I am a retired electrical engineer who worked in the solar panel industry for a number of years. There are many thing about solar that are not explained well, or in some cases distorted. I would like to help clarify some of those.
Is solar right for me?.
There is not a simple answer to that question. It depends on many factors, including where you live, the cost of electricity, the availability of electricity, the orientation of your home, and many others.
Resources
Much of the information presented here is based on the "Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors" published by the National Renewable Energy Laboratory (NREL) in Golden Colorado. The information in that document is based on data collected and computer models. The data collected was between -, and conditions may have changed slightly since that time.
Solar Facts
Sunlight varies during the day even if the sky is clear. This is due partly to the amount of atmosphere the light travels through before striking your solar panel. Around mid-day the light is nearly overhead but this does depend on the latitude where you live and the season. At that time, the light absorbed by the atmosphere is minimum. In the early morning and late afternoon the light travels through the atmosphere at an angle and more light is absorbed. When directly overhead, the sunlight intensity is about watts per square meter. That means if you have a solar panel that measures about 40 inches by 40 inches, it will be exposed to approximately watts of sunlight. Double the size of the panel and you will double the power available.
Of course not all that sunlight is useful for producing electricity, and some is lost as heat. Very high grade solar materials used by NASA may have an efficiency or 40%, but normal consumer grade panels usually only are able to convert between 10-20% of the sunlight to useful power. If you have room for more panels on your roof, twice as many 10% efficient panels will produce the same power as a lower number of more efficient panels.
The angle the light strikes your solar panel affects the amount of power it can produce. The maximum power will be produced when the sun is exactly perpendicular to your panel since the light is most intense at that time. Some commercial systems use a tracker to tilt the panels so they always face the sun perpendicular in both vertical and horizontal directions. This does increase the amount of power produced, but the sun angle relative to the atmosphere cannot be overcome. Trackers include one and two axis trackers, one axis only tilts the panels in an East-West direction, while two axis include North-South tilt. Trackers are expensive to purchase, install and maintain, so they are seldom used for residential systems. Most residential solar panels are mounted at a fixed N-S tilt equal to the latitude and facing as near to South as possible. This results in the optimum that can be achieved with a fixed system. Note that most homes do not have steep roofs that are equal to the latitude, and often the roof area facing directly South is only a fraction of the total roof area. As a result installation of solar shingles on a roof will result in less than optimum performance.
Sunlight varies with the season, with a minimum around December 21 and a maximum around June 21 in the northern hemisphere. The further you live from the equator, the more pronounced this effect is. Even though the sun may shine for 12 hours during the day, the effective time is less than that. The NREL document referenced above lists the average amount of light collected in one day in terms of the number of hours of full sunlight equivalent, taking into account the atmosphere and angle factors mentioned above.
The electric company does not sell you Watts of electricity as such. Instead they calculate how many watts you use multiplied by the number of hours. This is normally reported and kWH, i.e. the number of thousands of watts times the number of hours. This is actually a measurement of total energy consumed. The NREL document lists the average available sunlight in the same units, kWH per day.
Here are some examples of the average full sun effective hours per day for various locations in the USA according to the Solar Radiation Manual. The data appear to include cloudy days since the maximum for some areas occurs in months other than June. There is a +/- 9% uncertainty in the values presented.
Daytona Beach, FL Fixed array, tilted to latitude 29 degrees
Average hours per day varies from 4.1 - 6.3 hours per day from month to month, with a yearly average of 5.2 hours per day.
Phoenix, AZ Fixed array, tilted to latitude 33 degrees
Average hours per day varies from 4.9 - 7.5 hours per day from month to month, with a yearly average of 6.5 hours per day.
Topeka, KS Fixed array, tilted to latitude 39 degrees
Average hours per day varies from 3.4 - 6 hours per day from month to month, with a yearly average
of 4.9 hours per day.
Anchorage, AK Fixed array, tilted to latitude 61 degrees
Average hours per day varies from 0.6 – 4.6 hours per day from month to month, with a yearly average
of 3.0 hours per day.
Shading
The effect of shade from nearby trees or buildings is another consideration. If a solar panel is even partially shaded, it will likely reduce the power it can produce by far more than you might expect. This can be overcome to some degree by installing local inverters on each solar panel rather than one big inverter for the entire array. In some cases shading may cause permanent damage to a panel unless it is designed to protect against this.
Rated power of panels
Solar panels are tested and rated for power output at room temperature. As with all semiconductor devices the voltage of each individual solar cell will decrease as the temperature increases (typically 2mV per degree Celsius). A typical solar cell will produce about 400-600 mV, with an average of about 500 mV. When placed in sunlight, a solar panel will rise in temperature by about 20 degrees Celsius above the ambient air temperature. If the outside air temperature is around room temperature, this will cause the voltage to drop by about 40 mV, or around 8% of the room temperature value, reducing the rated power by about 8%. So a solar panel rated for 100 Watts would typically produce about 92 Watts due to the temperature increase. In colder climates the panel will produce much closer to it’s rated power, but this usually occurs in winter when the available sunlight is less. The power will likely be slightly less in summer but then the sunlight is more intense too.
Knowing the average daily full sunlight equivalent and the expected power from a solar panel, we can calculate the expected kWH per day. The yearly average for most locations in the USA is about 5 hours, multiplied by 92 watts (100 watt panel) means you could expect about 460 WH or 0.46 kWH of energy per day for each 100 watt panel. The inverter is somewhat less than 100% efficient, and probably 90-95% efficiency is reasonable, resulting in about 0.425 kWH per day from each 100 watt panel. A typical system might be rated at 3 kW (30 each 100 watt panels), producing about 12.75 kWH of electricity per day averaged over a year.
Check your electric bill to see what you are paying for a kWH of electricity now. This varies widely around the country. I have heard of rates over $0.30 per kWH in California, while I am paying less than $0.10 per kWH through my REA Co-op. You may also be charged extra for peak times of the day. What makes economic sense to one customer may not apply to another.
If you are in an HOA, be sure to check the rules. Some HOA’s take a dim view of solar panels and prohibit them is some cases.
Grid Tied System
Unless you live on a mountain top with no power poles for miles, it is not common to have a battery storage system. Instead most residential users opt for a grid tied system. The idea is to produce more electricity than you need during the daylight hours and sell it back to the power company. At night you will buy the power back, hopefully breaking even at the end of the day. There are some pitfalls to be aware of with this type system.
1. There is no guarantee that the power company will continue buying your power at retail rates in the future. Many solar customers in states like California and Nevada have been blindsided when the power company decides to pay wholesale rates for power you generate and sell it back to you at retail rates. This frequently totally destroys the concept of paying for the system in 10-20 years as advertised when you bought (or worse yet leased) the system.
2. The grid tied system will stop producing power when the power company system goes down due to a downed power line or blown transformer, etc. This is for safety reasons, since it would not be safe for a lineman to be working on a power line that is supposedly dead. A safety switch device is required for all grid tied systems to prevent this hazard.
3. Your power bill will likely not drop to zero even if you produce all the power you need every day. Most power companies charge a monthly service fee just for being connected whether or not you use power. My power company charges $27.50 per month for example.
Myths debunked
Several websites claim to debunk some solar myths, and in some cases they are accurate. In some cases they are a bit misleading; for example claiming solar panels still produce power when it is cloudy. While this is true, they do not tell you that the amount of power produced may be so low as to be almost useless. The fact is half intensity of sunlight produces half the power of full sunlight or perhaps slightly less.
Be cautious of the claim that if you save $ per year on electricity that you will pay for a $30,000 system in 20 years. While the numbers seem to add up, consider what you could earn if you invested the same $30,000 in something that pays interest or dividends such as a CD or mutual fund. The S&P 500 claims to average about 10% per year return over many years. If you invested in an index mutual fund, you could easily average a $ return each year, pay your $ electric bill and have money left over to grow in value. Even a CD paying 5% per year would pay your electric bill, and you would still have the initial investment at the end of 20 years.
Consider the condition and life of your roof. If you need to replace the roof before the solar system wears out, you could incur a significant additional expense to remove the solar panels, replace the roof, and re-install the solar panels.
A solar system will increase the value of your house. I suggest talking to a few realtors to see if this is reality or not. This is especially true if you are considering leasing a system.
Bob Butcher
Throughout the country, residential solar panels have become an increasingly popular option for generating energy for homes. The rising costs of energy across the US, along with falling prices for solar panels, and excellent federal tax incentives, have made solar powers a much more attainable and economically beneficial option for homeowners.
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"If you looked at solar just a few years ago, costs have continued to come down since then," said Ben Delman, communications director at Solar United Neighbors. "It depends on your situation, but more and more homeowners and families are deciding that solar makes sense for them as a way to save money by taking control over where their electricity comes from."
Below, explore CNET's expert advice to get you through the process of purchasing solar panels.
Can solar panels save you money?
Interested in understanding the impact solar can have on your home? Enter some basic information below, and we’ll instantly provide a free estimate of your energy savings.
How do solar panels work?
Buying a solar panel system means buying a lot of equipment the average person doesn't have reason to know about. In the most basic terms, photons from the sun are absorbed by the solar panels and converted into direct current, or DC, electricity. For this energy to be used in American homes, it has to go through an inverter attached to the solar array to become alternating current, or AC, electricity.
Read up on what you'll actually be buying with the stories linked below:
- The Most Efficient Solar Panels
- How Sand Becomes Solar Panels
- Here's How Solar Panels Turn Light Into Power
- How Much Energy Does a Solar Panel Produce?
- What's a Virtual Power Plant? Should You Join One?
- Solar Energy Basics: The Magic of Photovoltaic Panels
- Solar Panel Efficiency: What Is It and Why Is It Important?
- Solar Cell, Module, Panel and Array: What's the Difference?
- The Solar Panel Angle That'll Generate the Most Energy Possible
- What You Need to Know About Solar Inverters: Essential Solar Equipment
- Bifacial Solar Panels Generate More Electricity, but Not When You Put Them Here
Is there a solar panel option that works for me?
Fortunately for the solar-curious, many options exist for homeowners and even renters to get some or most of their electricity needs met with energy from the sun.
The most common way to go solar for homeowners is the installation of panels on their roofs. These systems can be purchased directly through an installer (or assembled for the DIYers) as a large cash purchase or through relatively affordable financing (such as a 1.99% APR 15-year loan). There are also options for rooftop solar for those who may not have the capital to get a project started. These are solar leases, where a homeowner pays a fixed monthly cost to a company who retains ownership of a solar system; or a power purchase agreement, in which a homeowner pays for the electricity generated by solar panels rather than the system itself.
Finally, both homeowners and renters in many places have access to community solar. This option allows people to opt in to a nearby solar farm to enjoy some energy savings.
- Yes, You Can Use Solar Power as a Renter
- Solar Power Purchase Agreements, Explained
- Solar Energy Just Became More Accessible for Renters
- Here's How to Know if Your Home Works for Solar Panels
- Should You Buy Ground-Mounted Solar Panels? What to Know
- Tesla Solar Roof: The Sleekest Solar Option Isn't Your Best One
- Power Your EV or Home With Clean Energy From a Solar Carport
- Community Solar: Get Solar Power for Your Home Without Rooftop Panels
- New Solar Shingles Get Rid of the Ugly, Complex Hassle That Can Be Part of Rooftop Solar
How much do solar panels cost?
The costs of solar panels will depend on a few factors, including where you live, how much of your energy needs you want the system to cover, whether you install it yourself and whether you want a battery (which could cost as much as the system itself). The average cost was about $3 per watt in for an 8 kW system through an installer, according to the consulting firm Wood Mackenzie.
The way you pay for your system is vital. You'll notice the biggest hit to your bank balance by paying for solar outright, while financing will spread the expense out over years but with added interest. A lease or PPA is most friendly to the budget-minded, but you won't enjoy the long-term benefits that come with owning a system outright.
- How Much Do Solar Panels Cost?
- 4 Cheaper Solar Energy Options to Use at Home
- Free Solar Panels: Here's What the Fine Print Means
Here's How Solar Panels Can Earn You a Big Tax Credit - Tax Credits and Incentives Help Businesses Go Solar Too
- How to Finance Your Solar Panels: Cash, Loan, Lease and More
- Yes, You Can Get Tax Exemptions From Rooftop Solar — Here's How
How much do solar panels cost in my state?
Here's the average total cash price, cost per watt and system size for a solar panel system in your state, according to data from FindEnergy.com. These prices don't factor in tax credits or state incentives. Certain states don't have any FindEnergy solar data and are grayed out on the map.
How much money will solar panels save me?
If you're buying a system outright or financing it, you'll receive a 30% tax credit through the Inflation Reduction Act.
To get a better idea of when to expect a return on investment, look at how much energy you've consumed in the past year or two and how much it cost you. Then, working with an installer, figure out how much of your energy you'd like to offset with solar and how much the system will cost. Eventually, the savings from not having to buy electricity from your utility will be greater than the cost of the solar system itself.
"In terms of payback, broadly seven to 12 years is a decent average when you see returns from investment in solar after purchasing a system," Delman said.
- Do Solar Panels Save Money? Yes. Here's How
- How Net Metering Makes Home Solar Panels a Better Deal
- These 7 States Have the Best Tax Incentives for Solar Panels
- Solar Panels Eventually Pay for Themselves. This Formula Will Tell You When
- How to Approach Home Batteries if the New 30% Tax Credit Has Your Attention
- The Inflation Reduction Act Will Help You Pay for Solar Panels and Other Energy Upgrades
Can I install solar panels myself?
It is possible to install most of a solar panel system yourself — mounting the panels on your roof and connecting them to each other. But if your home is connected to a grid, you'll need to hire a licensed electrician for the final connection needed to feed electricity to your utility.
Want more information on High Power Solar Panels? Feel free to contact us.
"Another thing to keep in mind if you're doing it yourself is whether the warranties for the panels that you purchase require them to be installed by a professional," Delman said. "Often when people do it themselves, they'll hire an electrician to do the finishing work so it can get certified. It's also good if you're not an expert to have somebody with expertise to just go over the wiring and make sure that everything is where it should be."
- The Pros and Cons of DIY Solar Panels
- Yes, You Can Make Your Own Solar Panels
Where should I shop for solar panels?
If you want to buy panels directly, most hardware stores and larger retailers have them available. If you'd like to get them through a professional, a good place to start, according to Delman, is the website of your local solar industry association (for example, the New York Solar Energy Industries Association). These organizations should have a list of its members, which will often include installers and suppliers. Typically, installers work with one or two solar panel brands.
"Look for an installer who's experienced, particularly with the kind of situation you have at your home," Delman said. "Have they worked with the same roofing materials? Do you want a ground mount system installed? Check reviews on Yelp, Angie's List, Google and others, and get references too." (Solar United Neighbors also offers resources for going solar, free of charge.)
The best way to make sure you're getting the best deal on your solar panels is to get multiple quotes and ask as many questions of your potential installers as you need. CNET has reviewed many of the national solar companies, but it's a good idea to check into local installers, too, who sometimes can offer lower prices.
- Best Solar Companies
- 7 Tips for Finding the Best Solar Installers Near You
- Solar Panel Buying Guide: Everything You Need to Know
How do I maintain solar panels?
Solar panel maintenance is generally minimal and fairly easy. Even so, we've got the info you need to keep your panels in the best possible shape.
- Solar Panels Get Less Efficient Over Time. Don't Worry About It
- Solar Panels Are Super Durable. How to Make Them Last Even Longer
- Yes, Solar Panels Deteriorate Over Time. Here's What You Need to Know
- How to Boost Your Solar Panel Performance Through Snow and Ice This Winter
Does solar work where I live?
Solar panels, in general, will work in a variety of climates, even those with frigid winters. The more important questions to ask are: Does my roof get adequate sunlight? Are any trees shading my roof? And most importantly, does my utility offer net metering?
Net metering is perhaps the most important aspect of going solar, in that it stipulates that your energy utility will pay you for the energy created by your solar panels that you don't consume. Net metering ensures that the return on investment in going solar is financially sound.
Do I need a backup battery?
For most homeowners, buying a backup battery is an expensive proposition, costing almost as much as a solar system itself. Solar batteries can cost anywhere from $12,000 to $22,000, according to the US Department of Energy. If your home is connected to the grid, the high price of batteries puts it squarely in the non-necessity column.
That being said, there are instances where a battery may be worth the expense. If your area is prone to frequent blackouts and/or you have medical needs that, for example, require cold insulin or medical equipment, a battery is a good investment. Batteries will also be a necessity if you live off the grid.
- Best Solar Batteries
- What It Takes to Go Off the Grid With Solar Panels
- Solar Battery Buying Guide: Everything You Need to Know
- Why You Need Home Batteries — And It's Not All About Blackouts
Does solar increase the value of my home?
Going solar has another benefit for homeowners: It can boost the price of their properties if and when they decide to sell. According to studies by the Lawrence Berkeley National Lab and Zillow, homes with solar panels often sell for about $10,000 more compared to those that don't.
- Solar Panels Are a Big Draw for Gen Z House Hunters
- How Solar Panels Can Add Thousands to Your Home's Value
Are solar panels a scam?
No. Solar panels are a proven technology that can help you shift some of your energy use to cheaper, greener electricity. But that doesn't mean that scammy companies (while apparently rare) don't exist. The company discussed in the story linked below recently went out of business, but a bit of caution is a good thing.
- 7 Red Flags in a Solar Sales Pitch: How to Buy With Confidence
What is net metering?
Net metering — the process by which you're paid for electricity generated by your solar panels but sent back to the grid — is a critical factor in whether homeowners should go solar.
"Let's say during a beautiful sunny day, you're at work, the lights, TV and dishwasher are off, so you're probably generating more electricity from your system than you're consuming," Delman said. "When that happens, that electricity goes to the electric grid through your electric meter to be used by your neighbors. Net metering is what ensures you receive credit for that electricity so that your investment is still being paid back even if you're not using the electricity yourself."
You can see what your state's policy toward net metering is here.
- Are You Still Connected to the Grid if You Get Solar Panels?
- Net Metering Changes in California: How Will They Impact You?
- Net Metering: How You Can Get Paid for Solar Power You Generate
Should I go solar?
Solar won't be an option for everyone. If your home does not receive adequate sunlight due to shading on your roof, you live in a state without net metering or there's no community solar, going solar may not be viable for you.
But with rising energy costs and the falling price of solar panels, for many people there's never been a better time to go solar. There's options to go solar that should fit most people's needs, whether that's through financing, a solar lease, PPA or community solar, that will allow them to start seeing savings on their energy bills almost immediately. By most estimates, a solar system starts paying for itself after between seven and 12 years.
Powering your home with solar not only allows you to get your electricity from a clean source, but provides an unmatched return on investment that will save you money on your energy bills and boost the value of your home.
Contact us to discuss your requirements of Integrated Solar Metal Roofing. Our experienced sales team can help you identify the options that best suit your needs.