It’s a good time to get solar panels for your house, for they have improved in efficiency and declined in price ever since the first modern solar panels were developed in the 1950s. Back in the 1970s, solar panels were prohibitively expensive: they cost $96 per watt. A single solar panel that produced 100 watts thus cost a staggering $9600. By 2016, that price had dropped to 68 cents per watt, so that same 100-watt solar panel would cost $68.
According to the SEIA (Solar Energy Industries Association), the cost of getting solar panels installed has declined by over a staggering 70 percent during the past decade. In 2010, the average homeowner paid around $40,000 to get a solar system installed; that same homeowner would now pay around $18,000.
So, you have decided to get solar panels for your house, and you have a lot of questions about what the process involves. To start with, how many solar panels will you need?
Solar LED Barn Light
- Active Time: 3-5 hours
- Lumen: 1,000; Color Temperature: Super Bright
The answer will depend on a variety of factors. For example, how big is your house? How many hours of sunlight do you get? Do you want to use solar power for all of your energy needs or just some of them? How much energy do you typically use over a month or a year? When do you typically use the most energy, and when do you tend to use the least?
The answers to these questions will help you decide how many solar panels you will need.
What You Will Need
In order to get a feel for how many solar panels you should buy, you will need the following:
• At least a year’s worth of electric bills
• Information about your choices of solar panels
• List of appliances and electronics and estimated energy use
What can you learn from electric bills?
Your electric bill contains a lot of information that will help you decide how many solar panels you should buy. For example, your electric bill tells you how much electricity you used in a given month. The energy company will send one of their employees to read the meter once every month, and they will calculate the difference to determine how much electricity you used in a month.
Your bill gives the amount used in kWh (kilowatt-hour), which is the number of kilowatts used in an hour. For example, if a heater uses 1000 watts (1 kilowatt) for an hour, it uses 1 kWh.
Seasonal temperatures will affect how much electricity you use, for central heating systems and air conditioning require massive amounts of energy. Consequently, you will probably find that you are using less energy during the spring and fall than the summer and winter. This is why you should have at least a year’s worth of electricity bills on hand.
Ideally, though, you should have several years’ worth of bills. Solar panels can last for over 20 years, so you should consider long-term changes like moving or having children that will affect your energy usage.
Your electric bills will also tell you how much you paid for your electricity, and that will also change over time. Inflation can make your bill increase over time, even if the amount of energy you’re using remains the same. Conversely, the cost of renewable energy sources, including solar power, has actually declined over the years, so you would probably end up paying less after getting your solar panels.
How do appliances and electronics affect energy usage?
The number and type of appliances and electronic devices will affect how much energy your home uses. That, in turn, will affect the number of solar panels you will need.
Other variables you will need to consider include the size and age of the appliance. Generally speaking, newer appliances are more energy-efficient than older appliances. Appliances that have earned certifications like Energy Star use less energy than do those that have not.
Air conditioner
Central air conditioners use enormous amounts of energy. They generally use about 3.5 kWh or 3500 watts per hour.
Refrigerator
As of 2017, the average refrigerator uses 115 kWh every month. The refrigeration unit uses 57 kWh, and the freezer uses 58 kWh.
Television
There are several different types of televisions, and they come in a range of sizes. Not surprisingly, big televisions will use more energy than will small televisions.
Old televisions used to contain CRTs (cathode ray tubes). Modern televisions can have screens with LCDs (liquid crystal displays), plasma, and LEDs (light-emitting diodes). Smart televisions are simply those that can be connected to the internet; the amount of energy they use will depend on the type of display they have. Modern televisions are a lot less bulky than the old CRT sets and they use less energy.
The different types, however, are not created equal. Plasma TVs, for example, are the least energy-efficient. A plasma television with a 30-inch screen will use 150 watts (0.15 kilowatts) per hour, while an LED set of the same size will use 50 watts (0.05 kilowatts) per hour — 1/3 as much!
How much energy does a solar panel produce?
A single solar panel can produce anywhere from 45 watts to 400 watts of electricity with most of the solar panels on the market generating between 250 and 400 watts, which equals .250 kilowatts and .400 kilowatts.
Solar panels will be labeled with a number like 250W or 325W to indicate the number the amount of energy it can produce. The higher the number, the more energy the solar panel can generate.
Step-by-Step Instructions for Calculating How Many Solar Panels You Will Need
1. Examine your electric bills
Ideally, you should use several years’ worth of bills to get a feel for your energy needs and any long-term trends. For example, during which months do you use the most energy? Has your energy use gone up or down over the years?
2. Think about where you live
More specifically, think about the climate and how much sun you typically get. How many rainy or cloudy days do you usually get? While solar panels will still collect some energy during a cloudy day, they will collect anywhere from 25 to 40 percent less.
You will also need to consider the amount of “direct sunlight,” which is the amount of sunlight that can reach a given location without being obstructed. This number varies depending on the season and the location. Winter, for example, has less direct sunlight than does summer. Not only are the days shorter, but the sun is lower in the sky.
Your location will also affect the amount of direct sunlight you will get. Places nearer the equator will have more hours of direct sunlight because they are closer to the sun than are places near the poles.
There are several ways to find out how much direct sunlight you have, aside from just asking the professionals installing your solar panels. There are various maps and charts that list the hours of direct sunlight in specific cities or countries. Most places in the United States, for example, get between three to five hours of direct sunlight every day.
If you’re feeling ambitious, you can buy or even make an insolation meter to learn how many hours of direct sunlight you have. The meter will also provide information about temperature, light intensity, and solar power supply.
Knowing how much direct sunlight you get will help you determine how much energy you can get from a solar panel. For instance, if you live in a sunny state like California that gets five hours of direct sunlight a day, and you have a solar panel that produces 300 watts of energy per hour, that solar panel will produce around 1500 watts or 1.5 kWh every day. That means it will produce approximately 45 kWh every month.
LEDMO 200W LED Solar Flood Light
- Watts: 200
- Voltage: 120V
3. Consider your habits
How much time do you spend at home, for example? If you work at home, you will use more energy than your neighbor who works in an office will – even if you live in identical apartments that contain exactly the same appliances. If both of you use a computer in your work, you’re using the computer at home, while your neighbor is using the one at their office. You are thus consuming more energy than they are.
Also, consider how much you use your various appliances and electronics. For example, if you run your AC for about four hours every day, that equals about 120 hours per month. Since the average AC uses 3.5 kWh an hour, you’re using around 420 kWh every month. Assuming you have the 300-watt solar panels described earlier, you will need nine or ten of them for your air conditioning. On the other hand, if you have 200-watt solar panels, each one will produce around 1 kWh per day. Since each solar panel will produce roughly 30 kWh during a month, you will need 14 of them to keep your AC running.
If you have a 30-inch television with an LED screen, it uses a meager 0.05 kilowatts per hour. If you watch 180 hours every month, or around 6 hours a day, that equals 9 kWh per month. A single 300-watt solar panel will do the job, with ample power to spare. Even one 200-watt solar panel can keep your LED television running.
As already mentioned, a refrigerator with a freezer generally uses about 115 kWh. It will need three 300-watt solar panels or four 200-watt solar panels. A brand-new refrigerator that has earned Energy Star will need fewer solar panels.
Table 1. Sample Products and # of Solar Panels Needed
| Product | # of items | Power used per hour | # of hours used daily | Power used per month | # of 200-watt panels needed | # of 300-watt panels needed |
| AC | 1 | 3.5 kWh | 4 | 420 kWh | 14 | 9-10 |
| LED TV | 1 | 0.05 kWh | 6 | 9 kWh | 1 | 1 |
| Refrigerator | 1 | no data given | 24 | 115 kWh | 4 | 3 |
Each 200-watt solar panel produces 30 kWh per month
Each 300-watt solar panel produces 45 kWh per month
4. Consider how much solar energy that you want to use
Do you want to power everything with solar energy? What will you do if the sun generates more energy than you need at a given time? There are two possible solutions: buying a battery or selling the excess to your utility company. If your utility doesn’t have a buyback program and if you don’t have a battery, then generating more power than you need is pointless. People in that situation will thus decide to power only part of their house with solar energy. They might, for example, aim for around 70 percent solar. That way, they will still have a smaller energy bill, but they won’t be producing excess energy they can’t use.
This approach, however, will require you to calculate how much energy your appliances and electronics use during a month and then adding them to get the desired total. For example, if you want to use solar power for 70 percent of your energy needs and typically use around 600 kWh per month, you will want your solar panels to produce approximately 420 kWh every month. An easy approach is to start with energy hogs like the air conditioner and work downward. The solar panel installer will know how to connect the solar panels to the appliances being powered.
On the other hand, if you have a battery or your utility has a buyback program, then aiming for 100 percent solar power makes a lot of sense. It also makes it easier to figure out how many solar panels you need, since your electric bills tell you how much energy you use during a month. Once you know how many hours of direct sunlight you have and the wattage of the solar panels you are considering, you can calculate the number of solar panels that you need.
For example, if you get five hours of direct sunlight a day, a 200-watt solar panel will produce 30 kWh during a month, while a 300-watt solar panel will produce around 45 kWh during a month. If you typically use 600 kWh in a month, you will need either 20 of the 200-watt solar panels or 14 of the 300-watt solar panels.
5. Think about future expenses
Do you plan to have children or will an older parent be moving in? You will probably see your energy usage go up. Do you expect to replace a large appliance like an air conditioner or refrigerator in the near future? Are you considering getting an electric car? You will need a charger to power the car, and that will require energy.
6. Research the places that sell solar panels in your area
These can include home improvement stores like Home Depot, or they can be retailers that specialize in solar power like SolarCity. The latter is a subsidiary of Tesla, which also sells batteries called the Powerwall and Powerpack, which can both store solar energy.
Most of the solar panels sold by Home Depot generate between 100 and 300 watts. They are usually sold singly, but some are sold in pairs or packs of four. While many are designed for placement on the roof, some are designed to be used in solar arrays on the ground. A few have very specific purposes, like being used to power a boat or a fan.
7. Consider the type of solar panels you want
Do you want the standard roof-mounted panels or would you prefer an array placed in the ground? Do you want ultralightweight panels? If you choose an array on the ground, do you want panels that can track the sun?
Conclusion
To summarize, you need to know three things in order to calculate how many solar panels you will need. You need to know how much energy you use in a month, and you need to know how much direct sunlight you get. The biggest variable will be the solar panels themselves. You will have to research what is available in your area and how many watts they generate for an hour. With that information, you will be able to calculate how many solar panels you will need.
Did you find this tutorial helpful? Did you enjoy it? If so, tell your friends about it. Please post your comments in the box below.
Malcolm – Blog Author. I have several years of customer service experience in the energy sector. I am convinced that harnessing solar energy will soon be the norm around the world.
Leave a Reply