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SOLAR 101: HOW SOLAR ENERGY WORKS (STEP BY STEP)

Have you ever looked at the solar panels on roofs and wondered exactly what they do, and how? Well, those hi-tech expanses of shimmering glass are actually just one component in a complex network that harnesses the sun’s renewable energy to deliver electricity to the home within.

Let’s take a simple, step-by-step look at how solar power works.

How Do Solar Panels Make Electricity?

STEP 1: Sunlight activates the panels.

Each individual panel is constructed of a layer of silicon cells, a metal frame, a glass casing surrounded by a special film, and wiring. For maximum effect, the panels are grouped together into “arrays” (an ordered series) and placed on rooftops or in large outdoor spaces. The solar cells, which are also referred to as photovoltaic cells, absorb sunlight during daylight hours.

STEP 2: The cells produce electrical current.

Within each solar cell is a thin semiconductor wafer made from two layers of silicon. One layer is positively charged, and the other negatively charged, forming an electric field. When light energy from the sun strikes a photovoltaic solar cell, it energizes the cell and causes electrons to ‘come loose’ from atoms within the semiconductor wafer. Those loose electrons are set into motion by the electric field surrounding the wafer, and this motion creates an electrical current.

STEP 3: The electrical energy is converted.

You now have solar panels working efficiently to transform sunlight into electricity, but the electricity generated is called direct current (or DC) electricity, which is not the type of electricity that powers most homes, which is alternating current (or AC) electricity. Fortunately, DC electricity can easily be changed into AC electricity by a gadget called an inverter. In modern solar systems, these inverters can be configured as one inverter for the entire system or as individual microinverters attached behind the panels.

Regional Solar Potential in the US

than anything else, solar energy potential in the United States is heavily dependent on the panel’s physical location. In the image above, you can clearly see the best regions in the contiguous US for solar power production, stemming primarily from the Southwest.

Although they are not pictured, your assumptions of Alaskan and Hawaiian solar potential are probably correct. Hawaii receives an incredible amount of sunlight (and has tons of solar infrastructure), while any realistic, reliable Alaskan solar power is limited to only the summer season. According to data from the National Renewable Energy Laboratory. the state of Nevada has the highest sun index in the United States, followed by Arizona and New Mexico. Bringing up the rear of the list, the states with the lowest sun index include Washington, Oregon, Ohio, and Michigan.

Solar Energy Potential Throughout the Day

Throughout the course of each day, the intensity of the sun and its position in the sky influence the amount of radiance that can be captured by a solar panel. In the graph above, you can see that solar panels typically have a “peak” production period starting around noon when energy generation is at its highest potential.

With the combination of sun index and daily power potential, it is possible to calculate the approximate amount of solar power that can be generated by a single panel. Systems should be designed (either fixed in one location or transported) to capture as much sunlight as possible from 11 AM to 2 PM.

Seasonal Solar Panel Potential in the US

Last but not least, seasonality heavily affects solar panel potential in the United States, as the sun’s position and the number of sunlight hours differ throughout the year. In this diagram, you can see that solar panels have been positioned facing south at an angle that captures both the summer and winter sun.

Obviously, solar power potential is going to be lower in the winter, due to more dark hours throughout the night. Interestingly enough, however, solar panels tend to operate more efficiently in cold weather (like in most electronics) and sunlight reflecting off of snow can even increase solar power potential during peak hours.

Other Factors Influencing Solar Panel Potential

In any given solar panel system, the actual energy production is going to be heavily influenced by the quality of your materials. In addition to the panel itself, a full-home system with an inverter and wiring will also affect the amount of solar power that can be generated and used.

While we can certainly talk all day about designing the perfect solar kit. below we will answer some of the most commonly asked questions regarding external factors that influence solar panel production potential in the United States.

Do solar panels work on cloudy days?

First and foremost, yes, solar panels still work on cloudy days. Although it is true that solar panels produce electricity most efficiently in direct sunlight, the majority of high-quality generators are able to still harness some sunlight on cloudy days. In general, solar panels will produce roughly 10% to 25% of their peak efficiency in overcast conditions.

Do solar panels work in the snow?

No, if a solar panel is covered in snow, it will not be able to capture light and produce renewable energy. Thankfully, solar panels are usually installed at an angle and their slick surface helps snow slide right off, typically long before any other part of the roof is clear.

Will solar panels work in the shade?

Much like on a cloudy day, yes, solar panels will still work in the shade. If a tree is limiting the amount of sunlight that can reach a panel, it will produce energy at a far less efficient rate than with direct light. With this in mind, solar panel systems are designed to minimize the amount of unavoidable daily shade.

Do solar panels work in the rain?

If the sun is still out in some capacity, then yes, solar panels will still be able to work in the rain at a 10% to 20% efficiency rate. Solar panel systems are weatherproof, and the rain is actually very helpful in providing a free cleaning service. Rain washes away built-up dust and debris which can cause a solar panel to produce at far less efficient rates than normal.

Do solar panels work during a power outage?

In a grid-tie system, solar panels do not produce electricity during a power outage. However, if you have a battery-backed off-grid solar energy system, then you will still be able to produce and use solar energy during a temporary or prolonged grid power outage.

Angle

The angle or tilt of a solar panel is also an important consideration. The angle that a solar panel should be set at to produce the most energy in a given year is determined by the geographical latitude. A general rule for optimal annual energy production is to set the solar panel tilt angle equal to the geographical latitude. [6] For example, if the location of the solar array is at 50 o latitude, the optimal tilt angle is also 50 o. Essentially, the closer a solar panel is located to the equator the more the panel should be pointing straight up. The closer the panel is to the poles, the more they should tilt towards the equator. [3]

The angle of solar panels can also influence the power output due to climatic and environmental factors. In northern climates, snow accumulation on low-tilt panels can reduce or completely block the Sun’s rays from reaching the solar panel during the winter months. Although this effect will vary for every location, one study in Edmonton, Alberta, Canada concluded that the annual energy loss due to snow accumulation ranges from 1.6% at optimal tilt (53 o ) to 5.3% at low tilt (15 o ). [7] Additionally, low-tilt solar panels are more susceptible to soiling by dirt and debris which can also partially block the Sun’s rays.

For further reading

For further information please see the related pages below:

• Wikimedia Commons. (August 11, 2015). Fixed Tilt Solar Panel [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/2/2c/Fixed_Tilt_Solar_panel_at_Canterbury_Municipal_Building_Canterbury_New_Hampshire.jpg
• Robert Foster, PV Array Tilt, Solar Energy, 1st edition. Boca Raton, USA: Taylor and Francis Group, 2010, chapter 6/page 143
• 3.03.13.2 Dave Llorens. (August 11, 2015). Which direction should solar panels face? [Online]. Available: http://www.solarpowerrocks.com/solar-basics/which-direction-should-solar-panels-face/
• Matthew L. Wald. (August 11, 2015). How Grid Efficiency Went South [Online]. Available: http://www.nytimes.com/2014/10/08/business/energy-environment/how-grid-efficiency-went-south-.html?_r=1
• NRCAN. (August 18, 2015). Heating Your Building with Solar Energy [Online]. Available: http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/canmetenergy/files/pubs/SOLAR-HeatingBuildingWithSolarEnergy.pdf
• Gevorkian, Peter, Array tilt angle loss, Solar Power in Building Design, 1st edition. United States of America: McGraw-Hill, 2008, chapter 4/page 109
• Northern Alberta Institute for Technology. (February, 2018). Solar Photovoltaic Reference Array Report [Online]. Available: https://solaralberta.ca/sites/default/files/NAIT%20Reference%20Array%20Report.pdf

Solar power in the United States

With 95,209 MW of solar power online and more on the way, the U.S. currently has enough solar power capacity to power 18 million households. A report from the National Renewable Energy Laboratory determined that solar panels covering a collective area of 22,000 square miles—roughly the area of Lake Michigan, or just over six tenths of a percent (.6%) of the country’s total land area, could provide enough electricity to power the entire United States.

Solar energy is typically harnessed using either photovoltaic (PV) or concentrated solar power (CSP) systems. Photovoltaic systems are by far the more common and versatile of the two. Photovoltaic systems generate electricity directly from sunlight via solar cells: When solar radiation (sunlight) strikes a photovoltaic solar cell, the light’s photons ionize semiconductor material (usually silicon) in the solar cell, which causes electrons to break free of their atomic bonds and creates an electrical current that can then be either directed or stored in a battery.

Solar cells absorb specific wavelengths of light. Other wavelengths are either reflected, too weak to be efficiently converted (infrared), or create heat instead of electricity (ultraviolet). However, solar cell technology continues to improve, increasing the efficiency of the conversion process.

The second-most-common method of harnessing solar energy is the concentrated solar power (CSP) installation. CSP plants produce electricity indirectly using devices known as solar thermal collectors, which FOCUS solar energy to heat water, which then becomes steam and moves a turbine whose motion generates electricity. Globally, current CSP installations generate only a fraction as much energy (6,387 MW) as photovoltaic systems (843,086 MW),

Solar power by country

Worldwide usage of solar energy varies greatly by country, with the top 10 countries representing approximately 74% of the photovoltaic market. As of 2021, China has the largest solar energy capacity in the world at 306,973 megawatts (MW), which produces roughly 4.8%-6% of the country’s total energy consumption. It is followed by the United States at 95,209 MW and Japan at 74,191 MW.

However, total capacity is only one way to view solar production. Another method is to examine solar penetration—that is, the percentage of each country’s total energy consumption that comes from its solar installations.

Top 10 Countries with the Highest Percentage of Solar Energy Penetration (2021 IEA):

The origin of modern solar cells can be traced back to 1954, when Bell Labs introduced the first PV device capable of producing a usable amount of electricity. The energy crisis of the 1970s resulted in a groundswell of interest in using solar energy to produce electricity for homes and businesses. At the time, the high manufacturing costs of solar cells (a relatively new technology) made large-scale applications impractical. Over time, the cost of photovoltaic cells has dropped dramatically, including a decrease of more than 59% over the past decade, making solar affordable for not only utilities and corporate offices, but for private homes as well.

Here are the 10 countries with the most solar power capacity:

• China. 306,973
• United States. 95,209
• Japan. 74,191
• Germany. 58,461
• India. 49,684
• Italy. 22,698
• Australia. 19,076
• South Korea. 18,161
• Vietnam. 16,660
• Spain. 15,952