To begin exploring the factors that contribute to the overall efficiency of residential solar panels we must first define efficiency itself. Essentially, solar panel efficiency is its ability to convert sunlight into electricity. As we have previously covered, this conversion of energy occurs via the photovoltaic effect. Another way of thinking about efficiency is considering the ratio of maximum power output to the total power delivered to the panel by the solar irradiation. Currently the most efficient solar panels in the market have efficiency ratings up to 22.5%, however, majority of the panels installed in the U.S. range from 14% - 16%. While these numbers may seem low, solar panels are still able to generate plenty power for your home. And with solar technology advancing at extraordinary speeds, those ratings are always improving.
EXAMPLE OF EFFICIENCY CALCULATION
In the U.S., specifications about solar modules needs to be measured under Standard Test Conditions (STC). That is:
Solar irradiation of 1000 W/m^2 (1000 watts every 1 squared meter of panel area)
Module temperature of 25 degree celsius
Solar irradiation angle of 45 degrees
KEY FACTORS IN SOLAR PANEL EFFICIENCY
As one can assume solar panels need to be exposed to the sun in order for them to perform to their best potential, however, that is not always the case. Trees, buildings, clouds or other obstructions casting a shadow over the panels, can ultimately reduce the efficiency of the solar array. Most solar cells are connected in series, so whenever one solar cell is under shade its performance drops, therefore the performance of the rest of the cells also decreases. Fortunately, a new technology to address this problem is now available in the market. Bypass diodes can be inserted in parallel with a string of solar cells and they do exactly what their name depicts. They allow current to bypass a poorly performing set of cells that are under shade.
Solar panels in the Northern Hemisphere should always be facing south so during the day the panel can catch the greatest amount of solar radiation possible. Most of the energy reaching the panel from the sun comes in a straight line. An array will capture more energy if it is oriented directly at the sun. Perpendicular to the straight line between the position of the panels installation and the sun. This is why it is best to position panels towards the terrestrial equator (south for northern hemisphere or north if located in southern hemisphere). There exist certain solar tracking mechanisms that increase power output by tracking the path of the sun but for residential purposes the cost of solar trackers does not exceed the cost-benefit-analysis.
One would assume that if the temperature is higher a solar cell would be more efficient but this is actually false. As the actual temperature of a solar cell increases, its efficiency decreases. High temperatures within the cell create a certain resistance for the current flowing through. The hotter the material is, the slower the electrons can flow through the cell, which leads to a decrease in efficiency. There are different approaches that manufacturers and installers take to account for temperature effects. When a company is making panels, the use a thermally conductive substrate to help vent excess heat from the glass layer. Most installers ensure there is a free flow of air above and below the panels when they are mounted by elevating the panels a few inches off the roof.
For the most part, solar panels require minimum maintenance, especially if the system is grid-tied. However, it is recommended to clean them on a regular basis due. When dirt and dust accumulate on the panels, the efficiency of the array can be affected. There is no specific method as to how to clean them but water will do that job.
These are the main key factors that every homeowner who owns or plans to own a solar system should take in consideration to make sure their system is operating at its full potential.