Super efficient diesel/bio fuel 4kw generator design.

[TommeyLReed]

125,000 btu's x 75%=93750 btu's
93750btu / 3.41= 27,892total watts or 27.892kw
27.892kw/8hr=3.436kw per hour

[MarkE]

125,000 btu's x 40%=50,000 btu's
50,000btu / 3.41=14,662 total watts or 14.662kw
14.7662kw/8hr=1.83kw per hour

This is at 50% load data.

The units are not quite right:

1 BTU = 1055J
1 BTU/h = 1055J/3600s = 1/3.41 W
125kBTU * 40% = 50kBTU
50kBTU/8 hours = 6.25kBTU/h * 1/3.41W/BTU/h = 1.83kW

1.83kW * 8h is 1.83E3J/s * 8h * 3600s/h * 1 BTU/1055 J = 50kBTU = 40% of the energy in 125kBTU, and
3.44kW * 8h is 3.44E3J/s * 8h * 3600s/h * 1 BTU/1055 J = 94kBTU = 75% of the energy in 125kBTU.

I went straight to J.   If we work it in BTUs first, we get:

118kBTU/tank * 1 tank/8h = 14.75kBTU/h * 1/3.41W/BTU/h = 4.32kW input power equivalent.

Efficiency = Continuous output power / 4.32kW