1. Photovoltaic Solar Cells and Solar Energy Systems for Home Usages Mohammad Anisuzzaman

2. 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.

3. 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

4. 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. + Cells Panel Array

5. 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

6. System Wiring Diagram

7. 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.

8. 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.

9. 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 CO 2 during its lifetime. With proper disposal of depleted batteries and old cells, impact on the environment from solar panels systems is minimal.