Design Strategies

Photovoltaic System
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Photovoltaic System

1. Introduction

Photovoltaic systems use solar cells to capture the sun rays and convert that energy into electricity. Such systems allow homeowners to generate electricity in a clean, reliable, and quiet way that can offset the cost of future electricity costs and decrease their dependence on the energy grid.
Photovoltaic cells are generally made from modified silicon, or other semi conductive materials, that absorb and convert sunlight into electricity. Photovoltaic cells are long lasting (the first PV system ever installed in the USA – in 1954 – is still operating today). Most manufacturers warranty their products power output for a minimum of 20 years. But most solar professionals agree that a system should last at least 25 – 30 years. (1)
2. How does it work?
Due to the nature of solar energy, two components are required to have a functional solar energy generator. These two components are a collector and a storage unit. The collector simply collects the radiation that falls on it and converts a fraction of it to other forms of energy (either electricity and heat or heat alone). A storage unit is required because of the non-constant nature of solar energy. At certain times only a very small amount of radiation will be received. At night or during heavy cloud cover for example, the amount of energy produced by the collector will be quite small or null. The storage unit can hold the excess energy produced during the periods of maximum productivity and release it later when the direct prodution drops.
3. Benefits
• The electricity generated by the solar power system is clean, renewable and reliable. It will help reduce the amount of greenhouse gases emitted and help mitigating climate change.
• Using solar power helps reduce energy bills.
• Excess electricity is feedback into the grid when you generate more than you use during the day.
4. Applications
• Grid tie homes and businesses. This is PV’s most common application. This is where a building is tied to the utility grid but also has a PV array to offset the utility energy costs. When the PV array is producing electricity the home or business consumes that power and what it doesn’t use goes back into the utility grid. The utility company then credits back the difference for what is called net metering.
• Off grid homes typically in remote locations. Again the cost of bringing in a power line is prohibitive. In the past most solar PV was for this application. Obviously battery banks for energy storage are required and perhaps a generator for those times when it is cloudy for several days in a row.
• Remote well pumping where the cost of bringing in a power line is prohibitive. There are also landscaping and drip-feeding irrigation with solar powered water pumping applications.
• Grid tie hybrid systems where some of the photovoltaic energy is stored in batteries to back up critical appliances during power outages. This is not commonly done since it adds to the cost, but if your home or business is prone to long utility outages it is something to consider. Otherwise, UPS devices (uninteruptible power supplies) and/or a generator might be a better solution.
(3) Handbook for Green Products, edition2: Technical-contructive green housing products and green services.

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