The Feasibility of Renewable Energy

 

A 2/21/19 NYT article headlined, “A Green New Deal is Technologically Possible. Its Political Prospects Are Another Question,” quotes Harvard professor John P. Holdren: “If the planet follows its current trajectory, the result by century’s end would be ‘catastrophe’…The world would be almost unrecognizable compared to today’s world.”

He believes that the Green New Deal goal of attaining carbon-neutrality by around 2030 is not feasible.  “As a technologist studying this problem for 50 years, I don’t think we can do it…There’s hope we could do it by 2045 or 2050 (limiting global warming to 1.5° C above the pre-industrial level, projected by the IPCC) if we get going now.”

For the U.S. and the world, the society-wide political consensus to achieve carbon neutrality by 2050 has not yet been formed. Whether this consensus will take the form of achieving a survivable climate, viewed through the lens of social change, or more directly by programs to reduce carbon emissions, will depend upon the outcomes of the U.S. political process. The near-term technological prospect of achieving renewable energy, however, is a lot better than that of achieving fusion energy. We discuss suggested solutions to WWS (wind, water and solar) intermittency, either at the electric grid level or at the energy storage device level.

We do not have an expertise in electric power systems design, so we present study conclusions and leave it to our readers to have their experts assess the evidence and develop the best feasible policies.

 

The Electric Grid

When we flip a light switch, we get our power not from specific generators, but from the electric grid. The electric grid is a finely tuned machine that pools the power of individual generators and makes that available on demand over a wide area. Since the grid operates on alternating current, the numerous generators and electronic sources feeding it have to supply power at equal voltages and frequencies. But in this finely tuned world, WWS supplies power only intermittently, depending on the time of day and, of course, the weather. 

According to various studies, this intermittency problem is either solvable or not at the grid level.

A.   The impossibility of handling intermittency at the grid level.

 

Jack Ponton, emeritus professor of engineering at the University of Edinburgh, notes (2019) that, “…current approaches are either technically inadequate or commercially unviable…a lack of suitable storage technologies (not only short-term but also long-term, for weeks) cannot replace dispatchable coal, gas and nuclear power and so a sensible energy policy cannot be based on them. ‘Wind and solar power are not available on demand and there are no technologies to make them so. Refusing to face these inconvenient facts poses a serious threat to our energy security.’” 1

 

A thorough survey of the renewable energy literature (Heard, 2017) notes, “While many modeling scenarios have been published claiming to show that a 100% renewable electricity system is achievable, there is no empirical or historical evidence that demonstrates that such systems are in fact feasible.…Evaluated against…objective criteria… simulating supply to meet demand reliably at hourly, half-hourly, and five-minute time scales, with resilience to extreme climate events…none of the 24 studies provides convincing evidence that…basic feasibility criteria can be met.” 2

 

We note that fossil fuels essentially store sunlight energy from millions of years ago. The following is an example of electrical system simulation and discusses the technological progress that has to occur before 100% renewable energy is possible.

 

B.   Grid solutions with storage.

 

The type of stored energy system adopted depends upon the state of a technology and the degree of social cooperation desired and possible.  IN THE FOLLOWING “WWS” MEANS THE RENEWABLE ENERGY SOURCES OF WIND, WATER AND SOLAR. “GIV” MEANS GRID ENERGY STORAGE IN VEHICLES. The following electrical grid study contains a large number of variables and values, but its presentation is clear (for a grid study) and can provide the reader with an idea of what to look for when considering renewable energy.

 

In 2012, Professor Willett Kempton of the University of Delaware, et al published “Cost minimized combinations of wind power, solar power and electrochemical storage, powering the grid up to 99.9% of the time.” 3

 

The authors began by running a computerized grid model against real world data, in this case the hourly fluctuating 1999-2002 calendar year load requirements of the PJM Interconnection, a large electric grid that connects the Mid-Atlantic states with Eastern Michigan. The PJM managed 72 Giga(billion) watts of generation with an average load of 31.5 GW. It therefore had a maximum capacity of 2.28 X its average load. It crucially assumes that the power generated can be stored in GIV, electric vehicles that are integrated into the grid.

 

Fossil fuel grid power can be sold at a wholesale rate of 8 cents/kwh. Assuming no demand growth, no load management and no transmission to adjacent grids (omitting a few real world complications) – WWS using GIV can supply enough power 99.9% of the time from the following sources, assuming 2030 technological costs.

 

 

Source    Power Capacity (GW)     Average Power (GW)

 

Solar                   16.2                               2.64

Offshore Wind    89.7                              38.3

Inland Wind        124                               50.3

Fossil                  28.3                               .017

                          258.2                              91.2

 

 

1)    The maximum capacity of the system is 2.83X its average load. (Engineers are concerned with the solution’s efficiency.)

2)    In this optimized system, the major portion of the energy is produced by inland wind. The power produced by solar is surprisingly small.

3)    The 2030 price of energy (in 2010 dollars) will be 17 cents/kwh. This is about double the wholesale fossil fuel price. It should, however, be noted that in Germany the retail price of electricity is 36 cents/kwh after taxes, levies and surcharges are added. Most likely, under this solution the U.S. use of energy will be more like Europe’s.

 

 

This storage solution assumes a social cooperation, maybe not so practical at the time of this writing. Furthermore, global warming will cause more intense storms, changing weather patterns. A concerted effort should be made to develop technological solutions for energy storage, producing industrial products that can also be exported.

 

Energy Storage Devices

Energy storage is expensive. Both the National Renewable Energy Laboratory (NREL) and Siemens of Germany present the same energy storage alternatives for short durations (hours) and small power capacities (1MW or less). They are capacitors, flywheels, batteries and compressed air.

But large utility systems must store energy for long durations (days to weeks) and at large power capacities (100 MW and up). There are only two technologies that do this, pumped storage hydropower and electrochemical hydrolytic fuel cells, the latter are the subject of intensive research.

A.   Pumped storage hydropower.

 

The idea is simple; store energy by pumping water to an uphill reservoir and then release it to provide energy when needed.

 

This alternative has a high round-trip efficiency of 80%. It is capable of storing energy for periods of 8 hours on up.  It is the largest energy storage technology deployed in the United States. Unfortunately, the NREL reports that the state and local permitting processes from permitting to construction can take up to six to twelve years. 4 In the past, the application of this technology has been limited by low natural gas prices, regulatory treatment of the project, environmental concerns and construction costs. 4a According to the NREL, the installed cost for each project, with a lifetime exceeding 60 years 5, may range from $1,000/kwh to $5,595/kwh depending upon the geology of the site. 6

 

A Stanford study notes, “Pumped hydro is energetically quite cheap, but the number of geologic locations conducive to pumped hydro is dwindling, and those that remain have environmental sensitivities.” 7 We think this is a key observation that could be verified in detail.

 

B.   The development of electrolytic fuel cell storage is a second alternative. This idea is also simple, (but very complicated in practice, Stanford is a major renewable energy research center). Remember a high school chemistry experiment that used DC current to decompose water into hydrogen and oxygen gases? At the most general level, the chemical reaction is: 2H2O + energy → 2H2 + O2 . Here, hydrogen gas molecules become carriers of energy because they are produced by a source of energy, such as electricity.

 

There are three major types of water electrolysis chemistries and fuel cell specifications: (Schmidt and Gambhir, 2017) 8

 

Alkaline Electrolytic Cells (AEC) - Widely used in large-scale industrial applications since the 1920s, such as metal treating and food processing.

 

Solid Polymer Electrolyte (PEMEC) Systems – Introduced by General Electric in the 1960s to remedy some of the drawbacks of AEC systems, most used for small-scale applications.

 

Solid Oxide Electrolysis Cells (SOEC) – operates at significantly higher temperatures and therefore efficiencies, but at the cost of severe material degradation. Can operate in the reverse mode as a fuel cell to produce electricity.

 

Carbonate – A CO2 emitting fuel cell chemistry that we include for comparison. These fuel cells run on LNG and biomass, i.e.methane.

 

The following table illustrates some of the operating characteristics of these technologies:

 

 

Electrolyte:                            AEC             PEMEC            SOEC           CARBONATE

                                                                                                               

Capital Cost ($/kw)               1,320                2,508               >2,400          

Lifetime (years)                        8.6                    4.6               <1.1

Operating Temperature (°C) 60-80                50-80              650-1000

Typical Capacity (kw) 9          100                   100             up to 2,000       up to 2,800

CO2  Production 10                       0                      0                       0              .27 kg/kwh *  

  *  with waste heat recovery, lignite coal is .36 kg/kwh and diesel fuel is .27 kg/kwh  

 

What’s the main problem? Electric utilities require renewable energy storage plant capacities exceeding 100,000 kw, maybe 2,800 kw per cell stack. (We can’t find much reference to this in the literature.) Although hydrogen electrolysis is quite a mature technology, there is a lot of work to do before renewable energy can be stored and made practical. We better start a large-scale effort now to scale up the technology.

 

 

footnotes

 

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          Sled dogs running across melting Greenland sea ice.

                                                                      - Steffen Olsen

 

 

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