Alternative Generation & Storage
What this domain tests
Alternative generation and storage questions test PV output, capacity factor, battery sizing, and the economics of demand reduction.
Core rules
- PV annual energy = kW × 8,760 × capacity factor; typical CF is 15–20% in temperate climates.
- Apply inverter efficiency, soiling, and degradation (about 0.5%/yr) before claiming savings.
- Battery value comes from demand reduction, time-of-use shifting, and resiliency, not just kWh arbitrage.
- Round-trip efficiency for lithium-ion is roughly 85–90%.
- CHP feasibility depends on a year-round thermal load; a power-to-heat mismatch kills the economics.
Worked example
A 100 kW PV array with CF 0.18 produces 100 × 8,760 × 0.18 = 157,680 kWh/yr. At $0.12/kWh, bill savings are about $18,900/yr. If the array costs $250,000 installed, simple payback is 13.2 years before incentives. Where demand charges are high, adding storage may improve economics more than adding more PV.
Traps
Using nameplate kW as annual kWh; ignoring inverter clipping and shading; and valuing battery energy at retail rates while ignoring round-trip losses and demand-charge structure.