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Solar energy comprises two components – light energy from the sun, also referred to as photovoltaic or PV energy, and heat or solar thermal energy.
Photovoltaic energy is collected using PV panels, commonly referred to as solar panels. A phenomenon known as the photovoltaic effect converts sunlight directly into electricity. Light particles (photons) strike the surface of specially prepared elements incorporated into solar panels, releasing electrons and generating an electric current. Adding more PV panels generates more electricity.
Residential and commercial buildings can employ thermal collectors to trap solar thermal energy by heating water within the collector, then piping it throughout the home or building to heat spaces within.
Solar thermoelectric systems used for utility-scale electrical power generation make use of mirrors to concentrate the sun's heat energy into a receiving medium such as molten salt to as high as 1,000 degrees Celsius. This stored thermal energy then converts water to steam to power a turbine connected to an electrical generator.
Photovoltaic (PV) solar panels exposed to sunlight convert the light spectrum of solar energy into electrical energy – a phenomenon known as the photovoltaic effect.
A PV panel consists of dozens of solar cells made of special light-sensitive semiconductors that conduct electricity when light strikes them. Each solar cell consists of a 'p-type' semiconductor and an 'n-type' semiconductor joined to form a 'p-n junction.' The p-n junction is where the photovoltaic effect occurs. Adding (or "doping") the semiconductors with specific materials promotes the flow of electrons from one side of the interface to the other when light strikes, generating electricity.
Energy and power are closely related. Energy is the ability to cause change. Power is the rate at which energy is applied – in other words, power measures how quickly energy is used or transmitted.
The standard unit of energy is the joule (J). Dissipating one joule of energy in one second defines the watt (W) as a standard power unit. In mathematical terms:
In electrical terms, commonly used power units are the kilowatt (1 kW = 1,000 W) for residential and commercial solar systems and megawatt (1 MW = 1,000 kW) for large, utility-scale solar installations.
From a power output standpoint, a residential solar installation may incorporate 30 solar panels, each capable of generating 390 watts of power, and be rated at 30 x 390 = 11,700 W or 11.7 kW.
If the sun shone for five hours with enough intensity to generate the full power rating of the solar installation, the 30-panel solar installation would have developed 11.7 kW x 5 hr = 58.5 kilowatt-hours (kWh) of energy.
The surge of interest in solar energy to help feed our power-hungry world is accelerating. There are plenty of reasons why this is so.
Solar is a renewable energy source, always available somewhere on our planet and virtually inexhaustible. Estimates suggest that fully harnessing the energy the earth receives from the sun in one hour would satisfy our global energy requirements for one year. The Union of Concerned Scientists calculated that 18 days' worth of solar energy received from the sun is equivalent to all the energy stored in our global reserves of coal and fossil fuels combined.
Solar energy conversion using PV panels to generate electricity is non-polluting and silent.
Solar-generated electricity is an effective way to reduce a homeowner's or business owner's electrical utility bill. Where net metering is available, surplus power generated from solar can be fed back to the electrical grid and paid for by the utilities to lower electrical bills.
Solar energy is versatile. Aside from generating electricity using solar panels, solar thermal devices can store heat from the sun to heat buildings and drive turbine electric generators.
Solar systems can be deployed effectively in almost any location. In colder climates, solar panels operate more efficiently by reducing losses that occur at elevated temperatures. Further, the power conversion efficiency of PV panels has improved dramatically over the years, allowing installations to generate viable power even in less sunny locations.
Solar energy systems are relatively simple to install and operate, making them ideal for remote locations where no other electricity sources are economically viable.
Solar installations can be readily scaled in size to generate power sufficient to supply single-family households or utility-wide power generation requirements.
Generating solar energy involves minimal operating and maintenance costs and effort. The primary requirement is to keep solar panels clean to allow maximum solar energy to reach the active PV material. In simpler solar systems, there are no moving parts. Solar panels can last decades. Inverters used to convert the direct current (DC) electricity from the panels to alternating current (AC) power used by households can operate reliably for 10 years or longer.
Installing a solar power installation may increase the value of the home or building.
Local, regional, and federal government sources often extend tax credits, low-interest loans, subsidies, and other financial incentives to support green solar power initiatives.
Technological advances are rapidly transforming the solar energy field. Innovative discoveries in quantum physics and nanotechnologies offer nearly limitless opportunities to develop new ways to convert solar energy into electricity more efficiently and cost-effectively.
Developing the solar energy industry offers a comprehensive and expanding range of sustainable job creation prospects. Those transitioning from traditional fossil fuel occupations can find a rewarding career in the solar energy industry.
For all the benefits available from solar energy, some drawbacks deserve consideration.
The current cost of residential and commercial installations may result in the breakeven point for the return on investment being several years out. In areas where utility energy costs are low, the decision to convert to solar power may be driven more by an altruistic philosophy ("let's not harm the environment") than a financial one. However, as with computers and other technologies, advances in solar tech are driving costs down. According to Espen Moe, professor of political science at Norwegian University of Science and Technology in Trondheim, California boasts a well-advanced solar energy industry, and costs have dropped by 90% from 2010 to 2020.
Solar energy is intermittent by nature. Output can be altered significantly by inclement weather and seasonal changes and naturally, power generation drops to zero at night.
Storing solar energy can be a costly proposition. Fortunately, battery technologies undergo continuous improvement and become more efficient and cost-effective solar energy storage for use at night or during low-light conditions. However, for many homeowners, the most economical option is to use the energy generated by solar during the day and rely on the electrical grid overnight.
Solar panels require a lot of space. The surface area of photovoltaic panels increases in direct proportion to the amount of electricity to be generated. Space limitations can dramatically limit the amount of power available from an installation.
Many view solar panel installations as unsightly. Where esthetics are concerned, the practicalities of solar often become a secondary consideration.
Questions remain about the environmental impact that solar technology imposes over its entire lifecycle. It is useful to assess the potential toxicity of solar components and the greenhouse gases emitted to extract the raw materials, manufacture the goods, and collect and recycle them at the end of their useful life. Such data drives improvements in these areas.
There are multiple steps involved to design and install a residential or commercial solar installation that performs as expected. After all, who needs surprises? Although the recommended steps mentioned below refer to residential solar installations, they apply equally to most commercial applications.
Confirm there are no legal restrictions to installing your solar system. Consider present or impending bylaws or regulations set by your local government or neighborhood association and strata council that may impact your plans.
Review your home insurance policy. Confirm that appropriate coverage is available and affordable.
Perform a home energy audit. Become familiar with a home's total electricity usage – there may be some cost-effective efficiency measures to implement before considering a solar energy system.
Energy audits analyze energy flows that highlight ways to improve efficiencies and reduce wasteful losses of energy.
Weather-proofing leaky windows, doors, and vents are practical first steps.
Assess large appliances and electronics for energy efficiency – it may be time to replace older equipment with more efficient options.
Switch to LED lights – they use much less energy and typically last many times longer than their incandescent counterparts.
Rebates and other financial incentives to support the purchase of a solar system may only be available after undertaking a qualifying energy audit.
Before selecting a solar system, it's a smart move to consider what other changes in a homeowner's electrical requirements may arise. Perhaps by making the home more energy-efficient, the electrical demand drops significantly and will stay that way for years. If an electric vehicle becomes a future reality that will increase the electrical demand. Sizing a solar system will need to accommodate such changes.
Have a qualified professional assess the physical aspects of your home to determine its solar potential.
Is the roof large enough? Is it sufficiently exposed to the sun, or will the panels require ground mounting? Is ground mounting an option and if so, at what cost?
In what condition is the roof? Is new roofing required before panels get mounted? What is involved to re-roof once panels are installed?
Are there nearby trees or structures that can create shading concerns? Will they become an issue in the future?
Investigate the options available to support a solar installation. Sole ownership of a solar system may not be the only choice. Other programs may offer alternatives worth considering.
Shared solar or community solar – Such a program benefits members who pool their financial resources to purchase solar power from an on-site or off-site system owned by a utility, the community, a solar development company or a non-profit concern. This option is ideal for those who rent their home, for those whose residence does not have the right physical requirements to support a standalone solar installation, for those who cannot or choose not to pay for their own system, or for those who don't want to be responsible for operating and maintaining a system.
Solar leasing – This option is similar to a shared solar arrangement – purchasing solar power from another entity that owns and maintains its system. Payment is generally a fixed monthly fee involving a small sign-up cost or none at all.
Power purchase agreements or PPAs – In this financial arrangement, a solar developer undertakes all the steps to get a solar installation permitted, financed, designed and installed for a homeowner, usually incurring no upfront costs. In turn, the homeowner signs a PPA guaranteeing to pay the developer a fixed rate for energy produced over the installation's lifetime. This fixed rate is typically lower than that available from the utility grid.
Solarize program – Some areas support a Solarize program, enabling homeowners to pool their financial resources, select their solar installation company and negotiate lower-cost energy rates than that offered by the local power utility. The process of building a more extensive community solar system takes advantage of economies of scale to lower per-unit installation, operation, and maintenance costs for homeowners who wish to participate.
Collect at least three quotes from qualified solar contractors. The standard certification for solar installers in the United States comes from the North American Board of Certified Energy Practitioners, or NABCEP. Topics to discuss with potential installers include:
Their familiarity with local permitting and power utility interconnection procedures
References for installations from other customers in the area
Proof of licensing and certification, including their electrician contractor's license and possibly their general contractor's license if local governing authorities require it
Details of their warranty on the installed solar system and its components and who is responsible for what
Any existing or pending judgments, liens, or other legal actions against the contractor.
Your quotes should inform you about:
The upfront cost of your installed solar installation
The system's performance specifications and warranties
Existing and forecast utility energy costs you pay for
Whether your utility supports net metering and will purchase your surplus solar energy to feed back to the electrical grid
Monthly energy savings that determine the number of years it will take to pay back the cost of your solar installation
The life expectancy of the system
The expected energy savings to be realized over the life of the system.
Sign a contract with the PV system installer offering the best value based on:
Price, estimated cost per kilowatt-hour of energy generated and terms of payment
Their ability to secure required permits and inspections
Their willingness to help identify and access available rebates, tax benefits and other financial incentives
Quality and performance ratings of the equipment offered
Component and system warranties
Delivery and installation timeframes
The quality of training offered to operate the installed system
Their ability to provide timely after-sales service as required.
Apply for utility and government rebates if the installing contractor does not do so directly for their benefit. Applications require that the solar installation is complete and operational. Refer to the N.C. Clean Energy Technology Center at N.C. State University's Database of State by State Incentives. In addition to state incentives there are federal income tax credits for energy efficiencies to consider as well.
Be prepared to change your energy consumption habits to squeeze the most value from your PV system. Understand the rate structures that your utility applies to your monthly bill, such as tiered rate or time-of-use rates where you'll pay premium prices for electricity. Your solar installation may be the ticket to reducing or eliminating such premiums, especially if you incorporate solar batteries with your system.