Grid-tied vs Off Grid

If you are considering solar PV for your home, business, or a remote location, it is important to understand the key differences between grid-tied and off-grid systems. Your energy and environmental goals will help you determine which of these systems will work best for your situation. A solar contractor can help you weigh your options and provide cost estimates for each type of system.

Grid-Tied Systems

Also Known As: On-Grid, Utility-Interactive, Grid-Intertied, or Grid-Direct

iStock 000006548644SmallGrid-tied systems are the most common type of solar PV system. Grid-tied systems are connected to the electrical grid, and allow residents of a building to use solar energy as well as electricity from the grid. Grid-tied systems do not need to produce 100% of the electricty demand for a home or business. When there is no demand for energy, the solar panels send excess electricity back out into the grid for use elsewhere. When a home or business is using energy, but the solar panels aren't producing enough energy (at night, or on a stormy day), electricity from the grid supplements or replaces electricity from the panels. Owners of a grid-tied system complete a net metering agreement with their utility. This agreement allows utility customers to receive credit for the excess energy they generate, typically credited as a kilowatt-hour credit on the next month's bill. Net metering policies and agreements are different for each utility. Living with a grid-tied solar PV system is no different than living with utility electricity, except that some or all of the electricity you use comes from the sun. Grid-tied systems do not provide protection from power outages. When the electrical grid fails, grid-tied systems will not continue to operate. This allows utility employees to fix the power lines safely without wasting time identifying solar energy systems that are still feeding electricity into the power lines.

System components:

  • PV panels (multiple panels make up an array)
  • inverter(s)
  • required electrical safety gear (i.e. fuses, breakers, disconnects)
  • monitoring system to monitor energy production (optional)

Off-Grid Systems

Also Known As: Battery Backup Systems

It is possible to install a solar system that is independent of the electrical grid. This is called an off-grid system, and it requires that the solar panels are able to produce enough electricity to cover 100% of the energy needs of the buildling. Most homes have higher electricity demand in the evening or at night, so off-grid systems usually incorporate either a battery (to store energy produced during the day), a backup source of energy (like a generator), or both. Off-grid systems are more complex and less flexible than grid-tied systems.


Off-grid systems are most common in remote locations without utility service. Off-grid solar-electric systems operate independently from the local utility grid to provide electricity to a home, building, boat, or RV (or remote agricultural pumps, gates, traffic signs, etc.). These systems typically require either a battery bank (to store solar electricity for use during nighttime or cloudy weather) a backup source of energy (like a generator), or both.  An off-grid solar system must be large enough to produce enough electricity to cover 100% of the energy needs of the buildling.  In all off-grid scenarios, electrical usage must be monitored and kept below the maximum output of the panels and batteries as there is no grid-source to supply excess power.

System components:

  • PV panels
  • battery bank
  • charge controller (to protect the battery bank from overcharge)
  • inverter
  • required electrical safety gear (i.e. fuses, breakers, disconnects)
  • monitoring system to balance energy consumption with production

Hybrid Systems

Also Known As: On-grid or grid-tied with battery backup

Grid-tied systems can be upgraded to include a battery backup: a bank of deep-cycle batteries. The backup battery is charged by both the grid and the solar panels. In the event of an outage, the backup battery will need to be switched on either manually or with an automatic system to provide backup power to the building.

  • PV panels
  • battery bank
  • charge controller (to protect the battery bank from overcharge)
  • inverter
  • required electrical safety gear (i.e. fuses, breakers, disconnects)
  • monitoring system to monitor energy production (optional)
  
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A hybrid energy system at Mt. Ranier National Park uses PV and a backup propane generator to power employee housing, water pumping, a ranger station, an entrance station and a tourist restroom. Photo credit: NREL

PV-Direct Systems

 

These are the simplest of solar-electric systems, with the fewest components. PV-Direct systems don't have batteries and are not connected to utility, so they only provide electricity when the sun is shining. This means that they are only appropriate for a few select applications, notably water pumping and ventilation. PV-Direct systems can also be connected to the grid but used to provide emergency power in the event of a grid outage, although they are typically used to supplement energy from a backup generator in this scenario.

System components:

  • PV panels
  • required electrical safety gear (i.e. fuses, breakers, disconnects)
 
 

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 PV-direct systems can be used for certain applications, like this solar water puming station which waters around 25 head of cattle. Photo credit: NREL

 

Solar Thermal (Hot Water)

Solar thermal systems can be designed with energy storage in mind as well. There is no way to feed hot water back to the water utility, so hot water must be stored on site. This is generally accomplished using a home's hot water tank, just as conventionally heated water would be stored. While there are many iterations of solar thermal design, most take advantage of the existing hot water tank. In some systems, the water tank can double as a back-up or supplementary heater.

 

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