Engineers develop tools to share power from renewable energy sources during outages

September 5, 2017 by Ioana Patringenaru, University of California - San Diego
Researchers have developed an algorithm that allows residential customers to share power from the renewable energy sources in their homes during an outage. Credit: University of California San Diego

If you think you can use the solar panels on your roof to power your home during an outage, think again. During an outage, while your home remains connected to the grid, the devices that manage your solar panels are powered down for safety reasons. In other words, this permanent connection to the grid makes it impossible for homeowners to draw on power generated by their own renewable energy resources.

A team of engineers at the University of California San Diego wants to change this. They have developed algorithms that would allow homes to use and share power from their during outages by strategically disconnecting these devices, called solar inverters, from the grid. The algorithms work with existing technology and would improve systems' reliability by 25 to 35 percent. Researchers detail the algorithms and their applications in a paper they presented at the American Control Conference in Seattle, Wash.

"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," said Abdulelah H. Habib, a Ph.D. candidate in mechanical engineering at UC San Diego and the paper's first author.

Just a few hours without power can cause massive losses to both product and revenue. 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.

How the algorithm works

The innovation here is the 's capability to prioritize distribution of power from renewable resources during an . The equations take into account forecasts for solar and as well as how much is available, including electric vehicles, batteries and so on. The algorithm combines that information with the amount of 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 programmed to include a priority function, based on different parameters. For example, customers who are willing to pay more could get priority to get power during an outage. Or customers who generate more energy than they produce during normal operations would not lose power during an outage. More importantly, the algorithm could give priority to customers who are in urgent need of power, because they use life support equipment, for example.

Credit: University of California - San Diego
Hardware and storage

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

"Houses connected together are much more resilient during outages," said Raymond de Callafon, a professor of at the University of California San Diego, and one of the senior authors of the paper. "They're also more resilient to price fluctuations. They can do a much better job at sharing resources and it benefits every house."

The algorithms work with existing technology but they require each home to be equipped with circuit breakers that can be remotely controlled—and these devices are not yet widespread. 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 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

Next steps include showing that the system is reliable in the lab, with software and hardware both in the loop. Finally, regulations would have to change nationwide. In most states, individual home owners are not allowed to sell power to other residential owners. Until new regulations are in place, researchers point out that the technology would also benefit businesses equipped with renewable power sources that need constant and do not have backup generator.

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5 / 5 (1) Sep 05, 2017
Just how do they plan to connect the producers with the users during such an outage? Say a hurricane or large snowfall hits your town an knocks down the power lines. What system is in place to share power other than the local lines? The number of outright major grid failures is not large and it is not really worth the costs involved trying to interconnect small sources of renewables.
5 / 5 (1) Sep 05, 2017
It is relatively easy and not too costly to connect an automatic transfer switch in a solar home thus enabling it to self power during an emergency. Once you try to share this power with a neighborhood costs get out of hand quite quickly.
1 / 5 (1) Sep 05, 2017
If you think you can use the solar panels on your roof to power your home during an outage, think again.

Not entirely true. SMA offers in some of its Sunny Boy line of solar inverters something called Secure Power Supply. It only offers up to 2000 W of your own solar power during an emergency, but that's enough to run a few necessaries like the fridge and cell phone chargers.

And of course any solar system with a battery bank can supply battery power from previously collected sunshine.
5 / 5 (2) Sep 05, 2017
Another reason why you can't put electricity back on the grid is for the safety of power line workers and other people near downed power lines. The 220v in your panel gets back to 8000 V on the line outside the house.

If you know exactly where and why the gird is down you might be able to do something, but in storm situations it would not work. Its also cheaper to just put a $800 small Honda generator and a gallon of gas in the garage to keep lights TV and cable box on.

The way electric prices are skyrocketing in places like California, Ontario, much of the EU, Australia, etc means that its actually as cheap or cheaper to simply burn natural gas at your home to make electricity. You gain if you also use the 80% or so of the energy that is 'wasted' heat. Micro co-gen from Yanmar is an example.
1 / 5 (1) Sep 06, 2017
Generators running off the regular flow of natgas are a good idea. Better than relying on solar, or splitting power with a neighbour that's for sure.
Da Schneib
1 / 5 (1) Sep 06, 2017
How about if we have a cutoff that turns off the grid connection manually?

Just askin'.
not rated yet Sep 06, 2017
How about if we have a cutoff that turns off the grid connection manually?

Why would you want to? Even if you generate more than you can use all year round:
- Your power generators are a backup if the grid fails
- The grid is your packup if your power generating capacity fails.
- You can make money by feeding power to the grid

I see no downside in staying connected (unless you consider system-wide hack-attacks a high probability)
5 / 5 (1) Sep 06, 2017
- Your power generators are a backup if the grid fails

If the grid fails, you're likely to find yourself in a power "island" that is cut off from the rest of the network, which produces load matching issues. Non-dispatchable sources such as solar panels must be kept out or risk further breakdowns.

The smaller the grid, the less it is able to absorb disturbances like clouds passing over the panels. Hence in your neighborhood "minigrid", unless you have significant two-way battery capacity or fast standby generators, the lights will start to go in and out and appliances get damaged via under/over-voltage and fast transients.

1 / 5 (3) Sep 06, 2017
If papers like this are the best that our educational system can produce we are in serious trouble.
1 / 5 (1) Sep 06, 2017
The way I see it? There is good news and there is bad news and there is a hellova lotta confusing news. Especially generated by hucksters flooding neighborhoods with a tidal wave of infomongering.

Many of us want technology that works better, more reliably and cheaper. In an emergency, we would settle for reliable even if inefficient and/or more expensive.

The general default is we will usually wind up paying more and still suffering through the failure of the technology. Though if we were honest, we ourselves abuse the capacity of the machines and delude ourselves that we are entitled to perfection.

P.S. Puhleeze! Before you store gasoline within your habitat? Make damn sure it's not sharing atmosphere with a water heater or other open flame source.

Including where your kids sneak off to secretly smoke whatever noxious weed they swiped from your stash.
Da Schneib
3 / 5 (2) Sep 06, 2017
How about if we have a cutoff that turns off the grid connection manually?

Why would you want to?
In order to avoid damaging your inverters, in case there is a power outage and you want to go with your internal power only until they get it straightened out. I thought that was obvious from the article.

On edit: @Eikka also makes valid points about your appliances; I'd say any modern renewable system that has batteries would take care of transients for clouds and so forth, and would cut the power off rather than brown out.
1 / 5 (1) Sep 06, 2017
Another reason why you can't put electricity back on the grid
But surely any state, or country, or region that has net metering - is doing exactly that? In the real world - micro grids are starting to emerge - and the energy landscape is getting ready to change - https://www.nytim...?mcubz=0

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