Medora Corporation

SolarBee Technical Bulletin


Courtesy of Courtesy of Medora Corporation


1. Origin of the SolarBee. Pump Systems, Inc. (PSI) developed, built and installed its first solar powered mixer in Dickinson, ND, in the summer of 1998. It was installed into a 30 acre x 13 foot deep municipal wastewater reservoir which had a long history of toxicity associated with ammonia, odor, and stratification problems. In six weeks the entire reservoir cleared up to the point where the holes in the 10 foot deep intake strainer could be seen from the surface, the water smelled much better, and wildlife began returning to the reservoir. PSI continued to develop the technology and in Sept., 2001, established the SolarBee© brand name for this equipment. In 2002 the high-flow models were developed, which increased the flow by almost 10 times per watt of sunshine. In 2004 the current 'v12' models were introduced, with 25-year-life high-efficiency maintenance-free motors and 24 hour-per-day operation on solar-supplied power that is stored in a battery.

By early 2005, PSI had installed over 600 machines in the U.S., and had conducted over 250,000 water tests. There is an ongoing program to extend the SolarBee's capabilities. New models and technology advancements can be kept abreast of by referring to Also, please note that in the rest of this document, the word 'reservoir' and 'lake' and 'pond' are used interchangeably.

In fresh water lakes and reservoirs, the SolarBee can be deployed in two different methods regarding hose settings and spacing: (a) for blue-green algae and invasive macrophyte control or (b) for hypolimnetic aeration.

When deployed for blue-green algae control, the SolarBee prevents phosphorus and nitrogen from being turned into inedible blue-green algae blooms that can cause toxic conditions. Instead the SolarBee mixing causes nutrients to be uptaken by 'good' planktonic organisms which are then eaten by zooplankton which in turn are eaten by fish. Since the nutrients are being pushed through the food chain, controlling the levels of phosphorus and nitrogen becomes less important, and the lake become highly productive while at the same time water clarity and odor improves, dissolved oxygen (DO) increases, pH and chlorophyll a decline, diversity increases, and fish become more vigorous. We have also seen increased fish spawning rates, up to 20 times higher, than before SolarBees were installed. Another benefit appears to be a slow reduction of invasive weed species as the blue-green algae is eliminated. Another benefit may be mosquito control. PSI is conducting testing to determine the mechanisms behind all of the effects of SolarBees on the epilimnion of lakes.

When deployed for hypolimnetic aeration, the SolarBee can transport oxygen down to the sediments to prevent the release of manganese, iron, H2S, and phosphorus. This is accomplished without disturbing the sediment or de-stratifying the lake, so that the cold water fishery is preserved. We have found, in most cases, that by controlling the blue-green algae in the epilimnion the oxygen demand on the sediment is reduced enough to minimize anoxic conditions in the hypolimnion.

In potable water distribution reservoirs, the SolarBee can be installed to provide thorough mixing to reduce problems associated with long water age and loss of disinfectant. The SolarBee can also be used for boosting chlorine or chloramine in the reservoir, and for break point chlorination if the reservoir is taken off line. In these applications the SolarBee is typically installed through a top hatch (using bolt-apart or collapsible models), and the solar modules and battery are mounted on the roof.

In wastewater, the SolarBee's continuous removal of the surface lipid film allows increased outgassing of methane which in turn increases anaerobic sludge digestion Also, the mixing of the surface water, having high DO and higher pH due to algae, throughout the selected mixing depth results in odor control as well as improved reduction of BOD, TSS, ammonia (N) and phosphorus (P). The likely reasons for the beneficial results of the SolarBee can be found in the huge volume of research conducted by Dr. William J. Oswald, Professor Emeritus at University of California Berkeley, and others, beginning in the 1960's and continuing through today.

2. Basics of the SolarBee Technology. Versatility. SolarBees are deployed in different ways to solve different problems. Primary system design variables include sizes and models of machine, quantity and placement of machines, depth the intake hose is set at, single-mix or dual-mix flow patterns, upflow or downflow, photovoltaic (PV) modules mounted on the machine or on shore, and whether a shore-power assist kit is needed. Options also include chemical injection kits, buoy market lights, bird roosting protection, and SCADA (Supervisory Control And Data Acquisition) output readers. With this versatility the SolarBee has been used successfully to accomplish a wide variety of goals in lakes, ponds, estuaries, potable water storage reservoirs, aerobic wastewater reservoirs, anaerobic wastewater reservoirs, storm water reservoirs, and total evaporation reservoirs.

Upflow, Usually. Most SolarBees are deployed in the upflow direction. In several cases there are advantages to using downflow instead of upflow, and a simple flip of a switch is all that is needed to switch the flow direction.

Surface Renewal. Because the surface of the reservoir is continually being renewed, if it is low on oxygen it absorbs oxygen from the atmosphere at a rapid rate, just like the lungs in a human being. The absorbed oxygen is then distributed throughout the mixed depth of the reservoir. The SolarBee's method of surface renewal creates 'rolling' conditions very similar to those of large slow moving streams as studied and disclosed by the scientists Imhoff and Fair in the 1950's, and by scientists studying the surface of the ocean in the 1990's. These studies indicate that constant surface renewal increases the gas transfer into and out of a body of water by up to 7 times as much compared to a stagnant surface (e.g., more oxygen is absorbed and more gases such as methane or ammonia are gassed off, etc.). The most frequent observation is that immediately after a SolarBee is installed the reservoir or lake water seems 'looser' and more active, with many more small lapping waves than previously observed.

Near-Laminar Long-Distance Flow. The SolarBee is designed to minimize turbulence and establish a gentle horizontal near-laminar flow which moves radially outward from the SolarBee at the top of the reservoir, and radially inward at the bottom of the reservoir. This near-laminar flow was difficult to achieve because getting water to move long distances in an open reservoir is similar to 'pushing a rope'; if too much force is applied, most of the energy produces undirected turbulence, with no long-distance flow patterns. Laminar flow is described as 'frictionless' and each water molecule will continue to travel onward until some force disturbs its flow. Normal wave action and wind ripples do not stop the laminar flow, and small particles entrained in the surface flow outward from the SolarBee can be observed to travel both upwind and downwind from the machine until they reach the far edges of the reservoir. With turbulent flow created by typical aerators and mixers, short circuiting occurs where the water goes outward just a short distance and then turns around and comes back to the inlet of the aerator. Virtually no other aerators or mixers we have seen, even systems costing millions of dollars, are effective beyond 0.75 surface acres, whereas the SolarBees are effective for up to 50 acres, depending on model size.

Radial Flow Mixing, Different From Wind Mixing. When the near-laminar radial flow projects outward from the SolarBee at the reservoir surface, the water streamlines are 'diverging' from each other, like hands on a clock, and water from deeper in the mixed zone is pulled up to the surface to fill the voids that would otherwise be created between the streamlines. This upward flow everywhere in the reservoir is aided by the 'converging' streamlines down at the end of the intake hose. The streamlines there become compacted as water tries to flow toward the machine radially from all directions, so some water moves upward to fill the voids at the top of the reservoir. Thus the horizontal laminar flow away from the SolarBee at the top of the reservoir, together with the horizontal laminar flow toward the SolarBee at the level in the intake, causes a vertical circulation upward between the shallow and the deep horizontal flow layers. This vertical mixing occurs throughout the entire mixed zone, at a higher rate near the SolarBee and a lower rate near the edges of the reservoir. This pattern is distinctly different from, and adds to, the effect of any wind mixing of the reservoir. Wind mixing is mostly in parallel force lines and does not have any consistent vertical element, so it does not affect micro-environments like a SolarBee does. In many SolarBee applications the reservoirs are in windy or very-windy environments (regular winds over 50 miles per hour), yet the SolarBee eliminated blue-green algae blooms and made a huge improvement to the ecology.

Sophisticated Electronics for Extended Mean Time Between Failures (MTBF). The 'v12' machines, our standard machines by the end of 2004, have many features which earlier models did not have. The maintenance-free 25-year-life motors operate 24 hours per day on solar-supplied power. Once per day the motor rotation is reversed for a few moments to clean the impeller. And if a stick or other item momentarily obstructs the impeller, the motor will reverse to clear out the clog. There is a dip switch that allows the user to select upflow vs. downflow, and another dip switch to optimize nighttime run speed for the application and climate. Finally, each machine broadcasts wireless signals which contains critical operating data so that a multitude of machines can be monitored remotely from shore via a handheld device, or through the Internet or a SCADA system via land lines.

3. Commitment to Testing. PSI is committed to continual testing to achieve SolarBee machine reliability as well as predictable and favorable results. Most of our factory-trained service and installation crews are in the field virtually every business day, and we believe we are collecting and cataloging more data each year from more water reservoirs, of all types, than has ever been assembled before. Water testing is done from a boat and is conducted at multiple depths and GPS-marked locations within each reservoir. The test methods employed are aimed at understanding the reservoir and system conditions both before and after SolarBees are installed. The collected data has given PSI deep insights into reservoir ecology, and has led to constant improvements to SolarBee equipment and the manner in which SolarBees are deployed.


The SolarBee optimizes the utilization of solar energy striking the reservoir in a two-step process: (1) the solar panels generate sufficient electrical power to operate the high volume pump for thorough mixing to the selected depth, and (2) this enables the sun's rays, through photosynthesis and other means, to naturally treat the water which had previously been in a dark environment at the bottom of the mixed zone.

1. Solar-Energy-Powered Pump. The total flow leaving the SolarBee can be described as: Direct flow + Induced Flow = Total Flow. In this section, the SB10000v12 is discussed, but the same principles apply to all SolarBee models. In full speed, the SolarBee Model SB10000v12 pumps 3,000 gallons per minute (gpm) of direct flow which, in turn, causes an additional 7,000 gpm of induced flow to come up from under the flow dish on the machine, for a total flow of 10,000 gpm that leaves the 17-feet diameter machine.

Direct Flow. At full speed, the impeller on the SolarBee pumps 3,000 gallons per minute of direct flow upward through the 36-inch diameter intake hose. Flow testing to establish this figure has been performed using dyes and a stopwatch, flexible bladders, and weirs, and has been corroborated by independent testing which can be found at

The impeller, almost 3 feet in diameter, has a combination of both axial flow and positive displacement characteristics. It rotates at less than 100 rotations per minute (rpm) to achieve long motor bearing life. The pumping action creates about 0.2 inch of lift above the reservoir surface and, due to the physical configuration of the machine, causes the pumped water to flow 360-degrees radially-outward across the surface of the reservoir. Applying the universal pump horsepower formula to this model, and assuming a pump efficiency of 40%, the horsepower required for the direct flow of water can be calculated as follows: Pump shaft hp = (3000 x (0.2 inch/12 inches per foot)) / (3960 x 0.4 eff) = 0.032 hp. Converting this to watts, 0.032 hp x 746 watts/hp = 24 watts of energy required at the input shaft of the SolarBee pump. (This formula demonstrates the remarkable high flow rate and energy savings attainable by the SolarBee's design!) The 1/2-hp-rated DC brushless motor, which weighs almost 100 lbs, has a small inefficiency (less than 10%), and there is also a small overhead power loss in the electrical control system. Even with these two inefficiencies the wattage required to operate the pump and controls is less than 33 watts. Each of the 3 solar panels on the SolarBee are rated at 80 watts nominal output and about 68 watts of field-usable output. The equivalent of 1.5 panels, or 102 usable watts, are always exposed to the sun due to the triangular mounting configuration, so there is plenty of extra power supplied to the battery during daylight hours to allow for 24-hour-per-day operation. In most climates this model, with the photovoltaic (PV) modules mounted on the machine instead of on shore, will operate at full speed during the day year-around, at full speed during nights in the summer, and at reduced speeds during nights in the winter. Where high mixing is needed at night-time year-round, such as in wastewater systems, the PV modules can be moved to shore or else a shore-power system can be added. A shore-power system draws about 200 watts (110 v.a.c., 2 amps) from the grid power, and converts it to low voltage d.c. (direct current) which is sent to the SolarBee battery.

Induced Flow. When the primary flow departs the impeller and moves radially outward over the patented flow dish of the SolarBee in a near-laminar manner, it causes an induced flow to occur which is directed upward from beneath the SolarBee. The induced flow rate is approximately 7,000 gallons per minute, and it joins the direct flow being spread radially outward across the surface of the reservoir. Dye and stopwatch tests, in reservoirs to 25 feet deep, indicate that the induced flow is in a vertical column of water that is directly under the SolarBee and is approximately the same diameter, 17 ft, as the SolarBee SB10000v12. The induced flow extends downward to the depth of the intake hose inlet if the reservoir is not stratified, but stops at the thermocline if the reservoir is stratified. The induced flow, which can be predicted by Bernoulli's principles as applied to the flow dish, is aided by the diverging streamlines at the surface of the reservoir and the converging streamlines near the bottom of the reservoir, as discussed in Section A. above.

More Flow than just Direct + Induced Flow. In a conventional pump and piping system where water is being moved through a pipeline from Point A to Point B, a flow meter in the pipeline gives an accurate picture of the total flow. But in open reservoirs, a long-distance circulator can put the entire reservoir into motion since the entire reservoir has to 'move over' to accommodate both the incoming and outgoing flow. The SB10000v12 has been shown to put into motion a volume of 50 acres x 20 feet deep = 1000 acre feet = 325 million gallons. The average velocity imparted by the SolarBee onto such a large body of water will be low, due to the law of conservation of momentum, but the velocity is still high enough to change micro-environments that result in large ecological benefits to the reservoir.

2. Improving the Utilization of Solar Energy Striking the Reservoir. The sun's rays produce about 1000 watts per square yard in the outer space surrounding the Earth's atmosphere. Of that power, about 800 watts, or 1 hp, per square yard penetrates through the atmosphere and strikes the surface of the earth at noon at the equator. In mornings and evenings, the solar rays have a longer travel-path through the atmosphere to the surface of the Earth, so less power gets through to the surface. The result is that, in most latitudes, the sun produces a total energy of about 1 hp per square yard for the equivalent of 7 'equator solar hours' per day in the summer, and about 4 'equator solar hours' per day in the winter. Thus on a one acre reservoir the daily summer solar insolation can be calculated as: 1 hp / sqyd x 4840 sqyd / acre x 7 hours/day = 33,880 hp-hours per day, which is an incredibly high amount of power. On a 24 hour per day average, this is equivalent to inputting 1411 continuous hp / acre into the reservoir during the summer months and 806 continuous hp/acre during the winter months. This energy, all radiant, is in the form of light and heat. The light energy, through photosynthesis, allows the beneficial algae to produce dissolved oxygen (DO), much of which the SolarBee can capture and mix throughout the mixed depth before it escapes the surface. And the UV from the sun neutralizes many harmful bacteria such as fecal coliforms. The heat energy which is captured and mixed into the reservoir, depending on intake hose depth, can greatly accelerate the bacterial and chemical reactions which are vital to the breakdown of waste materials.

In a typical lake or wastewater pond that doesn't have a SolarBee, most of the solar light energy is often being turned into harmful blue-green algae production by late summer, since blue-greens thrive on long daylight hours and can vertically position themselves to shade out beneficial algae. The effect, in a lake, is that the nutrients of eutrophication are tied up in an inedible biomass which can lead to toxicity, odor, high pH, fish kills and other negative results. With a SolarBee, its mixing disrupts the ability of the blue-green to vertically position itself, and helps the smaller 'good' algae remain viable all year long so it can capture the sunlight and channel the lake nutrients into zooplankton and, in a lake, into fish production.

In wastewater ponds, in the front-end cells, aerators usually create too much turbulence and turbidity to allow for much algae growth to take advantage of 'free' photosynthetically-produced dissolved oxygen. And if their are no aerators in a wastewater pond, the oxygen produced by algae is often not sufficiently mixed throughout the pond by the wind, so a lot of it is gassed off the surface and lost. The SolarBee can capture this oxygen and put it to good use within the entire pond. In most cases a SolarBee SB10000v12, for instance, with its 1/2 hp motor, can replace 1000 hp-hrs per day of grid-powered aerator run time (for example, 40 hp x 24 hours per day) and still achieve better results in terms of overall water quality, BOD and TSS reduction, sludge reduction, and odor control.


See for the information PSI needs to evaluate a system prior to a possible SolarBee installation. Many factors are considered. All information is compiled into a comprehensive system design worksheet which is provided to the prospective customer. In most cases all of the customer's goals can be met though some may be met immediately while other may take several months or years.


Studies and References.
See for various SolarBee case studies and testimonial letters. Regarding SolarBees in lakes, for independent studies see More studies are being conducted every year and more peer-reviewed papers are in the process of being written.

Regarding SolarBees in potable water reservoirs, for independent studies see

Regarding SolarBees in wastewater reservoirs, for independent studies see Regarding a 'Clean Water Oxygen Transfer Rate (CWOTR) for wastewater, It is impossible to establish a CWOTR for SolarBee because it is impossible to predict, for any given day in the future, exactly how strong the photosynthetic oxygen production will be. However, based on numerous studies by others, and based on PSI's own experience, in a wastewater primary reservoir, the SolarBees can reasonably be estimated at providing 300 lbs of dissolved oxygen (DO) per surface acre per day, or more. Because a CWOTR is not available, the SolarBees cannot be used to replace aerators in heavily loaded ponds. Rather, they must be used beside the aerators to reduce the aerator run time. (This concept can be compared to the way a house is constructed; you don't install just a furnace for heating and an air conditioner for cooling, you also install windows and doors since they will pay for themselves in energy savings.) In most aerated ponds the SolarBees will save enough energy through reduced aeration run-time to pay for themselves in 12-36 months while also improving the water quality.

Laws, Regulations, Safety. PSI insists that SolarBee customers comply with all laws, regulations and safety recommendations which pertain to the customer's system regardless of whether it's a lake, potable water reservoir, or a wastewater system.

PSI welcomes the opportunity to work with engineers, regulators, and reservoir owners to demonstrate the capabilities of the SolarBee technology in new and existing systems, both as a stand-alone solution and as a tool to supplement other equipment. The Ten States Standards encourages the viewpoint that promising new technologies should be given the chance to prove their worth. Installation of a SolarBee does not require permanent or irreversible infrastructure changes, and no SolarBee has ever caused irreversible damage to a facility or reservoir.


The water industry has seen more than its fair share of equipment which was long on promises and short on performance. A serious industry problem is that every water reservoir develops a unique chemical and biological ecosystem over time. For instance, there are an estimated 80,000 man-made and natural chemicals in use today, and there are literally trillions of effects which are possible by combining these materials in different manners and concentrations. When equally complex biological factors are added to the equation, and historical factors and future considerations are taken into account, the result is that remediation results in one reservoir cannot be used to predict success in any other reservoir with 100% certainty. Therefore, to address legitimate customer concerns about the effectiveness of the SolarBee in their application, PSI has developed these philosophies and programs:

1). Set our customers' expectations lower than what PSI expects to achieve.
2). Provide a SolarBee rental program so the customer has the option to try out the SolarBee in actual field conditions before making a purchase commitment. When satisfactory performance has been established, allow the customer to apply a fair portion of the rental cost to the purchase price.
3). Where the rental program is not feasible, offer a performance guarantee to SolarBee customers so that if the SolarBees do not perform to expectations they can be returned to PSI for a fair credit.
4). Insure that well-trained PSI crews perform all deliveries and installations. Conduct an initial evaluation of the reservoir before or during installation, and provide on-site training for optimum operation and maintenance of the SolarBees.
5.) Provide continuous, responsive service to our customers though data collection and analysis, the use of experienced field crews, and well-staffed application engineering and manufacturing departments.

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