Turning Light Into Energy

Ever wondered how solar panels convert the sun’s energy into electricity or what to look for when researching solar panels? 

The idea of a photovoltaic (PV) system seems simple; however, with the cost of solar in the tens of thousands of dollars and the return on investment (ROI) extending beyond 10 years in most cases, questions surrounding photovoltaic energy have become more prevalent. 

Given United’s constant pursuit of the Seven Cooperative Principles, the fifth being “Education, Training and Information,” United is always here to help educate and inform its membership on the complexities of solar.  

We know solar panels harness the sun’s energy to generate power for homes and businesses, but what is the science behind a solar panel?

According to the National Renewable Energy Laboratory (NREL), “Photovoltaics gets its name from the process of converting light (photons) to electricity (voltage), which is called the photovoltaic effect.” Solar panels are made up of a series of solar cells, and a vast majority of them are made of an element called silicon. Silicon is a resourceful element found in a multitude of everyday products such as electronics, alloys, construction materials, engine blocks, lubricants and medicine. It is also helpful in solar cells as a semiconductor because it possesses special electronic capabilities, and it is low-cost.

Think of the silicon solar cell as an electrical field made of positive and negative semiconductors holding electrons, awaiting photons (sunlight). After absorbing the photons, semiconductors release electrons that then create an electric current flowing towards the designated negative end of the cell. 

The electricity generated from one single cell is added to the other cells that make up one solar panel. Each solar panel is unique, but the average grid-tied solar panel contains 60 cells or more. A series of solar panels (array) can produce a large amount of direct current (DC) through the photovoltaic effect. Most houses worldwide use alternating current (AC) for electricity.

With this said, DC power created by solar panels must first be converted to AC power before being delivered to the home. Solar inverters, either central or micro inverters, convert photovoltaic DC power to consumer-friendly AC power.

Silicon solar panels are offered in monocrystalline and polycrystalline modules. Both have been proven helpful in different applications. Created using only one crystal, monocrystalline panels offer improved efficiency. Unfortunately, this increased efficiency comes at a greater cost for the consumer. When challenged with limited installation space, monocrystalline panels may be a great option. 

Polycrystalline construction consists of multiple smaller crystals melted together to form a cell. This type of construction is often slightly cheaper. Although less efficient overall and larger in size, the cell construction of polycrystalline allows the panel to attract sunlight from various angles for unfavorable light exposure locations. The choice between the two could come down to the color of the panel. Monocrystalline panels possess a black hue, while polycrystalline panels have a blue color.

The efficiency of solar panels depends a lot on the weather. On sunny days, panels perform much better than on cloudy ones. Energy production from a solar system plummets when it gets cloudy and ceases after sunset. Temperatures also play a significant role in the output performance of each solar panel. According to www.energy.gov, “Solar cells generally work best at low temperatures. Higher temperatures cause the semiconductor properties to shift, resulting in a slight increase in current, but a much larger decrease in voltage.” Existing PV owners may notice that solar systems hardly ever, if ever, produce rated power.

Solar panels conform to Standard Test Conditions (STC), where solar panels are tested with an ambient temperature of 25°C or 77°F. The STC gives a power rating for ideal conditions; however, when solar panels get exposed to real-world weather conditions, the panels rarely see the STC set point. 

It is not uncommon for temperatures to rise above 77°F in Texas, resulting in a slight decrease in production capabilities. All solar panels list the temperature coefficient, which explains the percentage of production loss for every degree over 25°C. The optimal performance of a solar panel occurs during extended daylight hours and cooler weather. NREL provides estimating tools like PVWatts Calculator pvwatts.nrel.gov/pvwatts.php, which considers weather patterns to guide consumers while building a PV system.

Regardless of the solar cell construction, solar panels are durable, with an expected lifespan of 25 to 30 years, often matching the manufacturer’s warranty. The efficiency of a solar panel is highest in the first year. Solar panels degrade slightly every year, effectively producing less and less power. 

NREL says, “A major question in the solar energy industry is exactly how much we should expect solar modules to degrade each year (generally 0.5 percent to 1 percent) and when they will eventually degrade so much that they no longer produce adequate power (often about 20 percent loss from their original output) or become unsafe.”

The first-year degradation loss is typically higher than the annual degradation rate. For example, it is not abnormal for a solar panel to have a first-year degradation rate of 2 percent and an annual degradation rate of around 0.5 percent. Using the example above for a 25-year test, subtracting 2 percent for the first year, equaling 98 percent, and a degradation rate of 0.55percent over the next 24 years results in the panel producing 84.8 percent of the original output. Other weather conditions, such as extreme heat, hail and high winds can affect the effectiveness and lifespan of the solar panel. 

Research and development continues to improve, shortening the degradation gap from year 1 to 25.

Solar panels are an essential source of renewable energy. To maximize the benefits of solar panels, understanding their performance in real-world conditions and using estimation tools is critical.

United is committed to educating members in the ever-changing industry of photovoltaics. United’s energy solutions team has educated and guided members through this puzzling financial investment for years. The cooperative’s new solar solution now takes members from solar education to installation through a third-party installer. United offers this service to its members to educate them and allow them to make informed decisions after being presented with all the facts.

A new way to array is upon us. To learn more about United’s solar solution, contact us at (817) 556-4000 or sign up for a free energy audit if interested in solar.