Researchers from Western University in Canada have investigated different types of semi-transparent photovoltaic (STPV) modules with different levels of transparency in tomatoe greenhouses in an effort to identify the best panel configuration.
“Experimentally we tested a bunch of semi-transparent PV configurations for greenhouses growing Red Robin tomatoes including crystal silicon with 44% and 69% transparency, as well as with luminescent solar concentrators with 53% and 69% transparency, and red and blue thin-film panels with 50% transparency,” the research corresponding author, Joshua M. Pearce, told pv magazine. “The agrivoltaic systems maintained stable leaf chlorophyll content and comparable growth trends relative to the control, however 69% transparent crystal silicon PV improved yield the best by 38%. We’ve seen this before: crops often respond well to the mix of full sun and partial shade created by these types of modules. The effect is similar to the dappled shading plants experience beneath a tree canopy, where they still receive plenty of sunlight while benefiting from periods of reduced heat and light stress.”
Based on the experiments, the research team ran an open source stack with EnergyPlus, python and SAM to model industrial scale greenhouses. “The results show replacing the typical gas heater with a heat pump fully eliminated fossil fuel consumption, and increased electricity use by only about 1.5 times,” Pearce went on to say. “Integrating the selected 69% transparent PV system with a heat pump enabled fully electrification of an agrivoltaic greenhouse. This only covered approximately 13% of the total annual electricity demand. Indicating if you want a fully agrivoltaic greenhouse including heating it needs to be supplemented with agrivoltaic arrays on the fields.”
In the study “Integration of semi-transparent photovoltaic modules and heat pumps into agrivoltaic tomato greenhouses: Energy, economic, and environmental savings,” published in Energy and Buildings, the researchers explained that, although previous xperimental and simulation studies demonstrated the potential for solar PV systems to meet part or all of the energy demands of heat pump-integrated greenhouses, none of them investigated the use of roof-mounted STPV modules nor specifically examined the direct impact of partial shading or transparency on plant growth metrics.
The team evaluated agrivoltaic greenhouse systems through five main stages: agrivoltaic experiments, greenhouse energy modeling, greenhouse–heat pump integration, semitransparent photovoltaic (STPV) modeling, and overall system analysis. Three software tools—EnergyPlus, Python, and SAM—were used to simulate and analyze three greenhouse scenarios: a conventional gas-heated greenhouse, a heat pump-based greenhouse, and an agrivoltaic greenhouse integrated with a heat pump and rooftop STPV modules.
Experimental investigations were conducted at the WIRED platform in London, Ontario, Canada, using two identical tomato greenhouses. Red Robin tomatoes were cultivated for 19 weeks under several agrivoltaic treatments and a control condition. Different bifacial STPV technologies with varying transparency levels and spectral properties were tested, including crystalline silicon, cadmium telluride (CdTe) thin film, and luminescent solar concentrator (LSC) modules.
Plant growth conditions were identical except for differences in light intensity and spectrum caused by the STPV modules. Chlorophyll content and environmental conditions were monitored, while thermal interactions between the greenhouse and the outdoor environment were modeled using local meteorological data and heat transfer principles. Supplemental LED lighting, evapotranspiration effects, recirculation fans, humidity control, and ventilation strategies were incorporated to reproduce realistic greenhouse conditions for tomato production.
The whole system performance was evaluated using key performance indicators related to energy intensity, electricity and fuel consumption, operating cost savings, greenhouse yield, and carbon emission mitigation. Economic analyses incorporated local electricity and natural gas tariffs, while environmental impacts were assessed using Ontario-specific emissions factors for grid electricity and natural gas combustion.
The experiments showed that healthy cherry tomatoes could be successfully cultivated under all semitransparent photovoltaic (STPV) treatments as well as under conventional greenhouse conditions. Measurements of chlorophyll content and harvested fresh mass demonstrated that most agrivoltaic treatments maintained plant health and productivity comparable to or better than the control.
Among the tested configurations, the 69%-transparent crystalline silicon modules produced the most consistent and statistically reliable improvements in crop yield. Moreover, total harvested tomato yield increased by up to 74% under some STPV treatments compared with the control, largely because partial shading reduced excessive light and heat stress on plants.
In addition, simulation results showed that replacing natural gas heating with heat pumps completely eliminated fossil fuel use while substantially reducing greenhouse carbon emissions. Although electrification increased annual electricity demand, the higher efficiency of heat pumps limited the increase in operating costs.
“This marriage of agrivoltaic fields with partially-powered agrivoltaic greenhouses I think makes for a nice synergistic strategy,” concluded Pearce. ” You can use the incredible amounts of energy you can generate in agrivoltaic field crops with behind the meter net metering to make full-year greenhouse production viable economically and sustainable.”
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