Facts about Solar Power

Published 2:55 pm Wednesday, November 12, 2008

Solar power is the hot topic in the world of renewable energy (or green power) and has gained increasing interest by homeowners. With rising fuel and energy costs, homeowners are looking for viable answers to reduce their usage of electricity and are open to new ideas. This can be a dangerous combination for a homeowner that doesn’t have some basic understanding of how a solar system works and doesn’t know what questions to ask when looking at potentially purchasing a solar system for their home. This article contains some basic facts concerning residential solar energy systems and hopefully provides a basic understanding of the main components of a typical system and how they operate.

There are independent dealers riding the fears of increasing energy cost and offering, what seem to the homeowner, a whole house solar energy system. Not only is the idea given that the system will and can serve the whole home, but that the homeowner will be able to have excess energy to sell back to the local power company. This is hardly the case for a typical residential solar energy system.

A photovoltaic (PV) installation typically includes an array of PV modules or panels, an inverter, batteries (for non grid tied applications) and interconnection wiring. Solar panels come in different sizes and output but most solar panels marketed to residential customers have an output range of 150-200 watts maximum per panel. With a typical panel having an output of 150 watts, it would take 10 panels in an array to generate 1500 watts. To put this in perspective, an element in a typical 50 gallon water heater is 4500 watts. With a 10 panel system putting out 1500 watts at peak performance, not even half of the water heating can be covered.

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The main thing to remember about a solar panel is if the sun is not shining on it, it is not producing energy. The electrical output of photovoltaic cells is extremely sensitive to shading. When even a small portion of an array is shaded, while the remainder is in sunlight, the output falls dramatically. Therefore it is extremely important that a PV installation is not shaded at all by trees, architectural features, flag poles, or other obstructions. Sunlight can be absorbed by dust, fallout, or other impurities at the surface of the module. This can cut down the amount of light that actually strikes the cells by as much as half.

During non-generating hours, cloudy days or at night, it is necessary to have a battery back up system if the solar panel is expected to produce 24 hours a day. Battery size and capacity will differ with the needed output, but is a critical part of a solar system if it is to be used 24 hours a day.

Within a typical home solar panel system an inverter is the most important part of the puzzle. An inverter is a mechanical or electromechanical device that converts DC power into AC power that can be utilized in a home. Solar panels convert sunlight into DC current and this energy must be “inverted” into AC current in order for it to be utilized in the home.

Also, a licensed electrical contractor that is familiar with solar energy systems must be used to install any system purchased by the homeowner and will be subject to local electrical inspections. The labor cost plus all additional wiring devices must be included in the overall cost to the homeowner.

As you can see it is not as simple as putting a few panels on the roof top and running wires to the meter box. The typical system is a lay out of panels wired to a battery pack to store the energy so it can be used when needed. When the stored energy in the batteries is called on, it must run thru an inverter to create AC voltage that can be used in the home.

Maintaining a clean module surface will increase output performance over the life of the module. Module output and life are also degraded by increased temperature. Allowing ambient air to flow over, and if possible behind, PV modules reduces this problem. However, effective module lives are typically 25 years or more, so replacement costs should be considered as well.

Solar power is a viable source of some incremental use such as solar water heating. Understanding the whole picture and how alternative energy sources can be cost effective today is important. Knowing the questions to ask or where to get the answers is just as important. For more information on solar power here are a few web-sites, www.affordable-solar.com, www.doe.gov, www.energystar.gov.

Mark Wallace is theDirector of Residential Energy Management at Coast Electric Power Assoc. He has 17 years experience in Residential Energy Management. He is certified by Air Conditioning Contractors of America (ACCA) in Residential Load Calculations and System Design. He is also a current board member and past president of Pearl River County Homebuilders Assoc.