Overview of Photovoltaic and Solar Hot Water Systems Mike Morris National Center for Appropriate Technology New England Farm Energy ConferenceManchester, NH March 16, 2010

Photovoltaics (“Solar electric”) solar cell PV panel or module solar array Typical cost $7 per peak watt of DC (direct current) power. Add inverter to convert DC to AC (alternating current).

Electricity 101 For example, two, 12-volt panels wired in series runs a 24-volt DC pump. From Backwoods Solar, Most panels 12, 24, or 24 volts and watts. Amps X Volts = Watts Wire in series to increase voltage or in parallel to increase amps.

Siting Panels very sensitive to shade. Array should be un-shaded from at least 9 AM - 3 PM. Move array to avoid shading, or oversize array.

Solar mounts Pole mounts, roof mounts, trackers (active or passive). Mount collectors at an angle equal to your latitude for year round performance (43 degrees in Manchester). For better summer production, decrease tilt angle For better winter production, increase tilt angle

Do panels have to face south?

Agricultural Uses Common Electric fence chargers Pumping Lighting Small motors, e.g. fans Irrigation system surge valves Less common Wheel line (side roll) sprinkler mover. Solar tractors

Solar Pumping

How a Solar Pumping System Works Storage Tank PV Array Motor/Power Controller Pump/Motor

Work with a dealer.

Solar (DC) water pumps: many to choose from Surface Pumps Submersible Pumps Slowpump Suncentric Solar Force Solar Ram Grundfos SQ Flex Lorentz PS Shurflo 9300 Series

FAQs How is the system sized? Batteries? Or no batteries? Tracking or fixed rack? (Or trailer mount?) Reliability? Durability? Vandalism? AC or DC pump? Diaphragm pump? Can I run my sprinkler irrigation system with solar panels? How do PV, wind, and (gas, diesel, propane) generator compare?

25 cow-calf pairs; 2-3 miles from power Two 120-Watt solar panels Submersible diaphragm pump (DC) delivers 1 GPM from 160’ well or 900 GPD Cost of solar components: $3,200 Benefits: Improved reliability and convenience, compared to gas-powered generator Tomlinson Ranch, Gold Creek, MT

Schraudner Ranch, Lavina, MT 150 cow-calf pairs; over a mile from power Seven 60-Watt solar panels (trailer-mounted) Submersible centrifugal pump (AC) delivers 6.5 GPM from 60’ well or 3,600-4,000 GPD. Cost of solar components: $10,650 Benefits: Increased forage base to extend grazing season; reduced pressure on riparian area; water source during drought.

Ueland Ranch, Anaconda, MT Cost of solar components: $7,700 Primary benefits: Fisheries benefits from reduced pressure on riparian areas, drinking water for cattle at feeding area. 500 cow-calf pairs; ½ mile from power Twelve 64-Watt solar panels Submersible centrifugal pump (DC) delivers 17 GPM (Feb. through April) from 50’ well.

Sauerbier Ranch, Alder, MT Cost of solar components: $24,500 Primary benefits: Increased forage base, increased herd size, fisheries benefits for rare population of West Slope cutthroat trout. 350 cow-calf pairs; >5 miles from power Watt solar panels on two tracking racks Surface piston pump (DC) delivers 11 GPM or 7,500 GPD from stream.

Sauerbier Ranch, cont’d Pumps surface water over two miles to the top of a ridge, against over 400 feet of head. Fills 8,000 gallon storage tank and six 1,000+ gallon stock tanks

Solar Water Heating (“Solar thermal”) One of the most cost-effective uses of solar energy. Currently eligible for 30% federal tax credit. Image problem dating back to the 1980s; modern equipment works very well. Suitable for any farming operation that uses a lot of hot water. Dairies should probably do heat recovery on refrigeration system and/or heat exchange on milk first. Works well with radiant floor heating.

The basic idea (with many variations) From

Flat Plate Collector Durable copper, aluminum and glass design Sheds snow well because collectors get warm SC Solar, Inc.

Flat Plate Collector Drawing courtesy of SC Solar, Inc.

Evacuated Tube Collector New technology; most expensive. Highest temperature output. Do not shed snow & ice. SC Solar, Inc.

Transfer Fluids Propylene Glycol- Non-toxic Ethylene Glycol- Toxic Hydrocarbon Oil (bray oil) Synthetic Oils Distilled Water De-mineralized Water Potable Water

Active vs. Passive Active systems use a pump to circulate fluid Passive systems rely on tendency of hot water to rise. Direct (“open loop”) vs. Indirect (“closed loop”) Direct systems use potable water in the solar collectors Indirect systems use water or glycol in a separate loop from the potable water. System Types

Passive Batch System

Active Indirect System (“Drainback”) System controller measures temperature difference between sensors. ON 8-20  difference OFF 3-5  difference

Solar Water-Heating for Greenhouses Design issues Freeze protection a must. No toxic fluids around crops or leaking into soil. Need to dump heat (or disable) in summer months, if sized for winter needs. Backup heating system desirable. Tubing can be buried or above-ground, depending on use of greenhouse.

Cherry Research Farm, Goldsboro, NC Cost $8,000; $3,900 after NC and federal incentives. 250 gallon water “drain down” system Cut propane costs from $3,000 to $1,000 per year.

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