There are various reasons to buy a solar system and to invest in harnessing power from the sun. Two of the largest reasons are to deplete your carbon footprint and to save money in the process. Before you go and buy a solar system, however, it is important that you examine your roof to see if a set of solar panels is suitable.
No matter if you are reading this during the day or at night, the Summer heat can invade your home at any time of day. You likely own an air conditioner, but it costs money to run, as we all know, and sadly it doesn’t cool the second floor of your home, where you sleep in your bedroom.
If you’re thinking about going solar, you’re probably wondering: Is solar cost effective? Is my roof suitable for solar panels? Will solar energy generate enough electricity to power my home? Who makes the best solar panels?
But first, it's important to explore if solar panels for your home make sense. Here are some key questions we ask anyone interested in buying or leasing a solar energy system to make sure their home is best suited for making power with solar panels.
1. How much is your energy bill?
Knowing how much you pay for energy is the first step in evaluating whether your house is a good candidate for solar. The main question is, will it save you money? In some areas, electricity is very inexpensive. For most homeowners, the electricity bill is a dreaded monthly expense. The general rule is that solar makes the most financial sense for someone with a monthly electricity bill of at least $75. Why? Because going solar replaces utility energy with solar energy, and we want our customers to see a return on that investment by paying less for that energy. A utility bill of $75 is the threshold at which residential solar customers will see solar savings. There are several ways to go solar, depending on a customer’s needs and goals. SunPower offers zero-down lease, loan and cash purchase options — each with different benefits. Ask your local solar expert about local and federal incentives and electricity policies where you live.
The overall idea is to pay less than you currently pay, lock in your electricity rate and save money by generating your own clean energy onsite.
2. What kind of roof do you have?
Solar panels work best with strong, durable roofing materials, such as composite or asphalt shingle, concrete tile or standing seam metal. For roofing materials such as wood shake and slate tile, or for roofs made of clay with mortar or composite metal/stone coated steel, you can still go solar but you’d want to choose a solar professional who has experience installing solar panels on those types of roofs. Also, the type of mounting hardware your solar installer plans to use is important. SunPower Equinox™ uses InvisiMount™ hardware that is designed to work with most roof types and is visually attractive.
3. Does your roof need to be replaced?
It’s a good idea to replace a roof that is near the end of its life before installing solar because SunPower solar panels have an expected useful life of 40 years, and you wouldn’t want to unnecessarily have to remove them. Solar panels should be installed on roofs that are in good condition and will not need to be replaced in the near future. Considering that your savings from high efficiency solar panels could pay for the cost of a re-roof in as little as five years after installation, it may be worth it to do any needed roofing work before your solar installation.
4. How much sunlight does your roof receive?
To see if your house is a good candidate for solar, try out a solar panel suitability checker such as Google’s Project Sunroof. Then set up an appointment for a solar consultation with an expert who will visit your home to inspect its orientation (solar panels facing south capture more energy), roof angle and tree shading to see if your roof will receive enough sunlight to meet your family’s energy needs. SunPower’s solar consultations are free, and you can learn a lot about your home and best energy options. The more direct sunlight your home receives, the more power the panels will produce. While SunPower solar panels are known at being extremely efficient at generating power in low-light situations, excessive shading will reduce the amount of power that can be generated.
It’s also important to know that SunPower’s Equinox solar solution has factory integrated micro-inverters in each panel, an innovative solar design feature that means if one panel isn’t producing energy because of shade, neighboring panels that might be receiving more sunlight can still generate solar energy for your home.
5. What is your local climate like?
Solar energy can be generated in all sorts of extreme climates, from rainy areas such as Seattle, to extremely hot locations such as Los Angeles, California Solar suitability checker tools can help you understand how this could affect solar on your house. High-efficiency solar panels convert direct and indirect sunlight into electricity, so they work even on cloudy days. A solar consultant will estimate the amount of energy your system will produce so that you can see the potential savings before you decide to go solar.
If your area is prone to severe weather, check the durability rating of the panels you’re considering for your home. SunPower panels are rated No. 1 in third-party durability testing, which means they can withstand some of the harshest weather conditions, including hail up to 1 inch in diameter.1 In fact, SunPower technology is so reliable that NASA chose our solar cells to power its GROVER project, which explored Greenland’s vast and inhospitable ice sheets. Solar that’s tough enough for Nasa is tough enough for your roof, too.
Determining how many solar panels you’ll need for your home means first knowing what your goals are. Do you want to minimize your carbon footprint? Maximize your return on your investment? Save as much money as possible? Most people want to save money while minimizing their environmental impact.
To calculate how many solar panels you need, you need to know the following: how much energy your household uses; your roof’s usable surface area; the climate and peak sunlight in your area; the wattage and relative efficiency of the photovoltaic (PV) panels you’re considering; and whether net metering is available.
One simple way of answering the “How many solar panels do I need” question is to consult a professional installer, who can give you a free home solar evaluation.
1. How much solar power will you need?
To determine your home’s average energy requirements look at past utility bills. You can calculate how many solar panels you need by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage (150W) and high-wattage (370W) example to establish a range (ex: 17-42 panels to generate 11,000 kWh/year). Note that how much sunlight your roof gets and factors such as roof size and battery storage will figure in as well.
If you work with SunPower, our solar experts will handle all these calculations for you. But to give you some idea of how many solar panels are needed for the average home (or for your home in particular), here is a sample set of questions that a solar professional might use to figure it out:
2. How many watts do you currently use?
Look at your electricity bill for average usage. Look for “Kilowatt Hours (or kWh) Used” or something similar, and then note the time period represented (usually 30 days). If your bill doesn’t show kilowatt hours used, look for beginning and ending meter readings and subtract the previous reading from the most recent one.
You want daily and hourly usage for our calculations, though, so if your bill doesn’t show a daily average, just divide the monthly or annual average by 30 or 365 days, respectively, and then divide again by 24 to determine your hourly average electricity usage. Your answer will be in kilowatt-hours (kWh). (And just in case you are wondering, a kilowatt-hour is how much power you are using at any given time multiplied by the total time the power is being used.)
A small home in a temperate climate might use something like 200 kwh per month, and a larger home in the south where air conditioners account for the largest portion of home energy usage might use 2,000 kWh or more. The average U.S. home uses about 900kWh per month. So that’s 30 kWh per day or 1.25 kWh per hour.
Your average daily energy usage is your target daily average for to calculate your solar needs. That’s the number of kilowatt-hours you need your solar system to produce if you want to cover 100 percent of your energy needs.
It’s important to note that solar panels don’t operate at maximum efficiency at all times. (See Solar 101: How Does Solar Energy Work?). Weather conditions, for example, can temporarily reduce your system’s efficiency. Therefore, experts recommend adding a 25 percent “cushion” to your target daily average to ensure you can generate all the clean energy you need.
3. How many hours of sunlight can you expect in your area?
The peak sunlight hours for your particular location will have a direct impact on the energy you can expect your home solar system to produce. For example, if you live in Phoenix you can expect to have a greater number of peak sunlight hours than if you lived in Seattle. That doesn’t mean a Seattle homeowner can’t go solar; it just means the homeowner would need more panels.
The Renewable Resource Data Center provides sunlight information by state and for major cities.
Now multiply your hourly usage (see question No. 1) by 1,000 to convert your hourly power generation need to watts. Divide your average hourly wattage requirement by the number of daily peak sunlight hours for your area. This gives you the amount of energy your panels need to produce every hour. So the average U.S. home (900 kWh/month) in an area that gets five peak sunlight hours per day would need 6,250 watts.
4. What affects solar panel output efficiency?
Here’s where solar panel quality makes a difference. Not all solar panels are alike. Photovoltaic (PV) solar panels (most commonly used in residential installations) come in wattages ranging from about 150 watts to 370 watts per panel, depending on the panel size and efficiency (how well a panel is able to convert sunlight into energy), and on the cell technology.
For example, solar cells with no grid lines on the front (like SunPower ® Maxeon cells) absorb more sunlight than conventional cells and do not suffer from issues such as delamination (peeling). The construction of our cells make them stronger and more resistant to cracking or corrosion. And a microinverter on each panel can optimize power conversion at the source, in contrast to one large inverter mounted on the side of the house.
Because of these wide variations in quality and efficiency, it’s difficult to make generalizations about which solar panels are right for you or how many you’ll need for your home. The main takeaway is that, the more efficient the panels are, the more wattage they can produce, and the fewer you will need on your roof to get the same energy output. Conventional solar panels usually produce about 250 watts per panel, with varying levels of efficiency. In contrast, SunPower panels are known to be the most efficient solar panels on the market.
To figure out how many solar panels you need, divide your home’s hourly wattage requirement (see question No. 3) by the solar panels’ wattage to calculate the total number of panels you need.
So that average U.S. home in Dallas, Texas, would need about 25 conventional (250W) solar panels or 17 SunPower (370W) panels.
5. What is the effect of solar panel size?
If you have a small or unusually shaped roof, solar panel size and numbers are important considerations. With a large usable roof area, perhaps you can sacrifice some efficiency and buy more larger panels (at a lower cost per panel) to get to your target energy output. But if your usable roof area is limited, or if it’s partially shaded, being able to use fewer smaller high efficiency panels may be the best way to make the most possible power over the long term, ultimately saving you more money.
Typical residential solar panel dimensions today are about 65 inches by 39 inches, or 5.4 feet by 3.25 feet, with some variation among manufacturers. SunPower panels are 61.3 inches by 41.2 inches.
These dimensions have remained more or less unchanged for decades, but the efficiency and output from that same footprint have changed dramatically for the better. In addition, SunPower designs entire systems to have virtually no gaps between panels and uses invisible framing and mounting hardware to keep the rooftop footprint as tight, efficient and attractive as possible.
Knowing the answers to the above questions will give you an idea of the ideal number of panels for your electricity generation needs — or at least a realistic range. Next, a professional installer needs to assess your roof architecture, angle to the sun and other factors to see if and how you’d be able to physically arrange the right number of panels on your roof to achieve your daily energy production goals.
You should also consider net metering as you’re considering figuring out your ROI for your solar system. Net metering is how your utility company credits you for producing excess solar energy when the sun is shining and then lets you draw from those credits when you’re using conventional power grid at night, if you don’t have a solar battery storage system.
It's important to find the right Solar Installation Company for you. Solar is an investment and a worthy one, but choosing the right company to do the job can be tough when there are so many options out there. Here is a great article written by SunPower that provides some great tips for those shopping around for Solar.
Finding a Solar Installation Company
Unless you’re an electrician or an experienced DIYer, if you want to switch to solar you’re not just going to buy solar panels for your roof. You’re going to choose a solar installation company for your home that you can trust.
It’s crucial that you pick the right solar installation contractor to install your solar system so you can start saving money on your electric bill. To help, SunPower created this downloadable guide: “How to Find the Right Solar Installer for Your Home.” Here are some of the top tips from our new guide.
Choosing a Home Solar Installer
The right installer will customize a solar system that meets your family’s electricity needs. The best way to pick the right solar home installer is to ask lots of questions. Those questions should start by focusing on the installer’s experience. For instance, is it a locally based company? A local installer will understand your climate and will have experience with your local building and electrical codes and will have strong relationships with your local permitting offices and inspectors. If not, your home solar project could face potentially costly delays.
Once you find a local company you like, make sure it is licensed and bonded and ask pointed questions about the experience of everyone on the crew. You want to make sure they’re up to the job and that they won’t make rookie cost-cutting mistakes, such as using a templated solar array configuration when a customized one would ensure your system is capturing the maximum amount of sunlight to save you the most money possible.
Next, ask about the equipment. Don’t fall for anyone who tells you one brand of solar panel is more or less as good as the other. Not all solar is alike. Factors such as durability in extreme weather conditions, degradation rates and solar panel efficiency matter if you want to make the most possible energy over time.
A good installer will customize your solar system by taking your house and its surroundings in mind. Is there a lot of shade or a lot of sun? What’s the contour of the roof like? What aesthetics do you have in mind? We know curb appeal is important. The most attractive solar panels will not have visible parts and wiring. Your installer should be looking at these and other factors and letting you know upfront how they’ll impact the equipment needed.
SunPower solar installation contractors use a great digital design solar app that allows homeowners to see in real time what their array will look like on the roof, how much power it will make and how much it will cost, all right at the kitchen table. You can even make changes to the design if, say, you want to generate more or less power or choose a different style and wattage of solar panel.
Finding the Best Solar Warranty and Finance Options
It’s important to ask your solar installer about the warranty. A best-in-industry warranty should cover the panels and their power output for 25 years. Also, the warranty should cover the whole system, not just the panels.
While some solar panel providers piece together their systems from multiple vendors, SunPower’s Equinox™ solar system is designed, engineered and manufactured by one company, so we offer one warranty for the entire system. Some solar companies offer shorter warranty terms for key parts, and then refer you to another company if something goes wrong. So, if something does go wrong in 10 or 15 years, it may be difficult to sort out who’s responsible for fixing it.
A good installation company will also let you know all of your solar financing options. Depending on your location, those options may include cash purchases, loans or leasing. The solar company also needs to be transparent about who’s financing or underwriting your loan or lease.
And, as with the solar company itself, look for a finance company that has experience with solar. They’re the ones most likely to understand how to get you the most favorable terms. All of this hinges on receiving a detailed proposal from the solar company that spells out how much you can save on energy over the entire life of solar system.
When you're choosing the best solar panel for your home or business, the manufacturer makes a difference. Not all panels are created equally. Here's a helpful infographic that summarizes why SunPower is different.