Wednesday, March 30, 2011

Cost of solar power (6)

I regularly scan press releases in order to obtain details about new solar projects.  According to my methodology for estimating the cost of solar power, I need three key pieces of information about each project: the peak power output, the annual output and the project cost.  Of these, the project cost is usually confidential and therefore not given.  In a few cases, project developers give the cost as if they are almost boasting of their capacity to put together an impressive deal.  In a few other cases governments contribute financial support and, as a result, project costs have to be disclosed to taxpayers.

Even then, there is sometimes a problem with the annual output of the project.  On occasions you can make an educated guess about the output from statements like “the project will save xxx tonnes of CO2 emissions”.  But that is always going to be rather risky.

To prepare today’s post, I investigated about 40 projects until I finally found one that provided the requisite three items of information.  The project is described as follows on the website of the developers, ABB:

“ABB, the leading power and automation technology group, has won a $50 million order from Phenix Renewables to deliver a 24 megawatt (MW) photovoltaic (PV) solar power plant in Lazio, central Italy.

Once connected to the grid, the Phenix solar plant will supply up to 35 gigawatt-hours (GWh) of electricity a year, avoiding the generation of over 25,000 tons of CO2 emissions, equivalent to the annual emission of over 10,000 European cars.

ABB will be responsible for the design, engineering, erection, civil works and commissioning of the plant. ABB’s modular EBoP (electrical balance of plant) concept will enable fast track execution within four months.

The 24.2 MW plant is based on single-axis trackers, which precisely follow the position of the sun to position PV panels at the best angle for maximum energy production. Key ABB products in this project include low- and medium-voltage switchgear, transformers, cables, the automation and control system and protection equipment. ABB will also build a 150 kilovolt (kV) substation equipped with the latest monitoring and control system to facilitate reliable and efficient integration of the electrical power generated by the solar panels into the grid. The PV panels will be supplied by the Norwegian company, REC (Renewable Energy Corporation) in consortium with ABB.”
[Press release dated 7 March 2011]
Note the outstanding construction time (four months) and the comments about CO2 emissions saved.  Note also the clear description of the breadth of engineering competencies required for projects such as these.

To estimate the cost of solar power from this project, I make my usual assumptions:
·         there is no inflation,
·         taxation implications are neglected,
·         projects are funded entirely by debt,
·         all projects have the same interest rate (8%) and payback period (25 years), and
·         all projects have the same annual maintenance and operating costs (3% of the total project cost), and
·         government subsidies are neglected.

That gives for the Lazio project:

Cost per peak Watt     USD 2.08/Wp
LEC                            USD 177/MWhr

The components of the LEC are:
CAPEX           {0.094× USD 50×106}/{35×103 MWhr} = USD 134/MWhr
OPEX             {0.030× USD 50×106}/{35×103 MWhr} = USD 43/MWhr

By way of comparison, here are LEC figures I have calculated for some other projects:

Cost of solar power (2): AUD 199/MWhr (Nyngan, Australia, PV)
Cost of solar power (3): EUR 547/MWhr (Olmedilla, Spain, PV)
Cost of solar power (3): EUR 205/MWhr (Andasol I, Spain, trough)
Cost of solar power (4): AUD 257/MWhr (Greenough, Australia, PV)
Cost of solar power (5): AUD 432/MWhr (Whyalla, Australia, dish)

Saturday, March 19, 2011

Atmospheric CO2 levels due to fossil fuels

In my last post, I provided a simple model that predicted when the Earth’s fossil fuels will be exhausted.  The model, or perhaps I should say scenario, was based on current reserves and current rates of consumption, with switching of energy supply from oil to gas when the oil is depleted, and from gas to coal when the oil and gas are depleted.

Today’s post is concerned with the atmospheric CO2 levels that will result from combustion of these remaining fossil fuels.  I’ll take as given the data and methodology in my last post and I’ll keep any further assumptions as simple as possible.  With an exercise like this, I’m trying to make broad inferences rather than dwelling on fine details.  I’m only going to consider CO2 emissions from consumption of fossil fuels; emissions from other sources (such as fugitive emissions, leakage, agriculture, cement production, …) are not included here.  Also ignored will be feedback effects such as CO2 emissions from melting of permafrost.

The starting point is a few facts about the Earth’s atmosphere:

Mass of the atmosphere                      5.144×1018 kg [1]
Molar mass of dry air                          0.0290 kg/mol [2]
Mols of air in atmosphere                   1.77×1020       
Molar mass of CO2                             0.044 kg/mol
Atmospheric concentration of CO2    386 ppm by volume (for 2008)
Mass of CO2 in atmosphere               1.77×1020×386×10-6×0.044 = 3.01×1015 kg   

That estimate for the atmospheric mass of CO2 agrees reasonably well with other estimates, e.g. it’s a 5% discrepancy from the figure given by [3] (3.16×1015 kg).  Perhaps the neglect of water vapour explains some of the discrepancy?  In any case, for the purpose of this post, my estimate is accurate enough.  I’ll need the above estimates to convert the mass of CO2 in the atmosphere into parts per million by volume.

Next, I need a result for how much CO2 is produced when a barrel of oil is consumed (note consumed, not burnt).  Fortunately Jim Bliss [4] has done this calculation very nicely.  He points out that when oil is consumed, not all of it is burned, thereby releasing CO2.  Some goes to bitumen for roads, some goes to the petrochemical industry, and he estimates that of the oil in a barrel (169 litres) only 101 kg is used as a fuel.  Bliss continues:
“When fuel oil is burned, it is converted to carbon dioxide and water vapour.  Combustion of one kilogram of fuel oil yields 3.15 kilograms of carbon dioxide gas.  an average barrel of crude oil will produce a minimum of 317kg of CO2 when consumed.”

We know that 2008 world oil consumption was 84.5 million barrels per day, with each barrel producing 317 kg of CO2 as Bliss has shown.

Next we need similar estimates for natural gas.  If natural gas is assumed to consist only of methane that combusts according to
CH4 + 2O2 → CO2 + 2H2O,
then since the molecular masses of CH4 and CO2 are 0.016 kg and 0.044 kg respectively, each kg of methane will produce 0.044/0.016 = 2.75 kg CO2.   Now, 1 m^3 of natural gas contains 1000/22.4 = 44.6 mols with mass 0.714 kg (under standard conditions, 0°C and 1.00 atm pressure).  So each m^3 of natural gas produces 0.714×2.75 = 1.96 kg CO2, which is what I need since I know the natural gas consumption, currently 3,018.7 billion m^3/yr. [5]

Coal has a wide variation in water and ash content, which affects the carbon content by weight.  I’ll make the assumption that on average commercial coal contains 70% Carbon by weight.  One mol of CO2 (molecular weight 0.044 kg) is produced for each mol of C (molecular weight 0.012 kg) used.  Therefore each kg of Carbon produces 0.044/0.012 = 3.7 kg of CO2, so each kg of coal will produce 0.7×3.7 = 2.6 kg CO2.  According to [6], world coal production in 2008 was 6,781 million tonnes (and increasing by several per cent per year, although that won’t be taken into account here), so the CO2 released would be 17.6 gigatonnes/yr.

In summary, the following are my estimates for CO2 currently released from the various fossil fuels (in gigatonnes/yr): oil 9.8, natural gas 5.9, coal 17.6.   

By way of comparison, reference [6] cites the following CO2 releases as provided by the Energy Information Agency: oil 11.0 Gt/yr, natural gas 5.8 Gt/yr, coal 11.4 Gt/yr.  Reference [8], directly sourced to the EIA gives CO2 emissions from coal as 12.5 Gt/yr in 2007.  Another figure comes from reference [9], which states

“In the entire world, annual CO2 emissions approach 30 billion tons per year, and it is safe to say about half of these emissions come from coal”

Perhaps my CO2-from-coal estimates are a bit high, but I think my overall CO2 release figures should be sound enough for me to proceed with my scenario, particularly since I am assuming no increase in emissions in the future.

Next, we need to know the airborne fraction, AF, or how much of the CO2 remains in the atmosphere after CO2 absorption by ocean and land.  Following [7], take AF = 0.45.

And finally we need to accommodate the assumptions in the scenario that once the oil has gone, the energy demand is switched to natural gas, and once both oil and gas are gone the energy demand is switched to coal.  This issue relates to the relative Carbon intensities of oil, natural gas and coal, and is required only after 46 years, which is how long my previous post predicted that oil will last.  Simple proportionality arguments were used here.

Figure 1 shows the results of these calculations, with my scenario forecasting the atmospheric CO2 levels for the next 75 years, by which stage the model says all the fossil fuels have been consumed.  The end value at 2084 is 560 ppm, which climate science would say will lead to significant warming and raised sea levels.  Also shown on Figure 1 is the historical CO2 record since 1960, as measured at Mauna Loa [10].

Figure 1: Atmospheric CO2 levels at Mauna Loa over the
past 60 years and as predicted by this scenario.

The projected CO2 levels in Figure 1 look quite plausible, especially for the near-term future.  The slight kink in the scenario curve at year 2062 is when the oil and gas have both been depleted and all the fossil fuel demand is met by coal, which has a higher CO2 intensity than oil or gas.  In my judgement, the scenario is likely to underestimate atmospheric CO2 levels, especially under a business-as-usual scenario over several decades. 

I think these results confirm important messages from the professional climate science community, of which I’m not a member.  The estimates vividly illustrate the enormity, perhaps impossibility, of the task to stabilise CO2 levels at a level like 450 ppm.  They also show the gravity of the situation facing humankind if we don’t break our Carbon habit.

In doing this post, I came across several excellent web sites devoted to atmospheric CO2.  Reference [11] is a good exemplar.

Acknowledgement: thanks to Robin Johnson’s Economics Web Page for suggesting I prepare these estimates.


[1] K.E. Trenberth & C.J. Guillemot, J Geophysical Research, 99 (1994), 23079-23088
[5] BP Statistical Review of World Energy.

Monday, March 14, 2011

How long until fossil fuels are completely used?

Today, I’d like to explain the reasoning behind the statement I made in yesterday’s post:

“The planet’s fossil fuel resources are finite and on current trends will not contribute much to the earth’s energy demands one hundred years from now.”

This issue requires perhaps more in the way of heroic assumptions than the customary focus of this blog – namely to estimate the cost of solar power.  Some countries have strict standards for reporting mineral reserves, others do not.  In some countries, everything is reasonably transparent, whilst other countries actively seek to hide or falsify information.  Production and consumption figures might be more certain than reserves, but again this is not uniformly true for all countries.

The source for all data in this post is the BP Statistical Review of World Energy (2009).  The word ‘reserves’ is interpreted to mean “those quantities that geological and engineering information indicates with reasonable certainty can be recovered in the future from known reservoirs under existing economic and operating conditions”.

At the end of 2008, world reserves were:

Oil                   1,409 billion barrels (including Canadian oil sands)
Natural gas      185 trillion cubic metres
Hard coal        411.3 billion tonnes (anthracite and bituminous)
Other coal       414.7 billion tonnes (sub-bituminous and lignite)

Consumption rates were:

Oil                   30.83 billion barrels per year (84.455 million barrels per day)
Natural gas      3.019 trillion cubic metres per year
All coal            3.304 billion tonnes of oil equivalent per year

Conversion factors:

1 barrel oil = 0.1364 tonnes oil
1 billion cubic metres natural gas = 6.60 million barrels of oil equivalent
1 tonne hard coal = 0.67 tonnes of oil equivalent
1 tonne other coal = 0.33 tonnes of oil equivalent

On those figures, with current reserves and current rate of consumption, the oil will be gone in 46 years, the natural gas in 61 years and the coal in 125 years.  But that is not the end of the story; we need to consider the overall rate of consumption of energy from fossil fuels.

Assume that when the oil has gone, the energy demand previously met by oil is transferred to natural gas (in addition to the existing consumption).  In turn, when the natural gas is gone, assume all the fossil fuel demand is met by coal.  That gives Figure 1.  The overall rate of energy consumption from fossil fuels is constant, and the resources are gone in 75 years.

Figure 1: Remaining reserves (in Mt oil or oil equivalent) of oil, natural gas and coal.

Since I first made these calculations in mid 2006, reserve estimates for oil have increased somewhat, mainly due to inclusion of 150 billion barrels from Canadian oil sands.  That increase has not really altered the overall conclusions.

As I explained earlier, figures for reserves, production and consumption need to be used with great caution.  Two excellent websites that discuss these issues are The Oil Drum ( and ASPO International, the association for the study of peak oil and gas (  The Oil Drum is a very active site.

So, what does all this mean?

1.      Whilst there will always be another kg or litre of fossil fuels available on Planet Earth, for practical purposes the reserves will be depleted within a hundred years.  Yes, more reserves might be found, which would act to extend the time estimate, but on the other hand consumption rates will also surely go up, at least in the immediate future.
2.      The near-unanimous view of climate science is that consumption of Earth’s fossil fuel reserves will be disastrous.  I accept that scientific opinion.  Two excellent sites that discuss these matters are RealClimate ( and Skeptical Science (  Here, I am explicitly ruling out large-scale implementation of Carbon Capture and Storage, which perhaps I’ll explore in another post.
3.      To preserve our way of life, humankind has to develop new energy infrastructure.  As I explained yesterday, there are strong reasons why nuclear fission should not be a big part of that development.
4.      Sooner or later, we must make the transition away from fossil fuels.   It’s best to do that whilst we still have the chance to mitigate or avoid the worst of anthropogenic global warming.

Sunday, March 13, 2011

Cost of nuclear power

This blog aims primarily to present information concerning the cost of solar power.  I would like today, however, to make some comments about nuclear power, particularly from an Australian perspective.  Australia is endowed with numerous energy options such as brown coal, black coal, natural gas, uranium, geothermal, solar, wind and wave power.  Any move towards nuclear fission needs to be considered in a cool, fair, honest and logical manner.

I am aware of the claims that large-scale uptake of nuclear fission will reduce CO2 emissions, thereby helping to mitigate anthropogenic global warming.  For the purpose of this discussion, let us assume those claims are correct, even though there are those who dispute them.

I am also aware of the theory of peak oil, peak coal and peak everything else.  The planet’s fossil fuel resources are finite and on current trends will not contribute much to the earth’s energy demands one hundred years from now.   [I shall defend the previous sentence in a future post.]  Moreover, if the fossil fuels are exploited to exhaustion, the near-unanimous position of climate science is that the impact on our planet will be disastrous.

My view is that nuclear fission might have a role to play in a few (very few!) places in the world.  Imagine a responsible and technologically advanced country with a large population, a small land area, situated in mid-high latitudes, perhaps landlocked or in any case with poor wind and solar resources.  Such a country needs energy.  Perhaps in the future this can be imported in the form of solar-power-by-wire or solar-derived liquid fuels?  Perhaps it might come from geothermal energy?  For such a country, I would regard nuclear fission as an option provided renewable alternatives are not available or are low-grade.  Such a country would have to deal with the known problems of nuclear fission:
·         security and avoidance of nuclear weapons proliferation,
·         the overall fuel cycle (mining, beneficiation of ore, production of 235U and fuel rods, processing of spent fuel rods, disposal of radioactive waste),
·         decommissioning of the plant,
·         long-tail risks (rare accidents that can cause major damage), and
·         capital cost, including interest during construction.

As discussed earlier on this blog, clever people devote a lot of effort to estimating the cost of power generation.  I recall the old joke about a mathematician, engineer and accountant asked to evaluate 2×2.  The mathematician had no problem giving the answer 4, exact, an integer.  The engineer checks his slide rule (OK, it’s a very old joke!), finds the answer is 3.98 and rounds it to 4.  The accountant draws the questioner aside and asks sotto voce, “what do you want the answer to be?”

And so it happens on numerous occasions.  A review is commissioned with an answer in mind, experts are appointed and lo, the right answer is duly found.  As Sir Humphrey in the TV series Yes Prime Minister would say: never hold a review unless you know what you want it to find.
In Australia, there was a big review about 5 years ago – Uranium Mining, Processing and Nuclear Energy Review (UMPNER) – which duly identified and applied appropriate assumptions to give the desired answer: a Levelised Energy Cost of AUD (2006) 40-65/MWhr.  Others disagree vehemently.  For example, long-term wind proponent Mark Diesendorf says the report (see
“makes questionable assumptions that are highly favourable to nuclear power.  ….  The report's very low estimates of the costs of nuclear electricity are achieved by means of a magician's trick.”

Relevant to this discussion is a survey paper presented to the 2006 conference of the Australian Solar Energy Society: “Comparison of solar, nuclear and wind options for large scale implementation”, by David Mills.  Mills, a pioneer of the solar industry, concluded that in the Australian context

“ advanced solar and nuclear typical of the next decade have similar cost/efficiency and each can supply the electricity load if necessary.  Nuclear has a severe global fuel resource problem not shared by solar.  Solar has almost no fuel cost and decommissioning uncertainties while nuclear has long term back end and fuel cost uncertainties.  The author proposes … each technology must openly pay its own real costs for meeting radiological and environmental standards, security charges, insurance, fully insured waste disposal, fuel enrichment, and fully insured decommissioning.

Mills thus identifies huge issues facing nuclear fission.  In the case of the UMPNER review, the following assumptions contributed to the low Levelised Energy Cost for nuclear power:
·         a discount rate set at a lower level than that used for costing of solar plants, and
·         government guarantees on insurance, waste storage and decommissioning.
Without government guarantees, commercial insurance would not merely be much more expensive than estimated by UMPNER, it would be unobtainable.  That would rule out nuclear projects as bankable propositions.  In plain words: nuclear fission is not commercially viable without government guarantees.

Finally, what of the great hope for the future – nuclear fusion?  There are several teams around the world working on nuclear fusion, including ITER (  From the ITER web site

“ITER is a large-scale scientific experiment intended to prove the viability of fusion as an energy source, and to collect the data necessary for the design and subsequent operation of the first electricity-producing fusion power plant.”

I admire the audacity and technological brilliance of projects such as ITER.  But the challenges with fusion are enormous and the technological complexity means that the power – if it comes at all – won’t be cheap. 

To me, solar and wind are the logical long-term solutions to Earth’s energy demands.

Note added one day later:

On reflection overnight, I think the above post should include more discussion on geothermal power.  Everything I’ve read indicates that geothermal power is suitable for base load generation, provided the power can be supplied to the grid.  However, the Levelised Energy Cost will be high.  In the near future, I’ll do a post on power generation from hot dry rocks (in the Australian context).

Tuesday, March 8, 2011

Cost of solar power (5)

Before I launch on the main theme of today’s post, I’ll describe progress of late.  I have a few projects under way:
·         I’ve committed to attend the International Solar Energy Society’s 2011 Solar World Congress to be held in Kassel, Germany from 28 August – 2 September 2011.  I’ve lodged my abstract, and assuming that’s accepted I’ll have a paper to write.  It will be on the performance of my engine-canopy system at Wellington NSW in the case where the canopy slopes at the latitude angle.  To give a preview of the results (which were completed late last year and are as yet unpublished) – compared to the horizontal canopy the sloping case has a lower maximum output, but  larger annual output that is more uniform throughout the year.  Results for the horizontal canopy were presented at the 2010 meeting of the Australian Solar Energy Society (AuSES).
·         I’m excited about the prospects of thermal storage with my heat engine.  Back-of-the-envelope calculations indicate that storage will be feasible and cheap.  What’s required now is a substantial simulation, which I think I know how to do but will take me some months.  That’s a job for the near future.  If successful, I’ll present the work at the 2011 AuSES meeting.
·         I also have another substantial project under way that regrettably must remain confidential for the moment.  That has occupied all my research time since mid January.
And so to the main topic of today’s post – cost of power for the Solar Oasis.

Solar Oasis (

From their web site …

“The Project will use 300 Big Dish solar thermal concentrators to generate 66GWh of electricity each year; enough electricity to power ~9,500 Australian homes and reduce GHG by 60,000 tonnes/year - an equivalent reduction of ~17,000 cars/year. The Project will deliver the first commercial scale concentrating solar thermal plant to dispatch power to the Australian electricity market and will also assist with the commercialisation of Wizard Power's Australian owned and developed Big Dish concentrating solar thermal technologies.”

The ‘Big Dish’ is a concept of the solar thermal research group at the Australian National University, which has been at the forefront of solar thermal research for several decades.  In 2005, the Big Dish technology was licensed to Wizard Power, one of the participants in the Solar Oasis.  Recently, a new Big Dish has been constructed on the ANU campus.  It’s very impressive!

The Solar Oasis project is based at Whyalla in South Australia.  Solar energy will be collected by 300 parabolic dishes, each of approximately 500 m^2 aperture.  The heat energy drives a conventional Rankine-cycle steam turbine, with power sent directly to the grid.  (The ANU team have worked extensively on storage of solar energy by splitting ammonia, but there is no mention of that with the Solar Oasis project.)  Other project details as announced in mid 2010: site area estimated at 0.8-1.0 km2, peak output 40 MW, annual output 66 GWhr, cost AUD 230 million.

To estimate the cost of solar power from Solar Oasis, I make my usual assumptions:
·         there is no inflation,
·         taxation implications are neglected,
·         projects are funded entirely by debt,
·         all projects have the same interest rate (8%) and payback period (25 years), and
·         all projects have the same annual maintenance and operating costs (3% of the total project cost), and
·         government subsidies are neglected.

Cost per peak Watt     AUD 5.75/Wp
LEC                            AUD 432/MWhr

The components of the LEC are:
CAPEX           {0.094× AUD 230×106}/{66×103 MWhr} = AUD 328/MWhr
OPEX             {0.030× AUD 230×106}/{66×103 MWhr} = AUD 105/MWhr

On the numbers above, the Solar Oasis project is not cheap for a project that won’t be operational for a couple of years. Using the same methodology, Andasol 1 (parabolic trough, molten salt storage, online in March 2009) has a LEC of EUR 205/MWhr.  See Cost of Solar Power (3).