solar panels inside a greenhouse for transplant and crop production
TRANSCRIPT
Solar Panels Inside a
Greenhouse for Transplant
and Crop Production
Funding
Purpose
System Overview
Uses
Benefits
Cost/Payback
Lessons Learned
Calculation Tool
Results
• Use sun, water, and wet
soil to grow plants out of
season
• Increase sustainability
of farm by decreased
fossil fuel use
Funding • VT REAP Grant
Renewal Energy for Ag. Grant Program
• Create tool to replicate
system
Purpose
System Overview
Results
Agribon Cover
Germination
Chamber Greenhouse
High 108.7 109.9
Low 7.6 2.8
Average High 83 83.4
Average Low 29.4 26.4
Reflectix Cover
Germination
Chamber Greenhouse
High 116.4 114.1
Low 41.2 24.9
Average High 90 92.8
Average Low 50.5 41.3
Uses
Transplant Examples • Spinach 2/15
• GH Eggplant 3/5
• Field Tomato 4/5
• Winter Squash 5/3
Crop Examples Ginger 3/11
Uses
Benefits
Heating small volume is more efficient
Decreased fossil fuel use/ CO2 output
Cold weather growing capacity
Bottom heat for plants
Using stored energy provides a buffer
Low maintenance/ operation cost
Cost/Payback
Initial investment
Materials $6850
Labor (100hrs@ 30/hr ) $3000
Total $9850
Operating costs
Electricity (3KWh/day @ .12/KWh) $.38/day
$.38 X 365 Days $138.70/yr.
Energy Collected
Average of 3.3 kWh/day x .$.12/kWh $.40/day
$.40 x 365 days $146/yr.
Payback from Energy saved…
90 trays @ 10 6-packs/tray 900/6-packs
Cost of production $500
Gross Sales @ 3.50/6-pack $3150
Net profit $2650
System with labor
$9850/$2650 3.7 years
* Payback time decreases with added crop or successions of seedlings.
Cost/Payback
With labor
$9850/$146 67.5 yrs.
Without Labor
$6850/$146 47 yrs.
Payback with transplants…
Tool
User inputs highlighted in yellow
Calculated Values in Blue
Important notes highlighted in green
Soil Table Calculations Oct. - April Units Notes
Soil Table Length 40 ft User Input
Soil Table Width 4 ft User Input
Soil Table Depth 1 ft User Input
Soil Table Temperature to be Maintained 45 °F User Input
Energy Use Calculation Tool for Solar Heated Soil Table
Total 24 Hour Heat Loss 9670 Btu Q day + Q night
Thermal Storage Calculations
Water Storage Tank Length 3.10 ft User Input
Water Storage Tank Width 3.10 ft User Input
Water Storage Tank Depth 3.75 ft User Input
Water Storage Tank Insulation Thickness (Blue Board) 4 in User Input
Water Storage Tank Volume 270 gal
Weight of Water in Tank 2248 lbs
Water Storage Thermal Mass Available for Heating 86842 Btu Q=(MCpΔT)-Heat loss
Soil Table Weight 9920 lbs Based on Wet Soil 62lb/CF
Soil Table Thermal Mass Available for Heating 121520 Btu Q=MCpΔT
Total Thermal Mass 208362 Btu Q of soil + Q of water tank
Note: Soil Table Heat loss is accounted for in 1st section, water storage tank heat loss is accounted for in second section.
Energy Input Calculations
Heat Loss from Storage Tank (BTU per 24 hours) 3084 Btu/day
Heat Loss from Soil Table (BTU per 24 hours) 9670 Btu/day
Assumed Heat Loss from Piping (10% of total) (BTU per 24 hours) 1275 Btu/day
Total System Heat Loss (BTU per 24 hours) 14029 Btu/day
Solar Heating InputsRated Thousand BTU/panel a day 9.4 KBtu Use SRCC data for Water Heating (Cool Climate) Mildly cloudy
Solar Collector Efficiency 81% Manufacturer's data
Total Number of Solar Panels for daily loss 2
Total Number of Solar Panels for 3 day loss (assuming some cloudy days) 6
Total Number of Solar Panels to maximize hot water tank mass 13
Total Number of Solar Panels to maximize soil table mass 18
Total Number of Solar Panels to maximze tank and soil table mass 31
Backup Heat Source Energy RequirementHeat Loss from Seed Table (BTU per 24 hours) 9670 Btu/24 hours calculated above
Heat Loss from Seed Table (Watts per 24 hours) 2826 Watts/day (Btu*0.012178)*24
Heat Loss from Seed Table (BTU per hour) 569 Btu/hr (Btu/day)/17 based on heat loss for 17 hrs
Heat Loss from Seed Table (Watts per hour) 166 Watts/hr (Watts/day)/17 based on heat loss for 17 hrs
Lessons Learned Greater capacity for thermal storage in the soil of the germination chamber than in the
water of the thermal storage tank. It would be worthwhile to research redesigning the system to exclude the hot water storage tank and solely rely on the thermal storage
capacity of soil. Based on the data collected, it appears that to maintain the soil temperature up to 43°F passive solar gain alone is
adequate. This implies that a well-constructed insulated germination bed could suffice.
Efficiency of design related to maximizing solar energy gain. The observed data shows many days where it was hot enough to collect solar energy but there was no energy gain in the system. The
reason for this is because the water in the storage tank was hotter than the temperature in the solar panels.