Solar & Renewable Energy FAQs

Q: Do PV modules store energy from the sun?
A: The electricity generated by your system is used directly by your home when it is produced. Power generated in excess of a home's requirements is sent out to the utility grid, turning the meter backwards.

Q: What can a solar system power?
A: The electricity generated by a PV system is used to power any items plugged into your home's electrical service. Solar systems do not provide power for a single device, but instead offset the total sum of your electricity usage.

Q: In what way is an estimate made of the cost of a solar electric system for a home or business?
A: Analyzing recent utility bills are the first step. This determines how much electricity is consumed per month (measured in kilowatt-hours) and on an annual basis (multiplying monthly consumption by 12). Then, specific issues that are unique such as available roof area and shading are factored in. With this information, calculations provide the system and dollar investment required to produce as much as 100% or as little as 20% of electrical power needs.

Q: How efficient are solar panels? How much power can they produce per square foot?
A: Commonly used solar modules often have efficiencies ranging from 11%-14% and produce about 10-13 watts per square foot. New modules are on the market that attain 20% efficiency. In general, the price per watt rises significantly with increasing panel efficiency. So, even though efficiencies can reach up to 30% or more, the cost is prohibitive.

Q: How many solar PV modules are needed?
A: The number of PV modules needed depends on the amount of solar radiation available at your site and the site's energy demand.

Q: How much roof space is needed?
A: A rule of thumb is 100 sq. ft. per every kilowatt (kW) of electricity the PV system produces. Module efficiency correlates with the power that is generated in a given amount of roof space. For basic planning purposes, a good rule of thumb is 10-12 watts per square foot. A typical solar electric system for a home will require approximately 200-400 square feet.

Q: What is the size of a typical solar electric system?
A: Averages are not a good way of sizing a solar system for a specific home or business. Sizing a solar PV system involves consideration of three factors: 1) project budget, 2) electricity requirements, and 3) available sunny space for the modules.

Q: Can the cost of a solar system be determined based on the square footage of a home?
A: A rule of thumb shows it can cost about $10 per square foot (house size) to supply 100% of electrical needs. But, again, rules of thumb are just good estimates designed to fit all situations. It is best to consider all aspects and plan and design a system based on a specific site, its energy needs, and budget.

Q: How are PVs modules attached to the roof?
A: A racking (mounting) system is made from anodized aluminum and stainless steel. The system attaches directly to the roof rafters. Sealant is used to provide a waterproof penetration. Q. What is the weight of a PV module rooftop array? A. Solar electric systems are light--a system weighs approximately 2.5-3 pounds per square foot including modules, racking, and hardware. Most roof structures can handle the additional weight of a solar system.

Q: Installation time…how long?
A: Typically it takes 2-3 days for installation of a 3 kW system (the typical residential solar system size). With rebate paperwork, utility interconnection agreements, permits etc., total turn around time is 4-6 weeks.

Q: What's an inverter?
A: An inverter converts the DC (direct current) power produced by solar PV modules to household AC (alternating current) power. Manufacturers provide warranties of 7-10 years for inverters.

Q: What is the difference between grid-tied, on-grid, and a utility interactive system?
A: Nothing. They are synonymous. These terms refer to solar PV systems that are connected to the utility grid and both produce power that is fed into the grid as well as consume power from the grid.

Q: A roof receives sun for most of the day-is it be adequate for a solar system?
A: Though a roof gets sun for most of the day, it may or may not be enough to make a solar electric installation cost-effective. The optimal sun "window" is six to eight hours of direct sunlight or approximately 9 a.m. to 4 p.m. A site evaluation can determine this. If there is not full access to the sun, on a year-round basis, it will likely take longer for the system to pay for itself.

Q: If the utility power goes out, will the solar electric system continue to produce electricity?
A: No, if the power goes out, the electricity will be off. While there are storage solutions (batteries), the cost combined with their short lifespan and maintenance requirements makes them less of a solution. Unless you're off the grid, storage rarely make sense.

Q: How long do solar electric systems last?
A: Most solar PV modules have a 20-25 year power output guarantee and many are expected to last 40+ years. The power output guarantee provided by the manufacturer typically states at the end of the 25th year, the output will be a minimum of 80% of the original.

Q: What is the optimum angle for the PV modules?
A: The tilt from the horizontal is equal to the latitude of the site.

Q: What is the orientation (compass direction) for the PV modules?
A: True south.

Q: If the modules are installed at less than optimum angle or orientation, what is the performance penalty?
A: The performance penalty will vary with deviations from either of the optimals. That said, those penalties are usually minimal, especially if the deviations are not excessive. Local climate and environmental considerations play a part, too. Modeling the actual deviations can predicate the exact performance penalties. Q. Is it necessary or desirable to adjust the tilt of the PV module to increase seasonal performance? A. Tilting is not necessary. The systems are designed to be low maintenance. The tilt is fixed.

Q: What is the voltage of a typical solar PV module?
A: It's module dependent. A single module usually has an operating voltage between 20 and 60 volts. When the modules are wired together in a high voltage series string they will have a voltages between 200 & 400 volts DC.

Q: Is there any need to rewire a house before or after installing a solar system?
A: No. Grid tie systems feed into a circuit breaker in the main service panel. That is the only point of connection.

Q: Will solar affect the value of my house?
A: According to one study, solar can add $20 of home value for every $1 of yearly energy cost savings. For more information about how solar can increase your home's value, visit: www.irecusa.org/articles/static/1/binaries/wfnews.pdf.

Q: Are tax credits available?
A: Yes, there are state and federal tax credits. The federal government currently offers a $2,000 tax credit the first year of purchasing a solar system. For more information see the Rebates & Credits page.

Q: Are rebates available?
A: The Solar*Rewards Program, run by Xcel Energy is currently at $4.50 per DC Watt for systems up to 10 kW. For systems larger than 10kW, Xcel Energy can provide details. Other utilities in the state offer rebates. Click here for more on solar rebates.

Q: How can I maximize my solar energy investment?
A: Use electricity as efficiently as possible. Period. Appliance upgrades to EnergyStar-rated models make a big impact. As an example, an EnergyStar refrigerator or clothes washer purchased today uses about half the energy of a standard model just 5 years old. Improvements to a home's lighting, insulation, windows, appliances, etc., all will reduce electrical demand. Energy efficiency improvements are clearly the low hanging fruit. They are also the most effective way to make a difference: economically and environmentally. Consequently, if you then decide to install a solar electric system, that system will be able to offset a larger percentage (maybe even all!) of your home's electricity consumption.

Q: How do I know if my system is producing it rated output?
A: Solar electric systems have various monitoring systems: from simple ones viewed on the inverter, to more complex and sophisticated methods available by wireless displays and over the Internet. Calculating system production by using historical sun data from the US NREL (US National Renewable Energy Laboratory) allows for comparisons to actual inverter daily and accumulated production.

Q: What is net-metering?
A: Net-metering measures the difference between the electricity bought from the electric utility the electricity produced by the PV system. Excess electricity produced by the system spins the meter backwards. The meter spins forward when the solar system is not producing all the electricity currently being used. The overall result tracks the "net" difference as electricity is generated and sent to the grid and as electricity is consumed. During times when electricity is actually sold back to the utility, retail credit is typically given. The electric meter may spin backwards and forwards on a daily basis, but billing is only according to the net reading on the meter at the end of each month. Net metering allows you to get retail credit for electricity the solar electric system produces. If more power is produced than is used each month, the credits typically carry over for later use--usually for up to 12 months. At the end of the 12-month billing cycle, and if a credit remains, the utility may pay for the excess power produced.

Q: Why is net-metering important?
A: Net-metering is important because solar energy is intermittent. The power being generated by the PV system may not be used at that time. Net metering allows full value for the electricity produced regardless time of consumption. Net-metering directly affects the economics and payback period for the investment in the system. Net-metering also provides an easily managed means for billing electrical use and crediting electrical production.

Q: How will the weather affect my solar electric system?
A: Solar electric systems are designed to withstand most weather conditions. Lightning, wind up to 90 miles per hour, and extreme temperatures. Clouds and snow most affect the output-but only temporarily. Systems are designed using a data and methods based on the specific site that considers weather conditions as they affect the average annual availability of sunlight.

Q: What's the effect of rain and fog?
A: In fog or heavy clouds systems will still produce about 25-30% of normal. A steady rain cuts production slightly (depending on the cloudiness)-but provides cleaning of the modules that removes dust and other materials that reduce output.

Q: Can solar modules withstand hail?
A: Solar electric panels are built with high-impact tempered glass. Solar industry standards necessitate that panels are able to withstand 3/4" diameter hail at 90 mph. If the solar panels suffer hail damage, typically a homeowner's insurance policy will cover damage but it's always recommended to contact an insurance agent to discuss coverage of solar electric systems.

Q: Will snow cover on the PV modules affect power production?
A: Immediately following a snowstorm, when the PV modules are covered the system production will be minimal. Luckily, PVs are in the perfect spot: where sunshine is greatest. Typically the first area to melt off is where the modules are located. In addition, the modules are tilted and with a surface of smooth glass, snow easily slides off.

Q: What happens when lightning strikes a PV module?
A: The solar electric system is designed to sustain a lightning strike by being adequately grounded under National Electric Code. The NEC stipulates methods to ensure safety, not necessarily survivability. That said, a direct lightening strike will most likely damage some or all of the modules. The remaining equipment and inverter should be OK. Typically a homeowner's insurance policy will cover damage but it's always recommended to contact an insurance agent to discuss coverage of solar electric systems.

Q: What happens if there's a utility power outage?
A: With grid-connected solar electric systems, there will be loss of power when the utility grid is down. This is intentional: when there is an electricity outage, there may be people working on the power lines during or after. If PV systems remained active during an outage, workers would run the risk of being electrocuted.