Renewable Energy in Agriculture
Renewable Energy in Agriculture covers solar, biogas, biomass, wind and micro-hydro systems used for pumping, drying, lighting, heating and rural enterprise. The exam tests system components, sizing calculations, resource assessment and maintenance.
Core rules
- Solar PV sizing: daily energy (Wh) = array watt-peak × peak sun hours × performance ratio (derating). Inverters, cables, dust and battery losses reduce output.
- A solar pump’s hydraulic energy depends on flow, head and water density; pump efficiency and motor efficiency further reduce delivered output.
- Biogas is produced by anaerobic digestion of dung, crop residues and food waste. A digester needs a slurry, consistent temperature, and a gas-tight dome; fresh dung alone is not enough-it must be mixed with water.
- Biomass combustion and gasification produce heat or producer gas; moisture content strongly affects calorific value.
- Wind and micro-hydro require site-specific resource data; do not size from averages alone.
- Maintenance-cleaning panels, desludging digesters, checking pipes-is part of the design.
Worked example
A 1 hp solar pump runs 6 hours daily. Hydraulic power = 0.746 kW; daily energy = 0.746 × 6 = 4.48 kWh. With 4.5 peak sun hours and a performance ratio of 0.75, array size = 4,480 Wh ÷ (4.5 × 0.75) = 1,327 Wp, about 1.33 kWp. Reasoning: convert pump power to daily energy first, then divide by usable sun hours and derating. A 1 kWp array would be undersized.
Traps
Do not treat peak sun hours as 24 hours of full output. Do not confuse kW and kWh. In biogas, do not calculate gas from slurry mass without checking the dry-matter and volatile-solids assumption. Panel dust and partial shading can cut output sharply, so a theoretical sizing without derating is unrealistic.