Solar Direct (or Day-Use Solar)
These systems are intended to be used only when the sun shines. There are no storage batteries, so as soon as the sun goes away, the power stops. These systems are great for certain water pumping applications, venting fans, and certain electronics. Rare in application, they are very affordable and easy to install.
DC System with Batteries
These systems are great for small electronics that need to run day or night. Often times you'll see these systems employed on highway sign lights, gate openers, and communication boxes. Simple and affordable these systems have a wide variety of uses and are perfect for remote locations that require low voltage.
Hybrid Solar-Generator Systems
For off-grid and back-up power applications, most folks turn to a hybrid system. The hybrid system usually consists of a PV array, a charge controller, a battery bank, an inverter, and sometimes a tertiary power source such as a wind turbine or a gas generator. These systems are fairly complex and require a high level of expertise to design and install. With the popularity of off-grid living, however, there are more and more packaged systems for people to choose from. These systems will provide power if the grid shuts down and can still sell power back to a grid if desired.
The biggest disadvantage of these systems is the cost and complexity. The battery bank requires regular maintenance and must be replaced long before the panels are done generating. They are also fairly expensive. These costs, however, are often a better alternative to the cost and hassle of bringing in grid power to remote locations.
Off-Grid Solar Dependent Systems
For cheap power in remote locations, often these systems are the only choice. They generally consist of a small battery bank, a charge controller, and a solar array. People with these systems choose to use all DC appliances so as to avoid the cost and inefficiency of inverters. These systems have the advantage of lower initial cost. The batteries are still an issue for maintenance cost. And there is no backup power if weather doesn't allow the panels to charge the batteries.
Grid-Tied Solar Systems
This is the easiest and most popular way to get started in PV power. These systems simply tie into your existing home power system and the utility grid. If your array generates more energy than you use, the energy is sold back to the power grid and creates a credit for you. The advantages of these systems are the relative simplicity and lower initial cost. A system like this typically requires a few panels, some wiring boxes and disconnects, and an inverter. The inverter converts the electricity from your panels to power that your home and the grid can use.
This system also requires an interconnection agreement with the local utility. This outlines just how the connection to the grid should be made and what the inspection schedule is. It is generally advisable to get your power company involved early on for a grid-tied system. Since there are often incentives and rebates in place from the state and the utility, it's well worth the call.
Advantages of a Grid-Tied System
•Initial Cost: The upfront cost of purchasing a system that would provide for a home's entireelectrical 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. Grid tied systems are much cheaper than off grid
•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.
•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.
•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.