There are two basic types of solar power systems – grid tie and off grid. The simple explanation of the difference between them is that grid tie systems connect to the grid and off grid systems don’t connect to the grid. Whether or not they connect to the grid makes a big difference in how they are designed.
First let’s define what we mean by “grid”. The grid is the utility company’s network of conductors and equipment that bring electricity from the power plant where it is made to the end user’s home or commercial building. If a building is getting electricity from the electric company, it is connected to the grid.
So what makes a grid tie system different from an off grid system is that the grid tie system must interact with the grid and there are some requirements and some advantages to this interaction. First, a grid tie inverter must sync up exactly with the grid. Its AC output wave must be exactly in time with the AC wave that the grid is delivering to the building. It also means that you must choose the correct grid tie inverter based on how the power is delivered to your building. A typical home receives 120/240 Volt Single phase (aka split phase) power so the solar power system would have to use a single phase inverter. Commercial buildings are usually three phase power which is typically 120/208 Volt or 277/480 Volt and could be wye or delta configuration. It must be determined exactly what type of power is being delivered to the building so that you can choose the correct grid tie inverter.
The other big requirement for a grid connected system is that it can not feed power to the grid when the grid goes down. The reason for this is that the utility workers are trying to troubleshoot and correct the problem and if there are a bunch of solar power systems still feeding into the grid, it would be dangerous and it would affect the measurements the workers are making as they try to determine what is wrong and fix it.
One of the advantages to a grid tied solar system is that they can rely on the grid to provide power when the solar isn’t producing enough. This means the solar does not need batteries and the building never goes without power. In an off grid system, there is no grid to provide power so if you want power at night, you have to have stored enough power during the day. This means that off grid systems have to be much larger because the grid isn’t there to fill in the gaps. Many off grid solar power systems are installed with a generator so there is something that can take over when it’s been cloudy for too many days in a row, but a generator is going to be a much more expensive power source than the grid so even if you have one, you will try to use it as little as possible.
Now this doesn’t mean that grid tie systems don’t ever have batteries, it’s just not as common. Batteries can be added to a grid tie system so it will act like an off grid system when the grid goes down. When the power outage starts, the system can isolate itself from the grid and still feed power to the building. When the power outage is over, it will reconnect itself to the grid.
Another advantage to a grid tie system is that it can be smaller. Because any extra power that may be needed can come from the grid, it is not critical that the system be built large enough to meet the needs of the building every single day through bad weather and low sun availability in the winter.
Finally, the smaller size and the lack of batteries make grid tie systems much less expensive than off grid systems.
Whether you want an off grid system or a grid tie system, call the experts at GoGreenSolar.com who can customize a solar package that will meet all your needs.