The Azimuth Project
A path to sustainable energy



A path to sustainable energy is a plan of action developed by Mark Jacobson and Mark Delucchi. A popular overview is here:

  • Mark Z. Jacobson and Mark A. Delucchi, A path to sustainable energy: how to get all energy from wind, water and solar power by 2030, Scientific American (September, 2009), 58–65.

Two more technical papers and supporting documents are here:

In brief, they call for all energy to be generated by wind, water and solar (WWS) by 2030.

They plan to provide 11.5 terawatts of power by 2030. Today the power consumption is 12.5 TW, according to the U.S. Energy Information Administration. That agency predicts a demand of 16.9 TW by 2030.

The difference, they claim, will be made up by greater efficiency. For example, consider electric cars. They say, for example, that “only 17 to 20 percent of the energy in gasoline is used to move a vehicle (the rest is wasted as heat), whereas 75 to 86 percent of the electricity delivered to an electric vehicle goes into motion.”

This needs a bit of investigation, since not all the power generated by solar, wind, or whatever means actually makes its way down the power line and into the electrical vehicle.

In their plan:

9% of power will be produced by mature hydropower technologies.

51% will be supplied by wind, provided by 3.8 million large wind turbines (each rated at 5 megawatts) worldwide.

40% will come from photovoltaics and concentrated solar plants, with about 30 percent of the photovoltaic output from rooftop panels on homes and commercial buildings. About 89,000 photovoltaic and concentrated solar power plants, averaging 300 megawatts apiece, would be needed.

They say that the cost of generating and transmitting power would in fact be less under this scheme than the projected cost per kilowatt-hour for fossil-fuel and nuclear power. They say that ‘shortages of a few specialty materials, along with lack of political will, loom as the greatest obstacles’.


In slightly more detail, the abstract of their first technical paper says, among other things:

We find that barriers to a 100% conversion to WWS power are primarily social and political, not technological or even economic. We conclude that the world energy supply for all purposes can be converted to electricity and electrolytically-produced hydrogen with ~3.8 million 5-MW wind turbines, ~49,000 300-MW concentrated solar plants, ~40,000 solar PV power plants, ~1.7 billion 3-kW rooftop PV systems, ~5350 100-MW geothermal power plants, ~270 new 1300-MW hydroelectric power plants, ~720,000 0.75-MW wave devices, and ~490,000 1-MW tidal turbines. The additional footprint and spacing required for all devices planned for land (as opposed to ocean) is estimated as ~0.41% and ~0.59% of world land area, respectively. We suggest a practical goal of producing all new energy with WWS by 2030 and replace all preexisting energy by 2050. The cost of energy due to a conversion is expected to be similar to that today.

Latest Details

In new articles 100% Clean and Renewable Wind, Water, and Sunlight All-Sector Energy Roadmaps for 139 Countries of the World and Studies on Grid Reliability With High Penetrations of Wind, Water, and Sunlight (WWS) Jacobson, Delucchi et al try to provide a more detailled analysis. The supplement of the first article seems to provide concrete rates and parameters, which are however at least partially global parameters taken as an approximation for missing country values. Motivations for the assumptions made are not always easy to follow in particular since some information is based on reasoning eventually made in other references.

One example to exemplify a possible confusion: On page 5 of the supplement, section 3.1. the formula:

Total final consumption (TFC) (end-use) = Total Primary Energy Supply (TPES) + Transformation Processes (TP)

appears, which is from the IEA’s World Energy Balances report. It is explained in particular that

Transformation Processes (TP) include for example “energy industry own use;” transformation losses at electricity plants, combined heat - and - power (CHP) plants, and heat - only plants (these are negative values); and transformation-process output from electricity plants, CHP, and heat plants (these are positive values)

The reader may wonder whether it is meant here that if energy is “produced” as output (i.e. e.g. sunlight converted into electricity) then the energy need for such a transformation process (energy conversion) is apriori also produced but immediately consumed and would thus contribute to the total consumption as a positive number, however since it can’t be used for “consumption” as such most of it (?) should be accounted for as loss? So like if the energy is imported like in form of oil then the consumption for conversion to electricity would probably usually be accounted for as a loss.

Barry Brook

Barry Brook has critiqued this plan:

He does not believe their plan can get wind, water and solar technologies to provide 100 percent of the world’s energy, eliminating all fossil fuels.

According to Brook, their two technical papers:

are structured around 7 parts: (1) A discussion of ‘clean energy’ technologies and some description of different plans for large-scale carbon mitigation. (2) The amount and geographic distribution of available resources [wind, solar, wave, geothermal, hydro etc.] are evaluated, globally. (3) The number of power plants or capture devices required to harness this energy is calculated. (4) A limit analysis is undertaken, to determine whether any technologies are likely to face material resource bottlenecks that risk stymieing their large-scale deployment. (5) The question of ‘reliability’ of energy generation is discussed. (6) The projected economics of this vision are forecast. (7) The policy approaches required to turn vision into reality are reviewed.

Brook concentrates on items (5) and (6), where he believes the major flaws of the analysis lie.

He agrees with their point that “there is a huge amount of energy embodied in ‘wind, water and sunlight’ and points to Without the Hot Air for numbers.

He says they extrapolate of the total number of wind turbines, solar thermal facilities, etc. required to deliver 11.5 TWe of average power, but

curiously, they never really explain (in either paper) how they came up with their scenario’s relative mix of hydro capacity, millions of wind turbines, billions of solar PV units, and thousands of large CSP plants, wave converters, and so on—except in pointing out that some resources are more abundant in deployable locations than others (see Table 2 of the tech paper)“.

On the bright side, he says:

They do provide a useful discussion of possible material component bottlenecks for different techs… and argue how they can be plausibly overcome via recycling and substitution with cheaper/more abundant alternatives.

He attacks as dishonest their claim that:

Nuclear power results in up to 25 times more carbon emissions than wind energy, when reactor construction and uranium refining and transport are considered.

He writes:

Hold on. How could this be? I’ve shown here that the “reactor construction” argument is utterly fallacious—wind has a building material footprint over 10 times larger than that of nuclear, on energy parity basis. Further, Peter Lang has shown that wind, once operating, offsets 20 times LESS carbon per unit energy than nuclear power, when a standard natural gas backup for wind is properly considered. I’ve also explained in this post that the emissions stemming from mining, milling, transport and refining of nuclear fuel is vastly overblown, and is of course irrelevant for fast spectrum and molten salt thorium reactors. So…?

Well, you have to look to the technical version of the paper to trace the source of the claim. It comes from Jacobson 2009, where he posited that nuclear power means nuclear proliferation, nuclear proliferation leads to nuclear weapons, and this chain of events lead to nuclear war, so they calculate (?!) the carbon footprint of a nuclear war!

Indeed, the cited paper by Jacobson posits a war in which fifty 15-kiloton nuclear devices are used, setting cities afire, giving CO2 emissions of 92–690 teragrams. Bounding the probability of a war between 0 and 1, and working out the total nuclear power produced in some scenario, he then computes the emissions per kilowatt hour of nuclear power between 0 and 4.1 grams/kilowatt-hour.

However, this is just a small portion of the carbon footprint estimated by Jacobson. Jacobson’s figures for the lifecycle carbon cost of nuclear energy starts with a lower bound of 9 g/kWh coming from industry estimates and an upper bound of 66 g/kWh, which is a “number slightly above the average” from lifetime reviews of old power stations. To the upper bound, he then apparently adds the 4 g/kWh which he estimates for a nuclear war with fifty 15-kiloton explosions. Th is gives the range 9-70 g/kWh that he shows in Table 3, p. 154. (Section 4a.vii, p.155). See also Jacobson’s response to Brook.

So, despite Brook’s annoyance at including a small nuclear war as part of the carbon footprint of nuclear power, it seems that does not explain why Jacobson concludes that “Nuclear power results in up to 25 times more carbon emissions than wind energy”. We shall have to figure out the real reason!

Brook also critiques Jacobson and Delucchi’s analysis of the reliability of various sources of power:

First, the authors cite ‘downtime’ figures for each technology (i.e., the period of unscheduled maintenance, as opposed to scheduled outages). From this, they leave the uninitiated reader with the distinct impression [] that wind and solar PV is actually more ‘reliable’ than coal! (Who knew? We’d better tell the utilities). They also say that unscheduled downtimes for distributed WWS technologies will have less impact on grid stability than when a large centralised power plant suddenly drops out. Sorry, but I just don’t get this. If the downtime of solar PV is 2%, for instance, and you have 1.7 billion 3 kW units installed worldwide (their calculated figure), then 340,000 of them are out at any one time. That seems rather significant to me…

Next, to overcome intermittency, they claim that for an array of 13-19 wind farms, spread out over an 850 x 850 km region and hypothetically interconnected:

: … about 33% of yearly-averaged wind power was calculated to be useable at the same reliability as a coal-fired power plant.

Let’s parse this. By reliability of the coal plant, I assume in this context that they mean its capacity factor (rather than unscheduled outages), which would be around 85% of peak output. Now, wind in excellent sites has a capacity factor of ~35%, so the yearly-averaged power of a hypothetical 10 GW peak wind array of 13-19 farms would be 3.5 GW. Now, following their statement, 33% of 3.5 GW — that is, 1.15 GW or ~12% of peak capacity — would be available 85% of the time. Or, to put it another way, we’d need to install 10 GW of peak wind to replace the output of 1.4 GW of coal? Is that what they are saying? Did they cost this? (hint: no, see below). Perhaps someone else can confirm or reject my interpretation of the statements on p19 of the tech paper.

He also doubts this claim of theirs:

Power from wind turbines, for example, already costs about the same or less than it does from a new coal or natural gas plant, and in the future is expected to be the least costly of all options.

Brook says:

They make a token attempt to price in storage (e.g., compressed air for solar PV, hot salts for CSP). But tellingly, they never say HOW MUCH storage they are costing in this analysis (see table 6 of tech paper), nor how much extra peak generating capacity these energy stores will require in order to be recharged, especially on low yield days (cloudy, calm, etc). Yet, this is an absolutely critical consideration for large-scale intermittent technologies, as Peter Lang has clearly demonstrated here.

Furthermore, he considers their projections of future prices of solar power to be overoptimistic, and claims they neglect to take winter into account:

I also see that they are happy to speculate about dramatic future price drops for solar PV and concentrating solar thermal with up to 24 hours future storage (Although even they admit it would not provide sufficient power in winter—what do we do then, I wonder?—have huge capacities of coal and gas on idle and as spinning reserve?).

Jacobson’s response

Jacobson has responded in detail to Brook’s criticism:

Charles Barton

On his blog The Nuclear Green, Charles Barton has written critiques of A Path To Sustainable Energy:

Howard Hayden

Howard Hayden, a skeptic on global warming, has satirized the impracticality of the Jacobson-Delucchi plan here:

Also see


Mark Z. Jacobson, Review of solutions to global warming, air pollution, and energy security, 2008. (See Section 4d for his estimate of carbon emissions from a nuclear explosion.)