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Why Expanded Alternative Energy Increases the Need for Natural Gas

Renewable wind and solar power are important solutions to reducing carbon emissions.  These technologies have improved substantially in recent years.  Despite very significant advancements, wind and solar power costs continue to be greater than existing low carbon alternatives such as natural gas.  In addition expanding variable wind and solar power requires increasing amounts of peaking power backup capacity to properly control and maintain critical power grids reliabilities.  Why does expansion of wind and solar power continue to require increasing levels of natural gas electric power generation?

Daily Electric Power Demand Varies – When you woke up this morning you probably turned on the lights and might have turned up the heat to take the chill off the room.  You may have prepared a hot breakfast, and either turned on the TV to check the weather and traffic reports, or went on-line to check your emails.  Before you left the house you also might have turned on the dish washer and possibly started the day’s laundry.   Many of these activities are fairly common for most people in preparing themselves for the day’s activities.  While you were preparing yourself for the day, many commercial businesses, stores, offices, public schools, etc. also began opening and powering up their daily operations.

What most people do not think much about is that their electric power demand varies significantly during the day and the power grid operations must be continuously adjusted to meet changing demands.  For example, individual residences power consumption increases from minimum levels to maximum levels as the day progresses.  Refer to the following ‘power load curve’ for typical U.S. residences.


Average power load curve based on PATH data.

Typical U.S. Residential power consumption increases from about 0.5 KWH up to 5 KWH during the day.  During the late night-early morning your refrigerator/freezer, HVAC system, and charging laptop/tablets or smart-phones consume minimum power levels for a given day.  After you wake-up and begin turning on various lights, appliances, electronics and adjust room temperatures your power consumed rapidly increases to many times the minimum levels that occurred while you slept.

The Commercial sector has a similar daily average power demand load curve pattern compared to the Residential sector.  The Industrial sector’s daily power demand is relative constant.  As a result, total power demand varies significantly during a given day.

Electric Power Supply Changes with Demand – Power grids are normally designed to continuously adjust the level of power supply with varying demands.  The majority of Residential and Commercial customers are supplied ‘on-demand’ power.  This means that customers can increase or decrease their power demand most any time.  The operators of power grids must rapidly increase or decrease power generation supplies as required to meet daily demand changes and balance power supply-demand.  This is accomplished by rapidly increasing or decreasing intermediate or ‘peaking’ load natural gas power generation.  Most stable or baseline-minimum power demand is supplied by ‘baseload’ power generation.  To illustrate refer to the following supply and demand load curves.


Power load curves base on EIA MERNew England, and related studies data

As shown, total power demand varies from high levels during the mid-/late-day, to low levels at night-early morning.  Baseload power nuclear, coal and hydropower (including fully ‘dispatchable’  biomass) are normally operated at relatively constant rates.  Varying power demand is primarily supplied by baseload-intermediate-peaking natural gas power.  Note: due to the relatively small levels of wind+solar power, these renewables are assumed to be constant for this power load curve example.

Depending on the availability of ‘non-dispatchable’ wind and solar power, these variable power generation sources normally reduce the need for peaking natural gas power.   How much and when power is available from wind or solar sources depends on a number of variables.  Solar power cannot become significant until after sunrise and normally does not produce maximum power generation until mid-day.  Wind power generation depends on wind conditions during a given day.  If the renewable power facilities experience calm winds or cloudy conditions, both wind and solar power production will be reduced.

To illustrate how variable wind and solar power can be, Germany’s experience is an excellent example.  In 2012 Germany expanded its wind and solar power to record levels.  Recently published data on actual power generation performance shows how extremely volatile and unpredictable wind and solar can be in the short- and long-terms.  Refer to pages 87-138 of the recently published Fraunhofen Institute report.

Maintaining Power Grid Reliability – Power grid operators are responsible to continuously monitor and maintain the balance between supply-demand and overall grid (voltage) stability.  If supply-demand balances are not controlled within safe operating limits, power grid stabilities and reliability will be automatically adjusted.  Safety control devices (circuit breakers, power generation trips, etc.) begin automatically shutting off uncontrollable demand or shutting down excessive power supplies to protect power grid equipment and transmission systems from overheating and mechanical failures.  These auto-safety control actions result in black-outs and brown-outs for all customers on the affected power grid(s).

To reliably and safely control power supply without forcing demand changes, advanced control systems have been installed to maintain critical power grid supply-demand balances and stabilities.  What some people refer to as ‘smart grid’ technologies actual begins with macro system controls designed to react and make adjustments to short-term changes in power demand (feed-back controls).  These systems also include advanced computer system-controls that anticipate normal daily changes in power demand (feed-forward controls).  The combination of automatic control systems (and operator manual adjustments when needed) ensure that power generation capacity is continuous adjusted to maintain power grid dynamic, real-time stabilities as required for continuous efficient, reliable and safe operations. 

Wind and Solar Power Impacts on Power Grid Stabilities – Power grid supply-demand balances are normally controlled by adjusting the level of power generation supply in response to demand changes.  With the exception of a few industrial or public utility ‘interruptible’ customers and available hydropower pumped storage, most power grids can only maintain supply-demand balances by adjusting power generation supply.  Although wind and solar are technically power generation sources, these variable-unpredictable supply sources add significantly to the volatility and difficulty in properly controlling power grid supply-demand balances.

Unlike most power generation facilities that are fully dispatchable (can be scheduled, started up, shutdown and adjusted as demand requires), non-dispatchable or variable wind and solar power cannot be scheduled or readily adjusted as system demand requires.  The level of wind and solar power generation is conditional upon the weather and time of day.  While solar power is generally more predictable than wind power, it obviously cannot operate at night and wind can (part-time).  These performance differences have obvious advantages towards displacing fossil fuels, but also have the major disadvantage of making the control of power grid supply-demand much more difficult (depending on the percentage or level of ‘penetration’ into a given grid’s total power mix-supply). 

Due to the unpredictable or non-dispatchable nature of wind and solar, these power generation sources are commonly referred to as ‘negative demands’.  Since heavy cloud cover and too high/low winds cannot be predicted with a high level of certainty, wind and solar power must be fully backed up with peaking power supply capacity such as natural gas.  Similar to adjusting and balancing power grid’s supply-demand when ‘on-demand’ customers significantly change their power usage (without notification or constraints), the loss or gain of wind and solar power must be similarly controlled by adjusting (natural gas) peaking power generation capacities.

Expanded Wind and Solar Power Requires Increasing Levels of Natural Gas Peaking Power – Coal and nuclear power is normally only available for relatively constant baseload power capacity, which is planned and scheduled to minimize rate change frequencies and magnitudes.  Besides maximizing baseload power generation efficiency, coal power operating flexibility is further limited by the need to strictly control plant stack emissions.  Due to these operating constraints coal and nuclear power plants are not suitable sources as peaking or backup power to variable wind and solar power. 

Wind and solar power have average capacity factors of 33% and 20-25% respectively.  This means during a given period of time (day, week, etc.), renewable wind/solar is only capable of supplying full design power generation capacity to the grid on-average about 20-33% of the time.  Since wind and solar are variable and unpredictable, peaking power must be on-line 100% of the time.  Peaking power must be on-line at some minimum rate and available to quickly adjust to variable renewables power supply changes as required to continuously control power grids supply-demand balances within operating safety limits.

Natural gas is an excellent source of both peaking and baseload electric power supply.  Due to its high capacity factor (87%), high efficiency and relatively low fuel cost and emissions, natural gas power supplies power grids reliably and cost effectively compared to other currently available peaking power alternatives (petroleum, biogas, etc.).  These factors make natural gas peaking power the ideal backup for increasing penetration levels of wind and solar power supply.  Since variable wind and solar power cannot be used to displace constant-baseload power such as coal, these variable power sources are only capable of displacing natural gas peaking power capacity and associated fuel consumption.

Power Storage and Interruptible Demand Options – Current options to either storing electric power or reducing demand are relatively limited.  Hydropower pumped storage is the only industrial available  option for reasonably and efficiently storing and supplying on-demand power to connected grids.  Another available option is ‘interruptable’ Industrial and Public utilities customers.  Some Industrial customers can reduce their power consumption significantly on short notice by either reducing operations (throughput-production) or switching to backup (onsite) power.

Some Public utilities such as waste or fresh water treatment plants are also built to operate with interruptable power supply contracts.  This capability is achieved by building larger capacity water treatment facilities that can meet total customer demand by operating part-time at higher rates, and installing storage for receiving waste or supplying fresh water to customers during periods of power interruption.  Interruptable customers, of course, are normally compensated with lower power costs than non-interruptable customers.

Although hydropower pumped storage is the only industrial available power storage option available today, future develops are possible and are definitely needed for significantly expanding variable wind and solar power penetrations into existing power grids.  Possible power storage options such as various thermal or chemical energy conversion, capacitor/battery, static potential energy, compressed air, dynamic mechanical, etc. must be developed.  New future energy storage systems, however, must reasonably compete with or exceed the energy efficiency and costs of proven hydropower pumped storage technology.

Adjustable Wind and Solar Power Generation – While wind and solar power cannot be increased once maximum generation is achieved with available wind/sun, these renewable supplies can be reduced and adjusted to lower power generation levels to help stabilize local power grid supply-demand balances.  State-of-art wind turbine blade pitches can be readily adjusted to reduce power outputs and solar PV panel arrays can be adjusted to reduce power generation.  Most countries, however, put priority on maximizing renewable wind and solar power generation into connected grids.

In the U.S. the level of wind and solar power penetrations is relatively small.  Refer to the following table.


EIA MER data.  Note: Almost 90% of dispatchable renewable power generation is supplied by hydropower. 

Even though the level of U.S. wind+solar power has increased by 640% since 2005, today these renewables still only account for 3.5% of total net power generation.  Baseload coal power has decreased from 51% in 2005 to 38% today.  Nearly all of this reduced coal power generation has been replaced by natural gas.  Variable wind+solar power have reduced the need for total natural gas (peaking) power by about 10% 2012.

Germany, the world’s leader in wind and solar power, has increased these variable power sources to levels that are causing increasing regional power grid reliability issues.  Rather than building or ensuring adequate local peaking power is available to maintain in-country power grid stability, Germany has the advantage (or has taken advantage) of their neighbors who are integrated into regional EU power grids.  Rather than adjusting peaking power within Germany, the Germans are exporting their excess, variable power to adjacent countries.  This forces Germany’s neighbor countries to reduce their peak, intermediate and baseload power generation.  Although these variable, unscheduled exports are generally delivered at below market average prices, the lower costs do not necessarily take into account the full impacts of uncontrollable ‘negative demand’ impact levels on overall EU regional power grids performances.

In conclusion – Renewable wind and solar power are clearly among the strongest options to replacing fossil fuels power generation.  The penetration of these variable power generation technologies is constrained by costs and the available backup peaking power sources such as natural gas.   Until reliable backup-peaking power options including adequate industrial scale power storage is developed or substantially increased levels of interruptable power demand is made available, up to 100% backup power from reliable sources such as natural gas peaking plants will continue be required to support significant levels of variable wind and solar power in the future.  Required natural gas peaking power backup will continue to increase proportionally to expanded wind and solar power capacity until cost effective alternatives are developed.

Content Discussion

Alain Verbeke's picture
Alain Verbeke on January 29, 2013

" Despite very significant advancements, wind and solar power costs continue to be greater than existing low carbon alternatives such as natural gas.  "


depends where you live. In Europe, above does not apply for wind power. And peak power is partially compensated by pumped hydro, biogas and biomass power plants in europe, not with natural gas, since it is a more expensive imported fuel. And natural gas is not a low carbon alternative, have ever sniffed it ? The methane is full of carbon atoms ....


Wind cheaper than gas, says E&Y


Michael McGovern, Windpower Monthly, 15 October 2012


The net cost of European wind power is up to 50% lower than that of its main conventional power rival, combined cycle gas (CCGT), according to a comparative study by financial group Ernst & Young (E&Y).


In Spain, the costs required to produce 1MWh will generate Eur56 of gross added value from wind, as opposed to Eur16 from CCGT, says the study.


Gas is costlier in countries dependent on imports. But even in gas producing UK, E&Y places wind's net cost only slightly above gas, at Eur35/MWh against Eur31/MWh, respectively.
Across the six European focus countries (Spain, UK, France, Germany, Portugal and Poland), wind's net cost is competitive and, extrapolated across the UE26, cheaper. By factoring in returns to GDP, like jobs and local taxes, E&Y's analysis challenges the power sector's levelised cost of energy (LCOE) standard, which always places wind costs higher, mainly due to upfront costs.


31 March 2011 - Spain's central government objective for renewables to cover 40% of total electricity supply by 2020 is achieved in 2010. Red Electrica reported that in the first quarter of 2011, the renewable technologies covered 40.5 percent of the demand, a little less than in the same period in 2010 when it reached 44 percent.


In March 2011, 57.9% of Spain’s electricity was generated by technologies which do not emit CO2, and wind power energy was the technology with the largest production of electricity. Spain generated nearly 3 percent or 6.7 TWh of its electricity from solar energy, wind turbines generated 21 percent or 55 TWh, and hydroelectricity's share was 17 percent or 44 TWh.


The new renewables of wind and solar in combination provided nearly 24 percent of supply. Together both new and conventional renewables delivered 40.5 percent of Spain's electricity. Cogeneration (15 percent), natural gas CCGT (17 percent), coal (13 percent) and nuclear (19 percent) provided most of the rest.


Spain's climate, geography, and population are similar to that of California. Spain's 46 million inhabitants consume some 260 TWh per year. California's 37 million people consume about 300 TWh per year. However, wind energy generates less than 6 TWh per year and solar less than 1 TWh per year in California. Together wind and solar provide only 2 percent of California's electricity.


March 25, 2011 - The German Ministry for the Environment and Reactor Safety reports that in 2010 renewable energy from wind turbines, hydroelectric plants, solar cells, and biogas digesters generated more than 100 TWh of electricity, providing nearly 17 percent of the 600 TWh of supply.


Biogas plants powered with methane from manure alone generated nearly 13 TWh. The German solar PV industry installed 7400 MW in 2010, from nearly one-quarter million individual systems, according to the final report by the Bundesnetzagentur.


On Monday, February 7, 2011, PV produced 13 percent of supply at noon, wind reached nearly 1/3 of generation at midnight, wind and solar met 29 percent of demand at noon.


Germany has a target of meeting 39% of its electricity supply with renewable energy by 2020. Its system of advanced renewable tariffs has enabled Germany to exceed its 2010 target of 12.5% by a wide margin.




Germany is revealing that, from January to June 2012, renewable energy technologies accounted for more than a quarter of the country's electricity supply for the first time ever. Some critics have questioned whether Germany would be forced to increase its reliance on imported fossil fuels to make up for a shortfall in power supplies caused by the nuclear phase out. However, the BDEW spokeman said Germany has so far remained a net exporter of energy to the European market, even if export levels have fallen. "It's not as bad as some people thought it would be some time ago," he said. "We're still exporting energy but it's not as much as before, so it's really just a matter of scale."

January 26, 2011 - Roundup of Hydro Activity. Europe is the region of the world with the highest installed capacity of hydroelectric generation, according to the International Hydropower Association's (IHA) latest available figures. In addition, IHA estimates that there are 127 to 150 GW of pumped storage capacity globally, and it is anticipated that the market for pumped storage will increase by 60% over the next five years or so. According to the latest REN-21 Global Renewables Status report a further 31 GW of hydro capacity was added in 2009 for a rise in total capacity that — among all renewable sectors — was second only to that of wind power. In addition, about US$40–45 billion was invested in large hydropower over the year. In a recent company address, Iberdrola Chairman Ignacio Galán outlined the company's plans for 2011. He said that in Spain, the company will continue to work on major projects, such as the extension to the 2000 MW hydroelectric plant at La Muela near Valencia, making it the continent's largest pumped-storage complex. Galán also talked of major hydro development in Portugal with construction of the Upper Támega complex, with a capacity in excess of 1000 MW.

Biogas Is Renewable Energy's Cinderella. Just in case it’s not clear from the chart, in terms of net energy output, biogas from corn silage in this study was shown to out-produce ethanol from corn by nearly 8 times. Continuing the comparison with ethanol, Biopact reported that an earlier WTW study shows that the biogas from agricultural and municipal waste produces nearly four times the energy per unit of land as compared with corn-derived ethanol. The environmental cost of this strong energy advantage was quite low. According to the study, “[This WTW study] now in fact shows that compressed biogas is the most climate friendly of more than 70 different…fuels and pathways….”

In other words biogas had the lowest greenhouse gas emissions of any option studied, although biodiesel was close. (Ethanol, on average, was found to emit three times the GHG of biogas.)

The £2.5m Didcot facility uses an anaerobic digestion system to turn sewage sludge into biomethane. Impurities are then removed from the biomethane before it is fed into the natural gas grid. The whole process – from flushing a toilet to natural gas being piped to people's homes – takes about 20 days, said Centrica.

The completion of the pilot project represents a major step forward for a green natural gas sector, which according to a National Grid study could account for at least 15 per cent of the domestic natural gas market by 2020, allowing people in the U.K. to cook and heat their homes with natural gas generated from sewage.

20 July 2010 - Powered by manure from 4000 cows and a GE Jenbacher gas engine, the first biogas cogeneration plant in the Ukraine has completed nine months of successful operation at the Ukrainian Milk Company, located near Kiev. The CHP plant is able to substitute the equivalent of 1.2 million m3 of natural gas and prevent the emission of 18 000 tonnes of carbon dioxide annually. Once converted into biogas, the manure from the cows produces 625 kW of electricity and 686 kW of heat energy. The excess power produced at the plant is being sold to the grid. The initial periods of operation for the plant took place during the most severe winter in the last 20 years, with constant below-zero temperatures, reaching -30°C at times. Despite the low temperatures, GE says that the operation of the plant remained at a favourable level.

EPURON, a member of the Conergy Group, is currently developing a 1.79 megawatt biogas installation in Jüterbog, Germany (near Berlin in the state of Brandenburg). Energy generated would be sufficient to supply the entire Jüterbog community with electrical power. The installation, which will go on stream in April, is designed to handle the fermentation of approximately 24,500 tons of pig liquid manure and 31,500 tons of corn silage per annum. Input feedstocks will be supplied by a neighboring pig farm and the Jüterbog agricultural co-operative society. A long-term supply has been contractually secured. The fermentation substrates by-product from the power generation process will, in turn, be purchased by the agricultural co-operative society and used in local fields as organic manure. This mass has less odor compared to conventional manure and does not pollute the environment. Six and a half million cubic meters of biogas will be produced annually in three fermenting vats with a total capacity of 7,500 cubic meters. The biogas will thereupon be converted to approximately 13.7 million kilowatt hours of electrical power in three block power heating stations. The electrical power will be fed into the E.ON.edis grid over a period of at least 20 years. The annual electrical power output is sufficient to supply some 4,000 households; i.e., more than the population of Jüterbog. In addition, e.distherm, a partner company of E.ON.edis, has agreed to purchase a large portion of the heat produced by the power generation and feed this into its long-distance heating network.


Given the finite nature of fossil energy resources, major projects for the supply of electrical and thermal energy to public networks will become increasingly important due to rising energy costs and a growing dependence on imported raw materials. With its agricultural infrastructure, Eastern Germany has a bountiful source of biomass for generating bioenergy. In Brandenburg alone, some 40 biogas installations with an output of 25 megawatts are currently in operation. "Large-scale biogas installations, like the one here in Jüterbog, harmonise well with the agricultural infrastructure in Eastern Germany. Large farmland areas and high cattle breeding will ensure a long-term supply of input feedstocks to our installations – and good returns for our investors“, says Nikolaus Krane.


John Miller's picture
John Miller on January 29, 2013

AV, your comment contains a wealth of valuable information.  A few reply comments to consider:

·         Wind energy costs may be cheaper than natural gas power in those countries that must import natural gas.  This is not the case in the UK or the US.  EU wind power capacity still receives (and its development appears to need) fairly generous government support (subsidies, production incentives, etc.)

·         Spain has expanded its renewable energy capacity to very admirable levels.  The positive/negative impacts on its economy will be a point of debate for many years to come.

·         No question that Germany is a leader in developing renewable energy.  The strong debate in this country over nuclear will be another contentious issue in the very near future.  Since Germany gets over 20% of its (baseload) power from nuclear, I believe the feasibility of the emotional/political proposal to shutting down this industry is being reconsidered.

·         Germany’s ability to export its variable, excess renewable power will become increasing more difficult in the future if its neighbors were to increase their wind/solar power generation to similar levels that the German’s have and plan.

·         Europe has done an outstanding job in developing renewable hydroelectric power capacity.  Sharing this power source among EU members has been one of the major contributing factors for many countries, such as Denmark, in their ability to expand their variable renewable power sources (primarily wind).

·         Biogas is another major renewable development for many EU countries as you have referenced.  This source of renewable energy is normally only suitable for baseload power and cannot backup variable wind/solar to address power grid stability issues like natural gas, hydro pumped storage or more flexible coal power plants.

The EU has done a very good job of developing renewable energy sources over the years due to government priority setting and restricted availability of domestic fossil fuel resources.  Comparing the EU to the US electric power generation (percentage mix):  (EU/US)  Coal: 24/38, Natural gas: 25/30, Petroleum: 3/1, Nuclear: 27/20 and Renewables: 21/11.  Yes, the EU has made better progress towards lower carbon electric power technologies.  The costs, however, are significantly higher (towards double on average).

Randy Voges's picture
Randy Voges on January 29, 2013


A couple of follow-up points:

1) It's helpful to also point out that the magnitude of load fluctuations is related to local temperature due to the effect of air conditioning and to a lesser extent, heating.  This has some people freaking out when they start contemplating the projections of installing air conditioning in developing countries, especially ones in tropical climates.

2) You may also find it helpful to use two contrasting terms which emphasize the distinction in dispatchability for generators: capacity resources and energy resources.  Capacity resources are conventional generators dispatched by the system operator according to a schedule based on load forecasts, and it is important to grasp that there are penalties if they deviate from their scheduled power output (above or below). In contrast, wind and solar are energy resources because they are not dispatchable; no penalties are applied if they deviate from their forecasts (as you mention it is instructive to think of them as negative demand). 

3) Last but not least: in addition to Germany, California is providing their own laboratory.


John Miller's picture
John Miller on January 30, 2013

Randy, thanks for the feedback and references.  Yes, as countries increase the availability of appliances, such as air conditioners, daily power demand peak loads will increase in Developing countries to similar patterns found in most Developed countries.  Unless the Developing countries install or access adequate power supplies for these increased demand loads the results are less than positive.

As you are probably aware, one of the basic reasons why Utilities penalize independent generators for not meeting their scheduled power generation rates is because other peaking power plants output must be adjusted for these violations of contractual commitments.  The utility power grid economics are negatively impacted due to the fact that rapid and continuously adjusting peaking power capacity reduces the overall power generation efficiency (i.e. increases fossil fuel consumption & costs per KWH).  Governments that strongly support variable wind and solar usually give these renewable power supply companies a full exemption from these added costs (and the increased incremental carbon emissions).

Matthew Shapiro's picture
Matthew Shapiro on January 30, 2013

My firm has done a good bit of modeling of the Wind+Pumped Storage combination, and with a good pumped storage site with sufficient storage time, the combination has a lower all-in cost than the default combination of Wind+CT or Wind+CCCT. This works for a number of newly proposed pumped storage projects across the western US and in the east as well. What is lacking in some utility modeling tools is the ability to directly marry the pure capacity resource (pumped storage) with the pure energy resource (wind), where one captures the greatest value by creating a firm product with renewable energy content; rather, the current models still force the storage facility to rely too heavily on the old arbitrage model (peak vs. off-peak price spread) rather than allowing its tremendous capacity value to come through.  But we're making progress.

John Miller's picture
John Miller on January 30, 2013

Matthew, I am glad to hear that your organization is actively working towards what appears to be currently the most ideal (efficiency and cost effective) solution towards facilitating and increasing the penetration level of wind power into many power grids.  Unfortunately as you are probably aware, in the U.S. environmental and other special interest groups are not very supportive of expanding renewable hydropower and associated pumped storage.  This is another area where the EU appears to lead the U.S.; advancing critically needed technologies to facilitating the expansion of renewable wind power (or solar in some cases).

I look forward to hearing about your firm’s ongoing progress in the future. 

Nathan Wilson's picture
Nathan Wilson on January 30, 2013

John, no doubt many readers have noticed that a grid that combines equal capacity in solar and nuclear power would be an excellent match to the US load curve you've provided, especially if the solar component has a couple of hours of storage, for evening use.

It is often stated by renewable enthusiasts that wind plus solar would better match the seasonal demand variation (offsetting part of the solar shortfall that occurs every winter), provided sufficient short-term storage  (days?) is provide to smooth the wind variation.  Nonethless, such a system over-produces in the spring and fall (when demand is lowest), and usually underproduces in the winter.

Perhaps the best fit of all is accomplished by supplementing the renewable system with a large contribution from nuclear plants that incorporates enough storage to run at 120% of average for a couple of hours.  The reason for the good fit is that nuclear power plants perform their scheduled maintainance and refueling in the spring and fall, delivering summer and winter capacity factors near 99%.  Such a small amount of storage would also contribute spinning reserve and regulation services.

Today's nuclear plants do not incorporate energy storage.  But the high operating temperature of upcoming Gen IV plants is well suited to the use of thermal energy storage.  However, as mentioned upthread, US utilities have not been buying much grid storage, apparently unimpressed by the economics.

Matthew Shapiro's picture
Matthew Shapiro on January 30, 2013

Our firm, Gridflex Energy, is in early stage development of more than a dozen such pumped storage projects in the U.S., many of which are "closed loop", and the remainder of which are in areas where the sensitivity and impact will be minimal. We collaborate with utilities and with wind developers alike (and in some cases, transmission developers), and the value proposition is coming through strongly. I think we'll be seeing at least 5,000 MW of new pumped storage coming online before 2020.  

John Miller's picture
John Miller on January 30, 2013

Nathan, agreed, solar has some very attractive advantages.  Solar PV maximum generation capacity patterns do better match daily peak load demand during clear, warmer months of the year.  Capital costs of solar facilities and backup storage is definitely a major challenge for this renewable power source. 

Nuclear plants do have fundamentally huge advantages over most other zero carbon power generation options.  Besides operating at very high temperatures (a major thermodynamic advantage), which makes feasible thermal storage options magnitudes more efficient and likely more cost effective compared to alternatives such as solar thermal, I understand with the next generation of modular nuclear units there will have much more flexibility in their total capacities and unit specific designs than past technologies.  This flexibility could be feasibly used to build some of the power storage required for significantly greater penetration of solar into many power grids.

As long as solar + wind power capacity is relatively low, Utility companies should probably not be expected to get too innovative when it comes to power storage, for now.  When the costs of additional required natural gas peaking capacity and fuel costs increase significantly at some time in the future, their interest level will likely change.  

Nathan Wilson's picture
Nathan Wilson on January 30, 2013

"... lower all-in cost than ... Wind+CCCT"

Matthew, can you point to any published studies or white papers that explain how much storage is required for this to work and how much capacity value results?  

The DOE's NREL stopped publishing seasonal wind charts a while ago, but the last ones I saw showed that summer (when electrical demand is highest) was the weakest season for wind.  This suggests that a combination of Wind+PumpedHydro would have very low capacity value in the summertime, even assuming a few days of storage.

So while the pumped-hydro would be great for allowing higher wind penetration, the natural gas plant is still needed for backup.  So once again, we should compare the levelized cost of the wind power with the marginal cost of the CCCT power (no doubt in some areas pricing policies will conceal this true cost relationship).  

Furthermore, we should also look separately at the levelized cost of the wind power that comes out of the pumped hydro plant (no fair averaging this expensive power with the power straight from the wind farms, e.g. the pumped-hydro round-trip losses will add a third to the cost, and the capital cost will likely add another 1.3 factor?).


Matthew Shapiro's picture
Matthew Shapiro on January 31, 2013

Nathan - You touched on a number of important points. However, after running many models using empirical wind data in the context of actual PS sites, analyzing those patterns, trade-offs, etc., we have indeed found that a Wind-PS combo can effectively resemble a combined cycle plant with similar reliability and availability, at a competitive cost. You don't need a 1:1 ratio of wind MW to pumped storage MW, and you don't need to put all of the wind through storage (80% efficiency, not 66% as you suggest); typically only about 1/3 of the wind goes through storage. And you take a look at the results on a month by month basis to tailor the amount of firm capacity you can guarantee, within acceptable thresholds. If necessary, you can allow a certain amount of non-wind into the pumping mix to maintain the needed levels; typically that would not exceed 20% of the total energy mix.

We have determined, empirically, that you need about 17-25 hours of storage to do this, depending on the wind strength and its pattern (day vs. night peaking, etc). Most PS projects only have 12-16 hours of storage. But the MW to MWh allocations in the plant can be shifted to allow the amount needed. The result is a not a peaking product (you don't try to pack all that wind into a 4 hour delivery period), but rather a flatter product (roughly 40-45% capacity factor), which is at the lower end of a typical combined cycle operation. With the lower-cost PS projects (i.e., below $1,600/kW), you will beat anything else on the system in economic terms (when TOD gains, emissions reduction, curtailment avoidance, etc. are also taken into account). Note also that pumped storage projects have a lifetime of 75+ years, so roughly three times that of a CT. If that actually gets accounted for, we can extend the acceptable price threshold on the PS to $2,000/kW or beyond.

I'm not saying you can eliminate CT's altogether; they can just be put higher up on the stack in a new dispatch order that might look something like this: (1) energy efficiency and DSM; (2) wind and solar resources; (3) long-duration storage (PS and underground CAES, where viable); (4) combined cycle gas; (5) simple-cycle gas and short-duration storage.

As a developer busy doing project development, and using other people's proprietary wind data, we don't publish results. However, I do make the occasional appearance at conferences when not in discussions with utilities, wind developers, and market and grid operators.