I've got a Tucson client with Tesla solar panels and Powerwall who's getting hammered by Arizona Public Service demand charges. The battery is supposed to help reduce peak demand but APS is still billing $45-60 monthly demand charges on top of the minimum grid connection fee. The customer's solar/battery contractor swears the system is configured correctly. Anyone dealt with APS's convoluted rate schedules for solar+storage customers?
Arizona Solar + Battery Storage Billing Nightmare with APS
Alan, APS has some of the most complex solar billing in the country. The key issue is usually the battery dispatch timing. If the Powerwall isn't discharging during APS's peak demand window (typically 3-6pm summer), you'll still see those demand charges. Have you looked at the battery's actual discharge patterns vs APS's demand billing periods?
Randy, that's exactly what I suspected. The installer configured the battery for TOU arbitrage (storing cheap overnight power, discharging during expensive evening hours) but didn't optimize for demand charge reduction. APS measures peak demand during 3-6pm but the battery wasn't discharging until 7pm. Cost the customer $180 in avoidable demand charges over 3 months.
Alan, this is why I always recommend getting the battery programming details in writing before system commissioning. Down here in Louisiana with Entergy, we don't have the same demand charge complexity as APS, but I've seen similar configuration errors cost customers big money. The installers often focus on energy arbitrage and forget about demand management.
Estelle brings up a good point about getting programming details documented. Here in Oregon with Pacific Power, battery storage is still pretty new but I'm already seeing configuration issues. The key is understanding exactly when your utility measures peak demand vs when your battery controller thinks peak pricing occurs. Often they're different windows.
Thanks everyone. Got the Tesla installer to reprogram the Powerwall dispatch schedule to prioritize demand charge reduction 3-6pm, then do TOU arbitrage with remaining capacity. Should save the client $40-50/month. This stuff is way more complicated than the solar sales guys make it sound!