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Rooftop solar cells blossom, posing new challenges for power grid

Nov 09, 2009- North County Times

Solar power installations are sprouting on California rooftops like leaves in the spring, but all that renewable energy poses new problems for the aging power grid.

Solar panels and wind turbines offer the promise of clean electricity by deriving their power from wind and the sun. But both suffer from the problem of intermittency: A gust of wind can cause a mill to spin faster, producing a power spike down the line, and a cloud passing over a solar cell can cause a sudden drop in electricity.

Meanwhile, utilities are rushing to upgrade the ability of the region's interconnected power grid, which is based on 100-year-old technology, to tap renewable resources without causing problems for users.

"We're going to see more change in the next 10 years than we've seen in the last 100," said Chris Baker, chief information officer for San Diego Gas & Electric Co. "This is happening fast."

California utilities don't have a lot of choice in the matter, either. The state has required them to get 20 percent of their power from renewable sources by 2010 and 33 percent by 2020. Today, much of that power is derived from large installations of solar panels or windmills, a central generation model that resembles the traditional electrical infrastructure of nuclear, coal and natural-gas plants.

But the state and federal government have both enacted subsidies for homeowners who want to install their own rooftop solar cells. Those subsidies, combined with a 9 to 13 percent drop in the cost of solar systems, have driven a sharp increase in demand for new solar systems.

Utilities each manage their own branches of a subsidy program called the California Solar Initiative. Southern California Edison's branch of the initiative said it has received more applications for solar cells in the first three quarters of 2009 than it did in all of 2008. In San Diego County, the program helped install 2.1 megawatts of rooftop solar capacity in October, the most ever for a month.

As the program meets new capacity goals, the government subsidies are reduced.

"The incentive is decreasing, yet the adoption rate is increasing," said Timothy Treadwell, an analyst for San Diego's initiative.

Rooftop installers say they're so busy, they're hiring new staff and new crews.

Daniel Jagudnik, a sales manager with Natural Energy in Escondido, said he has hired eight new salesmen and the company has brought on 10 new technicians since the first of the year.

Jeff Van Dam, director of contractor services for HelioPower in Murrieta, said he had to hire a third crew last month, and his company has started a solar cell distribution division.

Managing energy variation

But renewable energy, and especially the kind produced all over the grid by homeowners, creates new problems for utilities' power infrastructure.

Traditionally, power has flowed from generator to end user, with occasional rerouting to manage peak demand.

Renewable energy flows at a variable rate: Solar power can't be generated at night, and winds can die down, cutting output from windmill generators.

Sudden drops could cause localized brownout conditions, or even brief blackouts that shut down computers or medical equipment. If winds suddenly gust, turbines spin faster, causing power spikes that could blow out expensive televisions or at least blow out fuses.

Rooftop solar complicates matters further because buildings with excess power can sell it back to the grid, creating a need for a system smart enough to reverse the stream every time the sun rises or a cloud passes by.

"That doesn't happen on today's grid naturally. The grid was built over 100 years ago; it does what it does," Baker said.

SDG&E's smart grid has five major components: smart meters, information processing, sensors, communications and storage.

A new wireless communication system will be funded by a $28.1 million federal grant won by SDG&E's parent company, Sempra Energy. The utility plans to upgrade all 900,000 gas meters with communications modules by 2011. At the same time, it will install 1.4 million "smart" electricity meters that will have the ability to measure and manage each household's energy use, or possibly, production.

Over the next 10 years, Baker said, they will install sensors on each part of the grid to measure the load and monitor usage, and an enormous information technology infrastructure will be needed that can take in all the real-time data and output it in a way that makes it possible for system operators to use.

Big batteries on the way

And then there's that cloud-over-the-sun problem. Traditional fossil-fuel generators can't modify their own output fast enough to compensate for power fluctuations caused by variations in wind and sunlight. Baker said utilities will need distributed energy storage to smooth out power supply levels.

Batteries and other types of storage will have to be placed at many different points in the electricity infrastructure, including generation sites, transmission sites and even on homeowners' property. When generation levels fluctuate, the batteries will absorb or release energy to even out the load.

Baker said he isn't worried about this problem -- yet. SDG&E's renewable energy portfolio will only hit 17 percent at the end of the year, and Baker said he's comfortable with the grid's ability to handle even 20 percent renewables. More than that, and he gets worried.

As for rooftop solar, the problem is still too small to be a concern. There are so few solar electric systems installed each month that SDG&E can make individual appointments to install smart meters.

And all of Edison's rooftop solar capacity put together adds up to just 150 megawatts, roughly 0.7 percent of its peak load of 23,000 megawatts. The problem of intermittency, and the real strain on the grid from small-time generators such as homeowners, hasn't really hit yet.

But the state's requirement for 33 percent renewable energy by 2020 means SDG&E and Edison have 10 years to get all this grid work done.

The California Independent System Operator has oversight of the state's energy grid. The agency is studying the challenges that will be involved in creating a large smart grid like the one that will be required, but it is optimistic that the job can get done.

"We are working towards these solutions," said Gregg Fishman, a spokesman for the ISO. "I don't want to give the impression that there's no problem, that everything is solved. The vision is there of how smart-grid technology can provide the tools and the information flow to make those tools work. It is coming together."

Call staff writer Eric Wolff at 760-740-5412.