Okanogan County Electric Co-op Microgrid
Winthrop, WA · Okanogan County Elecic Co-op · Operational Q4 2026
1 MW / 3,344 kWh storage · 24 kW solar repower · utility-owned peak shaving
Purpose
OCEC is a member-owned cooperative serving the Methow Valley. Its highest per-unit cost is the peak demand charge it pays its power supplier each month, based on the single moment of highest system-wide demand. The battery discharges during that peak and recharges off-peak, lowering the charge for every member rather than for one building. On a system that peaks around 25 MW, taking a megawatt off the top also gives the co-op room before brownouts.
MZ Solar Consulting led project development and conceptual design, helping OCEC secure full funding from the Washington Department of Commerce and ensuring the project could be completed at no cost to the cooperative or its members. Before construction, OCEC held a public meeting in Winthrop to walk members through how the system works and stays safe.
Technical Details
This is a utility-owned asset on the cooperative’s distribution system. Four ELM MG2 enclosures (836 kWh each) run through an EPC Power CAB1000 inverter, a 1,000 kVA isolation transformer, and a 3,000 A switchboard, then out through OCEC’s 1.5 MVA pad-mounted transformer at 12.47/7.2 kV. Grid isolation and protection run through an SEL-751 relay at the grid edge rather than behind a customer’s meter, which is the main thing separating this project from the rest of the Sulis portfolio. The switchboard also reserves positions for the pump house, shop, and administration building, so the co-op can later back up its own facilities.
The existing solar array was repowered rather than replaced. New modules were mounted on the existing two-and-a-half-inch pipe support frame, which required a custom mounting bracket because the standard IronRidge bracket for XR1000 rail fits only two- or three-inch pipe. The battery sits on a new 57-by-22-foot concrete pad set back 25 feet from the site fence. The chemistry is lithium iron phosphate at a 0.3C charge and discharge rate, the low end of the range.
As always, the dedicated IBEW crews at our sister company, Mills Electric, completed the field work. They took a break to speak with a CET group from the local high school when our project partner, MZ Solar Consulting, brought them by to learn more about the system and work in the electrical trade.
