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Energy sources and solar power generation

Short answer

Conventional sources (coal, oil, gas, large hydro, nuclear, traditional biomass) are exhaustible and polluting; non-conventional (solar, wind, micro hydro, biogas, geothermal) are mostly renewable and clean. Solar electricity is generated by PV cells (p-n junction converts sunlight to DC, modules/arrays with inverters) or solar thermal (mirrors concentrate sunlight to produce steam for a turbine).

What are the conventional and non-conventional energy sources? Describe with suitable sketches how electric power can be obtained from solar?

Conventional and non-conventional energy sources

ConventionalNon-conventional
Coal, oil, natural gasSolar (PV and thermal)
Large hydropowerWind
NuclearMicro/small hydro
Traditional biomass (firewood, dung)Biogas, modern biomass
Geothermal, tidal, wave, hydrogen

Conventional sources are long established, mostly exhaustible and polluting; non-conventional sources are mostly renewable, clean and still developing.

Electric power from solar energy

Solar energy is converted to electricity in two ways.

1. Solar photovoltaic (PV) – direct conversion

A PV cell is a p–n junction of silicon. Photons with energy greater than the band gap (about 1.1 eV for Si) create electron–hole pairs. The junction field separates them and a DC voltage (about 0.5–0.6 V per cell) appears. Cells are connected in series and parallel to form modules and arrays.

 Sunlight
   ||
   vv
 +------+     +-----------+    +---------+
 | PV   |---->| Charge    |--->| Battery |
 |array | DC  | ctrl/MPPT |    +---------+
 +------+     +-----------+         |
                  |                 |
                  v                 v
              +---------+     DC loads
              |Inverter |--> AC load / grid
              +---------+
  • Off-grid (stand-alone): PV + charge controller + battery + inverter.
  • Grid-tied: PV + MPPT inverter feeding directly to grid (no battery).
  • Module efficiency about 15–22%.

2. Solar thermal power – indirect conversion

Mirrors concentrate sunlight to heat a fluid, which makes steam to drive a turbine–generator.

 Sun --> Concentrator (trough/dish/tower)
             |
        Hot fluid --> Heat exchanger --> Steam
                                          |
                                      Turbine --> Generator
                                          |
                                      Condenser

Types: parabolic trough, central receiver (power tower), parabolic dish (Stirling engine). Thermal storage (molten salt) allows output after sunset.

Solar in Nepal

Nepal receives about 4.5–5.5 kWh/m²/day with around 300 sunny days a year, so PV is used in solar home systems, solar pumps and grid-connected plants of several MW.

✓ Answer checked by Claude Opus 5.5 (high effort)

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