As a certified solar photovoltaic designer and installer, one of the first things I often hear from a potential customer is that they want to become independent from their electrical utility company, and they want to have power in the case of a power outage from their utility company. To become completely independent and maintain power during an outage, an Off Grid photovoltaic system must be used. The more traditional alternative, the Grid Tie-in system, will not fulfill these goals, but is significantly less expensive.
With Off Grid systems, there is no agreement needed with your local utility company because you will not be using their power lines, and you will need to store a portion of the energy created on a large battery bank. There are three important factors to consider when designing a photovoltaic system:
Assess your needs
You will need to discuss what critical loads you have (heating, refrigerator etc.) These are loads that you wish to have power to at all times and are what determines the size of your battery bank.
Assess your weather conditions
If you have a several days of foul weather with very few sun hours than your battery bank will need to be able to provide enough power to these critical loads for the couple days of low sun hours. You will also need to install a charge controller for your battery bank so that the batteries are not over or undercharged.
Balance cost vs. other options
The pricing of an Off Grid system is often more than double the price of a Grid Tie-in system – which, in 2012 cost on average $40,000 before rebates. Another cost factor to keep in mind is that the battery bank will need to be replaced every 5 to 10 years and periodical maintenance will need to be done. The cost of replacing a battery bank depends heavily on the energy needs of a home. $6,000 for a full bank is not uncommon.
By way of comparison, Grid Tie Solar, which involves having a “smart meter” and an agreement with your electric utility company. If you do not already have a “smart meter” than the utility company must install one for you at no charge prior to the commissioning of your new solar PV system. The smart meter keeps track of the amount of electricity that you pull from your utility company (the grid) and the amount of electricity that your solar pv system produces and sends through your meter in the opposite direction. As a part of the agreement, in the account of a “blackout” your solar pv system will automatically shut down and stop sending electricity back to the grid. This is to protect the utilities technicians who may need to work on the power lines. Not so great in the event of a power outage.
What’s right for you?
Grid Tie systems are easier to design, cost significantly less than off grid systems, and provide a much better return on your investment. They will, however, not provide complete self-sufficiency, and will not always provide backup in the case of a blackout.
Ultimately, cost should be balanced with need. A quality solar-installer will help you design a system that meets your requirements.
Jim Noden is the founder of BrightEye Solar, LLC. a solar installation firm located in Lancaster, Pennsylvania.