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Ivanpah CO2 Emissions: More Than 10 Times Solar PV

Wikimedia Commons/Craig Dietrich

Wikimedia Commons/Craig Dietrich

UPDATE: About 10 days after original publication, NRG got back to me with corrected and previously missing data, necessitating minor changes throughout this piece. The upshot: Gas usage was up 62 percent, not 59 percent, in Year 2, and emissions were 229 pounds CO2-equivalent per MWh in Year 2, not 225.

Natural gas consumption at Ivanpah, the controversial power plant in the California desert, increased 62 percent in its second full year of operation, and the plant emitted the equivalent of about 229 pounds of carbon dioxide for each megawatt hour of electricity it generated.

How’s that compare?

It’s about one-fifth the emissions of the average U.S. power plant and a bit over one-quarter the emissions of a recently built combined cycle natural gas-fired power plant in California.

But of course Ivanpah is considered a renewable energy source by the state, like utility-scale solar PV, which according to the National Renewable Energy Laboratory puts out 18 to 22 pounds of CO2 per megawatt hour of energy produced. In other words, CO2 emissions at Ivanpah are at least 10 times those of solar PV.*

ivanpah gas first two years fully updated

Ivanpah used 1,251 million cubic feet (mmcf) of gas in the 12 months ended January 31, a figure based on preliminary data obtained from the U.S. Energy Information Administration.

The $2.2 billion Ivanpah Solar Electric Generating System, with tens of thousands of reflecting mirrors and giant “power towers” that heat water to generate thermal power, was fully online by February 1, 2014. It generated 430,488 MWh of electricity in its first 12 months of operation, according to the EIA, while consuming 773 mmcf of natural gas. That slow start left the plant in danger of defaulting on its PPAs with the utility PG&E (see: “Ivanpah Not Out of the Woods Yet“). In Year 2, the plant produced 655,926 MWh of electricity, a 52 percent increase.

Under its original licensing, Ivanpah’s three units were permitted to burn a total of 984 mmcf of natural gas annually. But a few months after the plant began commercial operations, Solar Partners – consisting of majority owner NRG, along with Google and technology developer BrightSource Energy – asked and then received approval from the California Energy Commission to use as much as 1,575 mmcf in a year.

So in Year 2, Ivanpah ended up using about 25 percent more gas than originally planned, but about 22 percent less than the revised limit.

The overall limit isn’t the plant’s only consideration when it comes to natural gas, however, not with PG&E and Southern California Edison counting Ivanpah electrical output toward their obligations under California’s renewable portfolio standard. To qualify as a renewable energy source, state law limits the amount of “non-renewable energy that may be included with renewable energy at no more than two percent of total fuel use.” But the law allows wiggle room up to 5 percent in special circumstances, an allowance granted to Ivanpah.

Is Ivanpah using less than 5 percent natural gas?

Depends on how you look at it.

Ivanpah relies on gas in “night preservation” and “auxiliary” boilers.  As BrightSource has explained, “night preservation boilers are very small boilers used overnight to maintain seals and preserve heat.”  As for the auxiliary boilers, again quoting BrightSource, they are used for:

  • morning startup;
  • daily shutdown;
  • supplementing solar generation during periods of transient clouds or at the end of the day;
  • standby to avoid turbine trips during passing clouds;
  • and if a trip occurs, to ensure the quickest restart, if feasible based on weather conditions.

BrightSource says “this type of natural gas does not produce electricity. In fact, it increases the amount of electricity produced through the sun.”

The gas used at Ivanpah in Year 2 would have produced 180,000 MWh at a modern natural gas-fired power plant like the Lodi Energy Center, opened in late 2012. Although that’s equivalent to 27 percent of Ivanpah’s total Year 2 electricity generation, regulators say Ivanpah has not been using more than 5 percent non-renewable fuel.

That’s because the regulators don’t count most of the fuel used for the purposes listed by BrightSource. If the gas wasn’t burned between the start of generation and the end of generation each day, it’s like it didn’t happen.

This allows NRG to say that less than 5 percent of the electricity generated at Ivanpah resulted from burning natural gas. (Under this calculation, in Year 2, 4.3 percent of electricity generated at Unit 1 came from burning gas; 4.1 percent at Unit 2; and 4 percent at Unit 3. Overall, the figure was 4.1 percent.)

But of course, the gas used for all the other purposes at Ivanpah was still burned, and presumably because it had to be in order for the plant to function. And the emissions were still emitted.

As Dan Danelski revealed last year in the Riverside Press-Enterprise, Ivanpah’s emissions are hefty enough to qualify it as a polluter under California’s cap-and-trade program.** Based on its natural gas consumption, emissions in Year 2 of the plant’s operation were about 68,097 metric tons. That’s 150,128,000 pounds – thus the 229 pounds per megawatt hour figure.

The Lodi gas-fired power plant pumps out about 837 lb/MWh.

It’ll be interesting to see what happens to Ivanpah’s gas consumption in Year 3. The most notable trend evident in Year 2 was a big increase in use at the end of the year – in the three month period from November 2015 through this January, consumption was up 142 percent.

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*NREL estimates full life-cycle emissions for solar PV at 88 lb/MWh, with 21 to 26 percent attributed to operational processes, including power generation and system operations and maintenance. See this PDF.

**Danelski reported on 2014 calendar year emissions. But the three Ivanpah units began delivering electricity at various points in January that year, and NRG and PG&E are using February 1, 2014, as a starting point in measuring performance of the two units under contract to PG&E. This analysis follows suit for the entire plant.