Solar power systems come in all shapes and sizes. The most popular systems are generally grid-tied residential systems. You may also hear them called line-tied or utility connected systems. Basically this means that they are installed on homes that are connected to an electric utility. Today, with advances in technology and legislation, it is easier to purchase and install these systems than ever before.
Utility connected systems generate electricity from the sun, supply the house with its needed electrical needs, and then push any excess electricity onto the utility grid. Thanks to the Public Utility Regulatory Act of 1978 (PURPA), public utilities are now required to purchase this surplus electricity from small producers, such as you and your house. This allows for net-metering, which means that utility must pay you for the electricity you put back into the grid. This generally causes your electric meter to run backwards and creates a credit on your power bill. However, the utility does not necessarily have to pay you for their electricity what you pay them for their electricity. This means there is often a 'gap' in the utility rates.
There are several advantages to having a utility connected system:
1. Initial Cost: The upfront cost of purchasing a system that would provide for a home's entire electrical needs can be very high. With variable climate and weather conditions across the globe, the use of off-grid systems requires expensive batteries. Off grid systems generally require a secondary power source, such as a gas generator, to provide backup power which adds significant cost to the system.
2. Operating Cost: The maintenance cost of grid-tied systems is very low. Solar panels routinely have 20-25 year warranties and some of the panels created in the 1950's as part of NASA's space program are still operational. Batteries associated with off-grid systems require regular maintenance and have a much shorter life than the panels. Backup generators also require significant maintenance and access to a cheap and reliable fuel source.
3. Reliability: Grid-tied systems are relatively simple and can have virtually no 'down time' where the customer will be without electricity. The increased complexity of battery and generator backup systems often leads to significant down time and can be frustrating to a home owner. Often poor weather that leads to little energy collected from the sun also means decreased battery and generator performance.
4. Flexibility: Having an alternative energy source AND a utility source means you can design your system to meet whatever needs you have now, and still have the flexibility to increase the system size later. It also allows you to change your system parameters to meet your different needs in the future.
There are generally two types of grid-tied solar power systems: Systems WITH Battery Back-up and Systems WITHOUT Battery Back-up.
1. Systems WITH Battery Back-up: These systems are very useful in areas with frequent power failures. Provided there is ample sunshine, these systems give the customer more autonomy, while still providing a backup system in the utility grid.
The advantages of these systems include:
a. With proper system design, provides continuous power to the customer regardless of utility availability or weather conditions.
b. These systems make it easier to manage your power consumption, production, and storage.
c. Depending on the utility company's policy, the cost of the batteries can sometimes make up for the rate 'gap', meaning it is worthwhile to store the excess electricity you produce as opposed to selling it back to the utility.
Some of the disadvantages of the battery back-up systems:
a. Increased system complexity, more components to install
b. Increased cost of the system
c. Increased maintenance of the system
d. Decreased efficiency of the overall system
e. Environmental issues: The manufacturing and disposal of batteries involves chemicals and metals that most eco-minded consumers would rather avoid.
2. Systems WITHOUT Battery Back-up: These systems are the most popular for their relative simplicity.
The advantages of these systems include:
a. Cost effectiveness: when combined with net-metering systems owners can see payback times from 5-10 years.
b. Simplicity of design and installation
c. Higher overall system efficiency
Some of the disadvantages of the systems without battery backup:
a. Does not necessarily provide backup power in the case of grid failure
b. Does not allow for power management