Wednesday, January 8, 2014

Grid Tied or Off Grid, What is the Difference?

When choosing a solar powered system, home owners are faced with a decision on 3 different kinds of systems - Grid-Tied, Battery Grid-Tied or Off Grid. So what does this mean?  Which one is better?  Well, it depends on how you want to use your solar power.

Each system has advantages and disadvantages.  Deciding on which system is better for your household should be based solely on what goals you have for the solar energy to do for your home.  For instance, do you need it for backup when the power goes out?  Are you installing solar to lower your monthly utility bill?  Or do you just want to get rid of the utility company completely and become self sustainable?  Here is a list of each system and its' benefits and drawbacks.

Grid Tied Solar System:

A grid-tied system connects directly to the electrical wiring in your home via an electrical inverter.  The inverter takes the low voltage DC current from your solar panels (or wind turbine) and converts it to the high voltage AC electricity which is what your home runs on (usually 120v AC).  It is setup like this:

grid tied solar

Whith this method, the system is tied to the electrical grid and your home will use up the converted solar energy during the day.  Any solar electricity you don't use gets sent out onto the grid to be used by neighbors.  The electricity returning to the grid runs through your meter and in most cases the electric company will pay you for it.  In the evenening when your solar panels are no longer producing power, your home will return to using power from the grid.  While this seems like the best option for some, it isn't much help if the electricity from the power company goes out.

To prevent electricity from leaving your house and energizing the power lines in the area, a safety mechanism shuts the inverter off if the power from the electric company shuts down allowing the power company to safely work on the power lines in the neighborhood to get the electricity back up and running.

So while the electricity is out in the neighborhood, you are out of power as well even if your solar panels are pumping electricity into the house.

Battery Grid Tied Solar System:

To compensate for this outage problem, many people choose to have a grid-tied system with battery backup.  This method works the same as a grid tied system, except for the fact you have a battery bank which will store electricity to use when the power goes out.  The power from the solar panels comes into your house just like the previous method, but instead of going straight to your home wiring, it goes to your battery bank via a charge controller.  The charge controller will determine the state of your battery bank and charge the system and maintain the full charge state before it will send any power to your house wiring. 

Once the batteries are charged, the rest of the power produced from your panels feeds the wiring in your house while your battery bank sits on standby. At night when your solar panels aren't producing any power, the power from the batteries begin feeding electricity to the house through the converter.  It will continue this way until the solar panels begin producing power again or until it depletes whatever stored electricity it has. 


In the event of a power outage, the main power in your house will still go out.  However, power that is stored in the battery bank can be utilized using a modified sine or pure sine inverter.  This usually wont be enough electricity to power the entire house, but it can be wired to run your emergency items such as lights,  fans, small appliances, laptops and such.   Of course the bigger the battery bank, and the larger the converters, the more appliances you'll be able to run for longer periods of time. 

Off Grid Solar System:

Finally, there's the long-sought off-grid setup.  Off-grid means no electricity from outside sources like the electric company.  It's similar to the grid-tied with battery backup, except it uses only the battery backup part of the system. 


All the power from the solar panels is used to charge and maintain the battery bank.  The battery power is then converted into 120v AC and can be wired throughout the house just like you would any standard 120v wiring.  This is a much more expensive setup and you have to monitor every watt of power you produce vs. every watt you use to ensure you don't run out of electricity.

You need a big enough solar panel array and a big enough battery bank to fully cover every watt of energy you use on a daily basis, including at night when the solar panels aren't producing any energy, and your home is running off only the stored power in your battery bank.  This type of system is completely unaffected by the utility company and neighborhood power status.  However you also don't have the utility's grid power to use as a safety net.  If you run out of power at night, or don't produce enough during the day due to cloudy conditions, you're out of power until the solar panels are back up and running.  Many people with off-grid setups also install wind turbines to help with production on cloudy days and night time.  In the few times when it's absolutely necessary, they usually keep a gas or deisel powered generator on hand for backup as well.

Here are a few books I've found on Amazon.com that should offer more help for those interested:


If you ever wanted to buy the Harbor Freight Solar Kit, now is the time!
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4 comments:

  1. I ordered the solar power for dummies book listed above. I figured it was a god start for me. what system do you have?

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  2. The system I have at my home is a battery grid tied system. Good luck with your solar endeaver and feel free to let us know how things are going with your solar system.

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