that our planet receives from the sun in just one hour. The sun sends to our planet around 222,500,000 terawatt hours (TWh) of energy every year. For comparison, in 2014, the total amount of energy we consumed was 109,609 TWh1. This means that in 2014 the sun provided 2,000 times more power than we used in all our activities.
But the sun’s energy is not readily available to our use. It has to be converted into electricity. The efficiency of this conversion affects the amount of solar energy we are able to harvest at the moment. The most efficient solar panels on the market have the maximum efficiency of 22%, but most solar arrays you see around reach only up to 15%2.
So even though, solar energy is free and abundant, there is still a lot of space for improvement when it comes to our ability harvesting it. And the efficiency of solar panels is just one of the limiting factors.
Factors affecting solar panel output
Although each solar array is different, there are seven general factors affecting the total electricity output of every system. These factors are:
- Size: Most of the residential solar systems range from 1 kilowatt (kW) to 5 kW in size. For better idea, 5 kW might consist of 20 panels (depending on your system), generating enough energy to cover the entire electricity need of an average family house 3.
- Direction: 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.
- Roof angle: 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 4.
- Location: Your geographical location determines how much sunlight throughout different seasons your solar system gets. The same panel will generate more electricity in California than in Seattle, because Seattle gets generally more cloudy days.
- Shade: 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% 5. Shade on some cells also makes other cells work excessively, and thus decreases the lifetime of the solar panel.
- Maintenance: 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% 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.
- Temperature: 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 76 degrees Fahrenheit. But when temperature increases by one degree Celsius, panels lose efficiency by approximately 0.4% 2. Colder temperatures are more desirable because cold materials conduct electricity better. The only problem in colder climate is reduced amount of sunny days.
It might seem like a lot to take into consideration, but the truth is – many of above mentioned elements are just a common sense combined with basic physics. Therefore, it should not be such a surprise that either one of these factors or their combination can compromise the production capacity of solar panels.
How much is it anyway?
The electricity produced by one solar panel
The energy output of a solar panel varies based on the size of the panel you have and its efficiency.
On average a modern solar panel produces between 250 to 270 watts under ideal sunlight and temperature conditions. This is the power equivalent to lighting 84 compact fluorescent bulbs for 1 hour a day6. Such panel consists of 60 solar cells. One solar cell generates 5 watts, with the efficiency between 15 to 18%. The size of the panel in this case is around 65 inches in length and 40 inches in width2.
But you can have also panels generating as much as 325 watts. You should know, though, that panels with higher output are more expensive and are usually installed when space is a limiting factor.
That’s not all…
On the back of each panel is a number stating a 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. Usually, they make around 20%7.
This means that from direct current produced by solar panels we get 80% of alternating current for our use. So, if you want to calculate how many solar panels are needed to cover your energy needs, you have to take this number into consideration.
For example, you need 5 kilowatts (kW) of alternating current. 5 kW has to be divided by 0.8 (as 80% efficiency during conversion). The final number you get is 6.25 kW of direct current, which equals 25 panels of 250 watts or 20 panels of 325 watts 7.
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.
In the end, you should know that the maximum power rating of a solar panel provides just a general information to guide your decision. The real electricity output will be always dependent on specific conditions at your location. And even if solar doesn’t sound promising to you at the moment, in this great era of the green technology advancement, we can expect astounding solutions for the future.