your car, moving a train. However, for electrical power supplies off the grid this is not necessary. We often don't use our electricity except in bursts, and there can be long periods where very little electricity is used.
If we expect to have be a power company then of course we'll need a high pressure steam engine. But if we are using it to supplement other modes of electricity, both stored either chemically via batteries or mechanically via springs, a low pressure boiler system is more than sufficient to drive a water wheel. In fact it doesn't even need to be a steam engine, it could simply be a hot water engine. Heating the pipes that have hot water in them as in a simple stove, would force the water through the pipes, driving a steady movement of a Pelton water wheel inside the system, with no more than a heat exchanger inside a wood stove.
The purpose here may not be to produce energy on the spot for the range, but to produce energy for the batteries or storage device, which can in fact trickle in all day long.
Offered by Eric.