Solar Powered Horticultural Off-grid Unit

SOLHO BV – Nouvelle-Aquitaine region (France)


A MICRO Rank® ORC equipment was integrated into a small-scale high-tech greenhouse facility in the South of France. This action is part of an innovative system called SPRHOUT (Solar-PoweRed Horticultural Off-grid UniT), developed by SOLHO BV. The system stores solar energy in a thermal battery. The stored thermal energy heats up greenhouses and/or to be converted into cooling or electricity. The MICRO Rank® ORC produces up to 2.5 kWe net power from 50 kWt renewable heat at 90 °C. This combination of systems results in savings of up to 90% in operating costs and 75% fewer CO2e emissions when compared to conventional systems.

schematic of geothermal ORC operation

Food production and greenhouses

In 30 years from now, the world’s population will have reached around ten billion people, with the most dramatic population growth seen in the world’s poorest countries. Hence, there will be 2 billion more people living in the so-called sunbelt region. Agriculture will have to double food production to sustain the global population, with sustainable production, fewer resources, and lower environmental impact.

Commercial greenhouses produce plants in large volumes for consumers, shielding crops from excess cold, heat, and unwanted pests. It makes it possible to grow certain crops, fruits, vegetables all year round, even in extremely harsh environments.

Heating in greenhouses is typically based on non-renewable fossil fuels like oil and natural gas consumed to build electric furnaces and convective heaters, which are energy-intensive, polluting, and expensive. Moreover, constructing a greenhouse and its connection to gas and electricity in some regions (the Middle East and North Africa) is challenging. They cannot have the necessary extensive infrastructure available, but they have abundant sunny hours per year.

The project – SPRHOUT

SPRHOUT (Solar PoweRed Horticultural Off-grid UniT), developed by SOLHO BV, is an innovative energy system providing an effective renewable solution to power greenhouse farms. They are designed to ensure the energy self-sufficiency of greenhouse farms, which require an ample supply of heating, cooling, and electricity.

The system operates by harvesting solar energy in solar collectors, transforming it into thermal energy (800 W per m2), and storing it in a thermal energy storage (TES) unit, which allows it to run continuously. The stored energy is withdrawn when needed to heat greenhouses or converted into cooling through a thermal driven chiller or electricity using a thermal conversion engine. It features a backup unit (e.g., a biogas or fossil fuel burner) for missing solar input and minimizes the risks for the crops.

The autonomous production of electricity, heat and cold offers resiliency to fuel price volatility and alleviates concerns in geographical areas with unreliable energy infrastructure. With this solution, off-grid horticultural projects can be deployed anywhere.

TES cuts cost by 30% compared to commercial solutions, resulting in savings of up to 90% operating costs (OPEX), allowing a payback time lower than five years. Additionally, it reduces 75% CO2e emissions compared to conventional systems, saving 4542 tons of CO2e yearly for a typical 5-hectares greenhouse farm. It is flexible in design (e.g., power output), modular (skid mounted), scalable for horticultural projects ranging from 0.1 to 30 hectares, and straightforward enough to be used by people without specialized technical knowledge.

The SPRHOUT proof of concept has been designed and built in the south of France, next to a 3-ha greenhouse facility producing kiwifruit in commercial operation. The SPRHOUT PoC was successfully commissioned in March 2019 and is running thanks to SOLHO proprietary software for real-time control and optimization automatically.

SPRHOUT schematic operation


SOLHO was founded in 2017. SOLHO is a high-tech company based in Delft (The Netherlands). SOHLOts team is mainly composed of Ph.D. level engineers and has more than 10 years of experience in the power and solar industry to develop large-scale solar thermal energy plants for the horticultural industry. Project sizes are in the range from 100 kWth up to a few MWth.

SOLHO has already won several awards for their SPROUHT system, including being selected among the finalist at the Start-up Energy Transition (SET) Awards 2018 (awarded the first prize in the category “Energy, Water, and Food”), VIDA demonstration voucher 2020, Solar Impulse efficient Solution Label, Climate-KIC EU Top 50 Millennial Start-ups, and IEEE N3XT® Star, among others.

SOHLO logo


Rank® MICRO is used to produce the electricity required by the greenhouse using the thermal energy stored in the tank and produced by the solar plant. This system can produce up to 2.5 kWe net power electricity, with an up to 50 kWt heat source inlet temperature between 90 and 120 °C, while producing hot water between 30 and 50°C. It is relatively small, only occupying 0.96 m2 in surface and 1.4 m in height.

Even though here is used in a horticultural industry, Rank® MICRO is ideal for very low power applications (microgeneration/micro-cogeneration), including residential and varied light commercial purposes.