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SolarPanelsTransplantProduction.pdf

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					  Solar Panels Inside a
Greenhouse for Transplant
  and Crop Production
   Funding

    Purpose

System Overview

    Results

     Uses

    Benefits

 Cost/Payback

Lessons Learned

Calculation Tool
Funding
 • VT REAP Grant
    Renewal Energy for Ag. Grant Program




Purpose
 • Use sun, water, and wet
   soil to grow plants out of
   season

 • Increase sustainability
   of farm by decreased
   fossil fuel use

 • Create tool to replicate
   system
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
Uses
Crop Examples
  Ginger 3/11
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.
Cost/Payback
  Payback from Energy saved…
   With labor
   $9850/$146                                                    67.5 yrs.

   Without Labor
   $6850/$146                                                    47 yrs.

   Payback with transplants…
   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.
Tool
                                                                                Energy Use Calculation Tool for Solar Heated Soil Table
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
                                           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 Inputs
                                           Rated 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 Requirement
                                           Heat 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.

				
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posted:12/18/2013
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