DC-to-AC Inverters for Your Solar Equipment
In your solar power system, you need inverters to take the low-voltage, high-current signals from the PV panels and convert them into 120VAC or 240VAC, which is directly compatible with grid power. Inverters cost around $0.70 per watt, or around $2,600 for a typical application. From a reliability standpoint, they are generally the weak link in any PV system, so quality is a must.
Most installations use only one inverter, but for big systems, having several inverters is common. You can install an inverter that's larger than the power output of the array you're installing, and then at a later time install more panels.
There are two basic types of inverters for residential applications: string inverters and microinverters.
String inverters: String inverters are large boxes mounted near your power meter or main fuse box. In the vast majority of applications, only one inverter is used. It's of critical importance to design the "strings" of PV panels that feed into an inverter, a job that's almost always better left to the experts.
String inverters are the least costly option for the amount of energy a system can output, and the technology has been proven over years of widespread use. But keep in mind that shading becomes a problem because arrays are arranged into series and parallel "strings." If a single panel is shaded, the entire string suffers, and the total energy output of the inverter suffers as well.
Microinverters: Microinverters are the new fad. Each PV panel is outfitted with its own inverter, and the output of each is AC (which matches grid power). The number of microinverters matches the number of PV panels. In the future, it's likely that the vast majority of systems will use microinverters, but for now they're relatively new and the reliability risk is high.
Pay attention to these specifications:
CEC-Rated Power Output: This tells you the maximum output watts from the inverter and varies over operating temperature.
Maximum recommended PV input power: This must never be exceeded by the power output from the combined panels or the output becomes clipped, which means that your inverter runs inefficiently. In other words, you must match the inverter to the panel array properly. Use PV Watts (enter "PV Watts" into your search engine) to find out whether your inverter is large enough for the array you're considering.
Maximum open circuit voltage: The PV array's maximum open circuit voltage must always be less than the inverter's limit or damage may occur. Calculating this number for a given array is a complex engineering problem.
PV Start Voltage: This tells you when the inverter will begin to operate. In the morning, when the sun comes up, the PV panels begin to output power, but inverters require a minimum amount before they start outputting their own power into the grid. This is an important specification because it relates to the overall efficiency of a system. You want your system to run as long as possible over the course of a day.
Maximum Power Point Tracking (MPPT) Range: MPPT circuits enable the inverter to harvest the most amount of energy over the course of a day.

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acid rain
A mild acidic solution that falls in rain or as dry particles caused when fossil fuel burning produces sulfur dioxide and nitrogen oxides. Acid rain has been linked to damaging effects on waterways and forests.

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active solar design
A strategy for designing high-performance, ultra-energy-efficient buildings. Active solar incorporates all the elements of a passive solar design with additional mechanical equipment, such as pumps or fans, to take advantage of the heat from the sun.

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alternative energy sources
Wind, hydro (water), biomass (fuel from natural material such as crops and agricultural waste), and solar power.

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biodegradable
Made from materials that will decay and break down into naturally occurring elements in a fairly short amount of time.

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biomass
Fuel made from natural material such as crops and agricultural waste.

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Bokashi
A Japanese term referring to a process of fermenting organic matter

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carbon emissions
Carbon released when many substances — particularly fossil fuels such as oil, gas, and coal — are burned by vehicles and planes; by the manufacturing processes of many consumer goods; and by the heating, cooling, and electricity for your home.

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carbon neutral
The state of reducing a person’s carbon emissions as much as possible and balancing the remaining carbon emissions by offsetting them with processes that consume carbon.

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carbon offsets; carbon credits
Paying for or participating in programs that reduce the carbon in the atmosphere. Purchased shares go toward reducing the same amount of environmental costs that an activity expends. Carbon offset programs or projects often involve tree planting because trees have a huge capacity to absorb carbon from the atmosphere. Other programs involve everything from supporting solar and wind power to replacing fossil fuel–burning stoves in developing countries with more sustainable energy sources.

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carcinogen
A cancer-causing substance.

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carpooling
Reducing the number of vehicles going to the same destination by having two or more people ride in the same vehicle. In most cases, carpoolers take turns being the driver and using their own vehicles.

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car-sharing
A system in which a person pays a fee that gives them access to a vehicle (or a pool of vehicles), usually parked in an easily accessible location. Car-sharing can eliminate the need for a personal vehicle.

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climate change; global warming
Changes in the concentrations of various gases in the atmosphere that are affecting the planet’s climate. Many scientists believe that the increase of carbon dioxide is a primary contributor to global warming, which occurs when gases trap warmth in the earth’s atmosphere instead of letting the atmosphere release it.

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compact fluorescent CFL bulbs
Fluorescent light bulbs that fit into a standard light bulb socket and use a fraction of the energy of their incandescent counterparts.

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compost
Decayed plants and other organic matter that breaks down into rich soil.

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core aerating
Poking small holes in the top few inches of lawn to encourage the flow of air, water, and nutrients.

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corporate social responsibility
Principles adopted by a business to make sure that its operations harm no one and instead benefit everyone around it and involved in it.

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daylighting
Bringing natural light into a home.

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ecosystem
A community of living organisms and nonliving materials.

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ecotourism
Sustainable and ethical travel in a natural environment.

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Energy Star
The federal government system for rating energy efficiency in appliances.

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Environmental Protection Agency EPA
Federal agency that regulates environmental laws.

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Fairtrade
System to ensure that workers and producers receive fair value for their products and that mandates sustainable practices in producing those products.

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food miles
The distance food travels from where it’s produced to the consumer.

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foodprint
The amount of land that various diets require to sustain them.

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fossil fuels
The energy-rich organic substances, traced back to the remains of organisms that lived 300 to 400 million years ago, that modern societies burn to provide power.

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geothermal
Energy within the Earth in the form of heat.

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greenhouse effect
The warming of the planet caused by gases in the atmosphere trapping the sun’s heat instead of letting it get through to space. This action is very similar to what happens in a greenhouse.

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greenhouse gases
Gases such as carbon dioxide, methane, and nitrous oxide produced by the burning and processing of fossil fuels and that contribute to global warming and acid rain.

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greywater
Water already used for washing, laundry, or showering that is appropriate for household functions from toilet flushing to watering plants.

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Leadership in Energy and Environmental Design LEED
A scoring system to rate how ecologically friendly buildings are.

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light shelves
White or light-colored horizontal fins above windows that bounce sunlight up onto the ceiling to bring it deeper into the room.

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light-emitting diode LED
A tiny semiconductor that emits light.

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natural gas
An energy source that burns cleaner than coal and oil but still releases carbon dioxide when it burns and methane during production, storage, and transportation.

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organic
Of living things; in food, grown without chemical fertilizers or pesticides or genetically modified organisms.

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passive solar design
Building design that takes advantage of the fact that the summer sun is higher than the winter sun. Overhangs shade the building from the summer sun and allow the lower winter sun to enter the building and heat it.

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petrochemicals
Chemicals derived from petroleum.

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phantom load; standby power
Energy drawn by a plugged-in appliance even when the appliance is turned off.

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plastic identification code
A triangle with a number from 1 to 7 inside indicating what type of plastic an item is made from.

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PV cell
A photovoltaic cell; a cell with a thin semiconductor that converts solar power into electricity.

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recycling
Collecting goods that have reached the end of their lives and processing them, their parts, or some of their parts, into the raw materials from which new goods are made.

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renewable energy
Energy from sources that cannot be used up, such as wind, water, and the sun.

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skylight
A rooftop window that brings in twice the light of a traditional window of the same size.

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solar panel
A panel containing cells that convert sunlight into electricity.

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sun tunnel
A passage that brings light into a room by bouncing sunlight through a small dome skylight on the roof connected to another skylight on the ceiling of the room. (Also known as a sun tube, sun pipe, and solar tube.)

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sustainable
Using natural resources in a way that allows for continued viability.

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thermal hole
An opening such as a window that leaks heat and air-conditioning energy.

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thermal mass
The ability of a material to absorb and store temperature.

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three Rs
The environmental practices of reducing consumption, reusing items, and recycling.

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top-dressing
Applying a light scattering of compost, other mulch, or sometimes fertilizer, over soil surfaces to add organic matter or nutrients without digging it in

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toxic waste
Disposed materials that can cause harm to people, animals, or the environment.

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vermicomposting
Composting with worms.

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xeriscaping
Landscaping for water conservation; a practice of garden planning and maintenance.