Utility director outlines plan to reduce power‑system risk as borough buys local generators

Utility Director Harper told the Petersburg Borough Assembly on March 16 that the borough runs a “hydro‑first” system and is moving to shore up local generation to reduce reliance on diesel backup and on the regional hydro cable.

Harper said Petersburg’s supply comes primarily from SEPA hydro (Tai and Swan lakes), supplemented by the Blind Slough plant and a small diesel fleet kept as backup. "Our primary power comes from SEPA 100% hydro," Harper said, and the borough runs diesels only as a contingency. He showed two years of daily load data and said diesel engines ran in fewer than 3% of hours in 2025, with most diesel hours associated with scheduled maintenance, outages or brief peak‑shaving events.

The presentation detailed the borough’s capacity picture: SEPA has allocated a 12‑megawatt share for Petersburg, Blind Slough contributes roughly 2 MW, and the borough’s existing diesel backup provides about 13 MW — producing roughly a 27 MW local cushion when all sources are available. Harper warned that sharp winter peaks (he cited several days at or near 138 megawatts historically) can push the system to its limits and said a new local generator and SEPA upgrades are critical to avoid forced roll‑offs or costly diesel runs.

Assembly members pressed staff on technical points. Member Mucci asked about differences in the Swan and Tai lake capacities; staff replied that catchment area and elevation account for the different storage volumes. Member Valentine asked how recently purchased equipment and planned turbines would change the borough’s share. Harper and staff said SEPA’s third turbine and a borough 3.5 MW unit currently in procurement would raise Petersburg’s effective on‑hand capacity; Harper said the borough is expected to have about 36.5 MW of installed capacity by the end of 2027, which he said should remove the need for peak shaving for roughly 10 years under the forecasted load growth.

Harper cautioned that even with the additions the borough must manage reserves: "Even with the new one, we're going to be right on the cusp. We'll be good, but it'd be like taking your boat out and run it to half a tank," he said, noting the risk if the regional cable were to fail. He reviewed recent diesel run hours and said scheduled SEPA maintenance (a June shutdown for transformer PM and line work) accounts for a large share of planned diesel use but that conservation messaging reduced additional peak events.

Harper also explained equipment lifecycle issues at local diesel units and the need to stagger investments in new generators over time because aging units require ongoing replacement. The presentation concluded with staff saying the planned projects and SEPA upgrades together will significantly strengthen local resiliency but emphasized continued planning and funding work is required.

The assembly did not take formal action on the presentation; members thanked staff and moved to the next agenda item.