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Solar Panels on Garage Roof
 

Frequent Questions

Have questions about solar power? Here are the questions we are most often asked about solar power systems for homes, businesses and institutions. Click on a question to read the answer. Clicking again hides the answer. If you don’t see your question answered here, please send us an email with your question and we’ll get back to you with an answer. We try to answer all questions within 24 hours.

How does a solar power system work?

Solar power panels contain the same material—silicon—used in computer chips. Silicon wafers with special electrical characteristics are assembled in layers, into photovoltaic cells that produce electric current when exposed to sunlight.

Solar panels produce direct current. The lights, appliances and electronics in your home use alternating current. So a device called an inverter turns the direct current into alternating current before it is fed into your electric service panel. A solar power system can have either a single central inverter or several small microinverters.

Whenever your home’s power consumption is less than the amount of electricity your solar power system is producing at that instant, the excess electricity is fed through a special two-way meter back to the utility’s electric power grid. A special utility billing program called net metering credits you for this excess solar electricity production.

Do solar panels produce electricity in cloudy weather?

Yes. Solar panels can produce significant amounts of energy even on overcast days. If you have ever received a sunburn at the beach on a cloudy day, you know that plenty of solar energy is still available even when it’s cloudy.

Our solar power system design and estimating software uses several years of weather data to estimate a system’s electricity production. So for each month, several years of actual cloud cover and rain data are automatically factored into our estimates.

How much does a typical home solar power system cost?

We have a page on this website that dicusses home solar power system prices and factors that can affect a system’s installed price.

Should I lease or buy my solar power system?

We are not big fans of home solar power leasing. Here’s why:

Solar power lease payments increase just like utility electric rates.  Home solar power system leases typically run for 20 years and have escalator clauses that increase the lease payments each year. The most common annual escalator is 2.99%. At a 2.99% annual increase, a solar power system lease payment payment will be 75% higher in the 20th year than the first year. If you buy your system with our solar loan financing, the payment stays the same every year for the life of the loan.

While history suggests that electric rates will increase by more than 3% per year, on average over the next 20 years, we still think this is a lousy deal. A prospective buyer of your home may feel the same way.

Somebody else gets the solar tax credit.  When you lease a solar power system, you don’t get the 30% solar tax credit. The leasing company’s investors do. This usually allows a lease to provide better cash flow than a loan financed purchase over the first few years, but giving the tax credit to the homeowner makes the purchase a much better deal over the long run. And of course, the loan payments don’t increase each year.

A leased home solar power system can make selling your home more difficult.  A leased home solar power system is usually encumbered by a security interest in the solar power equipment. The security interest is documented by filing a Form UCC-1 financing statement in the public records. While a UCC-1 filing doesn’t create a security interest in your home—like a mortgage does—mortgage lenders and title insurance underwriters usually treat it as a lien anyway. This can complicate or delay a closing, and you could be required to pay off the balance of a 20-year solar power lease to save a pending sale of your home, if the buyer is unwilling or unable to assume the solar power lease.

Our solar power system loans are unsecured, so a purchased solar power system won’t impact the sale of your home. And of course, if a solar power system is included in a mortgage loan, it will just get paid off with the mortgage at closing.

Our most popular home solar power loan financing has a 12-year term. If you buy your solar power system and then sell your home before the loan term is up, you can choose to either pay off the loan out of the house closing proceeds, or just pocket any increase in resale value from the solar power system and keep making monthly payments on the unsecured loan. It’s your choice.

What if I sell my home?

Independent studies show that homes with solar power systems can sell more than twice as fast as homes in the same community without solar power. Also, your home will be worth much more for a simple common sense reason: It will have significantly lower utility electric bills than a similar home without solar power.

In the largest research study to date, researchers from the U.S. Department of Energy’s Berkeley National Laboratory found that for home sales outside of California, a solar power system added about $3,100 per kilowatt of system size to a home’s resale value.

One bit of caution, though: Leased solar power systems will not produce similar results. (see the question on leasing above for more on this topic.) We think you’re much better off buying your solar power system using zero down payment, low interest financing.

What is the environmental benefit of a solar power system?

One home solar power system delivers an enormous environmental benefit. According to the U.S. Energy Information Administration, about two pounds of atmospheric carbon dioxide are created for each kilowatt-hour of electricity generated by a coal-fired powerplant. Natural gas-fired powerplants burn clearner, but still create 1.22 pounds of atmospheric carbon dioxide for each kilowatt-hour.1 While solar panel efficiencies and roof orientations vary, a typical 285 to 320 watt solar panel installed on a Florida roof will produce 30 to 42 kilowatt-hours of net usable electricty during an average month. Let’s just use 35 kilowatt-hours, which works out to 420 kilowatt-hours per year.

So a home solar power system with, say, 32 solar panels, would produce about 13,440 kilowatt-hours of electricity. For a coal-fired powerplant, this would avoid about 26,880 pounds (over 13 tons) of atmospheric carbon dioxide each year. For a natural gas-fired powerplant, 16,396 pounds (over eight tons) of atmospheric carbon dioxide would be avoided annually.

It’s hard to wrap your head around eight to 13 tons of atmospheric carbon dioxide. So try this comparison: eight to 13 tons is roughly the combined weight of four to seven midsize American cars. Not the exhaust from four to seven cars… the weight of the cars themselves.2

The example system above would produce enough solar electricity to avoid 1.14 million pounds (over 568 tons) of atmospheric carbon dioxide over the 50 year expected service life of the solar panels. Incidentally, this calculation assumes that the panels lose about 0.7% (seven-tenths of one percent) of their energy output every year, over the 50 year period.

So does installing a single home solar power system deliver a meaningful environmental benefit? You bet it does.

Is my home a good candidate for solar power?

Probably. Most homes can benefit from solar power. The percentage of your utility electric bill that can be eliminated by a solar power system depends upon a variety of factors, including:

Tree shade.  A nearby tree or trees may shade your best roof locations for solar panels during the peak sun hours. Of course, it is possible to trim back or remove a tree so long as it is on your property. Also, depending upon property line setbacks in your community, a two-story roof next door can sometimes shade areas of an adjacent one story roof.

Directions your roof areas face.  South is best; southeast and southwest are very good; east and west are good; and north-northeast and north-northwest are acceptable. North is poor. North-facing panels installed in North America do not perform well during the winter months.

Available roof area.  Generally speaking, in Florida, offsetting 1,000 kilowatt-hours of average monthly electric power consumption takes 25 to 33 solar panels, with each taking up about 18 square feet of sun-facing roof area. That’s about 450 to 600 square feet of roof area. The difference in number of panels needed—and coverage area—depends mostly upon the direction the panels will face. Also, the solar panels are rectangular, so not all of the surface area on a hip style roof area is usable.

Roof obstructions.  Plumbing, clothes dryer and bathroom exhaust vents, attic ridge vents and fireplace chimneys can reduce the area roof available for installing solar panels.

We can answer most of these questions with satellite and aerial imagery of your home, which is input into our design software to custom design a solar power system for your roof, energy use and shade conditions. Once we have a preliminary system design and electricity production estimate, one of our solar advisors can work with you to answer your questions and explain your financing options.

Get a free solar power quote for your home.

 

How will solar panels look on my roof?

Usually fantastic. But very honestly, a lot depends on the solar panel model you choose and the layout of your solar panels. The most attractive solar power systems employ all-black panels—like the panels in the photo above, which present a beautiful, uniform appearance. All-black solar panels eliminate the “checkerboard” look of older solar panels, which had silver frames and blue photovoltaic cells with white backsheets (a white backsheet appears as a white border around a solar panel’s individual solar cells, resulting in the checkerboard appearance).

Also, any solar panels that will be visible from the street should be arranged in a clean rectangle, or follow the contours of a hip style roof. While independent studies show that solar power systems typically recover their net replacement cost when a home is sold, an unprofessional layout could negatively impact your resale value.

And a word of caution. Some solar contractors may offer you a front and side “trim option” that supposedly improves the appearance of a bank of solar panels by closing off the three to four inch gap between the roof surface and the solar panels. We believe this trim option has the potential to reduce solar panel performance.

Why? For solar power panels, heat is the enemy of efficiency. Hotter panels produce less electricity. Closing off the air space between the roof and the front and sides of a solar panel bank will increase panel operating temperatures, by reducing free air circulation underneath the solar panels.

I’ve been hearing about solar panels that look like roof tiles. Should I wait for these to become available for my roof?

We do not recommend solar roof tiles at this time, for the following reasons:

Higher cost.  Solar roof shingles—also known as building integrated photovoltaic (BIPV) solar products—have a higher installed cost per peak kilowatt of power output than solar panels that install above the roof surface. Part of this is the more exotic nature of the materials used in these products, and part is historically higher installation labor costs.

Lower operating efficiency.  Solar roof shingles are less efficient than solar panels that are raised slightly above a roof surface for two reasons. First, they operate at higher temperatures because they are part of the roof structure and cannot be cooled by air flow underneath the panels. As noted in the answer to the preceding question, heat is the enemy of solar panel efficiency.

Second, the efficiency of solar roof shingles is reduced by the color tinting that allows solar shingles to look like regular roof shingles. Unfortunately, this tinting increases the reflection of light off the solar cells, so less solar energy is absorbed.

More potential failure points.  While solar roof shingle manufacturers typically prefabricate their indivudal “shingles” into sheets of a couple dozen shingles each, these sheets are still only a third to half the size of today’s solar panels.3 This means two two three times more connections, and two to three times more potential points of failure.

Can my homeowners association stop me from installing a solar power system on my roof?

No. Your homeowners association has a right to review and approve any improvment that will change the exterior appearance of your home. However, Florida law forbids any government or association from denying approval for the installation of a solar energy device. This website has a page that discusses the Florida Solar Rights Law in detail.

Homeowners associations often try to limit the visibility of solar panels from the street. But as a practical matter, they are usually not able to dictate changes to a proposed solar power system roof layout. This is because the solar contractor will locate the solar panel array(s) on roof areas that face as close to south as possible, to maximize solar electricity production. Requiring that a proposed location of solar panels be changed to another roof area that faces farther away from due south will usually violate Florida law.

What is net metering?

Net metering is a utility billing program mandated by law that credits rooftop solar power system owners for excess solar electricity fed back to the utility’s electric power grid. A special bi-directional meter runs backwards when solar electricity is fed back to the grid. Rooftop solar power system owners receive credit on their monthly electric bills for this excess power.

Reverse electricity flow occurs whenever a solar power system produces more solar electricity than a home is using at that instant. For example, many homes use less power during the middle of the day—when solar power output is greatest—because the adult occupants are at work and any children are at school or daycare.

Net metering credit is often not significant for commercial and industrial utility customers because a close correspondence exists, on a time of day basis, between solar power generation and electric power consumption.

Net metering programs promote the expansion of clean and renewable solar power. Also, rooftop solar power systems help reduce utility peak loads on hot summer afternoons and clear sky, very cold winter days—and the inflated prices that utilities must pay to purchase extra power from third party generators during these periods. Florida’s summer heat waves and clear sky, very cold winter days tend to coincide with high solar power system output.

By encouraging distributed generation—electricity generation at the point of consumption—net metering also reduces the strain on distribution systems and reduces losses in long-distance electricity transmission.

Will I save less if my electric utility company reduces the price I am credited for net metered electricity?

No. It doesn’t really matter how much an electric utility company pays for net metered electricity, so long as a rooftop solar power system is properly sized. This is a commonly misunderstood issue, so let us explain.

Florida Administrative Code Rule 25-6.065, “Interconnection and Metering of Customer-Owned Renewable Generation,” requires that calculations of net electricity purchased by a rooftop solar power system owner be based upon electricity consumption and not price per kilowatt-hour. The issuance of any net financial credit only occurs once each year, at the end of the calendar year.

If a rooftop solar power system is right-sized to provide net solar electricity production that does not exceed 100% of a home’s electricity consumption over the course of a year, the excess solar electricity production at each calendar year-end will be near zero. So the amount of the dollar credit per kilowatt-hour paid for excess solar electricity production at year-end doesn’t really matter.

Are the credits on my electric bill for solar electricity sent back to the grid considered taxable income?

No. With net metering, you are simply credited for solar electricity you export to the grid, which reduces your net purchases of electricity. You have a lower electric bill expense, not taxable income. It is actually illegal under Florida law to sell electricity to a third party if you are not a regulated utility, so utility net metering contracts expressly avoid language that would characterize the reimbursement for exported solar electricity as a sale.

Do I need my electric utility company’s permission to connect my solar power system to my home’s electric meter?

Yes. We’ll help you with this process. Your utility will require that you enter into a net metering agreement that specifies, among other things, equipment specifications, safety rules for wiring and equipment, and an explanation of the utility’s policy for crediting you for electric power fed back to the grid from your solar power system. You will also receive either a new bi-directional meter or a second meter capable of tracking the electricity your system feeds back to the power grid.

Will I have solar electricity if I lose power during a blackout?

No. We install grid-tied solar power systems. A grid-tied system is connected to your local electric utility through a two-way electric meter. This allows you to feed excess solar electricity production back to the utility power grid, for credit on your electric bill. A grid-tied system also allows you to automatically switch to utility-supplied electricity at night and during rainy and very cloudy weather.

For safety reasons, the microinverters in our grid-tied solar power systems are designed to automatically shut down during power outages. The safety concern is that solar electricity flowing back to the utility grid during a power outage could injure utility workers.

Can my solar power system include batteries for power storage?

Yes. We expect to begin offering battery power storage systems soon. Once available, these systems can be easily added to any of our existing customers’ systems.

It’s important to understand that battery storage in a grid-tied solar power system is designed to store solar electricity produced during the day for overnight use. The system is designed to eliminate or significantly reduce reliance on utility net metering. It is not designed to provide emergency backup power.

How many solar panels does it take to charge an electric car?

Today’s electric cars average about 3 miles per kilowatt-hour of power consumed. For average mileage of 12,000 to 15,000 miles per year, this works out to 333 to 400 kilowatt-hours per month. If an electric car is used primarily for commuting to work and running local errands, most of the power consumption for charging an electric car’s batteries can be done at home.

In Florida, a south-facing solar power system with about 3 kilowatts of peak rated power output will produce about 350 kilowatt-hours of net usable AC power during an average month. The most common rooftop solar panels today have 285 to 320 watts of peak rated power output per panel. So it takes about 10 solar panels to meet the charging needs of one electric car during an average month.

How long can I expect my solar panels to last?

The useful service life for good quality solar panels is at least 40 to 50 years. Solar photovoltaic (electricity producing) cell technology dates back to the early years of the U.S. space program in the 1960s. SolarWorld solar panels installed here on Earth in the 1970s are still operating in the field after 40 years.

A solar panel’s electricity production falls by about half a percent each year, as it ages. The industry standard 25 year warranty for solar panel electricity production warrants that performance losses will not be more than 0.7% (seven tenths of one percent) per year. A solar panel that loses 0.7% of its performance each year will still produce about 84% of its first year performance in the 25th year. And about 71% in the 50th year.

Actually, a system’s inverter(s) will need to be replaced before the solar panels. If you purchase a system with a central inverter, the inverter will likely require replacement at 10–14 years. We only use microinverters in home solar power systems. A microinverter is a small solid state device installed behind each solar panel. Microinverters operate at much lower voltages than central inverters, so their components are subjected to far less stress. The current generation of best-in-class Enphase microinverters come with a 25-year warranty.

How will I know how much electricity my solar power system is producing?

Each of our solar power systems includes a subscription for online monitoring and a wireless phone app, so you will always be able to check and see how much electricity your system is producing. And because our solar power systems have a smart microinverter paired with each solar panel, the app can also show you how each solar panel is performing. The app will show if any of your solar panels or microinverters are not working properly.

What sort of maintenance does a solar power system require?

A solar power system’s performance should be monitored periodically (see the previous question) but should not need any maintenance other than keeping the panels clean (see the next question).

Systems with microinverters have no moving parts, which is one of many reasons why we prefer microinverters over central inverters. The solar panel brands and Enphase microinverters we install carry 25 year warranties. One of our manufacturers (SolarWorld) has solar panels that were installed in the field over 40 years ago and are still operating within warranty performance standards today.

How often should I clean my solar panels? And what is the best way to clean them?

You may find online recommendations that solar panels be cleaned every two or three months. While this may make sense for solar panels in locales with dry climates and more airborne dust, Florida usually has enough rainfall throughout the year to keep tilted solar panels relatively clean.

You should only clean your solar panels (or have them cleaned) if dirt, pollen, bird droppings, oily residues, leaves or other debris are clearly visible on the panels. If not, rainfall is probably doing an adequate job. In neighborhoods with lots of trees, cleaning solar panels after the spring pollen season is a good idea.

Google’s solar panel cleaning study.  Google published a 2009 study on the performance of a 1.6 megawatt solar power system installed at the company’s headquarters campus in Mountain View, California. Two of the system’s arrays were located a short distance downwind from an unplanted agricultural field that was tilled on a monthly basis. Electricity production from these two arrays doubled after the first professional cleaning. After a second cleaning eight months later, production increased by 36%. Electricity production for the system’s other arrays, which were not exposed to unusual levels of airborne particulates, increased by 12% after professional cleaning.

How to clean solar panels.  Cleaning solar panels involves safety risks. We recommend that you use a professional service that specializes in cleaning solar panels and has both liability and workers compensation insurance. If you decide to do the cleaning yourself, here are some tips:

  • Wear rubber gloves and rubber soled shoes.
  • Never stand, sit or walk on the solar panels.
  • Never touch the solar panels, racks or power cables with any part of your body.
  • Try to clean the solar panels when the roof is cool, in the early morning or late afternoonon, or on a cloudy or overcast day. Starting early on a morning with dew on the panels is best, as any dirt and grime will be loosened by the overnight moisture.
  • Work from the ground with a telescoping pole. Special water-fed, telescoping poles are available online.
  • If you must work from a ladder, or a scaffold against the side of the house, move the ladder or scaffold often enough so you don’t need to stretch to reach any panels.
  • Use a brush with soft bristles, and a soft rubber squeegee.
  • Do not pressure wash solar panels.
  • Do not use soaps, detergents or abrasive cleaners to clean solar panels. Just water.
  • Do not use hard objects to remove caked pollen, bird droppings or dirt. Any scratches on the panels will reduce performance.
  • Hard water can leave mineral deposits on the panels, which can shade the PV cells and reduce performance. Softened or distilled water is best.
  • Rake the panels with a soft rubber squeegee after cleaning.

Which is better, a central inverter system or a system with a microinverter for each solar panel?

We believe microinverters are superior to central inverters for several reasons:

Safety.  Alternating current is generally safer than direct current. Microinverters send alternating current from the solar panels to your home’s electric service panel (the panel—usually in the garage—with the circuit breakers). In a central inverter system, 600 to 1,000 volts of direct current can flow from the solar panels to a central inverter. In addition to the increased personal safety risk, if damage or improper installation results in an electrical arc fault in a solar power system’s wiring, the fire hazard is far greater in a central inverter system than in a microinverter system.

No single point of failure.  In a central inverter system, strings of solar panels are wired in series. This can give rise to the “Christmas tree light effect,” where the failure of one solar panel affects all the others in the string. Similarly, a problem with the central inverter affects the entire system. In a microinverter system, each solar panel and microinverter pair is wired in parallel with the rest of a string. A problem in one solar panel or microinverter does not reduce the performance of the rest of the string.

Greater power production.  Because the solar panels in a central inverter system are wired in series, each solar panel in a string can only perform as well as the worst performing panel in the string. An under-performing PV cell (each panel has 60 to 72 cells), partial shade from a tree or a cloud passing overhead, dust, bird droppings, leaves or debris on one solar panel negatively impacts the entire string. Also, a central inverter typically needs a certain minimum amount of power input to function, which can reduce performance in low light conditions.

Microinverters are wired in parallel, so each solar panel operates independently. This also increases system performance during low light conditions (early morning and late afternoon) and on cloudy days. And our best-in-class Enphase microinverters have a special burst mode that allows them to store energy in low and intermittent light conditions, then send the stored energy in bursts that maximize total energy production.

Longer service life.  Central inverters operate at much higher voltages than microinverters. This means much higher temperatures and greater stresses. Consequently, the typical service life of a central inverter is just 10 to 14 years. Microinverters typically operate at a maximum voltage of 50 volts or less. As a result, they experience less overall stress and don’t need cooling fans (moving parts that can fail over time).

The current generation of best-in-class microinverters are all solid state, with no moving parts, and should last 25 years or more. A microinverter system is a bit more expensive than a central inverter system, but offers a better return on investment when greater power production and longer service life are considered.

I just received a written estimate for a new solar power system. The solar panels specified in the estimate have a higher wattage rating than the microinverters. Won’t this waste power, or harm the microinverters?

No. And no. Oversizing is a good thing, up to a point. Here’s why:

Heat is the enemy of photovoltaic (electricity producing) solar panel efficiency. In warm climates, solar panels only produce electricity at peak output for a few hours a year. In Florida, this usually occurs during the early spring months, when relatively high available solar energy coincides with cooler air temperatures.

During the few hours each year when the solar panels produce more power than the microinverters can process, the microinverters only accept the amount they can process. This power limiting function is called clipping.

But even after taking clipping into account, a solar power system in a warm climate will deliver more net usable power on an annual basis if the panels are oversized, relative to microinverter rated power capacity. This is true up to a panel nameplate wattage to microinverter output wattage ratio of about 1.40.4 As a practical matter, we usually oversize solar panel DC peak output to microinverter AC rated output by 14% to 20%. These percentages have more to do with the wattage ratings of the specific solar panel and microinverter model pairings we use than any sizing rule or formula.

Our solar power system design software uses performance specifications for specific solar panel and microinverter models, so any clipping effects are taken into account and reflected in our written solar electricity production estimates.

Your photos show solar panels that follow the contour of the roof slope. Wouldn’t it be better in some cases to tilt the panels up from the roof, or face the panels south on a roof that faces a different direction?

No, for four reasons:

Less attractive.  Solar panels look best when the panels follow the contour of a sloped roof. You should recover the net replacement cost of your solar power system (i.e., the cost after the tax credit) if you sell your home, but appearance matters. It’s best to stick with a solar panel installation that follows the contours of your roof.

Increased system cost.  Placing solar panels on racks that tilt the panels up from the roof increases cost. The cost increase is significant in Florida, where raised racks must be strong enough to meet hurricane wind load requirements. Anything that increases a system’s cost can potentially reduce the net economic benefit.

Small performance gain.  The performance gain achieved by increasing the tilt of solar panels is quite small. Tilting panels up off the roof surface in the same direction they are already facing makes very little difference in performance.

Less efficient use of roof space.  Most home solar power systems have more than one row of panels. Ideally, the rows almost touch each other so more panels can fit into a given roof area, and for aesthetic appeal. In this scenario, raising the first row of solar panels will shade the second row; raising the second row will shade the third row; and so on. So the spacing between rows needs to be increased, which reduces the number of panels that can be installed within a given roof area. The performance gains from increasing the panel tilt will never offset the performance losses from fitting fewer panels within the same roof area.

Incidentally, when installing solar panels on a limited surface area of flat roof, it’s usually best to have more panels at a lower tilt angle, with less spacing between rows, than fewer panels at an ideal tilt angle. We tilt the panels just enough so rainwater can rinse the panels and allow them to drain. A tilt angle of 10° to 15° is usually sufficient.

Get a free solar power quote for your home.

 

Notes

  1. The atmospheric carbon dioxide produced by burning coal and natural gas actually weighs more than the carbon waste from the original fuel because two oxygen atoms in the atmosphere bond to each carbon atom. The end result is that a molecule of atmospheric CO2 weighs 3.67 times more than a molecule of carbon exhaust from a powerplant smokestack.
  2. A midsize American car is generally considered to have a curb weight between 3,000 and 4,000 pounds. We’ve assumed 3,500 pounds in our comparison above.
  3. The size of today’s solar panels—about 40 x 65 inches—is designed to make the panels as large as possible while still allowing safe handling by a single installation technician. Solar roof shingle sheets the same size as today’s solar panels would be problematic because—with less stiffness than a solar panel—they would be subject to unacceptable twisting and potential damage during handling and installation.
  4. Enphase, the leading microinverter manufacturer, studied the clipping issue and found that in warm weather regions like Florida and Southern California, rated solar panel peak output could exceed microinverter input power capacity by up to about 40% (a DC-to-AC power ratio of 1.40)before power losses from clipping surpassed the power gains from oversizing.