Solar, wind and biogas on farms
How farms use renewable energy: solar pumps and agrivoltaics, wind power, biomass and biogas, solar drying, costs and risks, and a solar pump sizing sum.
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Farms need energy for pumping water, running machines, drying and cooling produce, heating greenhouses and processing. Much of it has come from diesel and grid electricity, which can be expensive, unreliable in rural areas, and a source of greenhouse gas emissions. Falling prices of solar panels and batteries, together with well-established biogas and biomass technologies, now let many farms produce their own energy, or even sell it.
Renewable energy in agriculture is a growing topic in agricultural engineering, sustainability and farm management courses.
Solar energy
Solar photovoltaic (PV) water pumping
A solar pump uses PV panels, a controller and a surface or submersible pump. Water is pumped while the sun shines and stored in a tank or the soil, so most systems need no batteries. Solar pumps have spread rapidly in South Asia, Africa and Latin America, replacing diesel pumps and extending irrigation where grids are weak.
Advantages: no fuel cost, low maintenance, quiet, no emissions. Cautions: high upfront cost; output varies with sunlight; and because pumping becomes almost free, solar pumps can accelerate groundwater depletion unless paired with water rules, metering or feed-in arrangements that reward selling surplus power instead of pumping more.
Agrivoltaics
Agrivoltaics (agri-PV) combines crops or grazing with solar panels on the same land, using raised or widely spaced panels. A 2011 study in France by C. Dupraz and colleagues estimated land equivalent ratios of about 1.35 to 1.73, meaning the combination produced more than separate solar and crop areas. Partial shade can reduce heat and water stress for some crops, while others lose yield. Designs must suit the crop, machinery and climate.
Solar thermal
- Solar dryers for grain, fruit, vegetables, spices and fish: faster, cleaner drying than open sun.
- Solar water heaters for dairy cleaning and processing.
- Solar cold rooms for produce.
Wind energy
Small wind turbines and traditional windmills pump water for livestock on rangelands, and large turbines on farmland provide rental income to farmers while occupying little land. Wind power rises with the cube of wind speed:
where ρ is air density (about 1.2 kg/m3), A the rotor swept area, v the wind speed and Cp the power coefficient (theoretical maximum about 0.59, the Betz limit; practical turbines about 0.35 to 0.45). Doubling wind speed gives eight times the power, so site selection is crucial.
Biomass and biogas
- Biogas from manure and residues provides cooking fuel, heat and electricity, with digestate as fertiliser (see the article on biogas).
- Crop residues and wood for heating, drying and gasifiers that run engines.
- Biofuels: ethanol from sugarcane and maize, biodiesel from vegetable oils; they raise questions about competition with food and land use.
- Briquettes and pellets from residues, which can replace open burning of straw.
Efficiency first
The cheapest energy is the energy not used. Before sizing any system, farms can cut demand with efficient pumps matched to the head and flow, pipes of adequate diameter, drip irrigation, well-insulated cold stores, LED lighting and correct tractor ballast and tyre pressure. Every kilowatt-hour saved reduces the size, and cost, of the renewable system needed.
Choosing and paying for renewable energy
- Match the technology to the load: solar for daytime pumping and cooling, biogas where manure is plentiful, wind on windy rangelands.
- Compare lifetime costs (levelised cost) rather than purchase price: solar has high upfront and very low running costs; diesel the opposite.
- Finance and subsidies: many countries subsidise solar pumps, biogas plants and farm solar installations; pay-as-you-go and leasing models help smallholders.
- Grid connection: farmers can sometimes sell surplus solar power, which also gives an incentive to save water.
- Maintenance and quality: buy certified equipment and arrange servicing.
Sizing a solar pump
A farmer needs 40 m3 of water a day lifted through a total head of 30 m.
Hydraulic energy = ρ × g × volume × head = 1,000 × 9.81 × 40 × 30 ≈ 11.8 MJ = 3.27 kWh per day.
- With an overall pump and motor efficiency of 40 per cent, electrical energy needed = 3.27 ÷ 0.40 ≈ 8.2 kWh per day.
- With 5.5 peak sun hours a day (equivalent hours of full sunlight), PV power needed = 8.2 ÷ 5.5 ≈ 1.49 kW.
- Allowing about 20 per cent for heat, dust and wiring losses: array ≈ 1.49 ÷ 0.8 ≈ 1.9 kWp, so about five 400 W panels.
A small diesel pump set doing the same work, typically converting only about 15 per cent of the fuel's energy into lifted water (about 0.65 litres of diesel per kWh of hydraulic output), would use roughly 2 litres a day, around 750 litres a year, which helps compare costs over the system's life.
Key points
- Solar PV pumps replace diesel for irrigation, usually without batteries; they need water rules to avoid groundwater overuse.
- Agrivoltaics shares land between panels and crops; land equivalent ratios above 1 have been reported.
- Solar thermal uses include dryers, water heaters and cold rooms.
- Wind power = ½ ρ A v3 Cp; power rises with the cube of wind speed.
- Biomass and biogas provide fuel, heat and electricity from residues and manure.
- Compare lifetime costs; match technology to the farm's loads and resources.
What the exams ask
- School-leaving and entrance papers: types of renewable energy and their farm uses.
- Degree and research-fellowship entrances: solar pumping, agrivoltaics, wind power equation, biomass and biogas, solar drying, and economics.
- Agricultural engineering examinations: sizing solar pumps and PV arrays, wind turbine output, biogas plant design, and energy audits of farms.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Does a solar pump work on cloudy days?
It pumps less, roughly in proportion to sunlight. Tanks or soil water buffer short cloudy spells; for critical needs, a larger array or a backup pump may be needed.
Will solar panels over crops reduce yields?
It depends on the crop and design. Shade-tolerant crops and those stressed by heat may yield similarly or better; sun-loving crops may lose yield. Panel height, spacing and orientation are adjusted to balance both.
Is a small wind turbine worthwhile on my farm?
Only if average wind speeds are consistently good, often above about 4 to 5 m per second at hub height. Measure the wind first; in many places solar is cheaper.
Sources
- Dupraz, C. et al. "Combining solar photovoltaic panels and food crops for optimising land use: towards new agrivoltaic schemes." Renewable Energy 36, 2725–2732 (2011).
- FAO and GIZ. The Benefits and Risks of Solar-Powered Irrigation: A Global Overview. FAO, Rome, 2018.
- IRENA. Renewable Energy for Agri-food Systems: Towards the Sustainable Development Goals and the Paris Agreement. IRENA and FAO, 2021.
- Burton, T., Jenkins, N., Sharpe, D. and Bossanyi, E. Wind Energy Handbook, 2nd edition. Wiley, 2011.
- Shah, T., Rajan, A., Rai, G. P., Verma, S. and Durga, N. "Solar pumps and South Asia's energy-groundwater nexus." Environmental Research Letters 13, 115003 (2018).
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