The Mountain West electricity rates

The Mountain West is the most internally varied region in the country. Utah and Wyoming sit near the bottom of the national rate table on old, largely depreciated coal fleets supplied by in-state mines. Montana sits well above them despite similar geography. Arizona, Nevada and New Mexico run on gas, an enormous solar resource and, in Nevada's case, the largest geothermal fleet in the country after California.

Most of the region is served by vertically integrated utilities with no retail choice, under commissions that in several states are elected. Much of it also sits in a multi-state utility system, which creates a recurring fight about how much of one state's clean-energy transition costs another state's ratepayers should carry.

Customer density is the other common thread. Long lines serving few customers per mile push fixed costs per customer up, which is why Wyoming and Montana are not as cheap as their generation position alone would suggest.

The region contains both of the states whose rates fell over the past year, and the reasons are worth separating.

New Mexico retired coal under a law that let the utility securitise the undepreciated cost with low-interest bonds, while replacement solar was procured at prices low enough that the transition reduced costs rather than raising them. That is a genuine, permanent saving rather than a deferral, and other states have started to copy the mechanism.

Arizona benefited from the largest power plant in the country by output, the Palo Verde nuclear station, plus a rapidly growing solar fleet well matched to an air-conditioning load shape.

Montana went the other way, and sharply. Having sold its generation during a brief deregulation experiment and later repurchased hydro assets at a much higher price, its utility has been buying and building replacement supply into a small customer base.

Arizona has the most complicated residential rate menu of any state, with multiple time-of-use plans, demand-charge plans and flat plans, and a large gap between the best and worst choice for a given household. Both major utilities publish comparison tools that run your own usage against every tariff, and using one is worth real money.

Across the desert Southwest, summer peak-to-off-peak spreads are among the widest in the country. Pre-cooling in the morning and coasting through the afternoon peak is the most effective residential strategy available.

In Colorado and Utah, municipal utilities are frequently cheaper than the investor-owned utility next door, and the boundaries are irregular enough to be worth checking against a specific address.