This has always fascinating me.

> Living in Northern Sweden with with the heater on for the bigger part of
> the year: Could a stirling engine be used to drive an electric
> generator? Anyone tried that?

Short answer: No.
Conservation of energy applies.
You need an energy source to power the motor and all such motors will result
in an overall net energy loss.

However, if you had a low grade source of heat you could conceivably use it
to drive an engine to do useful work.
You could eg use a Stirling that ran off the difference between ceiling and
floor heat to drive a fan to pump hot air down to floor level. Would run
faster as difference increased :-)

A Stirling engine's MAXIMUM THEORETICAL efficiency is (Tin-Tout)/Tin.
T in degrees Kelvin = C + 273
actual efficiency is typically 1/2 to 1/3 of this although theoretical can
be approached more closely in a  good design.
eg Boiling water in and room temp out = 373 K in and 300 K out.
Eff = (373-300)/373 = 19.6% MAXIMUM.
Actual would be typically 5% to 10%.
Which shows why a HOT Tin is desirable.

A Stirling runs on the Carnot Cycle which is the most efficient cycle
possible BUT a good engine on another cycle can be more efficient than a bad
Stirling Engine.

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