About PV Solar

For all of the discussion about solar power, few people outside of the solar industry seem to understand how sunlight is converted into electricity, and more importantly for most homeowners, what the average solar power system costs, what it looks like, and what is required to install it.

The following information hopes to answer all of your questions and then some about home solar power. All external data sources include links to the respective websites for further information.

Solar Electric or Photovoltaic (PV) System Basics
Determining if Your Home is a Good Candidate for Solar
Other Pre-Installation Considerations
Net Metering
Warranties

Photovoltaic (PV) systems convert sunlight directly to electricity. They work any time the sun is shining, but more electricity is produced when the sunlight is more intense and strikes the PV modules directly (as when rays of sunlight are perpendicular to the PV modules). Unlike solar thermal systems for heating water, 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.

PV allows you to produce electricity without noise or air pollution from a renewable resource. A PV system never runs out of fuel and will not increase U.S. natural gas imports. Since many PV system components are manufactured in the U.S., solar power also strengthens our economy by creating well-paying jobs. These characteristics could make PV technology the U.S. energy source of choice for the 21st century.

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 about 10 watts to 300 watts. A PV system connected or “tied” to the utility grid has 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)
• Batteries (optional) to provide energy storage or backup power in case of a power interruption or outage on the grid.

Excerpted from: U.S. Department of Energy -
Energy Efficiency and Renewable Energy:A Consumer’s Guide - Get Your Power from the Sun

Determining if Your Home is a Good Candidate for Solar

A well-designed PV system needs year-round clear and unobstructed access to the sun’s rays for most or all of the day. You can make an initial assessment yourself by walking around your home on a sunny day and noting any shaded areas. Another method for judging shading is to view your home through Google Maps or similar services. Your PV provider will determine whether your home can effectively use a PV system before installing it and how shading may impact your eligibility for a full rebate.

The orientation of your PV system (the compass direction that your system faces) affects its performance. In the United States, the sun is always in the southern half of the sky but is higher 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. If you live in a state with a rebate program have your PV installer explain how system orientation may change your rebate amount. Some states will reduce your rebate amount if your system is not oriented towards the southern sky.

Flat roofs also work well for solar electric systems, because PV modules can be mounted flat on the roof facing the sky or bolted on frames tilted toward the south at an optimal angle. If a rooftop can’t be used, your solar modules can also be placed on the ground, either on a fixed mount or a “tracking” mount that follows the sun to orient the PV modules. Other options (often used in multifamily or commercial applications) include mounting structures that create covered parking, or that provide shade as window awnings.

The amount of space that a PV system needs depends on the size of the system you purchase. Some residential systems require as little as 50 square feet but others could need as much as 1,000 square feet. If your location limits the size of your system, you may want to install one that uses more efficient (percent of sunlight converted to electricity) PV modules. Greater efficiency means that the module needs less surface area to convert sunlight into a given amount of electric power.

Some types of roofs are simpler and cheaper to work with, but a PV system can be installed on any type. Typically, roofs with composition shingles are the easiest to work with, and those with slate are the most difficult. In any case, an experienced solar installer will know how to work on all types and can use roofing techniques that eliminate any possibility of leaks. Ask your PV provider how the PV system affects your roof warranty.

Excerpted from: U.S. Department of Energy -
Energy Efficiency and Renewable Energy: A Consumer’s Guide - Get Your Power from the Sun

If you live where a homeowners association must approve a solar electric system, you or your PV provider may need to submit your plans. You’ll need approval before you begin installing your PV system. However, some state laws stipulate that you have the right to install a solar electric system on your home irregardless of your HOA’s position on PV systems.

You will probably need to obtain permits from your city or county building department. These include a building permit, an electrical permit, or both. Typically, your PV provider will take care of this, rolling the price of the permits into the overall system price.

Connecting your PV system to the utility grid will require an interconnection agreement and a purchase and sale agreement. Federal law and some state public utility commission regulations require utilities to supply you with an interconnection agreement. The interconnection agreement specifies the terms and conditions under which your system will be connected to the utility grid. These include your obligation to obtain permits and insurance, maintain the system in good working order, and operate it safely.

The purchase and sale agreement specifies the metering arrangements, the payment for any excess generation, and any other related issues. The language in these contracts should be simple, straightforward, and easy to understand. If you are unclear about your obligations under these agreements, contact the utility or your electrical service provider for clarification. An experienced PV provider will also be able to help you understand the forms; however, they may refer you to your local utility or state agency for liability reasons.

National standards for utility interconnection of PV systems are being adopted by many local utilities. The most important of these standards focuses on inverters. Traditionally, inverters simply converted the DC electricity generated by PV modules to the AC electricity we use in our homes. More recently, inverters have evolved into remarkably sophisticated devices to manage and condition power. Many new inverters contain all the protective relays, disconnects, and other components necessary to meet the most stringent national standards. It is your obligation to make sure that your PV provider uses equipment that complies with the relevant standards so be sure to discuss this issue.

Excerpted from: U.S. Department of Energy -
Energy Efficiency and Renewable Energy: A Consumer’s Guide - Get Your Power from the Sun

Some utilities offer customers with PV systems the option to net meter the excess power generated by the PV system. This means that when the PV system generates more power than the household can use, the utility pays the full retail price for this power in an even swap as the electric meter spins backward, and your PV power goes into the grid. Net metering allows eligible customers with PV systems to connect to the grid with their existing single meter.

Almost all standard utility meters can measure the flow of energy in either direction. The meter spins forward when electricity is flowing from the utility into the building and spins backward when power is flowing from the building to the utility.For example, in one utility program, customers are billed monthly for the “net” energy consumed. If the customer’s net consumption is negative in any month (i.e., the PV system produces more energy than the customer uses), the balance is credited to subsequent months. Once a year, on the anniversary of the effective date of the interconnection agreement, the utility pays the customer for any negative balance at its wholesale or “avoided cost” for energy, which may be quite small, perhaps less than 2 cents per kilowatt-hour.

Net metering allows customers to get more value from the energy they generate. It also simplifies both the metering process (by eliminating the need for a second meter) and the accounting process (by eliminating the need for monthly payments from your utility). Be sure to ask your utility about its policy regarding net metering.

Under the federal Public Utility Regulatory Policies Act (PURPA), utilities must allow you to interconnect your PV system. They must also buy any excess electricity you generate, beyond what you use in your home or business. If your utility does not offer net metering, it will probably require you to use two meters: one to measure the flow of electricity into the building, the other to measure the flow of electricity out of the building. If net metering is not available, the utility will pay you only a wholesale rate for your excess electricity. This provides a strong incentive to use all the electricity you generate so that it offsets electricity you would otherwise have to purchase at the higher retail rate. This may be a factor in how you optimize the system size, because you may want to limit generating excess electricity. Such a “dual metering” arrangement is the norm for industrial customers who generate their own power.

After your new PV system is installed, it must be inspected and approved by the local permitting agency (usually a building or electrical inspector) and most likely by the electric utility with which you entered into an interconnection agreement. Inspectors may require your PV provider to make corrections (which is fairly common in the construction business). A copy of the building permit showing the final inspection sign-off may be required to qualify for a solar rebate program.

Excerpted from: U.S. Department of Energy -
Energy Efficiency and Renewable Energy: A Consumer’s Guide - Get Your Power from the Sun

Warranties are key to ensuring that your PV system will be repaired if something should malfunction during the warranty period. PV systems eligible for some solar rebate programs must carry a full (not “limited”) two-year warranty, in addition to any manufacturers’ warranties on specific components. This warranty should cover all parts and labor, including the cost of removing any defective component, shipping it to the manufacturer, and reinstalling the component after it is repaired or replaced.

The rebate program’s two-year warranty requirement supersedes any other warranty limitations. In other words, even if the manufacturer’s warranty on a particular component is less than two years, the system vendor must provide you with a two-year warranty. Similarly, even if the manufacturer’s warranty is a limited warranty that does not include the cost of removing, shipping, and reinstalling defective components, the system vendor must cover these costs if the retailer/vendor also installed the system.

Be sure you know who is responsible for honoring the various warranties associated with your system—the installer, the dealer, or the manufacturer. The vendor should disclose the warranty responsibility of each party. Know the financial arrangements, such as contractor’s bonds, that ensure the warranty will be honored. Under some solar rebate programs, vendors must provide documentation on system and component warranty coverage and claims procedures. To avoid any later misunderstandings, be sure to read the warranty carefully and review the terms and conditions with your retailer/vendor.

Excerpted from: U.S. Department of Energy -
Energy Efficiency and Renewable Energy: A Consumer’s Guide - Get Your Power from the Sun