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. Polycrystalline Si Cell Thin Film Cells
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. + Panel Array Cells
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
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.