In one year, the sun sends an immense amount of energy to our planet, around 222,500,000 terawatt hours . This is more energy than we could ever hope to use, and it represents a vast potential for the solar power. However, to harness this energy, we need to convert it into usable electricity.
The efficiency of this conversion is a critical factor that affects the amount of solar energy we are able to harvest for our use.
Solar panels as devices that convert sunlight into electricity by the photovoltaic effect are the tool that should make this potent source of energy available to us. But the most efficient solar panels on the market today have a maximum efficiency of around 22 percent, meaning they can convert up to 22 percent of the energy from the sun that falls on them into usable electricity .
The twist is that most solar arrays you see around reach only up to 18 percent efficiency. This means that, even with the best technology available, we are only able to convert a fraction of the sun’s energy into electricity.
Understanding how much electricity does a solar panel produce is essential to predicting the monthly output of a solar system. This information helps when designing and installing solar systems that should provide sufficient electricity to meet a household’s needs.
So even though, solar energy is free and abundant, there is still a lot of space for improvement when it comes to our ability of harnessing it, and efficiency of solar panels is just one of the limiting factors on the way.
How much electricity does a solar panel produce per day?
The energy output of a solar panel varies based on the size of the panel you have, maximum efficiency and output rating in watts.
Solar panels are commonly evaluated according to the amount of direct current power they generate under standard test conditions. This power output is measured in watts and represents the panel’s potential to produce electricity under ideal sunlight and temperature conditions. Ideal conditions mean a temperature of 25 degrees Celsius or 77 degrees Fahrenheit and unobstructed sunlight hitting the whole surface of a solar panel.
The test temperature represents the average temperature during the solar peak hours of the spring and autumn in the continental United States. The problem is that in real life you have rarely the ideal conditions, so the values will differ.
Most residential solar panels have power output ratings ranging from 250 to 400 watts. This rating affects the total cost of a solar system. Premium solar panels with higher wattage produce more energy but also cost more than the lower rated ones, since the price for solar panels is calculated per watt.
The size of solar panels affects the final power output as well. Larger solar panels (with 72 solar cells) produce more energy than the 60-cell ones, assuming they receive the same amount of sunlight.
The 72-cell panels usually carry higher rating of 300 to 400 watts. Higher energy output simply correlates with the number of solar cells. More solar cells mean more energy produced. However, in most residential application, the smaller solar panels with 60 cells are used.
And similarly, solar panels with higher efficiency rating convert more of the sunlight their solar cells receive into usable electricity, resulting in higher energy output. Monocrystalline solar panels still represent the most efficient option for homeowners on the market.
Further reading: What Are the Most Efficient Solar Panels on the Market?
How to calculate the average solar panel output?
How much energy does one solar panel produce in a day also depends on environmental factors like the amount of unobstructed sunlight in a day.
An average solar panel with efficiency of 18 percent usually produces around 250 to 300 watts of power under ideal conditions. In reality, the actual output varies depending on the amount of sunlight available.
To estimate the expected energy output of a solar panel, we can use a simple formula that takes into account the wattage of a solar panel and the amount of sunlight it receives. This formula is as follows:
For example, if we have a 250-watt solar panel and it receives 5 hours of sunlight per day, the expected energy output would be:
Energy output = 250 watts x 5 hours = 1,250 watt-hours per day or 1.250 kilowatt-hours
How many hours of sunlight a solar panel receives is a crucial factor in determining its energy output. The intensity of sunlight varies depending on the location, time of day, and season. In such a large country like the United States, this significantly differs from one region to another.
According to the National Renewable Energy Laboratory (NREL) report, the amount of sunlight received per day can range from around 2.5 to 7.5 kilowatt-hours (kWh) per square meter, depending on the location . This means that a solar panel in sunny Arizona will produce on most days more energy than a panel in Seattle.
You can find a good data on the solar potential for your location in the Global Solar Atlas.
What environmental factors affect total energy output of solar panels?
Although each solar panel has slightly different technical characteristics, there are some environmental factors that affect the total electricity output of every panel. It is good to know them if you want to make sure that you are getting the best of your solar system.
These factors are:
The position of panels on the roof is crucial. In the northern hemisphere, panels should face south, eventually south-west or south-east, to achieve the best outcome. In the southern hemisphere, it is the other way around.
#2 Roof angle and tilt
Since the most affordable method is to mount panels on the roof, the angle depends on the pitch of your roof. Although, to maximize panels’ output, you can get adjustable installation, where you are able to tilt the panel according to the season.
The basic rule to determine the proper angle is to tilt the panel by 15 degrees more vertically from the starting position in winter and by 15 degrees more horizontally in summer. For example, panels in New York City should be tilted at an angle of around 40 degrees to maximize energy output .
#3 Geographical location
Your geographical location determines how much sunlight throughout different seasons your solar system gets. Cloudy or overcast days will result in lower energy output compared to clear, sunny days. The same panel will generate more electricity in California than in Seattle, because Seattle gets generally more cloudy days.
A rule of thumb is to avoid shading as much as possible. A commonly used solar panel consists of 60 solar cells. When just 4 solar cells out of these 60 are in shade, the energy production might decrease by 10 percent . Shade on some cells makes other cells work excessively, and thus decreases the lifetime of the solar panel.
Dust blocks sunlight accessing the panel in a similar way like shade. According to the recent study, the efficiency might drop by up to 25 percent due to the dust. To achieve the best performance, a regular cleaning of panels has to make it to the top of your list of household chores.
Solar panels convert the energy of light (not heat) into electricity. Panels are tested under “ideal” conditions, which is in terms of temperature 25 degrees Celsius or 77 degrees Fahrenheit. But when temperature increases by one degree Celsius, panels lose efficiency by approximately 0.4 percent . Colder temperatures are more desirable because cold materials conduct electricity better. The only problem in colder climates is reduced number of sunny days.
It might seem like a lot to take into consideration, but the truth is that the above-mentioned factors are just a common sense combined with physics. Therefore, it should not be such a surprise that either one of these factors or their combination can compromise the production capacity of photovoltaic solar panels that need direct exposure to the Sun.
How much power does a solar panel produce for my direct consumption?
An average quality residential solar panel produces between 250 to 270 watts under ideal sunlight and temperature conditions. Such panel consists of 60 solar cells. One solar cell generates 5 watts, with the efficiency between 15 to 20 percent. The size of the panel in this case is around 65 inches in length and 40 inches in width.
But you can have also good quality solar panels generating as much as 400 watts. You should know, though, that panels with higher output are more expensive and are usually installed when free space is a limiting factor.
On the back of each panel is a number stating the maximum power rating. This number expresses the direct current produced under standard test conditions. Since solar panels produce direct current and our houses run off alternating current, the generated power needs to be converted. During the conversion, further energy losses occur. The losses make around 20 percent .
This means that from direct current produced by solar panels we get 80 percent of alternating current for our use. So, if you want to calculate how many solar panels are needed to cover your household energy needs, you have to take this number into consideration.
For example, you need 5 kilowatts (kW) of alternating current in total. 5 kilowatts have to be divided by 0.8 (as 80 percent efficiency during conversion). The final number you get is 6.25 kW of direct current, which equals 25 panels of 250 watts (6,250 divided by 250 watts equals 25 panels) or 20 panels with higher rating of 325 watts.
Both systems generate the same amount of power, your choice depends only on the available space and money you want to invest, because the 325-watt panels cost more.
The energy produced by a solar system in a day
The expected energy output of a whole solar system is calculated by summing the energy output of all the panels in the system.
Our example, a 5-kilowatt solar system consisting of 25 panels rated at 250 watts each, would have an expected energy output of:
Energy Output = 250 watts x 5 hours of sunlight x 25 panels = 31,250 watt-hours per day, or 31.250 kWh per day
This is enough energy to power a typical American household for a day, assuming an average energy consumption of around 30 kWh per day .
Now that you know how much solar electricity you can expect one solar panel to produce and how much a whole system can produce, you might be wondering about the cost savings that solar panels can bring.
If you are considering getting solar and would like a rough estimate of the cost and savings of installing a solar system, you can use this solar calculator. The calculator will provide you with an upfront cost estimate and an estimate of long-term savings based on your location. Once you have a better idea of the potential savings, you can begin to explore your solar options in more detail and get real solar quotes from local installers.