Grid-Tied Solar-Electric System

Also known as on-grid, grid intertied, or utilityinteractive (UI), grid-tied solar-electric systems generate solar electricity and route it to the electric utility grid, offsetting a home’s or business’ electrical consumption and, in some instances, even turning the electric meter backwards. Living with a grid-connected solar-electric system is no different than living with grid power, except that some or all of the electricity you use comes from the sun.

In many states, the utility credits a homeowner’s account for excess solar electricity produced. This amount can then be applied to other months when the system produces less or in months when electrical consumption is greater. This arrangement is called net metering or net billing. The specific terms of net metering laws and regulations vary from state to state and utility to utility. Consult your local electricity provider or state regulatory agency for their guidelines.

The PV Module

Individual solar cells for PV systems are first combined into PV modules to provide easily manageable units with a suitable voltage level for various applications. A group of PV modules is called the PV array. The ability of the PV module to convert the sunlight it is exposed to is referred to as its efficiency. In terms of area, a PV module’s efficiency is always slightly less than that of the solar cell itself, because the active cell surface of the PV module is always somewhat smaller than its total surface area.

Today, depending on the quality of the solar cell, standard PV modules have an efficiency of approximately 12 – 15 %. The Sanyo panels in our Elite GTP system have an industry leading 17.2% efficiency! That means that 17.2% of the sun’s radiant energy collected by the PV module is converted into electricity. Keep this in mind when planning a solar power system because the lower the efficiency of the PV module, the greater the number of PV modules required to meet a desired power level.

The Solar Tracker: Your System’s Foundation

A solar tracker is a moving support system for keeping a solar energy collection unit pointed toward to sun.  The sun's position in the sky is dependent on your location and varies both with the time of day and with the seasons.  Solar panels gather the most energy when pointed at the sun. By keeping the solar array pointed directly at the sun as it moves across the sky, the tracking system is able to produce an average of 30-40% increase in power generation over a fixed mounted system. The earth moves and so should your solar panels.

Tracking can substantially improve the amount of power produced by a system. The use of trackers in non-concentrating applications is usually an engineering decision based on economics. Compared to the total cost of a photovoltaic system, trackers are relatively inexpensive. This makes them especially effective for systems using ultra high-efficiency panels.

The Inverter: the Heart of your System

The type of power produced by the PV array is direct current, or DC. This DC power needs to be converted to alternating current, or AC, before it can be utilized by your appliances or fed to the utility grid. The system component that converts the DC power into grid-compliant AC power is called the inverter. Inverters are a very important piece of the solar system. There are safety standards that need to be met for any device that is going to be connected directly to the public utility grid. It is important that an inverter be certified for use with the utility grid prior to selecting one.

Like PV modules, inverters also have an efficiency rating. That efficiency rating measures their ability to convert the DC power fed into them to AC power. No inverter is 100% efficient because it takes some of the energy supplied to complete the actual conversion process. Today, modern inverters have an efficiency of up to 98%. The efficiency is critical because it will determine the amount of sunlight that is actually converted and fed to the grid as AC power, which in turn, affects the amount of credit that is earned. The inverter is responsible for operating the solar power system so that the maximum possible energy production is achieved.

AC Breaker Panel

The AC breaker panel or “fuse box” is the point at which all of a home’s electrical wiring meets with the provider of the electricity. That could be the public grid or a solar-electric system. This wall-mounted panel or box is usually installed in a utility room, basement, garage, or on the exterior of the building. It contains a number of labeled circuit breakers that route electricity to the various rooms throughout a house. These breakers allow electricity to be disconnected for servicing, and also protect the building’s wiring against electrical fires.

Just like the electrical circuits in your home or office, an inverter’s electrical output needs to be routed through an AC circuit breaker. This breaker is usually mounted inside the building’s mains panel, which enables the inverter to be disconnected from either the grid or from electrical loads if servicing is necessary, and also safeguards the circuit’s electrical wiring.

Metering

Most utility companies in the United States have an interconnection program in place. Precisely how the system owner is compensated varies from company to company. However, the one thing they all have in common is the requirement that the power sent to the utility company be metered. Most meters look like any other power meter for home or business use. How the meters are connected to your system will vary depending on how the individual program works. For detailed information on metering requirements in your area, contact your local solar power installer.