Distributed generation allows for the use of small-scale power generation technologies located nearby the load being served. It can be applied in many different forms. There are various methods by which customers can generate their own electricity, with or without the backup grid.
The grid is a network of electric power lines and associated equipment used to transmit and distribute electricity over a geographic area.
Examples of how customers can use distributed generation technologies are through the following methods:
1. Cogeneration, which is the use of wasted exhaust heat as useful thermal output (like steam) that can be used for space heating or space cooling.
2. Peak shaving is the reduction of the amount of electricity drawn from a power utility during utility peak time periods. Examples could be the installation of generators, energy-saving devices or reducing usage during peak hours.
3. Selling power, which, if net metering is in place, when a customer sells its excess generation back to the grid at the same retail price as the customer buys power from the grid during other periods. The hope is to generate the power at a lower cost than they can sell it back to the grid for
4. Providing “standby” power to customers helps those who would incur high costs if an outage occurred in their businesses
5. On-site (continuous) generation of premium power that is backed up with grid-based power eliminates the cost and other complications of connecting to the grid.
6. Production of ‘green’ power means power having very low emissions. Though this method may cost more, customers who are environmentally inclined may purchase these methods for that very reason.
7. “Residential (small) fuel cells” are clean, quiet and highly efficient. The cells produce direct current electrical power by combining hydrogen and oxygen to produce electricity, with water and heat as the byproduct.
Of these many examples, a very familiar on-site power generation technology is photovoltaics (PV) or solar energy. This article gives you considerations and installation information about PV systems that you can use.
PV does not use the sun’s heat to make electricity. Instead, electrons freed by the interaction of sunlight with semiconductor materials in PV cells are captured in an electric current. The basic building block of PV technology is the solar cell.
Multiple PV cells are connected to form a PV “module,” the smallest PV component sold commercially. Modules range in power output from 10 to 300 watts.
A PV system connected to the utility grid can have these components: one or more PV modules, which are connected to an inverter; the inverter, which converts the system’s direct current (DC) electricity to alternating current (AC); and batteries to provide energy storage or backup power in case of a power interruption or outage on the grid.
AC electricity is compatible with the utility grid. It powers our lights, appliances, computers and televisions. Special appliances that run directly on DC power are available, but they can be expensive.
When buying a PV system, a customer must consider that PV only produces power when the sun is shining. This is not a problem for PV systems connected to the utility grid, because the utility can automatically supplement with additional electricity if required. In the case of non-grid or stand-alone PV systems, batteries can be purchased to store energy for later use.
If the user lives near existing power lines, PV-generated electricity is usually more expensive than conventional utility-supplied electricity. A solar rebate program and net metering can help make PV more affordable. There is no getting away from the fact that PV power requires a high initial investment, but it can be financed with its cost spread over many years, and rebates might also be available. Aside from the future direction of our energy sources, looking closer at photovoltaics shows us that the technology has many advantages:
1. No moving parts; minimal maintenance
2. Safe, silent and simple operation
3. Highly dependable and durable (30+ year life)
4. Easily expandable (from watches to homes to towns)
5. Maximum output to match peak utility power load
6. Sunlight is free
7. No emissions, no pollution
8. Portable, easy and fast to install anywhere
9. Available everywhere there is sunlight
10. Ability to integrate into existing and new buildings
11. Useable for centralized or distributed power generation
PV is also called a “renewable” energy source. For anyone involved in “green” buildings, solar matches those requirements—it is environmentally clean and virtually inexhaustible. The sun is the source of all energy, sending it in all directions.
A large amount of energy comes from the sun in the form of light. Because the sun does not shine in one place all the time, there are differences between the amount of energy reaching the earth’s surface in different countries. In the sunnier parts of the world, sunlight is an important source of energy because it can be used to heat water or make electricity.
The arguments against PV, or the use of solar energy, are high cost, limited energy production and the large surface area requirements of the PV array (which is the complete power generating unit, made up of the PV modules and panels). The requirments are due to the widespread nature of sunlight and the existing sunlight to electrical energy conversion efficiencies of PV devices.
Battery storage is required for critical loads such as backup for refrigeration, water pumps, lighting and other necessities. Normally, the system operates in a grid-connected mode, either serving the on-site loads or sending excess power back to the grid, and it can also power critical loads from a battery bank when the grid is de-energized.
But why PV? There are a variety of reasons to buy a PV system. Some people want to reduce air pollution. Others want to invest in an energy-producing improvement to their property. Some want to reduce the amount of electricity they buy from their utility because it makes them less vulnerable to future price increases. And others want the independence that a PV system provides. Often, the cost of extending conventional power to a residence is higher than the cost of a solar option.
A well-designed PV system needs clear and unobstructed access to the sun’s rays, throughout the year. And, to make the best use of it, the PV modules must have a “clear view” of the sun unobstructed by trees, roof gables, chimneys, buildings, and other features of the home and the surrounding landscape.
You can make an initial assessment yourself and if promising, you can determine whether the home or business can effectively use a PV system. The orientation of the PV system—the compass direction that the system faces—affects its performance. In the United States, the sun may be in the southern half of the sky, but is higher in latitude in the summer and lower in the winter. Usually, the best location for a PV system is a south-facing roof, but roofs that face east or west may also be acceptable.
Flat roofs also work well and PV modules can be attached directly to the roof as “PV shingles.” If a rooftop cannot be used, the solar modules can be placed on the ground, either on a fixed mount or a “tracking” mount that follows the sun to orient the PV modules.
Some potential sites for a PV system may be bright and sunny during certain times of the day, but shaded during other times. Such shading may substantially reduce the amount of electricity that the system can produce. The PV provider can help determine whether a site is suitable for a solar electric system.
PV installers may be found by researching the following:
1. The Source Guide for renewable energy businesses by name, product type, business type and location. This can be found by visiting http://energy.sourceguides.com/index.shtml.
2. The Solar Energy Industries Association at 202.628.7745 where you can find a list of solar service providers
3. A utility company to see which vendors it recommends
4. The Internet to find reputable, professional contractors with experience in PV systems
Experience in installing grid- connected systems is valuable because some elements of the installation— particularly interconnection with the local utility—are unique. Have experience in both grid-connected and stand-alone systems.
That gives experience with all aspects of PV system installation except connection with the utility grid. But a competent company with PV experience should be able to handle a grid-connected PV. Experience with off-grid systems is valuable, because grid-independent systems are more technically complex than grid-tied systems.
An advantage the electrical contractor has is that he is already licensed as a contractor and PV systems should be installed by an appropriately licensed contractor. Local building departments might also require that the installer have a general contractor’s license. The city or county where you are working will have additional information on licensing.
For installations where there is a homeowner’s association, that association might be required to approve the solar electric system. The contractor may need to submit plans before the PV system can be installed.
There are other stipulations that need to be investigated as well, such as getting a net-metering agreement, insurance and an interconnection agreement. There is also the possibility of whether the warranty being offered is valuable to the customer.
The decision to use a PV system is twofold for you. You can help your customer with all the information they need to get a system that performs as they expect, and then, when they decide in favor of a PV system, if you have the right experience, you are there to help them get it installed. EC
MICHELSON, president of Jackson, Calif.-based Business Communication Services and publisher of the BCS Reports, is an expert in TIA/EIA performance standards. To contact her, see www.bcsreports.com or send e-mail to firstname.lastname@example.org.