The Potential of Solar-Powered Water Circulators to Help Solve Serious Water and Energy Problems in the U.S.
With increasing human populations comes the corresponding increased need for improving water quality in lakes, wastewater ponds, potable water reservoirs, and other water storage facilities. Providing circulation within water reservoirs of all types has long been known to provide meaningful benefits, but the costs to achieve sufficient circulation through diffused aeration or mechanical mixers has been prohibitively high for water bodies with surface areas greater than 1 to 5 acres, or volumes over several million gallons.
This has all changed with the development in 2001 of floating water circulation equipment that can move up to 10,000 gallons per minute for long distances using only solar energy. This circulator, called the SolarBee®, has a unique distribution technology that enables water to move long distances in a near-laminar flow, so a single unit can effectively benefit a 35-acre lake or 25 million gallon finished drinking water reservoir or tank. Since its creation, over 1,000 units have been installed in recreational lakes, drinking water reservoirs, estuaries, stormwater ponds, wastewater lagoons, power plant cooling lakes, potable water storage reservoirs and recycled water enclosed tanks. This paper introduces the concept of solar-powered water circulation equipment, and summarizes the attained and documented benefits over the past 6 years for lake restoration (e.g., control of harmful algal blooms, improved water clarity, improved fisheries, and reduced aquatic weed infestations), wastewater treatment (e.g., improved biochemical oxygen demand and sludge reductions, odor control, and reduced total solids and ammonia concentrations in the effluent), and potable water storage (e.g., elimination of stagnation, more uniform water age, and reduced chemical requirements). Because these water quality improvements are accomplished using solar energy, there has also been a substantial economic savings while reducing grid-powered energy consumption. Greenhouse Gas emissions are also reduced by utilizing this renewable energy, energy efficiency, and energy conservation machine.
1. Overview: Water quality problems and energy demands are closely linked, and continue to escalate in the US and throughout the world. Currently about 7% of world energy, and 4% of US energy, is used to treat and transport water. In 2001, Medora Environmental, Inc. (MEI, formerly named Pump Systems, Inc.) of Dickinson, ND developed a solar-powered circulator technology called the SolarBee®, which is manufactured by SolarBee, Inc., a division of MEI. The SolarBee is a floating, up-flow machine that can move up to 10,000 gallons per minute and from depths up to 100 ft with a solar-powered pump. The machine can now run day and night with a brushless motor and on-board battery system. With more than 1,000 solar-powered circulation equipment installed nationwide in the past 9 years, SolarBees are now solving serious water quality and energy problems in fresh water lakes, wastewater lagoons, stormwater ponds, estuaries, potable and recycled water storage tanks and other reservoirs.
2. SolarBee, Inc. Company Background: PSI was founded in 1978 by Joel Bleth and Willard Tormaschy, who are both fluid engineers native to Dickinson, ND. MEI continues to grow, and by early 2007, the company had 65 employees with regional offices located in the states of CA, CO, ND, MN, DE, FL and WA. The company received the Greater North Dakota Association Industrial Development Award in 2004. The company has a General Services Administration (GSA) contract and received an Open Ratings, Inc. score of 91 out of a possible 100. In its effort to better understand the ecological benefits of long-distance circulation, SolarBee is collecting and reviewing extensive water quality data on hundreds of ponds, lakes, and reservoirs in the US each year. SolarBee, Inc. has earned high marks from its customers for its reliable equipment, factory installation and service crews, and after-sales support.
3. Application To Lakes, Ponds, and Estuaries: Lake and reservoir degradation associated with nutrient enrichment and subsequent eutrophication is getting worse worldwide, and economic consequences in the near future will be much greater. The US has an estimated 14,000 lakes over 125 acres in size, 110,000 lakes from 10 to125 acres in size, and 1,000,000 lakes and ponds less than 10 acres in size. About 60% of Americans get their drinking water from these lakes, and about 60% of them have harmful algae blooms (HABs), usually consisting of blue-green algae (cyanobacteria). It has been long known that blue-green algae blooms degrade water quality in terms of taste, odor, aesthetics, and health of the food chain. Eliminating HABs and associated negative impacts have greatly increased the cost of operating a drinking water treatment plant.
Furthermore, recent testing by many states indicates that the majority of HABs creates harmful microcystins and other potent toxins that could lead to long-term liver damage and other health problems in humans, possibly even Alzheimer's disease. In recent years, Nebraska has experienced increased animal deaths from HABs prompting the posting of various health alerts for several important lakes. Oregon has also been posting frequent health alerts and/or warnings at some of its most important lakes for several years. It appears that many more states will be following the lead of these two states, as well as the World Health Organization guidelines regarding HABs, and will be posting more health warnings at their lakes to avoid possible liability in the event of death or illness of people and/or animals. So the negative impacts of HABs are not only the aesthetic and public health and water treatment costs, the impact will also increasingly extend to the recreation industry, the resort industry, and property values as more states start closing more lakes during their peak seasons.
Nutrient Control does not achieve HAB control: The EPA's national TMDL (Total Maximum Daily Load, of nutrients) program for watershed protection, though an essential long-term strategy for protecting our lakes, is not eliminating HABs. In the 35 years since the Clean Water Act of 1970, there are virtually no lakes that can be pointed to where nutrient reduction of non-point sources through watershed protection activities sustainably reduced or eliminated a HAB problem. Even in watersheds where millions of dollars have been spent to meet TMDLs, detrimental HABs have continued or, in many cases, became worse.
In addition to watershed protection, hundreds of millions of dollars have also been spent on in-lake approaches to stop HABs, but virtually no lake can be pointed to where the HABs were eliminated with those methods. In virtually all cases the HABs remained the same or became worse. These methods include alum applications to stop 'internal loading' or re-cycling of phosphorus, aeration, hypolimnetic aeration, hypolimnetic oxygenation, bottom water release, drawdown, dredging, top-down strategies such as rotenone of a lake to kill all of the fish, reed rafts, calcium additions, and others. Aquatic herbicides can give short-term relief from HABs, at a typical cost of $300 to $1000 per acre per year or more, but they all have ecologically harmful immediate effects and unknown long-term effects.
What does work to control HABs: HABs typically require 1) nutrients, even a low level is usually enough (i.e., dissolved nitrogen and phosphorus), 2) suitable temperatures, and 3) quiescent or stagnant waters. As discussed above, controlling nutrient availability has not been effective at preventing HABs. However, it has been recognized in the scientific literature for several decades that creating enough horizontal and vertical water movement can sufficiently disrupt HABs' preferred quiescent habitat so that they do not grow and virtually disappear from the water column. This allows available nutrients to be taken up by non-blue-green algae (e.g., diatoms, chlorophytes, etc.). This is a real benefit to the ecosystem, as these non-toxic algae are readily consumed by zooplankton and fish, thus enhancing the food chain and improving water clarity while reducing the amount algal biomass in the water column as well as algal biomass that settles and decompose on the lake bottom.
Before the SolarBee there was no practical way to create sufficient mixing in a lake beyond 10-20 acres to effectively prevent HABs. With the SolarBee's unique and patented design, however, one unit can prevent HABs in a 35 acres lake. Because the mixing capability is additive, lakes of any size can be treated with multiple units. In fact, solar-powered SolarBees had proven successful at controlling HABs in over 160 lakes (out of about 170) by 2006. Below is a summary diagram showing how long-distance solar-powered circulators restore lakes to good water quality:
The typical cost in a large lake is about $40 per acre per year over the 25-year machine life, less than 10% of the cost of herbicides, and with none of the toxicity issues of herbicides. And because this method is a bio-manipulation approach, nutrient loading becomes nearly irrelevant. Furthermore, in addition to eliminating HABs, solar-powered circulators have also demonstrated that, with closer spacing, they can eliminate some invasive aquatic weed species from lakes. Multi-year success has been recorded with Eurasian Watermilfoil and several other nuisance and invasive submerged aquatic plant species in over a dozen lakes.
4. Application To Wastewater Lagoons and Ponds: Throughout the US there are tens of thousands of wastewater ponds with intense treatment for small cities and industries (e.g., the food processing industry), and perhaps just as many reactor basins in wastewater plants for large cities. In most cities, wastewater aeration uses more electricity than any other single power use in the city, and the aeration is significantly oversized due to the need for proper mixing of the water and oxygen. Over 400 solar-powered circulators have been deployed in recent years to reduce aeration run-time while maintaining or improving the water quality. Solar-powered circulators also increase odor control and reduce biosolid volume at the bottom or the pond or basin, thus reducing costs to dredge and dispose the biosolids. Below is a summary diagram showing the energy savings by using solar-powered circulators in wastewater treatment ponds and lagoons. In critical applications, the circulators can be connected to shore power to maintain a battery charge through extended periods of rain, fog and snow.
5. Application To Stormwater Ponds: The US has hundreds of thousands of stormwater ponds, and more are being constructed each year for both watershed protection and water conservation. The runoff entering stormwater ponds is typically about 25% as 'strong' as raw sewage and can contain toxins. Most stormwater ponds do not have access to grid power and are perfectly suited to solar-powered circulators, which can provide a number of benefits including: 1) odor control, 2) improved oxidation of organic matter with a high biochemical oxygen demand (BOD5), 3) improved water aesthetics, and 4) prevention of HABs, which would otherwise create even more HABs in downstream lakes and reservoirs.
6. Application To Estuaries: Estuaries are also plagued with HABs, usually dominated by dinoflagellates rather than blue-green algae. Dinoflagellates are armored with plates, and some contain intracellular toxins (e.g., causing lethal red tides) causing similar ecological impacts as blue-green algae. Also similar to blue-green algae, dinoflagellates are negatively affected by circulation. Solar-powered circulators were deployed in an estuarial lake in San Francisco Bay in 2003, and have eliminated all fish kills and allowed a near-extinct oyster to make a comeback in this recreational lake. Solar-powered circulators have the potential to clean up and reverse huge environmental problems in estuaries, including very large bay ecosystems.
7. Application To Potable Water Storage Reservoirs: After drinking water has been treated with chlorine or chloramine, it will typically flow through storage reservoirs, water tanks, and/or water towers in the distribution system. Water in these reservoirs can become stagnant and develop an unacceptably long water age, leading to a loss of disinfection and/or the formation of nitrites and/or nitrates as well as unpleasant tastes and odors. In order to maintain uniform water age, eliminate stratification, keep water fresh, and reduce treatment costs, solar-powered circulators can be put inside the tanks with their solar modules placed outside on top of the tank. San Francisco and Las Vegas are two cities with high-profile water systems that have adopted this method of keeping their treated water at high quality.
8. Other Applications: Depending on how the machines are deployed, solar-powered circulators can also be used for: 1) reducing or else increasing evaporation in a water body (US Bureau of Reclamation tests at Salton Sea Test Station, 2003-2004), 2) reducing manganese and/or sulfide buildup at the bottom of a water body, 3) improving fish spawning in natural water bodies, 4) firming up mucky lake bottoms, and 5) reducing heat buildup at the bottom of saline water storage ponds. New beneficial applications for solar-powered circulation are constantly being discovered.
9. Solar-Powered Circulator Benefits Are Becoming Well Documented: Scientific studies are always difficult to produce, especially when the 'before' data are either inadequate or non-existent. Nevertheless, the outstanding performance and benefits of solar-powered water circulators are becoming well documented. For example, the cities of Palmdale, CA and Thornton, CO both produced scientific papers showing how HABs were eliminated the past several years in their raw water reservoirs. The Ohio EPA published a study documenting the benefits to wastewater lagoons from solar powered circulators. Michigan EPA has become very strong supporters of solar-powered circulation. Shell Oil recently published a paper on solar-powered circulators solving tough odor problems in a stormwater pond at one of their California refineries. The City of San Francisco produced a 2-year study of solar powered circulators, and presented a paper at the AWWA national conference in 2005 regarding their choice to use solar-powered circulators in potable water reservoirs. And in 2006, SolarBees won an international environmental award in Australia.
Most of the beneficial effects of circulation in various water reservoirs are well documented in peer-reviewed journals involving either field tests or lab tests. And the physics of pumping large volumes of water at low head pressure with very low energy is also old science. So what is unique about SolarBee technology is the ability to pull water from a fixed depth and mix it throughout very long distances; compare SolarBee 35-acre mixing influence to the 0.5-acre typical influence for conventional mixers. SolarBee is in the process of producing several technical papers to be submitted for publication in peer-reviewed about the effectiveness of long-distance mixing.
10. Energy Savings and Greenhouse Gas (GHG) Emissions Reduction: Depending on the exact application, each SolarBee typically displaces about 30 hp (25,000 watts) of energy-intensive grid connected equipment, twenty-four hours per day, for at total of 219,000 kWhrs per year. This is enough energy saving to supply about 20 US homes, thereby reducing carbon dioxide emissions (the leading greenhouse gas ) by about 148 tons per year. This displacement is the equivalent of reducing the CO2 emissions from 37 passenger cars each year (based on 'efficient' car with 29 to 40 miles per gallon that produces on average 4 tons of CO2 emissions per car]. For entities that pay federal income taxes, there is a 30% investment tax credit for the cost of the SolarBees and accelerated depreciation is allowed.