How Much Sun Do Solar Panels Need
Solar panels need direct sunlight to produce the maximum solar output. To maximize the sunlight the solar panels receive, face the panels in a southward direction and install them in an area where they are not shaded by trees or other obstructions.
Just a small amount of shade on a solar panel can affect its power output. Your solar panel cells are connected in a series string, meaning that any cell thats affected by shade can weaken the other cell panels, reducing the overall power level. Before you go solar, youll want to check that you have an area for your solar panel with minimal or no shading , or use a string inverter with MPPT to minimize output loses associated with partial shading.
Our solar professionals can help you determine the best placement for your panels. In addition to our sun hour map, We do also have additional insolation data available for other parts of the world to determine how many peak sun hours you have to go solar. Email us at and give us the location of your solar project. Well help you design your solar power system. You can also call us at 1-800-472-1142.
How Many Solar Panels Do I Need To Power My Home
Heres what well cover in this guide:
- How to calculate the number of solar panels you need
- What factors influence your installation size
- How panel efficiency differs
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Solar Panel Size Dimensions
If you refer to the physical solar panel size dimensions, we can start off by saying that each manufacturer has its own optimal dimensions. This largely depends on their own technology.
As you might already know, solar panels are comprised of an arrangement of cells. Depending on the number of cells in the panel they are larger or smaller.
Traditionally, solar panels come in two different configurations: 60-cell and 72-cell. However, if you go to Panasonic or SunPower, they offer 96-cell panels.
But solar energy does not stop in large rigid solar panels.
You can also find small solar panels, and they are ideal to mount on motorhomes, boats, and caravans. Check out our guide on the best boat solar panels.
Solar panels also come in flexible and foldable configurations, making them more practical and easy to carry in case youd like to take them on your hiking or camping trips.
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What Are The Best Solar Panels For Off
We get this question a lot: is there any difference between the best solar panels for off-grid and grid-tie properties?
There is a bit of nuance to the answer.
The panels themselves can always work regardless of system type. There is no such thing as off-grid panels or grid-tied panels specifically.
However, panels must be paired with other components and sized accurately, especially in off-grid systems.
Historically, off-grid systems have used PWM charge controllers, which required that you match 12V solar panels with a 12V battery bank.
Now, most modern off-grid homes will use an MPPT charge controller, which can adjust the incoming PV voltage to work with almost any solar panel.
However, there are still string sizing considerations based on the panel and charge controller specs. All of the components must be supplied with the appropriate voltage and current. Batteries add another layer of complexity for off-grid systems, since the array must be sized to sufficiently recharge the batteries without overcharging them.
There are also a handful of best solar panels that are designed specifically for off-grid applications:
Rate Of Discharge And Depth Of Discharge
Another thing to note when determining the duration of your battery system is the rate of discharge, or the amount of time it takes for your batteries to go from fully charged to their appropriate depth of discharge amount.
While it may seem unnecessary, its important that you dont use 100% of your batteries stored energy. Discharging your lead-acid batteries down to 0% will shorten their lifespan. Depending on what the battery manufacturers advise, you may only be able to use 70% or 80% of your batteries capacity.
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How Many Watts Do You Currently Use
Look at your electricity bill for average usage. Look for Kilowatt Hours Used or something similar, and then note the length of time represented . If your bill doesnt 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, so if your bill doesnt 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 kW.
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 900 kWh per month. So thats 30 kWh per day or 1.25 kWh per hour.
Your average daily energy usage is your target daily average to calculate your solar needs. Thats the number of kilowatt-hours you need your solar system to produce if you want to cover most if not all of your electricity needs.
Its important to note that solar panels dont operate at maximum efficiency 24 hours a day. . Weather conditions, for example, can temporarily reduce your systems 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.
How Much Electricity Will Your System Generate
As we mentioned in the first section, a net metering system is intended to produce as much electricity as you consume in a year and any generation you produce over that amount is typically given to the utility for free. So getting the system sizing right is important to avoid spending money on solar energy that wont be as valuable to you, and getting the most out of your investment.
Enter solar design software, such as Helioscope or PVSyst. These allow us to determine how much electricity your solar system will produce based on the location specific characteristics of your building or field or parking area.
There are a variety of factors that influence solar energy production including tilt of the panels, if they are positioned due south , if there is near or far shading, what the soiling will be, both summer and winter/snow related, as well as the losses throughout the system like those at the inverter, or in the wiring.
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What About Snow Cover & Shading
We rarely have the ideal location for solar panels steep slopes, perfectly south facing, no shading, no snow in winter etc. The previous section showed how to calculate solar energy yield for locations across the world, and for all different orientations and tilt-angles. What it did not explain yet is how to deal with snow cover in winter, and shading. Unless you have a death-wish and plan to climb on the roof in winter to sweep the snow off the panels, snow cover is something we need to take into account for almost all locations in Canada!
First, let us take a step back and think for a moment about those annual energy yield numbers we have been calculating. In actual life every year will see a different amount of sunshine, and those numbers are an approximation, an average. They are not accurate to three decimal places, what they are is a pretty good idea of what to expect from solar PV for your particular location and case. The way we deal with snow cover should be seen in that light. We are just trying to improve our estimate, and get a better approximation:
For panels that are mounted at a tilt-angle of 40 degrees or more we expect snow to slide off pretty well in winter, and no correction is needed.
For panels that are mounted at a tilt-angle of 30 degrees or less we expect them to be covered in snow for part of the winter. So how do we account for that?
Corrected energy yield with snow cover = PV-Watts estimated yield Half the December yield January yield
Ballparking A Solar System Size With Your Annual Usage
Based on your annual electricity and monthly consumption pattern, we can ballpark a general system size for you. To do this, we use a rule-of-thumb number for solar production in NC to estimate your needed system size. Based on our experience, our rule of thumb is that 1 kilowatt of solar installed in NC will produce 1,300 kilowatt hours per year. So if your home uses 12,000 kWh per year, wed estimate you need around a 9.2 kW solar system to meet 100% of your energy needs .
Remember, this is just an initial rough estimate. We always refine your system size with more accurate annual production estimates based on the exact solar potential of your site after we perform a full site evaluation of your home, discuss your goals of going solar, and work through any limitations if encountered. With that said, this graph shows how this rough estimation translates to solar kW and number of solar panels.
Roof space needed for a solar system
If a space meets all those criteria, then it is ready to shine. For a roof mounted solar system, each panel takes up an area of approximately 18 square feet. So for the 100% energy offset 9.2 kW solar system we have been using as an example, we would need 31 panels or 470 sq feet of eligible roof space .
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Will The Size Of Your System Provide Affect Production In Overcast Weather
While panels can produce current at a reduced level during cloudy weather, no current will be produced at night. This means that you will still have to rely on the commercial grid to some extent. However, this doesnt necessarily mean that you will be paying for this current! The reason for this is that your panels will on average be producing much more current than you need. This extra current is automatically banked for you by a system known as Net Metering. Whenever you require additional current during bad weather or at night, you simply draw on this excess current. The way this works is that your system feeds unused current back into the grid, as it is produced, and your utility company banks this current by crediting your account. A well designed system can thus basically reduce your electricity utility bills to zero. Read our post explaining this concept.
Good Data In Good Data Out
First, lets debunk some common solar system sizing misconceptions. Using the total square footage of your building is NOT a great way to calculate your solar panel system size needs. Its also not about how many people live in your home. This might give you a ballpark estimate of your energy needs, but when dealing with sizing a solar system, you want to be as precise as possible. Like any calculation, if you put bad data into the equation, you get a bad answer out of it.
Remember what youre trying to do here. Youre trying to figure out how much energy your solar system should be capable of producing on any given day. Whether its generated from dirty fossil fuels or from clean renewable sunshine, energy is measured in kilowatts and youre billed for it based on kilowatt-hours . Because of this, your previous electric bills are actually the best guide for how to properly calculate your solar panel system size requirements. More on this later.
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Choose The Right Solar Panels
If you have a small or odd-shaped roof, solar panel size is an important consideration when deciding on the size of a solar system. Take these factors into account:
- With a large usable roof area, you can buy more larger panels to get to your target energy output.
- If your usable roof area is limited or partially shaded, using fewer smaller high efficiency panels will ultimately be the most cost-effective, long-term solution. You can add more panels later on to accommodate increased energy needs.
How To: Size A System
Sizing a system
The aim is to balance the power going in from the solar panel with the power going out of the battery over a period of days or weeks . A 10W panel will give 10W over an hour under standard test conditions . In the UK allow around 4 hours equivalent sunshine in summer and 1 in winter. In Winter a 10W panel will give 10W over a whole day, whereas in summer it will give 40W. These are fairly conservative figures some companies use up to 6 hours in summer. You can do the same calculations with the Amps .
Charging appliances eg mobile phones the bigger the panel the faster the charge. Beware, modern laptops are power hungry and often cannot be charged directly from a solar panel. We always recommend using a small 12V battery.
Some simple steps for sizing a 12V system:
Find the Wattage of your appliances. List all the 12V electrical appliances youll use in a typical day, and find out how many Watts they each consume. Usually this is on the appliance or in its handbook. If you can only find a figure for Amps, simply multiply this by 12, to convert it to Watts.
Calculate your daily total Watt-hour requirement. Estimate how many hours you would use each appliance for over a typical week, then divide by 7 for a daily rate. Multiply each appliances wattage by the hours youll use it for in a day. Then add all the totals together to get the final daily total Watt-hours you require
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Assess Your Energy Needs
Before you even start looking into solar panels, you need to know what devices youre powering, and how much energy they use. Make a list of all the electrical appliances youll be powering, and make sure to split them into AC and DC. Anything with a normal household plug is an AC device. DC devices run on 12V or 24V, and sometimes 48V. Click here for an explanation on the difference between AC and DC.
Once you know what devices you will be powering, then you can determine the wattage of each device. You can find the wattage by looking at the manufacturing sticker, searching online for information about the device, or by using a wattage meter to measure the wattage directly. Then calculate the amount of time you use each device daily in hours. Its always best to overestimate the amount of time you use each device.
The tables should look like this:
Base the voltage of your system on your estimated daily usage. In our example, the total daily consumption of our appliances, both AC and DC, is 900 watt-hours, but the potential peak power usage of our system is 1,325 watts. While we only expect to use 900 watt-hours on a daily basis, we want to accommodate our peak load, so were going to build a 24V system.
Now that we know what we will be powering and how much power we need, we can move onto our next step.
Select Your Mount Type
A roof mount is the simplest and most cost-effective solution since it costs less than other racks. To determine if you can use a roof mount:
2. If a roof mount is not an option, look into a ground mount or pole-mounted solution. On the flat ground, you can position solar panels in any direction you want to maximize sun exposure, unlike on a slanted roof.
To learn more about the pros and cons of each mount type, read this article: Ground Mount vs. Roof-Mount Racking: Whats the Best Way To Mount My Solar Panels?
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Factors That Affect Solar Panel Output Efficiency
All things being equal, the design of the solar panel determines how efficient it is. This, in turn, specifies how well each square foot can convert sunlight into energy.
For example, gridlines on most panels reduce the active surface area. Therefore, they are not as efficient as those without them. In addition, grid panels are susceptible to peeling, further reducing efficiency.
Quality plays a role, too. For example, if the construction is subpar and introduces corrosion and cracking, it can also impact the ability of the panel to absorb sunlight.
But as a rule of thumb, expect residential solar panels to give you between 150 370 watts. This translates to an average solar panels wattage per square foot of 15 watts.