Therm (US) to Megawatt Hour

Residential US natural gas prices typically range from $0.80 to $2.50 per therm depending on region, season, and utility. The wholesale Henry Hub benchmark translates to about $0.25 per therm at $2.50/MMBtu. Delivery charges, taxes, and utility markups roughly triple or quadruple the commodity cost by the time it reaches a home meter.

The average US home using gas for heating consumes about 500–900 therms per year, depending on climate, insulation, and home size. Homes in mild climates like Southern California may use under 300 therms; homes in Minnesota or Wisconsin can exceed 1,200 therms. Gas water heaters alone account for roughly 150–250 therms per year.

One US therm equals exactly 100,000 BTU, while one MMBtu (million BTU) equals 1,000,000 BTU — so 1 MMBtu equals 10 therms. Wholesale gas markets and pipeline contracts use MMBtu; residential utility bills use therms. The two are straightforward to convert, but confusing them by a factor of ten is a common mistake in energy cost comparisons.

Retail billing in therms gives homeowners manageable numbers — a winter month might be 80–120 therms at $1–2 each. Wholesale pipeline contracts deal in millions of BTU (MMBtu) because the volumes are enormous and the industry standardized on BTU-based pricing in the early 20th century. One MMBtu equals 10 therms, so converting is simple. The Henry Hub benchmark price of $2.50/MMBtu translates to about $0.25/therm before delivery charges, taxes, and utility markup roughly quadruple it at the meter.

A typical US residential furnace rated at 80,000–100,000 BTU/h uses about 0.8–1.0 therms per hour at full output. High-efficiency condensing furnaces (95%+ AFUE) extract more heat per therm, so they cycle less often. On a cold winter day, a furnace might run 8–12 hours total, consuming 6–10 therms. That translates to roughly $5–$25 per day depending on local gas prices.

MWh is the natural unit for grid-scale transactions because power plants and large industrial loads operate in the megawatt range. Quoting in kWh would produce unwieldy numbers — a 1 GW nuclear plant generates 24,000 MWh/day, not 24,000,000 kWh. Spot markets like the US PJM or European EPEX quote prices in $/MWh or €/MWh, typically $20–$80/MWh in normal conditions.

One MWh powers the average US home for about 1.1 months (since the average is 886 kWh/month). In Europe, where consumption is lower (~300 kWh/month), one MWh can cover about 3.3 months. A single MWh is also enough energy to drive an electric car about 5,000–6,000 km, or to run an industrial air compressor for roughly 4 hours.

US wholesale prices typically range from $20 to $80/MWh depending on region, time of day, and fuel costs. European prices are generally higher at €50–€150/MWh. During extreme events — heat waves, supply shortages — prices can spike above $1,000/MWh for brief periods. Negative prices (below $0/MWh) also occur when wind or solar oversupply the grid.

A modern onshore 3 MW turbine at 35% capacity factor produces about 9,200 MWh/year. A large offshore 15 MW turbine at 50% capacity factor generates roughly 65,700 MWh/year. Capacity factor — the percentage of theoretical maximum output actually achieved — varies with wind resource, turbine technology, and maintenance downtime.

Current lithium-ion battery costs (~$150–250/kWh) make 4-hour systems economical for peak shaving and solar time-shifting, but 24-hour storage would cost 6× more with diminishing returns. Grids instead layer solutions: batteries handle the evening peak (4 h), gas turbines cover overnight baseload, and pumped hydro or compressed air provide longer-duration backup. Iron-air and flow batteries are emerging for 100+ hour storage at lower cost per kWh, potentially closing the gap by the 2030s.