Overview of Photovoltaic and
Solar Hot Water SystemsMike Morris
National Center for Appropriate Technology
New England Farm Energy Conference Manchester, NH March 16, 2010
Photovoltaics (“Solar electric”)
solar cell
PV panel or
modulesolar 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, www.backwoodssolar.com
• Most panels 12, 24, or 24 volts and 5-200+ 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
StorageTank
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
• 24 120-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 www.builditsolar.com
Flat Plate Collector
• Durable copper, aluminum and glass design
• Sheds snow well because collectors get warm
SC
So
lar,
In
c.
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
So
lar,
In
c.
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.
Thank you for your attention!
NCAT: www.ncat.org or 1-800-ASK-NCAT
ATTRA: www.attra.org or 1-800-346-9140
Mike Morris: [email protected] or 919-251-9680
Farm Energy resources: www.attra.org/energy
