MIT: The challenge of integrating renewables

New report cites factors due to technology, economics

Phil Carson | Mar 20, 2012


If you're still debating whether renewable energy will become a utility-scale asset and critical to this country's power needs, you're tilting at windmills.

The issue on the table is how to integrate variable resources with the power grid in the most efficient and reliable manner. What are the challenges, both technically and in terms of policy?

I'll touch on three developments in this area, one from the Massachusetts Institute of Technology (MIT), one from the Electric Power Research Institute (EPRI) and another from the Utility Variable Generation Integration Group (UVIG). (You may know the UVIG as the UWIG, but that's changed for the very reason we're discussing RE integration in today's column.)

Last year at this time, MIT held a symposium on large-scale integration of renewable energy and earlier this month it held a panel on the release of the symposium's report. (Click on the link to access Web video of the March 12 discussion of the report, and the report itself.)

In a nutshell, the MIT effort brought together subject matter experts in generation, transmission and regulation to discuss the impacts of large-scale renewables integration. Although many systems are handling the challenge, MIT noted that "there is limited system-wide analysis of how the deployment of large-scale renewables physically affects conventional thermal plants, the limits of their capabilities for such accommodation and the degree to which the integration of renewables is changing the physical and economic operations of power systems."

Yes, take a deep breath. The MIT report really sets up the issue well, however, providing some clarity to a potentially daunting subject. In 29 states and many countries, policies have encouraged renewable generation but "as renewable capacity has increased, the intermittent nature of wind and solar generation ... has led to operational difficulties and unintended consequences for emissions and economic efficiency."

The characteristics of intermittency and the need to balance supply and demand on the grid is creating a need for system flexibility to meet reliability goals and policy mandates such as renewable portfolio standards (RPS), the MIT group said in an "issues summary."

"In the absence of economically viable, large-scale storage, the burden of maintaining system reliability will fall mostly on the flexible operation of thermal generation units such as coal, natural gas and nuclear [generation]. However, the ability of these plants to operate flexibly is limited by both physical plant constraints and economic profitability considerations."

The impacts on regulation vary from the "economic dispatch in the short term to generation capacity investments in the long term," according to the issues summary.

"Ensuring the adequacy of the regulatory structure is an extremely complicated undertaking. In the U.S., the regulatory landscape for market rules and renewable policies is fractured and complex; planning and policy making for electric power systems occur at the state, regional and national level."

The MIT group framed five key topics:

  • Emissions: The integration of intermittent renewables forces the existing system to adapt and less efficient ramping and cycling of traditional generation can reduce the low-emissions contribution of those renewables.
  • Unintended consequences: RPSs can change market structures. Policies, markets and system requirements impact system planners and market participants, potentially raising the cost of the generation mix.
  • Future generation mix: What does a well-adapted generation mix look like? And what types of regulations would support units that contribute to reliability but may have low-utilization rates?
  • Electricity markets: Should the market treat renewables as any other generator, subject to scheduling penalties?
  • Regulation: The current regulatory system encourages cost reduction and reliability, not innovation. This may be inadequate to incentivize the development of new transmission and generation technologies required to fully enable large-scale renewable generation.


In practical terms, baseload generation—mostly coal and natural gas—must be cycled up or down to accommodate intermittent renewables, which leads to shorter lifetimes for components due to the physical stress of temperature changes, according to Howard Herzog, a senior research engineer at the MIT Energy Initiative. Cycling also reduces a plant's efficiency, which incurs higher fuel costs and, ultimately, to higher costs per kilowatt hour. Emissions equipment also doesn't run as efficiently at low loads, Herzog said.

One solution will be to find improved materials to withstand temperature fluxes. Another: better understanding how cycling can be done more efficiently. For instance, in France where 80 percent of generation comes from nuclear reactors, one-third the fleet has been modified for load-following of intermittent sources. However, cycling can introduce human error, an undesirable element in the case of nuclear power.

"Natural gas—in the absence of affordable storage—remains the technology of choice for integrating large-scale renewable energy resources," Herzog said. 

In related news, EPRI's just-released "Generic Models and Model Validation for Wind and Solar PV Generation: Technical Update" is an ongoing effort to answer "a need for generic, standard and publicly available models for variable generation technologies for the purpose of power system planning studies," according to the update's abstract. Frankly, generic models and model validation go beyond my current knowledge, but I get that modeling and system planning are among the nuts-and-bolts issues in RE integration, especially as utilities attempt to meet RPSs.

Lastly, UWIG has become UVIG. Yes, that took place last October, but I wasn't paying attention and even UWIG acknowledged that this change in scope will take time (i.e., most of 2012). The change reflected the growing need to accommodate increasing solar power on the grid and the potential for other variable energy resources such as wave and hydrokinetic power to assume greater importance. UVIG has worked for more than three decades to be a forum for solid engineering and operational practices in renewables integration at utility scale. 

Phil Carson
Intelligent Utility Daily


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I haven't read the MIT report yet, but I've spent enough time on the issues in California to be reasonably conversant on this topic.

Cycling plants that were originally built for a base load duty cycle is nothing new.  Most of the remaining fleet of coastal plants in California were originally built with supercritical boilers for for base load operation.  Many of the coal plants that are being retired in response to new clean air regulations were built for base load operation and later modified.  The same holds true for a number of large, supercritical gas plants in and around the Houston area.  Many of those plants are more than 30 years old and are past the end of their economic lives.

I think it's also important for readers to remember that base load generation imposes costs of its own.  My observation over many decades in this business is that utilities and independent generators still look at busbar costs assuming a plant will operate at full load, and then they choose base load generation without taking a careful look at the plant's duty cycle over its lifetime.  AEP's giant coal plants are a perfect example.

Storage is still too costly, though in part its because there's not enough price variability.  If regulators and politicians are scared by the prospect of hourly and intra-hour wholesale prices that move dramatically from one period to the next, storage is never going to make sense. Price differentials have to be large enough to cover the cost of the losses that every storage device incurs, plus the storage device's O&M costs, plus some contribution to fixed costs.  If on average, the relative difference between the prices storage receives when it generates and the prices it pays when it charges is less than 2.5 or 3x, other options probably make more sense.  A high efficiency pumped storage plant needs on average a 1.33 differential, most existing pumped storage plants need at least 1.5, and flow batteries need 2.0 just to pay for their losses. 

If grids are built to make sure there's never ever a shortage of supply, we'll end up with a fleet of electricity production factories that is economically inefficient and operates badly.  We tend to overbuild supply based on engineering criteria and then wonder why the economic models for complementary technologies  like storage, DG and flexible demand that could help balance renewables never seem to make economic sense.  Perhaps its time to start thinking about electricity in terms of classical market economics and stop thinking about it in terms of the parallel economic universe that's been invented and refined over the years by utilities, regulators and rate economists. 

It's possible as Mr. Woodridge suggests that this push for renewable energy is a fool's errand.  We currently have abundant supplies of the fossil fuels used for electric generation and they are relatively cheap.  However current costs fail to account for the as-yet unknown impacts on those that live near extraction sites; the consequences of exhausting fossil fuel supplies; and the long-term climatic impacts.  I'd personally rather see renewable energy development proceed a little more thoughtfully so that there's time to more fully understand and solve problems like those outlined in the MIT report, but I'm not willing to say we should call a halt. 

Jack Ellis, Tahoe City, CA

the solution to climate change


The primary source of GHG is fossil fuel burning electrical generating facilities. 

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Tilting at Windmills

Renewables, specifically wind and solar, are not economically feasible as baseload power and are not physically feasible as peaking power due to their generation timing.  When one talks of utility scale wind and solar, one is generally talking remotely located facilities which means long distance transmission lines rated to carry X amount of power but, on average, delivering 0.3X amount of power in the case of wind and 0.2X amount of power in the case of solar.  These technologies  were forcibly deployed by use of RPSs, RESs, PTCs, and cash grants in order to promote an agenda.  The result of this forcible deployment is economic distress for the US and other OECD countries to no net environmental benefit.  Studies out of the UK (see the Civitas group) and out of the Netherlands (see report by Dutch physicist C. le Pair have shown that heavy investment in wind energy in those countries has resulted in no CO2 emissions decreases due to having to run fossil fueled power plants at low loads to provide rapid backup and to provide grid stability to make up for the intense variability of wind generators.  Further, the Civitas study shows that the installed cost of offshore wind exceeds the installed cost of nuclear power on a per unit capacity basis and the all-in costs of electrical energy on a per MWh basis when levelized exceed all other technologies.

A major problem with both of these technologies is non-dispatchability.  A second problem is variability which tends to destabilize the grid.  Both of these demand that there must be a matching megawatt of fossil power for every megawatt of wind or solar installed so one must either add fossil generation or keep an older fossil plant commissioned when it should have been retired to provide the needed backup and grid stabilization.  Theoretically, one could install some storage to provide backup and stability but just how much storage will one need to provide for days when a pressure cell settles in an area an virtually becalms it for days in the case of wind.  The parallel with solar is to have several days of overcast weather which seriously degrade the output of solar facilities.

It's is pretty stupid and pretty wasteful to jump through hoops to integrate energy technologies that achieve little or nothing to decrease emissions of CO2 or anything else for that matter.

Look at what happened to Spain according to an economic study there--for every job gained in green technology, they lost 2.2 jobs in other industries.  Each job added effectively cost in excess of $700,000.

The real joke is that for the amount of taxpayer dollars pumped into green energy by way of PTCs and cash grants, we could have built dispatchable gas turbine combined cycle plants and/or ultra-supercritical coal plants that would have actually decreased emissions substantially without laying waste to large swaths of forested regions or pristine wilderness areas to make access for windfarms and utility scale solar and the long distance transmission lines they so desperately need.

Utter idiocy

Mark Wooldridge

Which issue?


You wrote "Renewables, specifically wind and solar, are not economically feasible as baseload power and are not physically feasible as peaking power due to their generation timing."

Yet neither suggestion is made by MIT or in the article above. Your anger over renewable energy's place in the mix is understandable. Change is scary. But the MIT work was about RE integration and its affects on cycling baseload plants that run on fossil fuels.

Pioneering new technologies will always attract a debate. If you wish to discuss subsidies, which were not involved in the MIT study or the article above, then you'd do well to turn to Bloomberg News for its analysis of subsidies paid to the fossil fuel industries you tout.

Regards, Phil Carson

The problem is who pays for this integration


The reason I commented on this particular article in the way I did is that however the integration is done, someone will pay for it.  Any federal contributions to the program come from the taxpayers because the feds do not have any money they do not get from the taxpayers.  Even if they print new money to pay for the programs, they devalue what money the taxpayers still have after paying their taxes so the taxpayer ends up paying higher prices for everything, ergo the taxpayer pays.

If the integration is done by utilities, the ratepayers pay.  At least at present, the majority of ratepayers are taxpayers, therefore it is arguable the taxpayer pays.

The article talks about cycling baseload fossil power plants to integrate renewables.  If the baseload power plant is a utility power plant, the costs of that plant is paid for by the taxpayer/ratepayer thereby increasing the cost per unit of energy from the plant because the plant is now not running at the high capacity factor for which it is designed and the heat rate is going up causing the taxpayer/ratepayer's cost per unit of energy to increase still further while his taxes are being used to subsidize the energy output of the renewable power facility.  Sounds like a triple whammy to me.

If there were no renewable portfolio standards, renewable energy standards, production tax credits for wind, or cash-in-lieu grants for solar, there would be no need to pay for integrating these highly variable renewables, therefore no need to pay the costs of integrating them.  The PTCs and cash grants all come from the taxpayers.  The RPSs or RESs result in programs such as feed-in-tariffs or other such credits which basically increase the price of electricity for customers who cannot afford to invest in windfarms, solar farms, or solar panels on their homes or buildings.  The taxpayers who are not able to invest in renewables end up being burdened with the tax credits given to those who can afford to invest in them.

In short, what is the net result of investing taxpayer money in or causing the taxpayer/ratepayer to pay more for electricity produced by these wind or solar projects and to pay for them to integrate this green energy.  The answer--nothing.

I do not object to change if it is beneficial but not if the benefits either do not exist or the benefits do not outway the costs.  The benefits of wind do not outway the costs because there presently is no benefit to wind generation if you bother to read the Civitas or C. le Pair studies.  The benefits of solar do not outway the costs because solar was subjected to commercial deployment before all the R&D was done to get the costs of manufacture down.  Thus, since neither of the technologies result in benefits that outway the costs, the benefits of integration do not outway the costs.

The American taxpayer is being bled to death through taxes to pay rich people to develop and operate uneconomical power generation facilities, increased prices of foods and goods due to taxation of the companies from whom he/she obtains the foods and goods, increased costs of building materials resulting from the proliferation of windfarms that use massive quantities of building materials per MWh generated, loss of employment due to manufacturing businesses closing down or leaving the US to go overseas where they pay lower taxes and lower wages, and now this integration of renewables will raise the taxpayer's cost of living still higher.

In short, our own governments (federal and state levels) are participating in the destruction of America by squeezing the taxpayer (be they individuals or businesses not involved in green energy) to the point he has nothing left.  You are damn right I am mad.

Mark Wooldridge

Love the anger


While you'd like to blame "the government" for your taxes, which are some of the lowest in the industrialized world, your fellow citizens have required the utilities in most cases to reach renewable portfolio standards. So before you place blame on the faceless "government," remember, it represents your neighbors who demanded these policies.

I could mention the massive subsidies for fossil fuel production by the most profitable companies on the face of the earth -- so if you believe in the free market, where's the anger there? Your tax rate is largely determined because people and corporations with the time and money to lobby Congress (read: buy influence) have stacked the deck against you. The subsidies for integrating renewables is a drop in the bucket, but one that can take us to cleaner energy, fewer deaths by cardio-pulmonary disease and, possibly, freedom from monopolized central power.

We didn't hear your voice when we spent $500 billion to invade a country on false pretenses, resulting in 5,000 American deaths and 100,000 Iraqi deaths. Why the anger on the pittance for clean energy, that at least is going somewhere positive? That's a rhetorical question and I don't sense that your anger stops here.

Regards, Phil Carson

Idealized view of government

I will have to check on the lowest individual taxes in the industrialized world to see where our tax rates fit.  I know that 26% of my gross pay gets taken from me before I ever get my check.  The American corporate income tax rate is now the highest in the world from what I heard on the news the other day--we were second.  Corporations find ways to roll those taxes into prices that we have to pay for goods.  I believe those demanding green energy have been misled by those who promote green energy programs into thinking the energy is really free and cost competitive and that it really decreases CO2 emissions.  Read the Civitas group report on the effects of the UK's heavy investment in wind energy and the report done by C. le Pair in the Netherlands about the results there and you will see those countries have found wind has not decreased CO2 emissions--in fact, le Pair states it has increased CO2 emissions by 3%.  Nor do I believe that manmade CO2 is the principal cause of global warming--no wait that was global cooling originally--okay, global climate change.  I believe it contributes but is not the principal cause just as the waste heat from power generation contributes but is not the prinicpal cause.

If green energy was competitive, it would not require PTCs, cash grants, or RPSs to be implemented.  In ERCOT, generation is strictly market-based--all competitive.  At night, wholesale power prices routinely drop to under $30 per MWh--3 cents per KWh.  Not only does wind energy get the 3 cents but they get 2.2 cents from the feds as a PTC.   Wind is highly variable--when a front is moving in, the wind might blow strong enough for the windfarms to produce significant power around the clock.  If a stationary cell settles in, there may be no significant wind generation for a couple of days.  Normally, wind is available from midnight to 0800.  The result of this uncertainty, no one wants to build new thermal generation because they cannot project what their return will be and now, ERCOT is short of their reserve margin target in the warm months.  In addition, ERCOT consumers are now on the hook for some $7 billion to pay for a transmission line (that was supposed to be $4.3 billion) just to bring wind energy from the west to load centers. 

As for the massive subsidies to oil companies which are "...the most profitable companies on the face of the earth..."  Defining most profitable depends on whether you are talking quantity of money or profit margin.  You will find many other industries with higher profit margins than oil companies.  And, what about GE?  They did not pay any income taxes yet their CEO is an adviser to the President on job creation while they are moving some production lines to China.  No oil company gets a tax credit for producing oil--they may have deductions from income.  No, let me correct that--if you are so concerned about subsidizes to big (bad) oil, you better look at some of the big players in the green energy development field, because that is one route some big oil players (and others with higher profit margins than big oil) are using to reduce their tax burden.  Guess who picks up the slack. 

Last year, DoE spent $100 billion on green energy promotions.  $100 billion is enough to build 91,000MW of gas turbine combined cycle plants that could have replaced older coal-fired plants that do not have SO2 scrubbers and other emissions equipment while reducing CO2 emissions by roughly 162 million tons per year if run at  base load.  $100 billion is enough to build 45,000MW of ultra-supercritical coal fired power plant with all emissions controls (except CCS) that would have reduced CO2 emissions by 81 million tons per year running at base load.  And both of those technologies are fully dispatchable while neither wind nor solar are dispatchable.

On top of that, I wonder how many deaths would result from loss of electricity or lack of dependable electricity  compared to the EPA's (gue)estimate of power plant emissions related deaths.

As for the Iraq War--I think it was completely unjustified.  We have no business engaging in nation-building, especially among a group of peoples (differing ethnicities) whom we do not even understand.  My thoughts on the Afghan War--once we determined that Al Qaeda was the culprit and where they were, we should have pretended we had absolutely no idea what to do and publicly wrung our hands in despair while we sent the "black jets" and precision guided munitions to obliterate every Al Qaeda camp in Afghanistan and any other place we knew of using precision guided munitions without asking permission of Pakistan or any other country.  Once we started talking with countries surrounding Afghanistan to get their permission, you can be sure that while we were into opening "arguments", bin Laden was already warned and gone.  Maybe some special ops units to check things out later but no invasion, no nation-building, and minimum if any civilian casualties.  What that has to do with the DoE throwing money away now, I am not sure but you brought it up.

I think your views of the role of government is a bit idealized--but, that is my opinion.  It is also my opinion that Energy Secretary Chu is a highly educated man with no common sense to speak of.  It is also my opinion that the federal government should stick to the powers and duties assigned it in the Constitution.

Mark Wooldridge


MIT on integration

MIT is correct yet throughout the industry there has been touted a misconseption about pumped storage and it's flexibility. The lastest technology in pump turbines renders that arguement null. 

A variable speed pump turbine coupled with the digital stator can respond in 5 sec. and be at full capacity in 20 sec. For the balancing of large variable renewable these advances make pumped hydro very attractive.

Its also been said the the siting of pumped hydro is very difficut- true but doable, in fact its happening now with projects waiting on FERC licensing. By removing a pumped hydro from the aquatic resource and designing a closed loop system most of the environmental nexus is removed. This reduces the cost of licensing and mostly removes the nimbyism that arose when projects wanted to use recreational bodys of water.

Large scale grid sized storage does have one set back - it removes the need for combustion based ramping generation which is a large part of the major utilities inventory. No company wants to see their assets become obsolete and they do fight storage projects.

However the time has come for storage to take its place in the energy market if only for onee reason - to lessen the impacts of fossil fuel use.