Battery Based Grid Tied and Off Grid
While 99+% of all solar photovoltaic systems installed today in the United States are grid-tied, there is sometimes a desire to have the system operate and produce power when grid electricity is not available. Systems that operate in both grid-tied and “grid-not-available” environments are called hybrid systems, which require inverters that can operate in both modes. Off-grid systems, such as remote buildings, PV powered street or area lights, remote communications systems, etc., are always connected to a battery for operation when sunshine is not available. These systems may or may not have an inverter, depending on whether or not AC loads are connected into the system.
There are three basic types of PV systems:
- A Grid-tied system operates only when the utility grid is working
- A Stand-alone off-grid is not connected to the grid at all
- A Battery-based on-grid operates in grid-tied or stand alone mode
If your site is on-grid already, a grid-tied system is the least expensive to install and the simplest to operate and maintain. There is no need for owner maintenance or technical ability, only the pleasure of feeding renewable electricity into the power grid through your meter!
Depending on grid reliability and the length of power outages in a particular service area, some people opt for the simplicity of a grid-tied system with a portable generator for emergency back-up power. Others may opt for the reliable backup of a battery-based on-grid system, which will pick up loads seamlessly when utility power cuts out. The price of a battery-based on-grid system is higher installation cost, and more owner participation in maintaining the batteries. Modern battery-based on-grid systems are nearly (but not quite) as efficient as grid-tied.
If your site is remote and grid electricity is not available, then an off-grid system is the only choice. An off-grid system will be a good choice for you, and save you money over extending the power line, if the following are all true:
- Your residence is over 1/4 mile from existing power lines
- You are willing to accept that you may not have unlimited power on-demand
- You are willing to be the manager of your own power system
If some of these are not true, the cost of owning and operating a stand-alone off-grid system will increase, and may be more than the cost of extending the power line.
As a side note, property owners in Oregon are not required to have a license to make an electrical installation on residential or farm property that is owned by you, or a member of your immediate family (if the property is not intended for sale, exchange, lease or rent). You are still required to obtain a proper permit. Contact the Building Codes Division (BCD) if you have questions regarding homeowner installations.
Thanks to Jennifer Barker and Eastern Oregon Renewable Energies Non-profit (EORenew) for content and support.
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