System design for greenhouses relying on PV and ground source heat pump – pv magazine International

The system design proposed by Turkish scientists consists of combining rooftop PV with a geothermal heat pump in a greenhouse that is used for growing tomatoes, cucumbers and lettuce. The solar system works with net metering and mains electricity is used when the PV generation cannot meet the demand. According to their findings, the system’s payback period is between 2.6 and 7 years.

November 12, 2021

Scientists from Yaşar University in Turkey have developed a design concept for greenhouses that uses PV as the power source for LED lightingg and a heat pump for heating and cooling.

“We originally developed the system in 2017 and back then the The system had a payback time of 5.7 years, ”said researcher Levent Bilir PV magazine. “I’m not sure if the payback period is shorter today than it was in 2017, as energy prices are rising.”

The hybrid system was modeled on the assumption that a 5 x 30 m greenhouse with an area of ​​150 m2, the use of 66 south-facing solar panels with an output of 200 W each, which cover 50% of the greenhouse ceiling, and the use of a geothermal heat pump, which is a type of heat pump that is used both for the Heating as well as cooling can be used. The city of Izmir in western Turkey was chosen as the location, where the reference temperature is 25 degrees Celsius and solar radiation is 1,367 W / m2.

the maximum array efficiency values ​​in a year were estimated between 14.17% and 16.14%, with the roof angle being 38.4 degrees. In order to allow more even insolation into the interior of the greenhouse, which consists of aluminum frames and double-glazed windows with a 13 mm air layer, the panels were placed on the roof by creating a gap between the rows of modules. If the PV system produces more electricity than the greenhouse needs, the excess is fed into the grid. Electricity is also taken from the grid if its output is insufficient.

The research team evaluated the overall performance of the proposed greenhouse design taking into account the cultivation of tomatoes, cucumbers and lettuce, which require different internal temperatures of 28, 36 and 24 degrees Celsius. Since the cooling loads of the systems are extremely high, the cultivation will be discontinued in July and August. The greenhouse is heated or cooled by the heat pump 24 hours a day.

The scientists calculated the hEating, cooling and Lighting load, as well as the monthly and annual electrical taking into account the coefficient of performance (COP) values ​​in heating and coolinging. In addition, they calculated monthly and annual coverage values ​​for each crop and the costs for the PV system and the heat pump as well as costs for insurance, operation and maintenance.

Your analysis showed that in summer operation Months, that is May, June and September, the PV system can meet the electricity demand a coverage of 33.2 to 67.2%Age ratio range, which they explain by the fact that the energy requirement to cover the cooling load for the cultivation of all crops is very high. “For the winter months, however, higher levels of coverage are to be found,” emphasized the research team. “The coverage for tomato cultivation ranges from a minimum of 67.4% in December to a maximum of 522.3% in October, while for cucumber cultivation a minimum coverage of 37.6% is seen in December and a maximum coverage of 185.3% is found for October. “

An economic analysis of the data collected showed that the The payback period for growing tomatoes is 7.2 years, while that of cucumbers and lettuce is 7.4 and 7.0 years, respectively. “The system’s greenhouse gas payback period was 5.7 years or 2.6 years based on electricity generation from natural gas or coal.”

Looking ahead, Bilir said future work should include more detailed analysis and consider storage as an additional option. “Perhaps different types of renewable energy can be integrated,” he concluded.

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