Frequently Asked Questions about Solar
How Does Solar Work?
How do solar panels work?
Solar photovoltaic (PV) panels are composed of solar cells that convert sunlight into direct current (DC) electricity. The DC electrical charge is then converted into alternating current (AC) electricity by a power inverter so that it can be used for your household electricity needs. Many cells are assembled to create a module (also called a panel), and many modules can be linked together to form a solar array.
What is a kilowatt(kW)?
A kilowatt is a measure of electrical power that is equivalent to 1,000 watts. Kilowatts and watts both describe a rate of energy transfer; a watt is defined as one joule per second. Your electrical bill charges you for electricity in terms of kilowatt-hours (kWh). One kilowatt-hour is a unit of energy that is equivalent to one kilowatt of power expended for one hour of time. For example, an appliance that is rated at 1,000 watts (1 kW) and operates for one hour will use one kilowatt-hour of energy.
If you have a 1 kilowatt solar system and 5 peak sun hours per day (an approximate average for Utah), then your 1 kilowatt solar system will produce 5 kilowatt-hours of electricity per day (a certain amount of energy is lost as sunlight is converted to DC, then AC, power, so an average 1 kW solar PV system in northern Utah will generate, on average, 1,400 kilowatt-hours a year).
1 US Department of Energy, “Photovoltaic Basics.” Energy Basics. <https://energy.gov/eere/solar/articles/solar-photovoltaic-technology-basics>
What benefits does solar provide?
Solar is a fuel-free energy resource, which means it is an infinite and inexhaustible resource with no volatile fuel costs. Solar is also a pollution-free energy resource; the more solar energy we use, the cleaner our air and water. After the up-front initial cost, solar provides immediate energy savings and greater energy stability. Solar also reduces line losses on the grid and provides energy to the grid during the daytime, when energy is most expensive and in high demand.
What are solar PV panels made of?
A: The majority of solar PV cells are made from crystalline silicon. Silicon is the second most common element in Earth’s crust (after oxygen) and, by mass, is the eighth most common element in the universe. In addition to crystalline silicon cells, solar panels can be made of cadmium telluride, copper indium gallium selenide, gallium arsenide multi-junction, thin-film silicon, and other materials.
How long do solar panels last?
Solar panels have an expected lifespan of at least 25 years (there are panels installed in the 1970s that are still generating power), and they are typically warrantied for 25 years. They are generally made with tempered glass that is rated to withstand a direct vertical impact of a one-inch diameter hail stone traveling 50 miles per hour.
Solar inverter lifetimes range from 5 to 15 years (though micro-inverters and some string inverters have 20-25 year lifetime). Depending on the inverter, you may need to replace the inverters once during the life time of the panels (costs for replacement vary depending on the inverter). Solar panels and inverters are usually covered by warranties for the lifetime of the product, so if you need to replace a panel due to manufacturing defect it should be covered by the warranty. If you need to replace a component of your solar system due to damage, the solar contractor should be able to replace that specific component (panel, inverter, etc.) individually.
What is the carbon footprint of solar?
Producing solar panels does require energy, which produces pollution and carbon dioxide emissions. The good news is that as creating solar panels has become more efficient, and the energy payback time (EPBT) has decreased significantly. In 1970, the EPBT for solar was 40 years, but as of 2010 it’s only 6 months! This means that after 6 months, the green energy produced by your solar panels will offset the emissions produced during their creation.
Most solar cells and modules are made of crystalline silicon, which use wafers of purified silicon. Purifying and crystallizing silicon are the most energy-intensive parts of the manufacturing process, but other parts of the process that consume energy include cutting the silicon into wafers, processing the wafers into cells, assembling the cells into modules, encapsulating them in glass and frames, and the overhead energy used by manufacturing facilities. The PV industry generally uses “off-grade” silicon from the microelectronics industry that is then recrystallized. While producing energy with photovoltaic (PV) cells does not emit pollution or use energy resources, producing the panels themselves does consume energy, which, depending on the energy source, produces pollution and CO2 emissions.
According to a 2012 report issued by Columbia University, the average energy payback time (EPBT) for US solar is 6 months.
According to a 2004 National Renewable Energy Laboratory study that analyzes several different panel technologies, it takes 1 – 4 years for the energy savings accumulated by producing electricity from solar to equal the energy cost of producing the panel. Solar panels generally have life expectancies of 30 years, so 87% – 97% of the energy produced by the panels is clean energy (i.e. no pollution and/or greenhouse gas emissions).
NREL: What is the energy payback for PV?
Mother Earth News: Dispelling the Myths of Solar Electricity: Energy Payback
Columbia: How Long Does it Take for Photovoltaics to Produce the Energy Used?
Solar and My Building
What’s the difference between solar photovoltaic (PV) and solar thermal (or hot water)?
Solar PV systems convert sunlight directly into electricity using semiconductor technology. Solar thermal systems, also known as solar hot water, use the sun’s light to directly heat water and/or space for homes and businesses. There are several solar-thermal system configurations which employ the sun’s energy to heat water; the most appropriate for Utah’s climate, where freezing temperatures are common, is a closed-loop, active, solar hot water system. Closed-loop solar thermal systems use the sun to heat a heat-transfer fluid in the collector. Heated fluid is pumped from the collector in the bottom of the solar storage tank into a heat exchanger where heat energy is transferred from the fluid to potable water. Heated water is then held in the storage tank ready for use, with a conventional system providing additional heating as necessary.
How will I know if solar energy can work for me?
Solar panels work best when they are installed facing south or west. If you have a large area of roof that faces either south or west and does not receive significant amounts of shading, your home is probably suitable for rooftop solar panels. If you have a flat roof, or you do not have optimal roof space due to shading issues, you will either need to mount the solar panels on an angled rack or use a ground- or pole- mounted system located on an auxiliary structure (like a garage) or in a sunny part of your yard. If your roof is very steep, some contractors may charge an extra fee to install solar. Most buildings can accommodate rooftop solar installations, as long as you have some sunny, south- or west-facing roof space. To get more information about your site, contact a solar contractor.
Why do solar panels need to go on south- or west-facing roof?
There are a number of factors related to your roof that can drastically affect the suitability of solar on the roof of your home. Some of these include: orientation (north, east, south, west), pitch, shading, and others. Living in the northern hemisphere, it’s ideal to have a roof that faces due south, isn’t very steep or flat, and is free of shading from things like trees and chimneys. It’s important to understand these unique characteristics before installing solar panels on your home. Of course, a solar contractor can help determine the suitability of solar on your home.
How much electricity will my solar system generate?
The output of your solar energy system will depend on the amount of sunlight the panel receives, the tilt of the panel, and the type of panel you use. The average Utahn uses around 9,000 kilowatt-hours of electricity annually, and a 6.2 kilowatt system would cover 100% of that usage.
Why are solar permits required?
Like many other home improvement projects, solar installations require a permit to ensure the system is safe and meets all applicable codes, standards, and local requirements. The permitting process differs across jurisdictions, so be sure to inquire as to your local standards before getting started on a project. A solar contractor will make the process a snap, filling out and submitting forms to your local building department for you.
What kind of maintenance is required for solar panels?
There aren’t any moving parts in a solar panel, so maintenance is minimal. Solar panels should be sprayed down periodically (usually in the spring or summer) with warm water to prevent dust and pollen build-up (the thin film of dust cuts out a little bit of light from hitting panels, reducing the amount of electricity they make). Ensuring that your solar panels are free of debris will help them operate and their maximum potential. Be sure to be safe and never risk injury trying to climb up on your roof to clear the panels, and avoid scratching the panels while attempting to clear them.
Do solar panels work in the winter? What about snow removal?
Solar panels operate perfectly well in the winter, especially if you have good sun exposure and many sunny days a year (which Utah does!). Winter weather actually offers some advantages. Photovoltaic panels, like other electronics, work best in the cold. Too much heat actually reduces the output of silicon solar panels. Winter means fewer hours of daylight, but most homes use much less electricity in the winter (i.e. no cooling needs). As for snow removal, you will want to speak with the contractor about any recommended solutions for removing snow, depending on where your system is located and how steep your roof is. One viable solution is a “roof rake” to get rid of some of the snow. With some of the panels exposed, current will start to flow, creating some heat on the panels’ surface that should melt the snow. On many days, the heat of the sun and the panels themselves will take care of any snow.
What if I can’t install solar on my property?
If you can’t install solar on your roof, you may be able to install solar on a pole-mount system in your backyard, or on an accessory structure like a garage, shed, or patio shade. If you are a renter or live in an apartment, you probably can’t install solar at this time.
Is it possible to buy solar hardware for “do-it-yourself” projects?
You can install solar on your roof as a “do-it-yourself” project, but you will need to go through the permitting and approval process as specified by your local permitting jurisdiction. Your installation will need to be approved by professional engineers, building officials, and inspectors. In order to interconnect with Rocky Mountain Power, you need to receive a government inspection.
Connecting to the Grid
What’s the difference between an off-grid and a grid-tied system?
Grid-tied systems are the most common type of solar PV system. Grid-tied systems are connected to the electrical grid and allow residents of a building to use solar energy as well as electricity from the grid. Grid-tied systems do not need to produce 100% of the electricity demand for a home or business. When there is no demand for energy, the solar panels send excess electricity back out into the grid for use elsewhere. When a home or business is using energy, but the solar panels aren’t producing enough energy (at night, or on a stormy day), electricity from the grid supplements or replaces electricity from the panels. Living with a grid-tied solar PV system is no different than living with utility electricity, except that some or all of the electricity you use comes from the sun. However, a grid-tied system will not continue to provide power during a utility power outage. Due to current regulations and equipment requirements, grid-tied solar PV systems are designed to shut off when any change to the incoming power source (from the utility) is detected. This is a safety measure.
An off-grid solar system does not connect to the utility grid at all. As such, the solar PV system must be sized to cover the entirety of a homeowner’s electricity usage. Almost all off-grid systems require a backup energy source for times when energy consumption exceeds generation.