"While the solar panels themselves work identically in a grid-tied and off-grid system, the method of both storing the solar power and integrating that power into the home’s electrical system have some marked differences between the two, so much so that their paths diverge substantially. It’s not so much the panels themselves that we’ll be looking at; rather, it is what happens when the electricity leaves those panels and heads for your home that we’re examining."
If you take a drive down your average suburban street and spot a home with solar panels on the roof, you can almost be certain the system is a grid-tied system, which is by far the most common solar-powered system in use today. As the name implies, the system is tied to the grid – what grid, you ask? The electrical power generation and distribution grid – essentially, all it means is that the home is connected to the power grid that feeds it, which isn’t earth-shattering until you understand the implications thereof. Here’s how it works:
Grid ties have one fatal flaw however; one Achilles heel that most people don’t know about: Your grid-tied solar panel system will not be able to power your home during a power failure. This is because the power company will put a lockout box on the output of the solar panels such that if the power is off, the box will disconnect the solar panels from the home’s electrical panel to prevent a back-feed situation. As we discussed earlier, electricity flows both ways, and the power company is concerned that the output of your home’s solar panel system could inadvertently shock a power worker halfway down the block who is working on the power lines and assumes they are inactive.
Off-grid systems take solar panel technology to a new level. Essentially, they use the same solar panels as grid-tied systems, except they actually store the power they make, usually in batteries. This is an important distinction; the off-grid solar power user isn’t interested in generating power for some faraway utility; he or she is interested in keeping the power that is produced. The way the power is retained is by storing the output of the solar panels in an appropriately sized battery bank, and this provides another benefit most people don’t realize: You can use the solar power you generated during the day – at night. As the solar-powered system soaks in the sun’s rays during the day, it funnels this electricity into a purpose built battery bank which then can be drawn from at night or on overcast days, meaning that the off-grid system will be able to bank or save its output, whereas the grid-tied system will be running at a reduced capacity, or perhaps not at all."