Study sets clear path for U.S. ‘Energiewende’

Huge cuts in greenhouse emissions possible by 2030; boosting the power grid with a high voltage direct current overlay is key

NREL wind turbines near Golden, Colorado. Bob Berwyn photo.

Germany’s deliberate transition to renewable energy — the Energiewende — has made headlines around the world, but the U.S. also has the potential to make a big shift toward renewable energy. Solar, wind and other weather-driven renewable resources could supply most of the nation’s electricity by 2030 and potentially cut greenhouse gas emissions from the power sector by up to 78 percent, according to a new study by researchers with the National Oceanic and Atmospheric Administration and the University of Colorado.

Their paper, published online in the journal Nature Climate Change, suggests that upgrading transmission infrastructure is key, specifically pinpointing the need to expand high-voltage direct-current transmission lines, which reduce the loss of energy during transmission. Making that switch would make the power grid more efficient overall and help deliver the energy produced by renewable resources when and where it’s needed.

“Our research shows a transition to a reliable, low-carbon, electrical generation and transmission system can be accomplished with commercially available technology and within 15 years,” said Alexander MacDonald, co-lead author and recently retired director of NOAA’s Earth System Research Laboratory in Boulder.

The researchers started by theorizing that the key to resolving the dilemma of intermittent renewable generation might be to scale up the renewable energy generation system to match the scale of weather systems — in essence, being to take advantage of the renewable resources when and where they’re available.

Because renewable resources are, by nature, intermittent, utilities still invest huge amounts to ensure backup capacity with natural gas-fired generators and other reserves. But with smart grid planning, they may not need to, said Christopher Clack, a physicist and mathematician with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder.

The research team used detailed weather data to build a model that evaluate the cost of integrating different sources of electricity into a national energy system. The model estimates renewable resource potential, energy demand, emissions of CO2 and the costs of expanding and operating electricity generation and transmission systems to meet future needs.

“The model relentlessly seeks the lowest-cost energy, whatever constraints are applied,” Clack said. “And it always installs more renewable energy on the grid than exists today.”

In the best-case scenario — with lower future renewable energy costs and higher fossil fuel costs, the modeled system sliced CO2 emissions by 78 percent from 1990 levels and delivered electricity at 10 cents per kilowatt hour.

Even in a scenario where renewable energy costs more than experts predict, the model produced a system that cuts CO2 emissions 33 percent below 1990 levels by 2030, and delivered electricity at about 8.6 cents per kilowatt hour. By comparison, electricity cost 9.4 cents per kWh in 2012.

A scenario that included coal yielded lower cost (8.5 cents per kWh), but the highest emissions.

Via email, Clack explained how upgrading transmission infrastructure would work:

“The HVDC transmission in the model is an overlay on top of the existing transmission infrastructure. It can be thought of as an interstate for electrons. It is additional to, not in replace of existing transmission. The model has to build and pay for this transmission, if it is cost effective. The US has several HVDC links already. A famous one is from the pacific North West to South California. The national 48-state system simulation builds 139 million MW-miles.

“The HVDC would connect different markets together rather than renewable energy to load centers. It just facilitates regions with high resource to transmit their power to high demand regions. The cost of the new HVDC transmission would be 4% of the overall cost of the system per annum, and facilitate a $47 billion per year net saving versus not having that HVDC transmission built.”

Clack further explained the financing element of the findings outlined in their study:

“The model pays for infrastructure on an amortized basis, basically mortgages over 30 years. The total cost needed in capital investments is 2.6 trillion. This is compared with the 2 trillion already needed to maintain the current grid over the next 30 years.

The fuel costs are lowered by over $100 billion per year in the new system. Transmission of that cost is 150 billion total spend, or put another way around 11.5 billion per year for 30 years mortgaged.

So the $47 billion saving net is the saving to go from small scales to national scale minus the cost to build out the new transmission.”

Global climate goals

At the recent Paris climate summit, the United States pledged to cut greenhouse emissions from all sectors up to 28 percent below 2005 levels by 2025. The new paper suggests the United States could cut total CO2 emissions 31 percent below 2005 levels by 2030 by making changes only within the electric sector, even though the electrical sector represents just 38 percent of the national CO2 budget. These changes would include rapidly expanding renewable energy generation and improving transmission infrastructure.

MacDonald compared the idea of a HVDC grid with the interstate highway system which transformed the U.S. economy in the 1950s. “With an ‘interstate for electrons’, renewable energy could be delivered anywhere in the country while emissions plummet,” he said. “An HVDC grid would create a national electricity market in which all types of generation, including low-carbon sources, compete on a cost basis. The surprise was how dominant wind and solar could be.”

The new model is drawing interest from other experts in the field.

“This study pushes the envelope,” said Stanford University’s Mark Jacobson, who wrote an editorial praising the study in the journal Nature Climate Change. “It shows that intermittent renewables plus transmission can eliminate most fossil-fuel electricity while matching power demand at lower cost than a fossil fuel-based grid — even before storage is considered.”

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