• Alternating Current (AC)

AC is the form of electric power delivered to businesses and residences.  Solar arrays produce direct current (DC) electric power.  In order to convert from DC power to AC power, an inverter is needed.  In combination with other losses in the system (wiring, heat, etc.), about 23% of the power is lost, often referred to as the “Derate Factor”.

  • Array

An electrically linked collection of photovoltaic modules.  The modules are composed of multiple, interconnected solar cells.

  • Azimuth

Another word for orientation in latitudinal and longitudinal space.  For the purposes of solar, an azimuth such as 180 degrees represents an orientation of due South.  An azimuth of 270, represents an orientation of due west. In the Northern Hemisphere of the globe (the entire U.S.), solar panels should be oriented south in most circumstances.

  • Diffuse Insolation

The solar radiation that is scattered or reflected by atmospheric components (clouds, for example) to the Earth’s surface.  While diffuse insolation does contribute to power production, direct insolation produces more power per hour.

  • Direct Current

Solar panels produce direct current (DC) electric power.  Since businesses and residences require alternating current (AC) electric power, an inverter is required as part of the system.

  • Direct Insolation

According to Wikipedia: “solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun’s rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky).  Direct insolation is equal to the solar constant minus the atmospheric losses due to absorption and scattering.  While the solar constant varies with the Earth-Sun distance and solar cycles, the losses depend on the time of day (length of light’s path through the atmosphere depending on the Solar elevation angle), cloud cover, moisture content, and other impurities.”

  • Energy Payback

The amount of time it takes for a solar panel to produce enough electricity to offset the amount of energy it took to manufacture the panel in the first place.  Energy payback has recently been calculated to be 1 to 2.5 years, meaning that for the rest of the system’s 25-30 year life, the panel will be producing non-CO2 emitting energy starting from years 3 to 30 or 90% of the system’s life!  Find more information on this subject in our Solar FAQ.

  • Insolation

A measure of solar radiation energy received on a given surface area in a given time.  It commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day.

  • Inverter

A device that converters direct current (DC) electrical power to alternating current (AC) electrical power.

  • Kilowatt (kW)

1,000 Watts.  A watt measures the rate of energy conversion and is define as one Joule/second.  A 1 kW engine would produce about 8,900 kWh of power over the course of 1 year.  However, because solar arrays are around 15% efficient, in our area a 1 kW solar array produces about 1,100 kWh annually (depending on a number of factors including location, tilt, orientation and weather.

  • Kilowatt-hour (kWh)

Energy in watt hours is the multiplication of power in watts and time in hours.  Homeowners and businesses are doing everything they can to reduce the amount of kWh’s they consume. I f you leave a 50 watt light bulb on, you use 50 watts over the duration that light is on.  If you use that light bulb on for 8 hours, you use 50 watts x 8 hours or 400 watt hours of electricity (0.4 kWh).  If you are charged 11 cents per kWh by your utility, having that single light bulb on for those 8 hours cost you (11 cents/kWh x 0.4 kWh) or 4.4 cents.  Solar arrays produce variable amounts of power depending on the time of day, weather and other variables.  The longer the day is, the more kWhs that array will produce.

  • Megawatt (mW)

1 million Watts.  It is very rare to have roof-top solar get into the > 1Mw.  This only occurs on huge warehouses.

  • Microinverter

A type of device that does an inverter’s job for a single photovoltaic module instead of a regular inverter which works for an entire array.  Entire solar arrays can be built with micro-inverters, but each solar module (panel) will require a single micro-inverter.  In theory, power production would increase because any shading that occurs would knock only a single panel instead of as the entire string or entire array in a unified, one-inverter system.  In applications with no shading, micro-inverters can be cost-prohibitive, but since micro-inverters have only been on the market since about 2008, the industry is changing rapidly.  Mountaintop Greene Clean Energy thinks that microinverters are an excellent choice for residential and small commercial installations, especially at sites where there are shading issues, but they will usually add to the expense of an installation as opposed to using a standard “string” inverter.  According to Enphase, one of the companies that manufactures these inverters, microinverters can increase the energy harvest up to 25% above that of a string inverter.

  • Module

A solar module is another word for a solar panel.  A solar array is a combination of strings of solar modules, so, if you have a solar array composed of 36 total panels, that array may be composed for 4, 9-module strings of solar panels.  If each panel is a 175W panel, this array would be a 6300 watt or 6.3 kW system.

  • Monocrystalline

Mono-crystalline solar panels are the most efficient commercially available photovoltaic panels.  While they are more efficient, allowing for larger systems in a given space (rooftop) than polycrystalline or thin film solar modules, they often cost more money and while more efficient, may increase your payback relative to polycrystalline panels.  Mono-crystalline modules are easy to spot…they are made up of uniformly stacked rounded cells.  Each cell is made from a single silicon crystal which results in a more complicated manufacturing process than a polycrystalline module, but higher efficiency. Mountaintop Greene Clean Energy can help you select which panels make the most sense for your particular installation, but will generally specify monocrystalline modules for more long term energy production and aesthetic concerns, especially on residential installations.

  • Photovoltaic cell

Photovoltaic cells connected in series and then in parallel make up photovoltaic modules.  See more information in our FAQ’s in our “About Solar” section.

  • Photovoltaic devices

PV devices use semiconductor materials that directly generate electric power when exposed to light using the photovoltaic effect.  From Wikipedia; “The photovoltaic effect involves the creation of a voltage (or a corresponding electric current) in a material upon exposure to electro-magnetic radiation. The photovoltaic effect is different in that the generated electrons are transferred from different bands (i.e. from the valence to conduction bands) within the material, resulting in the buildup of a voltage between two electrodes.[1] In most photovoltaic applications the radiation is sunlight and for this reason the devices making use of the photovoltaic effect to convert solar energy into electrical energy are known as solar cells. In the case of a p-n junction solar cell, illumination of the material results in the creation of an electric current as excited electrons and the remaining holes are swept in different directions by the built-in electric field of the depletion region.[2] The photovoltaic effect was first observed by Alexandre-Edmond Becquerel in 1839.[3][4]

  • Silicon

Silicon is a widely used element primarily used in the production of semi-conductors.  Solar panels are, for all intents and purposes, but a modified semi-conductor and also use silicon as their primary component.

  • Tracking Array

A solar array with a tracking system that tracks the sun on its axis.  Tracking systems are typically larger arrays out in a field instead of in a roof-top system installation.

  • Voltage

The electrical force that drives an electrical current between two points.  When building solar arrays, contractors will design strings of solar arrays that must have the same number of panels so that they have the same voltage so they can easily be tied together.  Voltage mismatches can cause large problems for solar arrays often resulting in sub-optimal power production.