Glossary of Terms


The grid is a network of power lines that carries and transmits electricity from large centralized power plants to individual homes. The term “going off the grid” refers to a household that generates all of its own power and no longer relies on the grid. Vasco Solar systems are “grid-tied” (or connected to the grid) so you can still power your house when the sun doesn’t shine and can take advantage of the tax incentives that are available for grid-tied systems.


Interconnection is the point at which your solar system is connected to the electricity grid. The utility needs to give you permission to operate your power generator and “interconnect” it to their system. Vasco Solar completes all the necessary paperwork to get your system up and running.

Kilowatt Hour

A kilowatt-hour (kWh) is a unit of energy equal to 1000 watt-hours. Electric utilities bill customers in kWh.

Module Power Ratings

To help standardize measurement of a solar panel’s power output, several government rating agencies created power rating standards. Standard Test Condition Direct Current (STC-DC) is the nameplate power that provide a consistent standard for all manufacturers to use. It is the most common rating and measures a panels output in ideal laboratory conditions.

In California, all solar panels that are certified by the California Energy Commission to be used in a solar power system receiving a rebate from the local utility must also indicate their power under a second set of test conditions, known as the PTC rating (or PTC power) of the panel. PTC refers to PVUSA Test Conditions, which were developed to test and compare PV systems as part of the Photovoltaics for Utility Scale Applications project. These values are lower than the STC nameplate rating.

The California Energy Commission Alternating Current (CEC-AC) rating measures panel’s output in real life production conditions and factors in the inverter’s efficiency of converting DC to AC. The CEC-AC is always lower than the STC-DC rating, because it takes account of inefficiencies throughout the balance of the solar system.

Net Metering

A system in which solar panels or other renewable energy generators are connected to a public-utility power grid and surplus power is transferred onto the grid, allowing customers to offset the cost of power drawn from the utility.

When you install a grid-tied solar system, your utility monitors how much electricity your solar panels produce and how much electricity you use through the process called net metering. With an NEM account, the meter measures the amount of kWh consumed and the energy being generated beyond what you are consuming. When you generate more electricity than you consume, the net surplus energy is sent back to the grid.

If, at the end of the year, you have produced more than you used, some utilities will compensate you for this extra power but others will not.

Power Purchase Agreement (PPA)

A Power Purchase Agreement (PPA) is a financial agreement between an electricity generator (provider) and a power purchaser (buyer/trader). Contractual terms may last anywhere between 5 and 20 years, during which time the power purchaser buys energy from the electricity generator. The solar services provider or another party acquires valuable financial benefits such as tax credits and income generated from the sale of electricity to the host customer. PPA rates can be fixed, but they often contain an annual price escalator in the range of one to five percent.

Solar Inverter

The solar inverter is the electrical box that turns direct current (DC) electricity produced by solar panels into alternating current (AC) electricity. A grid-tied solar inverter allows this AC electricity to be sent back to the grid when you produce more energy than you use. The two main types you will hear about are string inverters and micro inverters. String inverters convert electricity from multiple panels or a string of panels. Micro inverters convert electricity from one panel. There are pros and cons to each, and opting for string inverters or micro inverters depends on your unique situation. It is important to partner with a company that offers both and helps you investigate all of your options and advise you on the best technology for your needs.

Solar Lease

After customers add up the payments on a zero-down solar lease, they will often find that they are paying double to triple the cost for a solar system when compared to purchasing a system. Today there are many financing options available that have nothing to do with an expensive lease, and you get to keep the tax credit.

Solar Panels

Also called solar modules, solar panels are made up of silicon cells that absorb photons (sunlight) to create a photovoltaic (PV) effect that allows for the conversion of sunlight to electricity. Solar panels are linked together to form “strings” and strings are combined to form “arrays.” This array is connected to your home via an inverter, delivering electricity to power your home — or back to the grid, if your system produces more electricity than you use.


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