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Variables Affecting Solar Panel Output

In addition to the amount of sunlight received per day, there are other factors that affect the output of your solar panel or system. 

Dirt

Anything that builds up on the surface of your solar panel can affect the output. This can include dust, leaves, snow, or bird droppings. A clean solar panel can be 6.5% more efficient than a dirty and dusty panel.4

Roof Direction and Angle

Solar panels are most efficient when directed in a south-east to south-west direction, at an angle of 30-45 degrees. Systems at other directions and angles can still work, but your outputs will be decreased.

Shade

Solar panels are very sensitive to shade, including trees, or a building next door. Minimal shading in the morning or evening is fine, but significant shading throughout the middle part of the day will significantly impact the amount of electricity a panel can produce.

Location 

The amount of sunshine and cloud cover will affect the amount of energy a solar panel can produce. 

Time of year

Solar panels can produce electricity year-round, even on overcast days. Through summer, the days are longer which generates more output, but shorter days in winter mean your output will be lower over these months. 

Age

As solar panels age, their efficiency decreases at around 0.5% each year. The life cycle of the system is approximately 25 years before performance has decreased to the point a new system is needed.

Temperature 

The efficiency of solar panels is usually measured at 77 F, and temperatures above this can end up decreasing their efficiency.Solar panels can work well in cold weather, and can still generate power in snowy conditions, too. 

How Much Electricity Does My Home Need?

One solar panel on its own isn’t going to create enough electricity to power your entire home, but a solar panel system can. To work out what size system you need, you’ll need to complete some basic calculations that we’ve covered in our article How Many Solar Panels Do You Need? 

To fully power an average home using 11,000 kWh per year, a typical solar power system will need between 21-24 panels of 320 watts each. The exact number and wattage of panels, as well as the output they can produce, will depend on where you live and the setup of your specific system. 

Types of Solar Panels and Output

There are three main types of solar panels used for domestic systems:

• Monocrystalline. These are the most popular type of panel, made with pure silicon. They have an efficiency of 24.4%, with a moderate cost and a long lifespan.
• Polycrystalline. These are made of silicon crystals that have been melted together. They have an efficiency of 19.9%, a low cost and a moderate lifespan.
• Thin-film. Made with a variety of materials including small amounts of silicon, thin-film panels have an efficiency of 18.9%, with a high cost and a shorter lifespan. 

The output of each type of panel will vary depending on the individual manufacturer, but will always be stated as a power rating in watts. The higher the watts, the higher the output. You may also see a kilowatt peak rating, which is the maximum power the panel can produce under the standard test conditions mentioned earlier. 

Cost vs. Value 

The solar market is very cost competitive, but some brands will offer you a more efficient system for a slightly higher investment. These systems will generate more electricity over the life of the system, so in the long run, they will create more value with consistent increased output. 

Remember to look into federal tax credits and other incentives designed to reduce the cost of solar panel installation.

Frequently Asked Questions

How much power does a solar panel produce in a day?

Given your house gets about six hours of daily sunshine, a standard 250-watt solar panel would produce 1.5 kWh of energy in a day.

How many solar panels would you need to fully power a home?

You would need about 20 250-watt solar panels to generate the amount of energy the average American home uses in a day.

How can you increase solar panel efficiency?

You can increase solar panel efficiency by cleaning the dirt off your panels regularly, pruning any trees that could be shading the panels, optimizing the panels’ angle (ideally to a 30- to 45-degree angle facing south), or installing an automatic solar tracker that rotates the panel to keep it aligned with the sun.

Solar panel energy output
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