Renewable energy: The 99.9% solution

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A combination of wind and solar power and sophisticated energy storage systems could keep a power grid fully supplied between 90 and 99.9% of the time, at costs comparable with today’s fossil fuel and nuclear mix, according to a new study from Delaware in the United States.

Computer simulation measured the performance of inland and offshore wind farms and photovoltaic cells, backed up by battery and fuel cell storage, under the lowest cost conditions, for a 72 gigawatt grid system (one gigawatt will typically provide power for about 750,000 to a million US households)..

Researchers from the University of Delaware and Delaware Technical Community College will report in the Journal of Power Sources for March 2013 that they tested 28 billion combinations of renewable energy systems and storage, under four years of real load and weather data from a working commercial system.

“These results break the conventional wisdom that renewable energy is too unreliable and expensive,” said Willett Kempton of the University of Delaware, one of the team. “The key is to get the right combination of electricity sources and storage – which we did by an exhaustive search – and to calculate costs correctly.”

Power demand and supply is an engineering headache: demand fluctuates according to hour, day of the week, the weather and the season, while wind power is vulnerable to calm weather and solar power is not supplied at night.

Storage costs are huge, and increase with the need to store for each extra hour. So right now, most electrical generators burn more fossil fuel to meet extra demand.

“The common view is that a high fraction of renewable power generation would be costly and would either often leave us in the dark or require massive electrical storage,” say the researchers.

But they found quite a different result. They tweaked their computer model and varied the conditions where they could: they found that consistent wind power could be obtained if the turbine fields were dispersed at distances greater than 1,000 kilometres.

They exploited not just hydrogen fuel cells and batteries for storage, but also grid-integrated vehicles: electric cars and trucks which when not being driven also served as sources for the grid.

They calculated the cost of renewable electricity generation without subsidies from either state or federal government, and when they made comparisons with fossil power, they factored in the external health and other costs of fossil fuel pollution.

The researchers worked with the prices for 2008, and with the projected costs of power for 2030, and they did not allow for any future advances in renewable technology.

They found that the cheapest solution was to generate far more power than consumers could demand. If they generated 180% of the necessary load, renewable sources could supply all that the grid needed for 90% of the time. If they generated 290%, then they could rely on renewable resources 99.9% of the time: that is, for all but nine hours a year.

And renewable energy, on this model, is the least-cost option, or close to it. “At expected 2030 technology costs, the cost-minimum is 90% of hours met entirely by renewable,” the team report. “And 99.9% of hours, while not the cost-minimum, is lower in cost than today’s total cost of electricity.” 

This article was originally posted on Climate News Network. Re-posted with permission.


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  • David

    Unfortunately this paper discounts the possibility of using pumped hydro storage which is by far the cheapest form of grid scale storage. This omission completely distorts the results in favour of excess generation over storage.

    • David Kerr

      Inclusion of wave power into modelling will also assist the renewable mix given it is more predictable than wind power and will be cost competitive within this decade at appropriate locations such as King Island, Tasmania.

    • David

      The other problem I have with this paper is the assumption that 100% of EVs will be available for grid connected storage. This is a very weak assumption given that most of the EVs will not even be connected to the grid for large stretches of time. Also, given that range anxiety is the major limitation on uptake, owners are simply not going to sign up to a system that does not guarantee their vehicle has the maximum charge possible at the time they wish to use it. I think EV batteries have extremely limited application to renewables grid support, and that is for demand management and possibly regulation, not storage.

    • Lukas

      Agree with you David, if there are pumped hydro storage facilities available then use them. The excess solar and/or wind power mentioned in the article can be used to fill the storage dams so that hydro will also be used as a renewable source of power.

  • Lars

    If this research only looked at the state of Deleware the possibilities of pumped hydro storage may not be feasible as the state is pretty flat, but wave power should be possible due to their long coastline. If this research is backed up by other studies it would also validate much of what BZE (Beyond Zero Emissions) claim is possible here in Australia. Curious what cost they put into their estimates for health impacts due to fossil fuels. Also they assume EV in the mix, but have they costed the infrastructure one may need with EV. Look forward to the report when it comes out in March- please post it RE

  • keith williams

    Amazing that at 2008 prices solar & wind with overcapacity is at all competitive.

    Given that they are, a couple of things are obvious:

    i) It will get cheaper as the innovations (cost reductions) in wind and solar are dramatic
    ii) Implementation of solar thermal (taking off now) will certainly mean some of the overcapacity isn’t needed
    iii) The concept of overcapacity means that for most of the time there would be substantial excess capacity …. which opens up the opportunity to explore how to use this power in a way that can be shut down. Perhaps a big user like aluminium production could be implemented with the understanding that there would be shut downs. If the energy comes very cheap, this may well be feasible.

    Exciting thing is that there are lots of opportunities here for creative ideas and certainly a whole new series of industries to employ people in.

  • Excess supply is an opportunity. Surplus renewable power is effectively zero cost power. It is a logical mix with electrolysis since electrolysis can be turned down when power is needed elsewhere. Think low cost, almost clean aluminium (Fossil carbon is consumed at the electrodes.) Think clean hydrogen from electrolysis. Think clean electrofuels such as ammonia, methyl alcohol,gasoline and diesel manufactured from this clean hydrogen. Think…