mrCloggy

At 28,000 RPM, it takes an additional 250 Watts

Have you measured the motor temperature, and experimented with partially blocking the air intake to that fan, to decrease the fan-power a bit?

Power use by the stepper motors:
Maybe you already use a system like this example, where 15V is used for the (high) power needed to accelerate/decelerate the moving mass, and once in place the voltage(and thus current) drops to 3.3V for positioning only.

kW/m² depends on your locality, higher latitudes have more airmass, therefore less solar energy.
http://pvwatts.nrel.gov/ is quite usable to figure things out.

You'll have to look at the price you currently pay for electricity in your cabin/community, use http://pvwatts.nrel.gov/ to get a feel for the solar possibilities, and compare the prices.
It seems everything is expensive there, if you pay a fuel price of $25/gallon for your diesel generator, every gallon saved when using PV helps.