The Retreat has its own stand-alone off grid hydro-electric power plant that supplies 100% of the power needs for the entire facility. A portion of the San Francisco River is diverted at a point approximately ½ mile north of the property boundary into a pipeline that delivers water to a storage pond on the property that is used for the power system, irrigation system, and for exercise and recreation. The pond has approximately 1 acre surface area and averages about 8 to 9 feet deep thus providing significant storage volume. The hydro penstock exits the bottom of the pond and travels about 765 feet to the power plant with 39 feet of elevation drop providing the water pressure necessary for power production.
Water availability varies significantly seasonally, and somewhat from year to year. Therefore, the plant is designed with two independent turbines that allow for variable flow through the plant. These turbines are irrigation pumps run backwards. The drawback is that the pumps have a steep efficiency bell curve peaking at the rated pump flow thus allowing for very little adjustment of flow, but the pumps are significantly cheaper than “power plant” specific turbines. We use two rated at 4 cubic feet per second (CFS) and 2 CFS. They can run individually or in tandem allowing for 3 set flow rates, 2 CFS, 4 CFS, and 6 CFS.
Each of the pumps has a “draft tube” on the outlet that drops an additional 10 feet of elevation back to the river. When installed properly and used with an appropriate turbine (like our pumps), a draft tube actually creates a suction at the turbine outlet based on the elevation difference between the turbine and the draft tube outlet. This suction is real power and translates to an increase in power plant production. We have valves installed that allow us to turn the draft tubes on and off. When the draft tubes are “on”, they actually increase the flow rate through the turbines too, so by selecting which turbines are on and which draft tubes are on we have 6 discrete flow/power settings to choose from. The lowest setting is 1.75 CFS producing 3.5 kW and the highest setting is 6 CFS producing 11 kW.
Our power production is direct 60Hz AC power. Frequency regulation is achieved with a “Load Governor” that maintains a constant load on the system by automatically increasing or decreasing the power diverted to “dump” loads based on the amount of user loads in use. There is also a load manager that functions similarly to the load governor except it diverts power to useful loads such as space heaters and/or hot water heaters when the power is available. The load manager has first priority over the load governor to maximize productive use of the power generated .
The plant was commissioned 7/4/96 and has been operating continuously since with only brief periods of down time for routine maintenance and only a few minor repairs. This system description has been significantly simplified to facilitate a brief and concise summary. More details and system features are available upon request.
