September 16, 2009 | General

Solar Power At Composting Facilities

BioCycle September 2009, Vol. 50, No. 9, p. 32
Innovative operators are installing solar arrays to reduce utility costs, heat building air or operate off the grid. All are reducing greenhouse gas emissions.
Robert L. Spencer

TO reduce electrical power and heating fuel needs, and the associated greenhouse gas emissions, a small but growing number of composting facilities are installing solar energy systems. Solar applications include off-the-grid locations such as at horse stables, making it economically feasible to install composting systems where an electrical connection is not available.
One of the first industrial-scale solar-powered applications to composting is at the New York City Department of Correction’s Rikers Island Correctional Facility. The Rikers Island food waste composting facility was constructed by the New York City Department of Sanitation (DSNY) in 1996. With funding from the NY Power Authority (NYPA), a portion of the roof of the 5,000 tons/year Siemens IPS Composting System (IPS) utilizes 216 glass-laminated 186-watt PV modules to generate 40,000 kilowatt-hours of energy annually. The PV panels were supplied by Atlantis Energy Systems, Inc. and designed by David Wright Associates. It is estimated that the translucent panels also transmit 17 percent of the natural light striking the panels into the building, thus reducing use of artificial lighting.
The Rikers Island correctional facility is the largest municipal prison in the country, with as many as 17,000 inmates housed in a series of men’s and women’s cell blocks with separate cafeterias. The IPS composting facility utilizes a significant amount of energy to operate the agitator that runs on two bays, the aeration bay blowers, the building air handling system fans, the biofilter blowers, artificial lighting, and the office.
Brian Fleury, Senior Project Manager for WeCare Organics, LLC, DSNY’s current contracted operator of the Rikers Island composting facility, reports that the PV array is owned by the NYPA and the solar-powered electricity goes directly through a meter and into the grid. As part of its operating contract, WeCare Organics, in conjunction with Stearns & Wheler GHD, has been tasked by DSNY to conduct an engineering assessment of the entire facility. The assessment included a review of the PV system and confirmed the system is operational, but as part of the rehabilitation of the plant, all conduit for the PV system will be replaced as it has been corroded by years of exposure to the harsh composting environment.
“Thirteen years of continuous operation has taken its toll on the IPS agitator, blowers, interior metal and the biofilter,” says Robert Lange, Director of DSNY’s Bureau of Waste Prevention, Reuse, & Recycling. “The City is committed to making the necessary improvements to keep the facility operating for another 20 years.”
Because the PV portion was designed as a joint pilot with the NYPA to test the PV panel array system’s viability for this type of application, the actual utility savings to the City is marginal. However, the system’s success to date has encouraged the DSNY, along with the NYPA, and Sims Municipal Recycling of New York, LLC, to seriously contemplate the installation of a much larger array at the soon to be constructed South Brooklyn Marine Terminal Materials Recovery Facility.


A composting facility in Ramapo, New York, owned by the Rockland County Solid Waste Management Authority (RCSWMA) and operated by WeCare Organics, processes 28,000 tons/year of biosolids and yard trimmings using the IPS technology. Solar-heated makeup air reduces fogging conditions in the composting building that is brought on by cool weather. Three sides of the building have collector panels manufactured by SolarWall Technology and installed by Conserval Systems. These specially perforated collector panels create an air cavity that is heated by the sun; ventilation fans create negative pressure in the air cavity, drawing in the solar heated air through the panel perforations.
The amount of airflow through the perforations is controlled to maintain a consistent drag across the entire wall surface, ensuring that cooler air beyond the heated boundary layer is not introduced into the air stream. The heated air is generally taken off the top of the wall (since hot air rises) and then ducted into the building to the intake of the oil-fired heater. SolarWall estimates that the air drawn from the panels is preheated between 30° and 70°F (16° to 38°C), thus reducing the amount of oil required to preheat the building air.
The SolarWall at the Rockland composting facility was completed in 2007 and has been operating for two years. However, due to lack of instrumentation to record temperatures in the solar panels or the ducts to the heater, there is not yet data on the heat production of the system. “I have no doubt that the Authority has saved tens of thousands of dollars each of the past two winters, but since there are no sensors to monitor the system we don’t know how much heat is actually produced,” says John Klos, Operations Manager at RCSWMA. “WeCare Organics will have sensors installed in time for monitoring the SolarWall performance this fall and winter.”
“The new instrumentation will include an automatic control system based on a set-point temperature at which the heater will come on when the SolarWall generated heat is too cool to adequately reduce fogging conditions in the building,” explains Fleury. “Generally, once the temperature outside drops below 50°F we need to turn on the oil heaters. Sometimes they are left on all day, and if it’s going below zero we may leave them on all night. Overall, the air preheating system is a very important safety feature since reduced fogging greatly improves visibility for the workers, and reduces slippery conditions due to less condensation as the heaters raise the dew point of interior air.”
Other energy saving improvements include installation of an interior coating on the metal buildings, which is designed to not only reduce corrosion of the building, but provide insulation. “We also installed new, high speed fabric overhead doors that reduce energy loss due to less opening time,” adds Fleury. “With the combination of the SolarWall preheating system, and the energy conservation impacts of the coating and the overhead doors, it is likely that significant amounts of energy costs are being saved.”
Barbara Petroff, Business Development Specialist with Siemens IPS Composting System, reports that other facilities using its systems have developed innovative means of saving energy, particularly the composting plant owned by Delaware County, New York. “Energy efficiencies have become increasingly important for in-vessel systems,” she explains. “Electrical costs can represent one-fourth to a third of a typical operating budget, with HVAC accounting for the majority of that demand. To mitigate winter heating costs, Delaware County captures heat released from the composting process, using an IPS bay wall as a conduit for tubes that transfer heated water between the front and the rear sections of the facility for the radiant floor heating system. The passive heat in the 235-foot long wall succeeds in maintaining a temperature range of 120° to 140°F in the returning water. This measure results in minimizing the use of the boiler to reheat the water.”


Ohio University in Athens, Ohio, launched its solar-powered, in-vessel composting system in February 2009, “claiming to be the largest of its kind at any college or university in the nation.” As of July, it had processed over 70 tons of organic waste, and produced more than 6,000 kWh of energy from its PV array. The Wright Environmental composting system is designed to process two tons/day of organic material, with an overall vessel capacity of 28 tons.
A PV array mounted on the pole-barn’s roof, which goes over the vessel, was installed by Dovetail Solar & Wind, an Athens renewable energy system provider, and is projected to produce 12,000 kWh of electricity annually, about 60 percent of total electricity needed for operation of the site. The pole barn roof was built with daylighting panels to illuminate the space beneath the roof. Capital costs for the composting system, building, PV system, access road, utilities, leach field, concrete pad, rain collection system and other equipment were about $800,000. Grants from Ohio’s Department of Natural Resources and Department of Development provided $335,000.
Molly Shea, a student staff member in the Ohio University Office of Sustainability, explains that the University initially thought that solar power might not be the most cost-effective green power option at the site since “this area of Ohio is not very sunny. We thought wind power might have worked as the facility sits on a ridge, but it turned out solar PV would give us more power per dollar invested.” The Office of Sustainability estimates that the avoided electricity usage will save 450 metric tons/year of carbon emissions, and the compost system will divert 25 percent of the Athen’s campus waste from the landfill, which translates into an annual greenhouse gas emission reduction of approximately 1,200 metric tons of CO2 equivalent.


Peter Moon, President and Owner of O2 Compost in Snohomish, Washington, estimates that at least one third of his customers are interested in utilizing solar energy to power the aerated static pile systems O2 Compost designs and installs. The company currently has two horse farms that use PV to supply power for the two or three fans that aerate the compost piles, which range between one-quarter to one-half horsepower each.
Laurra Maddock and Kent Lane, owners of a 20-horse stable located at Ortega Mountain Ranch in Laguna Niguel, California, decided to invest in the solar system because their property is completely off the grid for electricity, as well as water. “Our goal is to run everything on solar and we are working in that direction with our electrical system comprised of a diesel generator, solar panels (PV), and storage batteries,” explains Maddock. “We currently generate 70 percent of our power through solar, and within two months will double our solar capacity.”
The aerated static pile manure composting system is tied into the main electrical system and does not have its own separate power source. “The reason for composting our manure is a no-brainer, and having it operate from solar power allows us to reduce our carbon footprint even more,” adds Maddock. “Our overall goal is to be as environmentally responsible as possible in all aspects of our operation.”
The O2 Compost system is also installed at a 6-horse stable in Gales Ferry, Connecticut. Although the farm is connected to the grid, the owners decided to invest in the PV system. Moon says the biggest challenge for solar applications is the initial capital expense, but it can make a horse stable feasible where the cost of connecting to the power grid is high.
“We have teamed with a PV system supplier to provide the panels, batteries and converter that allows a horse stable, or other composting application, to be totally off the grid,” Moon explains. “We can generate power for the aeration fans, as well as lighting, heating, and wash water for the barn and animals.”
Moon reports that they are conducting research on applications of solar power to different sizes of stables. He is working with Steve Hauser, a consulting solar engineer, to assemble solar powered systems for two sizes of composting bins, one for 1 to 4 horses, and one for up to 10 horses. “These bins require only a one-quarter to one-half horsepower motor to power the aeration systems, and can be installed to run off AC or solar,” says Hauser. “The blowers typically run just 1.6 hours per 24 hour period, so the power savings from using solar are not as significant as the ability to have an aerated composting system off the grid.” Other equipment includes a sealed gel marine battery, an inverter to convert DC to AC, a controller to prevent the battery from over-charging, a circuit breaker box, and Kyocera PV panels – at a cost of about $2,000.
Moon adds that although O2 has one PV system operating in the northeast U.S., “it obviously can’t generate as much power when compared to areas with abundant sunshine such as southern California, Arizona, and Florida. PV systems still can be attractive, however, since they can power composting systems in areas that do not have electrical service, or where it is very expensive to obtain.”

Bob Spencer, a BioCycle Contributing Editor, is an Environmental Planner based in Vernon, Vermont.

Sidebar p. 34
Solar Innovation
WHILE not related to composting (yet), a solar collector developed by an engineer in Boothbay Harbor, Maine for his home illustrates the potential of harnessing the sun’s power. Michael Mayhew of Heliotropic Technologies describes his innovation as a “concentrating hybrid solar-electric and hot water system,” essentially capturing heat and electricity.
Mayhew estimates the unit will provide one quarter of the energy needs of his already efficient home. “What I’m trying to do is increase the output of standard solar modules by concentrating light on them,” he explains. “To keep the solar panels’ efficiency up I have to cool them. I end up with a waste product of heat, which is useful, and increased output from my solar panel.”
On the southern side of his home there are two prototypes, mounted on an adjustable rack that allows the panels to be tilted at a right angle to the sun in every season. On the sides of each solar panel there are parabolic mirrors designed to bounce sunlight into another reflector. “Those secondary panels are substantially different on each prototype,” says Mayhew. “One of them is curved and the other has two flat plate mirrors on either side of the center line. There are advantages to each design: one is a little easier to manufacture, and I predicted that the other would produce more heat and energy, our primary concern.” The light is finally redirected from these secondary reflectors into the solar panels.
The main reflectors, called parabolic troughs, gather about three times the sunlight the solar panel would collect on its own. However, the hotter the panel gets the less efficient it becomes. To compensate Mayhew built a cooling circuit beneath them. “Part of the energy gathered runs a little circulator pump, and when the sun shines it circulates cool water on the back of the plate to try to keep the panel under 200 degrees,” says Mayhew. The heated water is used in his home.
Next year a new generation of solar panels will be available to the public and Mayhew estimates that they will triple the output of the device from roughly 500 watts per hour of sunlight to 1500 watts. For more information visit or contact Mayhew at – Rob Goszkowski

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