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: mikem@ncat.org or 919-251-9680

Farm Energy resources: www.attra.org/energy