Grid integration connects the dots to expand PV distributed market

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2012 is likely to be a banner year for installations in the United States, with an estimated 3.2GW to be added by the end of the year to the cumulative capacity of 4GW. By the end of 2016, that figure is predicted to grow to 32GW according to GTM Research.

That gets many in the solar industry excited as they chase the Holy Grail of $1/watt for installed systems. But engineers in the private and public sector in the US are groaning at the technical challenge of making sure these levels of capacity can be integrated into the American electric power system.

“By the end of 2030 we could have 14% of our energy from solar – PV and CSP,” said Kevin Lynn of the US Department of Energy. “You can get the costs down as low as you like but if you don't solve some of the grid integration problems you can't reach those kinds of goals.”

In general, penetration levels of greater than 15% trigger a screening process that the industry says is out of date.

“The 15% threshold is based on a rationale that unintentional islanding, voltage deviations, protection mis-coordination and other potentially negative impacts are negligible if the combined distributed generation on a line section is always less than the minimum load,” said a report released earlier this year by researchers at the National Renewable Energy Laboratory, Department of Energy, Sandia National Laboratories and the Electric Power Research Institute.

In 2005, the Federal Energy Regulatory Commission (Ferc) introduced the Small Generator Interconnection Procedures (SGIP) for systems of less than 20MW. But it's a piece of regulation that has not kept pace with the industry, say solar advocates. Unsurprisingly, few utilities agree.

Grid connection complex for solar
Earlier this year, the Solar Energy Industries Association lodged a rulemaking petition with the Federal Regulatory Commission. “In many areas of the US, the interconnection process is complex and/or expensive, and it can be a significant barrier to bringing a solar energy system online,” according to SEIA. “The ability to interconnect to the grid on a cost-effective and timely basis may determine whether the project moves forward or not.

“[Ferc standards] become outdated due to the dramatic increase in solar market penetration. Interconnection poses particular issues for the growing solar wholesale distributed generation (DG) market as the volume of projects to be interconnected creates delays.”

Much like the Net Energy Metering clash between utilities and the solar industry (and consumers), utility companies have lined up to object to SEIA's petition.

Duke Energy, Pacific Gas & Electric, San Diego Gas & Electric and Southern California Edison and the trade associations that represent utilities across the country have raised their objections to varying degrees.

The Edison Electric Institute has claimed that “high penetration of solar DG can cause reverse power flow, affect voltage and reduce system protection”.

But SEIA counters that reverse flow power does not threaten the grid in Germany, which has much greater PV penetration (with 28.5GW – a figure that US solar advocates dream of).

SEIA also claims that modern inverters on PV systems can avoid problems such as unintentional islanding, which can damage transmission and distribution equipment.

SunPower has accused some utilities of using the 15% rule as a barrier to solar market rather than a cap which triggers a screening process. Some utilities, it says, have used the 15% penetration rate as justification to close certain circuits to more PV – a position which it says is unfair. Meanwhile, SunEdison had four projects with a total capacity of 6.2MW that failed the 15% screen and cost the company US$50,000 per project, even though one was only just over the threshold.

Solar fast track
So what's the solution? SEIA has proposed “fast track” interconnection of solar generation of 20MW or less. FERC's rules, as they currently stand, mean that solar projects under 2 MW may be “fast tracked” only if the total distributed generation is less than 15% of circuit peak load.

Robert Broderick of Sandia National Laboratories said that screening needs to balance the need for efficiency and technical rigour for all DG up to 2MW.

“As we get increasing penetration of PV on the distribution circuits we're finding that this is the screen that typically causes the interconnection to fail the screening process. We have found that the screening may be overly conservative for most PV installations.”

Michael Mills-Price, from Advanced Energy in Fort Collins, Coloardo, said: “We see why engineers are excited about this space. We're finally getting to a point in our industry where we truly need technological advances to integrate these systems into our existing infrastructure. Three to four years ago we would have talked about utility plants as 5 to 10 MW. Now we're showing data for 100MW power stations and we're putting megawatt installations on rooftops.

“From a manufacturer’s standpoint when the resource starts to cause problems and power quality issues on the distribution circuit, that's when we have to come up with a technological solution to overcome that.”

One solution is to aggregate PV systems and turn them into PV solar installations as traditional asset management through forecasting, system over-design, storage integration, ramp control and frequency regulation. “We're trying to treat these large PV utility plants more like something utilities are very comfortable with,” Mills-Price said.

More work needs to be done to figure out a solution that will be acceptable for the collaborating public research institutes, utilities and the solar industry. Common ground may be found in the collection of data as grid services become increasingly digitised.

Chris Trueblood works in the renewable integration unit at the Electric Power Research Institute, Knoxville, Tennessee. He said that EPRI is now collecting the highest resolution data from 200 projects across the country – every 15 minutes for plant performance, every 10 seconds for voltage observations and every second for ramp events.

EPRI's data could achieve the granularity necessary for FERC to remove the barriers to interconnection and open the floodgates to massive market growth, he said.

“Think about moving from the analogue, the older televisions, to high definition TV. You still get the same image, you still know the score at the end of the ballgame but you get a whole lot more information out of the picture and the show if you have an HD TV. This high resolution monitoring we like to collect one second data we get that crisp image that we are looking for and help utilities better understand the impacts of DG PV on their circuits.”

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