Farm Structures & Renewable Energy

Buildings and energy systems for the farm. Learn farm structures (storage godowns, silos, animal housing, poly-houses and greenhouses), greenhouse climate control (ventilation, cooling, heating), energy use in agriculture, biogas plants (anaerobic digestion, design and sizing, slurry use), biomass and gasifiers, solar PV water pumping (PM-KUSUM), solar dryers, agri-voltaics, and energy efficiency — with Python for biogas yield, digester sizing and solar pump PV array sizing.

Farms need buildings to store produce, house animals and protect crops, and energy to pump water, run machines, dry and cool produce. In India, agriculture uses ~18% of electricity, mostly for irrigation pumping.

Renewable energy — biogas from dung and residues, solar pumps, solar dryers and agri-voltaics — can make farms energy-independent and cut diesel use and emissions.

An analogy

A biogas plant is an artificial cow's stomach: microbes in a warm, oxygen-free tank digest dung and produce methane you can cook with — and the leftover slurry is excellent fertiliser.

Farm structures

Common structures:

• Storage — godowns, bins, silos (Janssen's theory for wall pressure), cold stores
• Animal housing — dairy sheds, poultry houses (ventilation, heat stress control)
• Protected cultivation — poly-houses, shade-net houses, greenhouses
• Threshing floors, machinery sheds, farm roads and fencing
• Designed for loads (wind, stored grain), durability, hygiene and low cost

Greenhouse engineering

Greenhouses control temperature, humidity, light and CO₂ to extend seasons and raise yields (5–10× open-field for vegetables). Cooling by natural ventilation, fan-and-pad evaporative cooling or fogging; shading nets; heating in cold regions. Design uses energy balance (solar gain vs ventilation and cover heat loss), structural loads and drip fertigation.

Bioenergy

Anaerobic digestion: hydrolysis → acidogenesis → acetogenesis → methanogenesis at 30–40 °C (mesophilic), producing 55–65% CH₄. Plant types: fixed-dome (Deenbandhu), floating drum (KVIC), bag digesters. Slurry is nutrient-rich manure. Compressed biogas (CBG, SATAT scheme) upgrades biogas for vehicles. Biomass gasifiers and pellets use crop residues — an alternative to stubble burning.

Solar and energy efficiency

Solar water pumps (DC/AC with MPPT controllers) replace diesel and grid pumps; PM-KUSUM supports standalone pumps and solarised feeders, letting farmers sell surplus power. Agri-voltaics raises panels to grow crops beneath (land-use efficiency > 1.3). Solar dryers, cold rooms and e-tractors reduce fossil use. Efficiency: BEE star-rated pumpsets, correct pipe sizing and foot valves can save 20–40% of pumping energy.

Formulas

• Biogas production: G = feed (kg/day) × Y_g
• Digester volume: V_d = daily slurry volume × HRT
• Hydraulic energy: E_h = ρ·g·Q·H/3.6×10⁶ (kWh/day)
• PV array: P_pv = E_h/(η_pump × PSH × PR)
• Greenhouse ventilation: Q_vent = Q_solar/(ρ·c_p·ΔT)

Worked example: Biogas yield

Given: 6 cows × 10 kg dung, 0.04 m³/kg

Find: Gas/day.

• 60 × 0.04

Answer: 2.4 m³/day

Worked example: Digester volume

Given: 120 kg/day slurry (60 dung + 60 water), HRT 40 days

Find: V_d.

• 0.12 m³ × 40

Answer: 4.8 m³

Worked example: Solar pump

Given: 20 m³/day, 30 m head, η 0.45, 5.5 PSH, PR 0.8

Find: Array size.

• E_h = 1.635 kWh
• 1.635/0.45/5.5/0.8

Answer: 0.83 kWp (~1 kWp)

Biogas plant and solar pump sizing

# Farm biogas plant and solar pump
cows = 10
dung_kg = cows * 10.0                        # kg fresh dung/day per cow
gas_m3 = dung_kg * 0.04                      # m3 biogas per kg fresh dung
print(f"biogas {gas_m3:.1f} m3/day")
print(f"cooking energy {gas_m3*21.5:.0f} MJ/day (~{gas_m3*21.5/46:.1f} kg LPG equivalent)")
HRT = 40
print(f"digester volume ~ {dung_kg*2/1000*HRT:.1f} m3 (1:1 dung:water, {HRT}-day retention)")
# Solar PV irrigation pump: 30 m3/day from 40 m total head
Q, H = 30.0, 40.0
E_hyd = 1000 * 9.81 * Q * H / 3.6e6           # kWh/day hydraulic
E_pv = E_hyd / 0.45                           # pump+motor efficiency 45%
print(f"hydraulic energy {E_hyd:.2f} kWh/day, PV energy {E_pv:.2f} kWh/day -> array {E_pv/5.0/0.8:.2f} kWp at 5 sun-hours, PR 0.8")
# biogas 4.0 m3/day
# cooking energy 86 MJ/day (~1.9 kg LPG equivalent)
# digester volume ~ 8.0 m3 (1:1 dung:water, 40-day retention)
# hydraulic energy 3.27 kWh/day, PV energy 7.27 kWh/day -> array 1.82 kWp at 5 sun-hours, PR 0.8

Ten cows produce ~4 m³ biogas daily — enough for a family's cooking (burner efficiency is lower than LPG's, so real LPG displacement is less than the energy-equivalent 1.9 kg). A ~1.8 kWp solar array can lift 30 m³/day from 40 m — typical of PM-KUSUM 2–3 hp solar pumps, with zero fuel cost.

Common mistakes

• Wrong: Undersized digester (short HRT). — Right: Low gas yield and undigested slurry — size for 30–50 days.
• Wrong: Sizing solar pumps on peak rather than seasonal need. — Right: Design for the critical month's water demand and sun.
• Wrong: Unventilated poly-houses in hot climates. — Right: Heat stress — plan ventilation and cooling.

Applications

• PM-KUSUM: Solar pumps and solarised agricultural feeders.
• Gobar-Dhan / SATAT: Village biogas and compressed biogas plants.
• Poly-houses: High-value vegetables and flowers.
• Agri-voltaics: Dual land use for food and power.

Key takeaways

• Structures protect produce, animals and crops.
• Biogas: G = feed × yield; V = slurry × HRT.
• Solar pumps: P_pv = ρgQH/(η·PSH·PR).
• Renewables cut diesel cost and emissions.

Going further

• Anaerobic co-digestion: Mixing residues and manure for higher yield.
• Greenhouse energy modelling: Dynamic climate simulation.
• Agri-PV optimisation: Panel height, spacing and crop shading.