A study evaluated using commercially available solar thermal panels designed for swimming pools to heat a greenhouse and extend the growing season. An 800-gallon insulated water tank heated by 5 solar panels maintained the greenhouse at 50°F. The system produced over 3 million BTUs of heat during the study period and required 1.6 million additional BTUs from a propane backup heater. The solar system cost $2,000 and provided over $150 in annual savings on propane, resulting in a payback period of 13 years.

1. Cost Effective Solar Heating for Season Extension of
Vegetable Production
Lantz, W.D.*
Malone, 1; Swartz, P.S.2; H.J. 3
1Extension Educator, University of Maryland Extension, Mt. Lake Park, MD, 21550
2Physicist and Software Developer, Garrett Engineering and Robotics Society, McHenry, MD, 21541
3Owner and Operator, 5 Aces Breeding, Oakland, MD, 21550
Purpose
Determine if commercially available thermal solar Tank Temperature
Abstract increased 50oF in 5
Tank Temperature drops 39oF in
panels used to heat swimming pools can be Local food production is limited by the growing days
three days = 258,960 Btu of heat
season. While high tunnels protect crops from adverse
economically used to heat a greenhouse structure weather and increase the heat units crops receive, high
tunnels cannot keep crops at ideal growing temperatures
for vegetable production in early spring and late during extended cold weather in early spring and late
fall. Heating a high tunnel with traditional fuels would be
fall in Garrett County, Maryland. very costly and not environmentally sound. The goal of this
project was to evaluate the use of water heating solar panels
designed for heating swimming pools to heat high
tunnels. Five 4’ X 8’ solar panels were installed and
Methods connected to an 800 gallon in ground water tank. Fountain
pumps are used to pump water through the solar panels and
Outside Temperatures in
move water from the tank through radiators to heat the
A solar thermal heating system composed of greenhouse. Heat from the system was used in April, May,
the mid 30oF
October and November. The system produced 3.1 million
commercially available swimming pool heating BTU of heat and 1.6 million BTU of heat was required from a
backup propane heater to keep the greenhouse at a
panels was used to heat water. The heated water minimum of 50oF. This period of time would allow farmers to
1 BTU = ∆1oF / lb water
confidently start growing 30 days earlier than is currently
that was stored in an 800 gallon insulated water practiced and would allow production to continue 30 days
tank attached to the greenhouse. Water from the
longer in the late fall. While some supplemental propane
heat was needed in this research to maintain 50oF, falling
below that for short times at night would not be problematic
Results
tank was circulated through a truck radiator to for most crops. The cost for the system installation and use is
o
 100 F water with 3-4 sunny days
around $35 per million BTU which is less expensive than the
heat the greenhouse to maintain a minimum o
o
operation and installation of propane heat.
 Maintain 55 F for 3-4 days without sunshine
temperature of 50 F. A microprocessor with input
from sensors, controlled the operation of the  Worked best in the late fall months of October
system. The microprocessor also recorded data and November
and exported the data to a server on the internet Project supported through a grant from  October of 2011- produced over 1 million BTUs
Northeast SARE Partnership Grant Fund.
allowing remote control of the system and viewing A full report of the project activities can of heat requiring no additional heat from the
be found by searching the SARE reports
of the system on the internet. The data from the at: propane back up heater
http://mysare.sare.org/mySARE/Project
system allowed for the calculation of the BTU’s of Report.aspx.  For the time period of the study - February 1,
heat produced from the solar thermal system. 2011 to December 31, 2011, the system
produced nearly 6 million BTUs of heat which is
23’ X 25’
4’ X 8’ Swimming Pool Thermal
Heating Panel
equal to 66 gallon of propane for a savings of
Greenhouse 800 Gallon Water
Reservoir $158.40 at a propane cost of $2.40 per gallon.
Evaluation
Microprocessor Control The solar thermal heating system cost $2,000 for
Truck Radiator use to
Distribute Heat this application. At an annual cost savings of
$158.40 the system will have a payback of 13 years.