Grid tie with battery backup
The technology exists where your home or business can be fitted with a grid tie power system that will give you the benefits of that technology but also a battery based backup system to power critical loads when the grid fails. Just like you may already have a UPS on your computer, this is on a larger scale to power circuits rather than just one device.
In normal operation your system will be exporting power to the grid when you generate a surplus. Should the grid fail, the backup system comes into play powering those loads that you decide are important and need to keep running. In a home this would most likely be the refrigeration and some lighting circuits, maybe a radio or TV circuit so you can keep up with news alerts and any essential medical equipment if you rely on it. The grid tie system becomes the power source to recharge the battery and the backup system will control it.
In a commercial environment the critical loads would be computers, lighting and perhaps some small power demand equipment such as tills, eftpos, drink coolers etc to enable you to continue to function, albeit at a reduced level of service. Imagine if you are the only store in a block able to offer a sales process to customers for a time! Large loads such as cookers, deep friers and airconditioning, although possible to power, are not practical.
It is not essential to incorporate the grid tied portion of the power system but without it the backup can only run until the battery energy is depleted. It is easy to incorporate a backup generator so the system can recharge the battery, but the overall plan is aimed at incorporating all levels of technoloogy with the emphasis on renewables rather than burning fossil fuel.
The benefits of this type of system are that the battery can be sized to carry you through the expected period of a power cut, however long that may be on average in your location. Longer power cuts require a larger battery. The battery does not have to be sized as the primary power source such as is done on a stand alone power system.
These style systems can also be utilised to support the grid in locations with limited power service or unstable voltage. The backup inverter can run in parallel with the grid to "top up" the grid supply when loads exceed the connection capacity. This can be a lower cost solution than upgrading a long supply line to meet a growing load.
