Small Solar Electric Systems

A small solar electric or photovoltaic (PV) system can be a reliable and pollution-free producer of electricity for your home or office. And they're becoming more affordable all the time. Small PV systems also provide a cost-effective power supply in locations where it is expensive or impossible to send electricity through conventional power lines.

Because PV technologies use both direct and scattered sunlight to create electricity, the solar resource across the United States is ample for small solar electric systems. However, the amount of power generated by a solar system at a particular site depends on how much of the sun's energy reaches it. Thus, PV systems, like all solar technologies, function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.

You can also use PV technology to provide outdoor lighting.

Here you can find the following information:

How Small Solar Electric Systems Work

Solar electric systems, also known as photovoltaic (PV) systems, convert sunlight into electricity.

Solar cells—the basic building blocks of a PV system—consist of semiconductor materials. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms. This phenomenon is called the "photoelectric effect." These free electrons then travel into a circuit built into the solar cell to form electrical current. To see a simulation of the photoelectric effect, please view our animation. Only sunlight of certain wavelengths will work efficiently to create electricity. PV systems can still produce electricity on cloudy days, but not as much as on a sunny day.

The basic PV or solar cell typically produces only a small amount of power. To produce more power, solar cells (about 40) can be interconnected to form panels or modules. PV modules range in output from 10 to 300 watts. If more power is needed, several modules can be installed on a building or at ground-level in a rack to form a PV array.

PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day.

Because of their modularity, PV systems can be designed to meet any electrical requirement, no matter how large or how small. You also can connect them to an electric distribution system (grid-connected), or they can stand alone (off-grid).

An illustration showing a residential grid-connected small solar electric or photovoltaic system. It shows two square-shaped solar panels, each containing nine smaller squares, on the roof of a house. You can see how the electric current travels from the solar panels to an inverter box. From the inverter box, the electric current travels to a meter box and then to an electricity transmission tower, referred to as the utility service. Inside the house, from the inverter box, you see the electric current powering two lights, a television, and a clothes washer and dryer.
A residential grid-connected small solar electric or photovoltaic system.

Considering a Small Solar Electric System

To help evaluate whether a small solar electric system will work for you, you should consider the following:

Your available solar resource

The solar resource across the U.S. is ample for solar electric systems—also known as photovoltaic (PV) systems—because they can use both direct and scattered sunlight. However, the amount of electricity generated at a particular site depends on how much of the sun's energy reaches it. Thus, PV systems function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.

Before you buy a PV system, you'll want to be sure your site has enough solar energy to meet your electricity needs efficiently and economically. Your local system supplier can perform a solar site analysis for you or show you how to do so on your own.

When evaluating your site, you'll also need to consider both the geographic orientation and the tilt of your solar panels—PV modules—as both can affect your system's performance.

System size

Accurately sizing the components of your solar electric system, also known as a photovoltaic (PV) system, helps ensure that your system will produce the amount of power you want it to produce. This is especially important for stand-alone systems, which are not connected to the electricity grid. However, because PV is modular, you can always add to your solar energy collector should you need more power down the road.

First, consider what portion of your current electricity needs you would like your PV system to meet. For example, suppose that you would like to meet a certain percentage of your electricity needs with your PV system. You could work with your PV provider to examine past electric bills and determine the size of the PV system needed to achieve that goal. You can contact your utility company and request the total electricity usage, measured in kilowatt-hours (kWh), for your household or business over the past 12 months or consult your electric bills if you save them.

If you reduce your electricity loads, you can generally buy a smaller, less expensive PV system.

PV systems are classified by their rated power output (the peak power they produce when exposed to solar radiation of 1000 watts per square meter at a module temperature of 25°C). Systems rated between 1 and 5 kilowatts are generally sufficient to meet most of the needs of home and small business owners.

The table below provides an estimate of the roof area needed for several systems. Your system supplier/installer can make, or help you make, more precise calculations at your site before you purchase a system.

Roof Area Needed in Square Feet
PV Module Efficiency (%) PV Capacity Rating (Watts)
  100 250 500 1,000 2,000 4,000 10,000
4 30 75 150 300 600 1,200 3,000
8 15 38 75 150 300 600 1,500
12 10 25 50 100 200 400 1,000
16 8 20 40 80 160 320 800

For example, to generate 2,000 watts from a 12%-efficient system, you need 200 square feet of roof area.

Is it worth the investment?

The economics of a small solar electric or photovoltaic (PV) system are determined by both the capital and operating costs. Capital costs include the initial costs of designing and installing a PV system. Operating costs include the costs associated with maintaining and operating the PV system over its useful life.

The factors that affect both capital and operating costs include the solar resource, system components, and system size discussed above, along with whether a system is grid-connected or stands alone (off-grid).

Electricity Consumption

Before selecting system components and sizing a PV system for an existing home, you should evaluate your energy consumption patterns and try to reduce your home's electricity use. You can start by performing a load analysis, which includes these tasks:

  • Looking at your utility bills over the past year

  • Calculating energy consumption

  • Recognizing consumption trends.

By understanding your "energy habits" and becoming more energy efficient, you can reduce the size of the PV system you'll need, lowering both your capital and operating costs.

If you're designing a new home, you should work with the builder and the solar professional to incorporate your PV system into your whole-house system design —an approach for building an energy-efficient home.

PV Cost Considerations

Ask your PV provider how much electricity your new PV system will produce per year (measured in kilowatt-hours) and compare that number to your annual electricity usage (called demand) to get an idea of how much you will save. As a rule, the cost per kilowatt-hour goes down as you increase the size of the system.

You should also compare the purchase price of utility-generated electricity to the higher costs of smaller PV systems. PV-generated electricity is usually more expensive than conventional, utility-supplied electricity. However, these costs will vary by geographic location.

Solar rebate programs, subsidies, and other incentives can help make PV more affordable. Tax incentives may include a sales tax exemption on the PV system purchase, a property tax exemption, or state personal income tax credits, all of which provide an economic benefit to consumers by lowering high capital costs.

Some solar rebate programs are capped at a certain dollar amount. Therefore, a solar electric system that matches this cap maximizes the benefit of the solar rebate.

Many homeowners use PV systems because other considerations—such as environmental benefits and energy independence—tip the balance in their favor.

Local permits and covenants

Each state and community has its own set of codes and regulations that you will need to follow in order to add a small renewable energy system to your home or small business. These regulations can affect the type of renewable energy system you are allowed to install and who installs it. They can also affect whether you decide to connect your system to the electricity grid or use it in place of grid-supplied electricity as a stand-alone system.

A local renewable energy company or organization, your state energy office, or your local officials should be able to tell you about the requirements that apply in your community. If you want to connect your system to the electricity grid, these groups may also be able to help you navigate your power provider's grid-connection requirements.

Some of the state and community requirements you may encounter are building codes, easements, and local covenants and ordinances and there may be other technology-specific requirements.

Building Codes

Electrical and building inspectors ensure that your system complies with standards. Building inspectors are interested in making sure the structure you are adding is safe. Your system may be required to pass electrical and/or plumbing inspections in order to comply with local building codes.

Many building code offices also require their zoning board to grant you a conditional-use permit or a variance from the existing code before they will issue you a building permit. Check with your building code office before you buy a renewable energy system to learn about their specific inspection requirements.

You are most likely to gain the inspector's approval if you or your installer follow the National Electrical Code; install pre-engineered, packaged systems; properly brief the inspector on your installation; and include a complete set of plans as well as the diagrams that come with the system. In addition, you should be sure your system is composed of certified equipment, and that it complies with local requirements and appropriate technical standards (the links at the bottom of the page provide more information on technical standards).

Note: Although local inspectors are often not required to follow the National Electrical Code (NEC), many look to Article 690 of the NEC for guidance on equipment and wiring safety for small renewable energy system installations. Article 690 of the NEC specifically discusses photovoltaics systems, but much of the information is pertinent to small wind and microhydro systems as well. If you, your installer, or your inspector want more information on Article 690, Sandia National Laboratory in 1996 published a useful guide [PDF 8.2 MB] to installing NEC-compliant photovoltaics systems.

Easements

Some states permit easements, which are a voluntary, legally binding agreement between owners of adjacent land regarding use of the land. For example, you might seek an easement specifying that no structure which blocks the renewable resource necessary to run a renewable energy system will be built. These agreements are binding regardless of changing land ownership. In addition, you may want to do a title search of your deed to determine if any prior easements or other agreements exist which could prevent you from adding a renewable energy system to your own property.

Local Covenants and Ordinances

Some communities have covenants or other regulations specifying what homeowners can and can't do with their property. Sometimes these regulations prohibit the use of renewable energy systems for aesthetic or noise-control reasons. However, sometimes these regulations have provisions supporting renewable energy systems. Check with your homeowners association or local government for details. In addition, you may want to discuss your intentions with your neighbors to avoid any future public objections.

Small Solar Electric System Components

A typical small solar electric, or photovoltaic (PV), system consists of solar cells, modules or panels (which consist of solar cells), arrays (which consist of modules), and balance-of-system parts.

Click to read more about Small Solar Electric System Components

Installing and Maintaining a Small Solar Electric System

Proper installation and maintenance of your small solar electric or photovoltaic (PV) system is essential for maximizing its energy performance. It's usually best to have an experienced professional install and maintain the system.

Click to read more about Installing and Maintaining a Small Solar Electric System

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