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The Cheapest Way to Scale Up Renewable Energy?

Replacing regional power grids with a national system could reduce carbon emissions without using storage technologies

Replacing regional power grids with a national system would save $47 billion a year, reducing the average cost per kilowatt hour from 12.7 cents to between 8.5 cents and 10.2 cents.
Image Credit: Tsuna72 / Creative Commons license / Flickr

Generating electricity with wind turbines or solar arrays instead of fossil fuel reduces carbon emissions, but these renewable generation sources are dependent on the vagaries of the weather, which means neither wind nor solar can produce electricity on demand at all hours of the day. This variability has led many to assume that greatly expanding wind and solar to reduce carbon emissions will cause electricity costs to skyrocket and require expensive energy storage.

My colleagues and I have just published a new study to show that this assumption is not correct. In fact, if the U.S. were to move to a national 48-state electric system, rather than the regional one in place now, the country would be able to transport more renewable energy around the country. That change could reduce CO2 emissions by 78% at lower costs than today without using any storage technologies.

Using a computer model, we found that this larger electric system would utilize power more efficiently regardless of the generators within it. The cost reduction between the national style system we modeled and the current one, which is divided into about 130 regions, is $47 billion per year. That translates into an electricity cost of between 8.5 and 10.2 cents per kilowatt-hour (kWh), compared to the current national average of 12.7 cents per kWh.

Electron superhighway

Our study was based upon a model called the National Energy with Weather System (NEWS) simulator. The NEWS simulator is a cost optimization model that relentlessly seeks the lowest-cost solution.

The model considers features of the electric grid, such as transmission, generators, electric demand, land use constraints, generator behavior, weather data, and cost data for generators. To figure out how to minimize costs, the NEWS model will calculate how to supply power every single hour for an entire year based on the available generators and transmission lines that transport power long distances.

Our model had something unique, though: a high-voltage direct current (HVDC) transmission overlay.

In concept, this is very similar to the interstate highway system overlaid upon the road network. HVDC technology has one big advantage over traditional power lines: there is less energy lost in transporting power from one point to another. It does this by using direct current, rather than alternating current, and operating at higher voltages.

HVDC is being used in the U.S. today. However, it is being deployed as a point-to-point system for single (or a few) generators to distant markets. One of the most prominent is called the Pacific DC intertie, which ships power from the Pacific Northwest, with its abundant hydropower, down to Los Angeles, supplying 48 percent of power during hours of peak demand. The difference in the NEWS model is that HVDC is deployed in a network, instead of a simple point-to-point configuration, which allows much greater utilization of the lines for power to flow between regions in multiple directions.

Critically, the NEWS model doesn’t assume that more transmission lines should be added to the current grid. But it does introduce new transmission capacity if the model deems it economical. Interestingly, the NEWS model always selects HVDC transmission when it can. Why? The availability of HVDC lines allows bigger markets to form, which then benefit from economies of scale.

In practice, this would mean that wind generators in the Plains states, for instance, could export more power to places in the country where there is strong demand, such as big cities. As it is now, wind generators only support power regionally and sometimes supply more power than is needed at some hours of the day.

In a regional system, one that is the size of, say, Kansas, wind and solar tend to result in periods of overproduction and under-production. This results in increased costs because wind and solar generators need to curtailed, or turned off, during overproduction. To meet lapses in production, grid operators need to rely on backup generation from fossil-fuel plants.

With a national system, the generators can be strategically placed over the contiguous U.S. to reduce this effect and lower the overall costs. The HVDC facilitates the movement of this electricity from distant reaches to cities with lower losses than traditional AC.

Renewables scenario

To perform the study, high-resolution weather data were compiled for each hour of the three years from 2006 through 2008. The weather data were then used as inputs into sophisticated power algorithms to estimate the power that could be generated by wind turbines and photovoltaic (PV) panels across the U.S.

Additionally, we compiled data on electricity demand during those times across the U.S. The data were needed because weather is a fundamental driver of the electric demand. Then we projected demand data to 2030.

Wind power potential for the U.S. Red indicates high potential, blue is low. (Illustration: Christopher Clack)

Because the deployment of wind and solar is subject to many constraints, we built land use considerations into the model. A land use data set was compiled to identify locations where the wind and solar can be deployed without interfering with protected lands.

Using these different sets of data along with the projected cost for power generation in 2030, we ran different simulations to investigate how these factors would affect the mix of power generators regionally while minimizing total cost.

The scenario that cuts emissions most has significant wind and PV deployed; 523 gigawatts (GW) of wind and 371 gigawatts of PV compared with 60 GW and 2.5 GW, respectively, in 2012. In this scenario, there was only 461 GW of natural gas (less than today).

This translates to 38% of electricity coming from wind, 17% from solar, 21% from natural gas and the remainder from nuclear and hydroelectric. In 2012, wind accounted for 3.5%, solar for less than 1%, and natural gas for 30%.

Again, this solution is the cheapest possible solution.

To get to this level of solar and wind – a significant jump from today’s levels – does require new transmission lines in the model.

The amount of new HVDC transmission that the model recommends is 139 million MW-miles, which is a big infrastructure undertaking. This sounds like a huge amount, but it would represent only 4% of the total cost of the system annually.

What about energy storage?

The NEWS model is unique in the study of integrating higher levels of wind and solar because it handles huge volumes of weather data, while computing the important aspects of the electric grid such as ramping constraints on generators, down times for generators, power flow in the transmission lines, electric losses shuffling power around the system, meeting demand at each hour in every market, and other operating constraints. Further, the model doesn’t exclude any technologies; it seeks only the lowest-cost options.

Electricity can be stored in a number of ways, such as pumping and releasing water from reservoirs or installing large battery banks. In initial model runs, electric storage was not competitive using cost estimates for 2030 compared to adding transmission or natural gas generators (purely based upon cost).

The NEWS model is a tool to help understand how an electric grid could be transformed while keeping costs low. Low cost is absolutely essential because increasing energy costs to reduce carbon reductions can cause economic hardships.

There are numerous headwinds to the development of a decarbonized economy and society. But the NEWS model has shown that wind and PV, combined with high-voltage direct current transmission, can actually go a long way in reducing emissions in the electric sector.

This is true even without a new miracle battery or innovation within the electric storage industry, although cheap, effective electric storage would be helpful in integrating renewables.

To remove carbon from the entire economy, electricity must be decarbonized first. If it can be done at low cost, then other sectors will be able to follow suit. Combining wind, solar, natural gas, and transmission is a possible bridge to a zero emissions future.

Christopher Clack is a research scientist at the National Oceanic and Atmospheric Administration. This post originally appeared at The Conversation.

6 Comments

  1. Bob Howell | | #1

    I think this article belongs on Popular Science or Mechanics
    I have a paid subscription to become "Advised" on "Green Building".

    The article Replacing regional power grids with a national system -- while an interesting and worthy topic -- does not provide the type of useful information I expect from this site. It just doesn't belong here IMHO. I am not going to be creating any power grids through my own efforts.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Bob Howell
    Bob,
    Thanks for your comments; we always appreciate hearing from readers, and we'll keep your feedback in mind.

    Our guest blogs cover a wide variety of topics; some blogs seem to hit the nail on the head for many readers, and others may not.

  3. Alan B | | #3

    @ Bob
    I agree with you, but not because it should not be here, but because it would then reach a national audience.

    Many of us who are interested in green building are interested in all parts of green technology, so it should most certainly be here, it should just be in both

  4. User avater
    Dana Dorsett | | #4

    There's also room to disagree, with a building context.
    Transmission lines aren't cheap, and siting a large fraction of the solar at the load (say, the high performance house you're contemplating building) reduces the peak loads, and with it the size of the grid infrastructure. Even though the per kwh cost of the power generated may be higher, it's not entirely the case that it's more expensive than shipping wind or solar 1000 miles by high voltage DC interconnects. I haven't fully read the study, but other studies have shown a more distributed generation model to be both more stable and cheaper going forward than a high-capacity grid approach.

    Much depends on what the starting assumptions are about how power will be moved, stored, used & traded in the coming decades. The rate of electrification of the automotive fleet has a huge impact on what's cheaper or not. (Smart chargers can draw down the locally produced excess, smart demand-response can limit the peak draws.) The notion that it takes a lot of storage to get there is misplaced- smarter loads is enough. Estimates of how rapidly and how deep the electrification of transportation will go vary by more than an order of magnitude, as does the potential cost to the electrical ratepayers, but even with flat or no increase in electric cars, paying for demand-response is probably still quite a bit cheaper than building out the transmission grid. HVDC is one affordable solution, but it's not necessarily the cheapest, most secure or best solution.

    With new construction one should consider the potential for future site-sourced energy. Being PV-ready isn't very expensive if it's designed in from the get-go, and it's all to easy to make retrofit awkward expensive or impossible if no consideration for that potential has been given.

  5. User avater
    Paul Kuenn | | #5

    Long distance transmission is a bad idea
    Anyway you look at it, these towers crumple to the ground like cheap toothpicks when we have the increased ice storms and an occasional earthquake. Then everyone is without. You don't have that in neighborhoods supported with local energy supported by utilities like NRG. Yeah Vermont! Let's just hope more money gets dumped into battery technology. There is hope but it's still way too slow in coming. I'll put my money behind more energy efficiency, less production.

  6. Bob Irving | | #6

    Good article Martin; thanks
    Good article Martin; thanks for publishing it. Like many of the builders on this site, we're building all electric houses. Many, but not all will generate their own power, but a number will rely on the grid to power their home, so it's to our benefit to understand the complications inherent in our reliance on electricity.
    The article hits home for a different reason, too - here in NH we're fighting a new DC transmission line through our scenic mountains and forests delivering Canadian Hydro to NYC. The towers are twice the height of current ones & far higher than trees. Our local utility intends to rely on the rental income as they lose customers to efficiency and renewables. There are many facets to the discussion.

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