Solar Panels > Solar Panels eBook > Chapter 5: Grid-tied versus Off-grid Systems

Chapter 5: Grid-tied versus Off-grid Systems

Solar powered electrical systems for the home, industrial or commercial building can be either on-grid or off-grid. The on-grid, grid-tied or tied to grid system is one that enables the user to produce some power while maintaining connectivity to other utility sources. The advantages of a grid-tied system generally outweigh the potential drawbacks in areas that are conveniently located with respect to a commercially available power grid.

The relative autonomy of a grid-tied system is also variable. Because power generated by a photovoltaic module can be used directly or stored in a battery, the size and storage capacity of the battery, the number and type of photovoltaic cells (solar panels) and the amount of available sunlight in a given location are all factors that come into play when selecting and using a system. Additionally, the presence of a thermal system for hot water, space heating or even the powering of a generator can dramatically reduce the energy demand placed on a grid-tied photovoltaic system.

The way a grid-tied system works is simple. Energy generated by the solar panels during the day can be used immediately or stored in battery or heat forms, and energy use at night draws on the stores. A standard connection to the power company, monitored via a power meter as usual, permits the system to draw on commercial power from the energy company when reserves generated by solar power are depleted. If the supply of power generated by a solar system exceeds that demanded by the residence or business, the grid system can actually draw from those individually-generated reserves. Thus, the electrical meter runs backward, and the power company can pay, rather than collect from, the individual. The Federal Energy Regulatory Commission (FERC) oversees solar systems tied to grid and a permit must be obtained by FERC in order to sell energy back to the utility grid.

Grid parity has already been achieved in island communities such as Hawaii, where the main energy sources traditionally rely heavily upon diesel. This means that in those regions, solar power is as cost effective as traditional power sources that burn fossil fuels or other nonrenewable power sources. As technology improves and costs go down over the next few years, an increasing number of regions will also achieve grid parity, and solar power may eventually become the norm for the generation of electricity.

The alternative to grid-tied systems is off-grid systems, which are completely independent of the utility grid. Although they lack the power back-up assurance of grid-tied systems, off-grid systems are sometimes the best choice in areas where a utility grid is not conveniently located. In these regions, it can be more expensive and difficult to run power lines to the location than to simply establish an effective off-grid system.

An off-grid system relies heavily upon storage of energy in the form of batteries or thermal sources. A thermal solar panel system can power one or more of several types of generators, and power is then drawn from those stores during dark periods or when sunlight is lacking. Off-grid systems are also particularly useful for powering recreational vehicles and other mobile devices that cannot be tied to an energy grid.