4.1 Solar Energy Collection, Storage, and Utilization
This unit is about the practical applications of solar energy — how we collect, store, and actually use it in real life.
- Collection: Using solar collectors (flat plate, concentrating, PV panels) to capture sunlight.
- Storage: Thermal storage (hot water tanks, PCM) or Electrical storage (batteries)
- Utilization: Converting solar energy into useful forms — heat, electricity, mechanical work.
4.2 Solar Water Heating
One of the most common and economical uses of solar energy.
How it works:
- Cold water enters the flat plate collector at the bottom.
- Water gets heated by solar radiation.
- Hot water rises to an insulated storage tank (thermosyphon principle — no pump needed).
- Hot water is available for bathing, cooking, washing.
Types:
1. Passive System (Natural Circulation):
- No pump needed.
- Works on thermosyphon principle (hot water rises, cold water sinks).
- Simple, low maintenance, economical.
2. Active System (Forced Circulation):
- Uses an electric pump to circulate water.
- Can be used even when the tank is not above the collector.
- More efficient but needs electricity.
Applications:
- Homes and apartments
- Hotels and hospitals
- Dairies and food processing industries
Savings: A 100-litre solar water heater can save about 1500 units of electricity per year.
4.3 Solar Air Heating
Used to heat air for space heating and industrial drying.
Working:
- Air is passed over or under a solar absorber plate.
- Air gets heated.
- Hot air is blown into buildings or drying chambers using a fan.
Applications:
- Space Heating: Warming buildings in cold regions (hills, northern India).
- Crop Drying: Drying rice, wheat, spices, fruits without burning fuel.
- Timber/Wood Drying: Used in wood industries.
Advantages:
- No risk of leakage or freezing (unlike water systems)
- Low cost and simple
Disadvantage:
- Air has low heat capacity, so efficiency is lower.
4.4 Solar Power Generation
Solar energy can be used to generate electricity at large scale.
Method 1 – Solar PV Power Plants:
- Thousands of solar panels connected together form a solar farm.
- Produces DC electricity → converted to AC by inverters → fed to the grid.
- India's largest PV plant: Bhadla Solar Park, Rajasthan (~2,700 MW).
Method 2 – Concentrating Solar Power (CSP):
- Uses mirrors to concentrate sunlight and produce high-temperature heat.
- Heat converts water to steam → steam drives a turbine → electricity is generated.
Types of CSP:
- Parabolic Trough: Long curved mirrors focus sun on a pipe at the focal line.
- Solar Tower (Central Receiver): Many flat mirrors (heliostats) reflect sunlight to a tower top.
- Dish-Stirling System: Parabolic dish focuses on a Stirling engine at the focal point.
4.5 Solar Refrigeration and Air Conditioning
Solar energy can also be used for cooling.
Solar Absorption Refrigeration:
- Uses heat (from solar collectors) instead of electricity.
- Working fluid: water-ammonia or water-lithium bromide.
- The heat drives the refrigeration cycle.
- Used in vaccine storage in remote areas, food preservation.
Solar-powered Air Conditioning:
- Uses solar thermal energy to drive an absorption chiller.
- Buildings can be cooled using the same energy that heats them up.
- Ideal for hot countries like India.
Advantage: Maximum solar energy availability coincides with maximum cooling demand (summer).
4.6 Solar Water Pumping
Used extensively in rural India for irrigation and drinking water.
Solar PV Water Pump:
- Solar panels generate electricity.
- DC or AC motor drives a pump.
- Water is pumped from bore wells or rivers.
- No fuel cost, no electricity bills.
Types:
- Surface Pump: Placed on ground, draws water from shallow sources.
- Submersible Pump: Placed inside the borewell, suitable for deep water.
Government Schemes: PM-KUSUM scheme provides subsidies for solar pumps to farmers.
4.7 Solar Water Purification (Desalination)
Solar energy can purify dirty, brackish, or salty water.
Solar Still:
- A simple, low-cost device.
- Dirty water is placed in a black-painted basin.
- Glass cover on top.
- Sun heats the water → it evaporates → water vapour condenses on glass → pure water drips into collection channel.
- Works like a mini water cycle.
Solar Desalination:
- Used to convert seawater into fresh water.
- Solar energy heats the seawater.
- Evaporated water is condensed and collected as fresh water.
Application: Coastal areas, islands, drought-prone regions.
4.8 Solar Fuels
Solar energy can also be used to produce fuels for storage and transportation.
Solar Hydrogen:
- Water (H₂O) is split into Hydrogen (H₂) and Oxygen (O₂) using solar electricity.
- This process is called electrolysis.
- H₂ can be stored and burned as a clean fuel — only water is produced on combustion.
Solar Biomass:
- Solar energy enhances photosynthesis in plants to grow biomass.
- Biomass is converted to biogas, ethanol, or biodiesel.
Significance: These fuels can be stored and transported, solving the intermittency problem of solar energy.
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