Engineers at the University of California San Diego have developed algorithms that would allow homes to use and share power from their renewable energy sources during outages by disconnecting solar inverters from the grid.

Researchers say the algorithms work with existing technology and would improve systems' reliability by 25-35%.

"We were inspired to start investigating a way to use renewable power during outages after Hurricane Sandy affected eight million people on the East Coast and left some without power for up to two weeks," says Abdulelah H. Habib, a Ph.D. candidate in mechanical engineering at UC San Diego.

Every year, 7 million customers experience power outages. Outages that last more than 5 to 10 minutes cost customers more than $80 billion each year.

The algorithm is able to prioritize distribution of power from renewable resources during an outage. The equations take into account forecasts for solar and wind power generation as well as how much energy storage is available, including electric vehicles, batteries and so on. The algorithm combines that information with the amount of energy that the residents are projected to use as well as the amount of energy that a cluster of homes can generate.

The algorithm could also be adapted to include a priority function, based on different parameters. For example, customers who are willing to pay more could get priority to power during an outage. Or customers who generate more energy than they produce during normal operations would not lose power during an outage. The algorithm also could give priority to customers who are in urgent need of power, because they use life support equipment, for example.

Researchers investigated what energy storage configuration would work best with their algorithm. Although having energy storage systems in each home leads to optimal performance, most customers preferred to share a community-scale storage system, which cut down costs.

The algorithms work with existing technology but require each home to be equipped with circuit breakers that can be remotely controlled. Utilities also would have to install advanced communications methods that allow the power systems in a residential cluster to talk to one another.

In addition, all homes with solar panels are equipped with inverters, which turn the direct current power generated by the panels into alternating current that can circulate on the grid. These are so called grid following devices, because they can only connect to the grid. To bring together a cluster of homes, each house needs to be equipped with a grid forming inverter, which can connect to similar devices at other residences.

Next steps include showing that the system is reliable in the lab, with software and hardware both in the loop. And regulations would have to change, the researchers say. In most states, individual home owners are not allowed to sell power to other residential owners.