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Leonardo David is an electromechanical engineer, MBA, energy consultant and technical writer. His energy-efficiency and solar consulting experience covers sectors including banking, textile manufacturing, plastics processing, pharmaceutics, education, food processing, real estate and retail. He has also been writing articles about energy and engineering topics since 2015. Panneaux Solaires
Tori Addison is an editor who has worked in the digital marketing industry for over five years. Her experience includes communications and marketing work in the nonprofit, governmental and academic sectors. A journalist by trade, she started her career covering politics and news in New York’s Hudson Valley. Her work included coverage of local and state budgets, federal financial regulations and health care legislation.
The best solar panels can generate clean electricity for decades, but there is a technical limitation buyers should consider for effective use. Because photovoltaic (PV) cells depend on sunlight to generate energy, their output is diminished on cloudy days and reduced to zero at night. While grid-tied solar systems can offset nighttime use with grid energy, you must pair solar panels with a battery storage system to go completely off-grid.
In this article, we at the MarketWatch Guides team review how weather conditions and the sun’s movement through the sky can affect solar panels. We will also cover how to use energy storage to compensate for the variable nature of solar technology.
Solar panels work based on a physical principle called the photovoltaic effect. Manufacturers combine solar cells made of high-purity silicon with controlled amounts of other elements like boron and phosphorus to create a material capable of absorbing photons, or light particles. Once sunlight hits the surface of a panel, photons transfer energy to electrons within the material. The electrons gain energy and start to move, causing electric current or energy.
All types of solar panels use the photovoltaic effect, but panel performance varies depending on the material used:
Sunlight is the Earth’s most prevalent energy source. According to the National Renewable Energy Laboratory (NREL), the solar radiation reaching Earth every hour contains enough energy to cover worldwide consumption for an entire year. However, because the sun doesn’t always shine, solar panels cannot consistently generate electricity at all times — like on cloudy days with obstructed sunlight.
Cloudy weather negatively affects solar panel productivity because clouds block sunlight. According to the solar installer SunPower, cloudy weather can reduce solar panel productivity by 10% to 25%. Fog has a more drastic impact, reducing solar energy output by around 50%.
However, rainy days can occasionally have a positive impact on solar panels. Rainfall washes away dust and other particles that land on your panels and block sunlight, resulting in clean solar panels that can operate more efficiently.
Since the sun is not out at night, solar panels cannot absorb sunlight to convert it into electricity. While solar panels can technically use artificial light to generate power, this method is not as effective as using a natural light source. Unlike sunlight, artificial lighting is not free — you would need electricity to power the light fixtures. As a result, your electricity consumption may be higher than the output of your solar panels, which can waste energy and money.
Alternatively, you can use a solar battery to store excess energy production for use at night. You can use stored energy whenever you want, whether it be at night or on cloudy days. You can also use a battery bank, like the Tesla Powerwall or Generac PWRcell, as an off-grid electricity source during power outages.
If you don’t want to invest in a solar battery, which can add upwards of $10,000 or more to your total system cost, you can also rely on grid power at night. As long as your system is connected to the power grid, you can draw energy as needed to power your home. However, you will have to pay full retail price for any energy you use.
If you have access to a net metering or solar buyback program, you can use the local power grid as your battery. With net metering, you send the excess energy your solar panels generate during the day back to the grid in exchange for power bill credits. Your utility will then apply earned credits to your power bill to cover your nighttime or other consumption.
For example, say your solar panels send 10 kilowatt-hours (kWh) of excess energy to the grid during the day, and you consume 15 kWh at night. With a net metering program that offers credits at the full retail rate of electricity, you would only have to pay for the 5 kWh difference in energy usage.
However, not all states offer net metering programs. If your electric company does not offer this benefit, your only option for storage is a home battery. While states with net metering policies require utility companies to give you credit for excess solar energy, not every program offers billing credits at the full retail rate of electricity.
Even if your state does not have a net metering policy, you may find energy companies that offer the benefit voluntarily. You can check with your utility company or solar installer to learn more.
Solar panels generate more electricity when exposed to direct sunlight, but can produce some power with indirect light. If your solar array has an energy monitoring system, you will likely notice the following pattern:
A solar power system generates most of its energy around noon, but the kilowatt-hours generated by indirect sunlight also count towards your power bill savings. You can use the World Bank Global Solar Atlas to check sunlight conditions in your location, including direct and indirect sunlight.
Solar experts determine the solar panel wattage and efficiency under standard laboratory conditions. In real-world applications, solar PV systems do not operate at optimal capacity due to changing sunlight conditions. Below are a few factors that affect solar panel efficiency.
The sun’s position in the sky constantly changes depending on the season and time of day. The positioning of your solar panels will also affect how much sunlight reaches their surface. The following
Your solar installer will conduct an assessment of your home and roof orientation to determine the best positioning for your solar panel system.
Solar panels are more productive on sunny days, but their efficiency drops in excessive heat. PV module specifications include a temperature coefficient, a metric that describes expected performance loss per degree Celsius.
For example, a solar module with a coefficient of -0.37% per °C will suffer a power loss of 3.7% with a temperature rise of 10°C (or 50°F). Efficient solar panels have temperature coefficients of less than -0.40% per °C, and some brands have achieved values below -0.30% per °C.
Shadows also reduce the energy production of solar panels. Even a small shadow can affect electricity production if it covers an entire PV cell. Solar installers will analyze shading conditions across your property before designing and installing your PV system to try and prevent sunlight obstructions.
Your solar installer may recommend microinverters if you live in an area where you cannot avoid complete shade. Inverters are an essential component of solar systems, converting the direct current (DC) energy your panels generate into alternating current (AC) electricity to power your home.
In traditional solar panel installations, installers connect all PV modules to the same inverter. This configuration is simple and affordable, but has a key disadvantage — since your panels are wired in series, the shading of one panel will affect the entire circuit. Alternatively, you can install a microinverter on each of your solar panels, which will convert energy directly at the source. This allows your panels to operate independently, reducing the impact of shading overall.
Despite limitations at night and on cloud days, solar can be a worthwhile investment for homeowners. While the upfront cost of a solar panel system is around $2.85 per watt or $15,000 to $20,000 on average, you can lower costs by claiming incentives and rebates. For example, if you buy a 7 kilowatt (kW) system for $19,950, you can save around $5,985 by claiming the federal solar tax credit. In this example, your net system cost would drop to $13,965.
A 7 kW solar panel system can generate more than 9,000 kWh of energy per year with favorable sunshine conditions. For a homeowner paying an electricity rate of 20 cents per kWh, potential energy savings can exceed $1,800 per year. The payback period in this example is 7.8 years, which is short compared to the 25- to 30-year lifespan of solar panels.
High-quality solar panels can last over two decades, saving you thousands of dollars in electricity bills over your system’s lifespan. But, solar panels generate less power during overcast days and produce no power at night. If you want to use solar electricity to cover your total energy consumption, we suggest adding a solar battery. It can also help to participate in net metering if a program is available in your area.
You can work with a solar installer to determine sunlight and shading conditions on your property. Reputable solar companies will conduct a site assessment to determine the best positioning for your panels to maximize sunlight and as a result, generate the most energy savings. Reach out to solar companies in your area to learn more.
Solar panels achieve the highest power output in the hours around noon. During this time, as long as the weather is not cloudy, your panels should receive maximum sunshine.
Solar panels suffer a 10% to 25% productivity loss under cloudy conditions. The impact on performance varies depending on cloud cover and solar panel quality. We recommend speaking with a solar installer to compare solar panel options based on efficiency.
Photovoltaic cells generate electricity whenever sunlight hits their surface. There is no minimum time requirement for sunlight exposure.
Clouds will not necessarily block 100% of sunlight. Even on cloudy days, solar panels can generate some electricity. However, clouds can reduce your system’s energy output compared to sunny days.
We closely evaluated seven crucial factors according to our solar panel installation company methodology to rank the best providers in the industry. Based on a 100-point scale, we came up with each provider’s score out of five stars. Here’s how we assessed each company: Cost and payment options (20 points): Companies that offer cash purchases and in-house loan financing earned full points in this category. Companies also receivebonus points if they offer solar panel leasing or power purchase agreements (PPAs). Services (20 points): Besides solar installations, companies offering backup battery and EV charger installations, energy efficiency audits and system monitoring earned the most points in this category. We also allotted points to companies that completed all their installations in-house (as opposed to contracting out installers). Reputation (20 points): We considered each company’s Google star rating, BBB customer review rating, BBB customer complaint response rate and NABCEP certification status to award each company its reputation score. Warranty (15 points): We verified that each company offers workmanship, product and performance warranties on all of its solar installs. Providers earned more points if their warranties were at or above the industry-standard length (10 years for workmanship and product warranties and 25 years for performance warranties). Customer Support (10 points): Solar companies that offered virtual consultations, a mobile app, 24/7 customer support and high customer satisfaction with backend support earned the most points in this category. Industry Experience (10 points): Providers with 10 or more years of experience in the solar installation industry earned a perfect score in this category. Sustainability (5 points): Companies with a detailed sustainability statement, ESG disclosures, end-of-life panel disposal programs and community partnerships earned all five points in this category.
Leonardo David is an electromechanical engineer, MBA, energy consultant and technical writer. His energy-efficiency and solar consulting experience covers sectors including banking, textile manufacturing, plastics processing, pharmaceutics, education, food processing, real estate and retail. He has also been writing articles about energy and engineering topics since 2015.
Tori Addison is an editor with over five years of experience in the digital marketing industry. Her includes communications and marketing work in the nonprofit, governmental and academic sectors. A journalist by trade, she started her career covering politics and news in New York’s Hudson Valley. Her work included coverage of local and state budgets, federal financial regulations and health care legislation.
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