Solar Seasonal Storage Cuts Greenhouse Heating

Overview – Small‑scale solar storage can heat greenhouses with a 4.1 COP heat pump

South Korean researchers demonstrated that a compact solar‑thermal storage tank, paired with a dual‑source heat pump, delivered an average coefficient of performance (COP) of 4.1 while heating a 3,850 m² greenhouse over three years. The system showed that seasonal solar heat can substantially reduce reliance on fossil‑fuel heating.

Technical Performance – 55 % storage efficiency and 31.8 % solar‑thermal conversion

The team installed 96 m² of evacuated‑tube collectors and 108 m² of flat‑plate collectors on the greenhouse roof, feeding a 350 m³ seasonal storage tank and a 100 m³ buffer tank. Over three heating seasons the storage tank achieved an average thermal storage efficiency of 55.1 %, while the collectors converted solar irradiation to heat at 31.8 % on average. Water temperatures between 10 °C and 35 °C supplied the dual‑source heat pump, which raised its COP as the source temperature increased, reaching the reported annual average COP of 4.1. When the dual‑source unit was offline, an air‑source pump delivered a still‑strong COP of 3.9(https://www.pv-magazine.com). The shallow‑ground thermal storage added temperature stability but suffered higher losses due to poor ground conductivity.

Economic Implications – Potentially sizable heating‑cost reductions for growers

Conventional gas‑fired greenhouse heaters typically have lower efficiency than the demonstrated system. By using stored solar heat as a source for the heat pump, growers can expect a significant reduction in heating energy consumption compared with traditional gas heating. The exact magnitude of savings will depend on site‑specific factors such as greenhouse size, climate, and fuel prices, but the technology offers a promising pathway to lower operating costs.

What it means for Israel – A template for cost‑effective greenhouse heating

Israel’s horticulture sector spends heavily on winter heating, especially in the north where residential tariffs are ₪0.48/kWh. Using the verified Israeli figures, a typical 10 kWp rooftop solar PV system yields ≈ 17,000 kWh/yr, worth ₪8,160 annually, and pays back in ≈ 3.9 years. If a greenhouse adopted a comparable solar‑thermal storage‑heat‑pump combo, the technology could substantially lower heating expenses, making seasonal solar storage economically attractive even without subsidies. This aligns with Israel’s 30 % renewable electricity target for 2030.

Future Outlook – Scaling up and improving ground storage

The researchers note that the small‑scale tank’s unit cost per volume is higher than that of large industrial tanks, but the compact design fits greenhouse footprints and reduces heat loss. Ongoing work aims to lower tank costs, improve insulation, and enhance shallow‑ground storage materials to boost long‑term efficiency. If these advances materialize, the technology could spread to Israel’s extensive greenhouse belts in the Negev and Arava, where solar irradiation exceeds 2,200 kWh/kWp/yr.

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Sources: pv magazine, Applied Thermal Engineering (journal article), KIER press release.