In a power plant, the conversion rate of MMBTU to MWH hours determines the plant’s efficiency and is known as the plant’s heat rate.

1 MWH is equivalent to 3.412 MMBTU. Thus if a generator could convert all of the energy from the fuel into electric energy, its heat rate would be 3.412 MMBTU/MWH.  1 MWH is thus equal to 3,412,142 btu. 1 KWH is equal to 0.003412 MMBTU or 3,412 BTU

Generators cannot come anywhere close to 100% efficiency. The better units being around 50% efficiency. This translates into a heat rate of 6.824 MMBTU/MWH, meaning that producing one MWH of electric energy requires burning fuel with a heat content of 6.824 MMBTU.

Power station capacity = e.g 350 MW Multiplied by hours a year = e.g 3600 hours = 350 MW * 3,600 hours = 1,260,000 MWH

Multiplied by 3.41 btus = 1,260,000 * 3.41 = 4,296,600 btu

Multiped by efficiency of station = so if station is 51% efficient in needs to consume that much more gas, so  4,296,600 btu divided by 51% = 8,424,705 btus

Then you need to convert from lower to higher heat rate, so multiply by 10% (*110%), so 8,424,705*110% = 9,267,176 mmbtus

If a power station buys gas, it usually pay for this in HHV terms. if one wants to convert the cost to a price in LWV when needs to add 11%. Or reduce the efficiency of the station by 9% (i.e. it needs more gas to generate that amount of electricity)