Solar-Powered Circulation: Applications in Electrical Power Utility Waters
Solar-powered circulation (SPC) of water is used to solve a variety of water quality problems in drinking-source and recreational reservoirs, potable-water storage tanks, wastewater lagoons, storm-water runoff ponds and industrial water bodies. This report describes SPC technology and current applications in electricity generating utilities. These applications include: 1) enhanced evaporation and heat loss in cooling basins; 2) oxygenation and warming of reservoirs during winters in northern climates; 3) suppression of harmful algal blooms (HABs) and invasive macrophytes in nutrient- enriched water bodies; 4) prevention of noxious odor events in water bodies with high sulfide levels, and; 5) enhanced degradation of the anticorrosive compounds, hydrazine and ethanolamine (ETA), in wastewater.
SolarBee, Inc., SPC units are comprised of three pontoons supporting a platform consisting of above water, near-surface and underwater components. Three 80 watt solar panels, an electronic control box, a low-voltage, high-efficiency brushless motor, and accessories are mounted on an above-water frame. The one-half horsepower, direct-drive motor operates at 90% or greater efficiency. A distribution dish, impeller and battery are attached to the frame and suspended just below the surface. A flexible intake hose, three feet in diameter, is attached to the base of the impeller. A steel plate suspended one foot beneath the hose causes water at that density layer to be drawn in radially with near-laminar flow from long distances. Water intake depth is adjusted using chains attached to the intake plate and secured to the frame. Two moorings attached to the frame with chains maintain the spatial position of the unit. The impeller operates continuously, day and night, at 80 RPM unless the controller is programmed to vary by time of day, or prolonged periods of low light incidence causes the electronic controller to reduce the RPM or deactivate the system temporarily. The largest units pump approximately 10,000 gpm (14.4 M gpd) of water to the surface. A direct flow of approximately 3,000 gpm ascends through the intake hose and departs from the unit at low velocity immediately above and below the distribution dish. Another 7,000 gpm of induced flow ascends outside of the hose and departs from the unit without turbulence below the distribution dish.
The SPC unit’s intake depth is set at a level determined by the water quality objective. For example, a shallow intake depth is used in hot water cooling ponds and lakes to enhance evaporative heat loss. The intake is typically set just above the thermocline for HAB and invasive macrophyte suppression. The intake is usually set near the bottom for odor control and oxygenation of the hypolimnion. Intakes in wastewater are generally set just above the anoxic zone where anaerobic bacteria in sludge digest some compounds.