Recently a potential client was asking us about an oddity in their Pasadena Water and Power (PWP) electric bill. PWP has a tiered rate structure, but the most visible component of that tiering, the Distribution charge, steps up above 350 kWh of usage in any one month, but it steps down above 750! Which lead us to the question, are PWP's electric rates regressive?
Designed that way
PWP's Residential rate structure, like many utility tariffs, is a model of complexity. On your bill there are a number of obvious charges, and a few that are not so obvious. The obvious ones are on the right-hand-side of the bill and include a Customer charge, a Distribution charge, a Transmission charge, and an Energy charge. (The not-so-obvious charges include those related to public benefit programs and paying to put power lines underground.)
All of these obvious charges are tied to the customer's usage, but only one, the Distribution charge, is tiered. At or below 350 kWh of usage per month, the customer pays just 1.5¢/kWh. Between 351 and 750 kWh of usage the Distribution charge increases dramatically all the way up to 11.65¢/kWh, nearly an eight-fold increase! Ok, the whole point of a tiered rate structure is to discourage higher use by making you pay more as your usage increases. But PWP's rate then does something truly odd - above 750 kWh/month the rate comes down, dropping from 11.65¢/kWh to just 8.5¢/kWh! What sort of an incentive is that?
But is it regressive?
That rate design is certainly counter-intuitive, to say the least, but is it regressive? In other words, is there a point at which a large residential user ends up paying less per kWh than does someone who uses less? To find out, we modeled daily usage from 10 kWh/day all the way up to 60 kWh/day. As a reference, a typical Run on Sun client in PWP's service area averages around 25 kWh/day. Since the Transmission and Energy charges are adjusted higher in the summer months, we broke out the overall rates seasonally as well.
Here are our results (click for larger):
The blue line is the winter rate and the orange is summer. If you use a tiny amount of energy you will pay between sixteen and seventeen cents per kWh, with rates rising sharply until you get to 25 kWh/day. Beyond that, the rate of growth flattens out markedly, but it never dips down. (That is true even if you carry the analysis all the way out to 200 kWh/day!)
Contrast this with the SCE Domestic rate - that is a truly aggressively progressive rate structure with energy charges of 14.5¢/kWh for those using within the smallest (baseline) tier of energy, going all the way up to 30.8¢/kWh for energy used in the fourth tier, which kicks in for monthly usage above approximately 900 kWh.
So no, PWP's Residential rate is not regressive, but by flattening out the rate for usage above 25 kWh/day, it sends at best a mixed signal if the utility is trying to encourage its customers to reduce their usage.
How does this relate to solar? Well, if your usage is above 20 kWh/day you are spending at least 20¢/kWh whereas the cost of a solar power system will be less than half of that! So yes, in PWP territory - and particularly while they still have rebates in place - installing solar will still pay you big dividends.