This is the way

Did you (OP) just move (or set up new billing because a roommate moved out)? If so, you'll be on Eversource's basic rate for a couple billing cycles before you get auto-enrolled in the Cambridge community program. If you've switched off the community program, you'll have to manually enroll.

Electric rates have been extremely high this winter. Community aggregation rates are usually negotiated for 2 years at a time. Cambridge lucked out and wasn't re-negotiating for this winter when prices were high so 10.2c is locked in. Somerville was negotiating for this winter which made their rate 15.654c.

It looks like electric rates are already starting to return to normal (after the huge winter scare over the lack of Russian natural gas). If you look at Eversource's "Monthly Variable Rate" you'll see things coming down to 13c this summer (https://www.eversource.com/content/residential/account-billing/manage-bill/about-your-bill/rates-tariffs/electric-supply-rates). Most customers are on the 6-month fixed rate which is fixed at 25.776c through June 30th, but given that the monthly variable rate is dropping fast, I'd expect the July-December rate to be a lot lower.

Still, the community aggregation is a good idea. It's not always cheaper, but it provides a consistent rate without huge spikes and it's negotiated in your interest by the city. For those in Somerville, there are cheaper rates currently available from third parties, but you need to keep on top of those rates once the initial term is up. Some (most?) suppliers switch you to a variable rate after the initial term that could be really high. Somerville got unlucky negotiating their 2-year deal in fall 2022 when everyone was super worried about energy prices.

Still, it might be best to stick with community aggregation even in the event of slightly unlucky timing. Somerville's rate might be 16c, but Eversource's 26c was really high. Eversource's rate would have to drop below 12.28c for the following 18 months to make up for the 26c spike January-June. That seems unlikely given that energy prices have generally been at least 10c and even if we've survived this winter without Russian natural gas, it will likely keep energy prices marginally higher - plus general inflationary pressure. Even if Eversource ends up having slightly cheaper rates than Somerville's community aggregation, it might be best to go with something negotiated in your interest. Plus, Somerville has a less-green 14.914c rate if someone really wants it. At that point, Eversource's rate would have to drop to 11.29c to be cheaper which seems even less likely.

Community aggregations are great. For any Somerville people reading this, you might get a better rate at https://www.energyswitchma.gov, but also beware to make sure you don't get switched to a higher rate at the end of your initial term and that you don't sign up for something with termination fees or enrollment fees. It might just be worth sticking with the community aggregation rather than pinching every penny.