As interest in solar energy grows, some members are considering the purchase of a photovoltaic (PV) a.k.a solar, system. If you are interested in installing a PV system to replace some of the electricity that we provide, we are here to help you by providing information and answering questions. We want to give you the tools you need to make an informed decision about a PV system
Before you decide to buy a PV system, however, you should examine the economics to determine whether such a system will lower your monthly electricity costs. The Energy Matters Web site—http://www.solar-estimate.org—can help you determine the annual operating cost of a PV system.
Ten Steps to a PV System
Is a PV system right for you? These 10 steps will help you decide.
1. Determine how much electricity you use and what it costs, both annually and by the kilowatt-hour. Then find ways to make your home more efficient and reduce your energy use.
A home energy analysis is a good place to start. It does not make sense to spend a significant amount of money on a PV system that will produce electricity to power an inefficient home.
Upon your request, one of our trained energy auditors will conduct a free energy audit of your home to identify ways of using energy more efficiently and reducing energy use. Implementing energy efficiency opportunities will almost always speed up the rate of return on your PV investment. Energy efficiency may also enhance the viability of a PV system project by giving you the lower capital expense associated with a smaller system that will satisfy the new lower energy load.
2. Determine your solar resource.
The solar resource is the average amount of sunlight that reaches a given site. The greater the solar resource, the more electricity a PV system will generate.
A qualified PV installer can provide information on your solar resource. Alternatively, you can evaluate it using an online tool, such as PVWATTS Version 1 from the National Renewable Energy Laboratory, available at http://pvwatts.nrel.gov/
Several site conditions can influence PV performance—shade, roof condition, space required, orientation, and tilt. Of these, shade is likely to have a greater impact on PV system performance.
A qualified PV installer can use software tools to assess the degree of shading a proposed array will experience throughout the year and determine the best PV design.
3. Determine your site’s suitability.
If your PV system is to be roof-mounted, the condition of the roof is important. The cost of repairs or a complete re-roofing will be substantially greater once the PV array is in place.
Another consideration is the space available for an array sized to meet your needs. In bright sunlight, a square foot of a PV module will produce approximately 10 watts of electricity. That’s a helpful rule of thumb for estimating how much area you will need. A 1,000 watt (1 kW) PV system, for example, is likely to need 100–200 square feet of area, depending on the type of module used.
PV modules should be oriented geographically to maximize the amount of daily and seasonal solar energy. In general, the optimal orientation for a PV module in the northern hemisphere is true south. However, your modules can face up to 45° east or west of true south without significantly decreasing their performance.
Most PV modules are mounted flat on the roof and so have the same tilt as the roof. The optimal tilt angle for maximizing annual energy production of PV modules is an angle equal to your latitude. Because most roofs are pitched at an angle less than the latitude, you and your installer will need to factor your roof angle into the performance calculations when sizing your system. Some roof-mounted systems can be adjusted for the sun’s higher position in the sky in the summer and lower position in the winter.
Although most PV systems are roof-mounted, pole- and ground-mounting also are options. Both have more opportunities for incorporating tracking to maximize electricity production than do roof-mounted systems. A tracking device can increase the output by 25–40% over a stationary-mounted system. In addition, a pole-mounted system can be located far from shading and the array can be tilted and oriented in the best position. However, adjusting the tilt of a pole-mounted array for summer and winter sun may require at least two people.
Talk with a qualified PV installer about the best mounting option for your site.
4. Determine the size of the PV system.
Realistically, the size of your system is likely to be determined more by cost than by desired output. It makes sense, however, to estimate the amount of electricity that you want your PV system to produce. If cost is a constraint, the system could be installed in phases.
You can ask your PV installer to help determine the size of your system. You also can begin by calculating your electricity usage and the annual average peak solar hours at your site. A peak sun hour is the average amount of sunlight—summer and winter—available at your site. The National Renewable Energy Lab (NREL) publishes solar radiation resource maps that provide data on peak sun hours at http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/.
Divide your annual electricity usage (in kWh) by the number of peak sun hours to determine the wattage needed for your system.
Alternatively, you can calculate your average daily electricity usage (in kWh) and refer to a chart that estimates the system size needed to reduce your electricity use by 25%, 50%, 75%, or 100%. See http://www.thesolarenergycompany.com/images/sizingPV/SizingChart.pdf for more information.
DOE provides an estimate of the area needed for variously sized PV systems—including 1 kw, 2 kw, 4 kw, and 10 kw systems—for various module efficiency, available at http://www.energysavers.gov/your_home/electricity/index.cfm/mytopic=10840.
5. Find out what incentives—rebates, tax credits, and loans—are available.
The Emergency Economic Stabilization Act of 2008 includes a residential solar investment tax credit provision. The provision extends the 30% investment tax credit (ITC) for residential solar property for eight years, through December 31, 2016. The provision also removes the cap on qualified solar electric property expenditures (previously $2,000) for a system placed in service after December 31, 2008.
The Database of State Incentives for Renewables & Efficiency (DSIRE) provides detailed information on each state’s incentives that apply to renewable energy systems, including PV. You can access the database at http://www.dsireusa.org.
6. Determine the estimated installed cost of the system and calculate return on investment.
PV systems are rated in kilowatts of DC generating capacity (kWdc), and tend to range in size from less than 1 kw to 10 kw.
For a pole- or ground-mounted PV system, installation costs will be greater than roof-top mounted. In addition, a tracking device on a pole-mounted system will boost the cost of your PV system. You can compare the cost-effectiveness of fixed mount and a single- or dual-axis tracking for your site at http://www.nrel.gov/rredc/pvwatts.
The payback for a PV system is the amount of time it takes for the system to pay for itself in energy savings. Depending on the level of government incentives, the payback period can range from fewer than 10 years to more than 20 years, depending on the cost of the system, the amount of electricity produced, and the retail price of electricity that you buy from Blue Grass Energy.
You can calculate the simple payback of a PV system by using the following formula:
Total of Life Cycle Costs (capital costs + finance costs + O&M costs – federal and state incentives) / Average Value of Energy Generated per Year (kWh generated * cost of power).
In addition, an online calculator is available at http://www.solar-estimate.org.
7. Determine what zoning regulations apply to the installation of a PV system, if any, and what building and electrical permits are required. Talk with your neighbors about your plans.
Local zoning laws may restrict where you can place PV panels on your home. Check with your city or county to find out about any restrictions.
You may need to obtain a building permit to install a PV system. Building and electrical codes also may apply. Contact your local planning and zoning comission or ask your PV installer to include the cost of permits in the cost estimate.
After your PV system is installed, it must be inspected and approved by the local electrical inspector. Inspectors may require your installer to make corrections. A copy of the building permit showing the final inspection sign-off is required to qualify for a net meter from Blue Grass Energy.
8. Review Blue Grass Energy’s interconnection requirements.
If you have not already talked with Blue Grass Energy about your plans, do so now. Discuss the steps you have taken to get to this point and provide information on the PV system you are considering. You need to make sure that the system meets the cooperative’s criteria for interconnection.
A copy of the requirements for interconnection are available by clicking here.
9. Find a PV system installer (if you haven’t already done so).
Using a professional, licensed PV installer is the best way to avoid installation problems with your system. A qualified, experienced installer will design a system that meets your needs and site conditions. The installer also can help you with the paperwork for tax credits and rebates.
Once you have a short list of installers, contact at least two of them for quotes for the equipment and installation. Question any quote that appears to be too high or too low.
10. Contract for installation of your PV system.
Before actually placing an order, ask the installer for the names of consumers who have installed a similar PV system. Contact those consumers to ask about system performance, reliability, and support from the installer. Also ask if the system is meeting their expectations.
Ensure that the PV panel manufacturer offers at least a 20-year limited warranty and the inverter manufacturer offers a five-year limited warranty. The panels and inverter should be Underwriters Laboratories (UL) listed. Also ask the installer about a warranty for the work.
Questions to Ask PV Installers
Members interested in installing a PV system should ask installers or contractors the following questions:
1. What are your credentials? How long have you been in business? How many grid-connected PV systems have you installed?
Look for installers that have been in business for at least five years. Installers certified by NABCEP must pass a rigorous examination and demonstrate that they possess a high degree of experience or education related to PV system design and installation.
In addition, you should ask the installer for a portfolio of recent residential projects and the names of at least two people who have had a PV system installed that is the same as, or similar to, the one you are considering.
2. What is the estimated total installed cost? What do the panels cost? What does the inverter cost? What is the estimated installation cost?
It is important to know the total installed cost of a PV system to ensure sufficient budgeting. Budget for installation labor expenses, as well as the cost of equipment rental, construction materials, electrical components, shipping, and sales tax.
3. How long is the warranty? What does it cover? Parts? Labor? Can it be extended? If so, what will it cost?
The PV panel manufacturer should offer a 25-year warranty for crystalline modules and 20 years for thin films. Warranties for inverters should be for five years. Make sure the warranty covers all aspects of the removal, shipping, repair, and reinstallation of components. Members should ask owners of PV systems purchased from the same installer about performance and reliability before making a decision on an extended warranty, if it is available.
4. Are the PV panels and inverter UL-listed?
Both the PV panels and the inverter should be UL-listed.
5. If the system is to be roof-mounted, how will the installer mount it?
The performance of PV panels mounted flush on the roof will decrease during the winter if the roof is at a shallow pitch. Some installers may address this issue by adding one or two panels to the array. While the additional panels will compensate for the decreased winter performance, they also will significantly increase heat gain during the summer, reducing output.
Consumers may wish to consider alternatives, such as mounting panels at a greater angle on the roof or mounting the array on the ground or a pole.
6. What are the advantages and disadvantages of adjustable rack mounts and tracking devices?
Adjustable rack mounts—both ground and roof—can be repositioned seasonally to optimize energy output, but they will increase the cost of a PV system. Members should ask the installer to estimate the improved performance of a system with adjustable rack mounts and then weigh the higher output against the increased cost.
Tracking devices—PV mounting devices that follow the sun—can increase the output of a PV system by 25% to 40%, compared with a fixed-mounted array. They are either electrically or thermally operated and usually are mounted on a pole. Trackers are most effective at sites with dawn-to-dusk sun, and provide a great increase in output in the summer. Because of their moving parts, trackers may require increased maintenance.
Although trackers increase the cost of a PV system, the total cost of a tracked system may be less than that of a fixed system because a smaller tracked system can produce more electricity. For example, a 3 kW tracked system can produce as much electricity as a 4 kW fixed system. The higher output of a tracked system makes it possible to scale down the size of the PV system.