Grid Tie

Grid Tie

« Previous12345Next »

Grid-Tie Versus Battery Based Solar Power Systems

Electricity is electricity however it comes, but not all ways of getting it are the same.  If you own or are considering a solar shingle or other sort of photovoltaic solar power system, there is a major choice to be made:  whether to use batteries or connect to the utility grid.  This article will sort out the benefits and costs of each method.

The division between battery based systems and grid-tie systems is profound, in terms of cost, utility, and hardware alike.  Let's start by taking a look at what each type of system entails.

A highly popular choice for home solar power users is the grid-tie system.  Under this system, your solar cells and the utility grid act as complimentary parts:  when you are producing more than consuming, you feed the extra power to the grid (sell it to the utility company), and when you are consuming more than your cells can produce, you make up the difference from the grid (buying that amount of energy that makes the difference from the utility).  While many public utilities are required by law to accept power fed into the grid, this law is not universally applicable, thus it is wise to check with your electric utility before connecting a solar panel roof to the grid.

Battery based photovoltaic systems are the other major option available.  While grid-tie systems use the electrical grid to absorb excess power or make up a shortfall, battery based systems connect to the grid but use batteries as a backup in the case that the power grid fails.  The hardware setup for this type of system is more complicated, and more expensive, than that for a grid-tie system, which explains much of the difference in popularity.  In addition to the extra cost of batteries themselves, a different type of DC to AC inverter is required by a battery based system in order to manage simultaneous connections to the power grid and a bank of batteries.

The major difference between using and not using batteries as a backup power supply is the trade-off between cost and the ability to retain power in the home when the grid has failed.  Your costs will differ depending on the size of the grid you want to be powered by battery backups (which need not be the entire home) and the length of time you expect your batteries to be able to run your house for, which combine to set the size of the battery bank.  Battery banks can vary in cost between several hundred dollars for a very small bank, to thousands of dollars for a large bank; extra annual maintenance costs are also associated with battery systems.

If you do choose a battery-based system, you next have to determine what will be powered by the battery bank, and how many of what sort of batteries to use.  It is possible to save costs by only using the batteries to power basic needs like lights, the refrigerator, and other basic appliances.  However, if you choose to do so it is possible to power the entire home, including the TV(s), computer(s), and others – for a price.

There are a number of different battery types to choose from, including wet-cell and sealed batteries.  Sealed batteries may be the best option for a number of reasons, including a reduced need for maintenance.  While typical wet-cell batteries need watering every few months, sealed batteries are designed to be installed and ignored until they are needed.  Despite their best intentions, many homeowners may forget to care for their wet-cell batteries, so a sealed battery system and its lower (but not nonexistent) maintenance needs can be attractive.

No battery bank will last forever, though a better system will last longer than a bargain system.  The best (but costliest) batteries may last up to twenty years, while a more pedestrian set may need replacing every five years.

As to computers, a good inverter may be fast enough to prevent your computer from crashing when a switch to battery power is made, but there is no guarantee:  under some circumstances, the switch won't be fast enough.  It is always wise to put down a hundred bucks or so to purchase a UPS (Uninterruptible Power Supply), a part that looks like an ordinary multiple-outlet extender, but includes a battery which will instantly kick in to prevent your computer from crashing in the event of a power interruption which would otherwise shut down your desktop computer.

As is often the case, added utility can always be purchased, for a price.  Whether or not you choose to add the functionality of a battery bank to your solar panel system is up to you; this information is provided in an unbiased manner to inform your decision.

About the Author

Cecilia Montrose is an office designer. She advocates using a wood filing cabinet instead of sharp metal cabinets in offices, and loves the wood file cabinet she uses in her home office.

TIE GRID INVERTER 2009