Photovoltaic Solar Cells and Solar Energy Systems for Home

Usages

Mohammad Anisuzzaman

What are Photovoltaic Solar Cells?

• Photovoltaic cells, commonly known as solar cells, are semiconductor devices that convert sunlight directly into electricity.

• Efficiency range from a few percent to above 40%.

• Most cell materials are non-toxic and produce to greenhouse gas.

• Usage range from portable electronics to spaceships.

Types of Solar Cells• Silicon Solar Cells:

– Single Crystal Si Cells: Commonly used. Usual efficiency of 20%. Long lifetime (>20 yrs). Approaching the theoretical limit of 29%. Cost of production $2.48/watt.

– Poly Crystal Si Cells: Less expensive. Efficiency is usually less than 15%.

– Amorphous thin film Si Cell: thin non-crystalline Si layers are printed on a substrate. Lightweight and less expensive. Efficiency around 10%.

• Cadmium Telluride Thin Film Cells– Inexpensive to produce; US$1/watt reported. Best efficiency

reported is 16.5%. Popular for solar panel arrays.• Copper Indium Gallium Selenide Thin Film Cell:

– Efficiency around 20%. Manufacturing costs are higher that amorphous Si thin film cells, but dropping fast.

• Gallium Arsenide Multijunction Cells:– Maximum reported efficiency of 42.4%. Much more

expensive to produce. Limited to scientific and high cost commercial usage. Thin Film Cells

Polycrystalline Si Cell

Solar Panels

• A single solar cell has very limited output capacity, e.g. a single crystal Si cell output is about 0.5V

• Cells are joined in series and parallel to increase their output capacity, e.g. 36 sc-Si cells are connected to produce a ~24v module.

• Further increase in output capacity, require joining panels into solar arrays.

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Cells

Panel

Array

Solar Panel System

In addition to the solar panel array, several other components are needed for a complete solar power system:

• Charge controller: prevent overcharging of the batteries

• Batteries: power storage• Inverter: DC to AC

conversion for AC appliances • DC and AC safety switches• Optional AC generator

Cost: $6,000 - $10,000

System Wiring Diagram

Electricity Consumption

– Average household electricity usage in the United States is more that 600 kWH/month.

– Average household electricity usage in developing countries like Bangladesh and India is less than half of that in the US.

– Electricity usage can be reduced to 200 kWH or less per month by adopting energy conservation techniques and moderation.

– Such conservation policies can make a reasonably sized solar panel system enough for the energy need of an average household.

Example Home System

• A typical home may need about 200 AH/day of supply capacity from the photovoltaic (PV) system. (ignoring heavy equipments like microwave oven, air conditioners etc.)

• A typical 80 watt solar panel gives 5.5 A of current under direct sunlight.A system with 10 panels with 6 hours of sunlight per day gives

5.5 A x 8 x 6 Hr = 330 AH• This ensure that the batteries will be charging even when the

system is under full load.• With fifteen 105 AH Lead Acid batteries –

Total battery capacity: 105 AH x 15 = 1575 AH • This ensures that the system has adequate backup for multiple

days and still maintain a shallow discharge level required for long battery life.

Conclusion

• Solar cells are a very clean way to produce electricity, with no greenhouse gas emission over their lifetime.

• The initial cost of setup may be high, but their long lifespan results in payback typically in about 20 years.

• Over its estimated life a photovoltaic module will produce much more electricity then used in its production.

• A 100 W module will prevent the emission of over two tons of CO2 during its lifetime.

• With proper disposal of depleted batteries and old cells, impact on the environment from solar panels systems is minimal.