Shift happens: Will artificial photosynthesis power the world?

[yowzayowzayowza]

Scientific American

One drinking-water bottle could provide enough energy for an entire household in the developing world if Dan Nocera has his way. A chemist from M.I.T. and founder of the company Sun Catalytix, Nocera has developed a cobalt-based catalyst that allows him to store energy the same way plants do: by splitting water.

"Almost all the solar energy is stored in water splitting," Nocera told the inaugural ARPA-E conference on March 2. Solar Catalytix is among five companies awarded government funding to develop "direct solar fuels," dubbed "electrofuels" by ARPA-E, the new Advanced Research Projects Agency for transformational energy technologies. "We emulated photosynthesis for large-scale storage of solar energy."

... 3 more paragraphs.

video: http://www.youtube.com/watch?v=WD9yr-Bf-Kw

Apparently this was mentioned a coupla days ago:

[kristopher]

1. When Nocera publishes the efficiency numbers for his process, we'll have a way to judge.

Since he hasn't published those numbers in the two years since he announced this process, we can assume the numbers do not compare favorably to alternatives. I mean think about it, if this were an advancement in efficiency or costs, why wouldn't you put the data out to attract attention and convince those who will bring the process to markets?

BTW, photosynthesis is an extremely inefficient process for storing energy.

[tama]

2. Inefficient?

Its the only one really available, humans can't do it at all, only plants cells can store energy from sun into chemical bonds that feed the rest of life on Earth, oil - the most efficient process known for storing energy for exergy - is just solar photosynthesis energy packed very tightly by geothermic forces and time. It's foolish to imagine one is brighter than Mother Nature. The exergy available from fission and uranium capital available is just a fraction of what the photosynthetic fossile hydrocarbon capital (exergy cumulation) was.

[Nederland]

3. Yes, inefficient

Photosynthesis is only 3%-6% efficient--far lower than photovoltaics.


Photosynthesis can be simply represented by the equation:

CO2 + H2O + light --> (CH2O) + O2

Approximately 114 kilocalories of free energy are stored in plant biomass for every mole of CO2 fixed during photosynthesis. Solar radiation striking the earth on an annual basis is equivalent to 178,000 terawatts, i.e. 15,000 times that of current global energy consumption. Although photosynthetic energy capture is estimated to be ten times that of global annual energy consumption, only a small part of this solar radiation is used for photosynthesis. Approximately two thirds of the net global photosynthetic productivity worldwide is of terrestrial origin, while the remainder is produced mainly by phytoplankton (microalgae) in the oceans which cover approximately 70% of the total surface area of the earth. Since biomass originates from plant and algal photosynthesis, both terrestrial plants and microalgae are appropriate targets for scientific studies relevant to biomass energy production.

Any analysis of biomass energy production must consider the potential efficiency of the processes involved. Although photosynthesis is fundamental to the conversion of solar radiation into stored biomass energy, its theoretically achievable efficiency is limited both by the limited wavelength range applicable to photosynthesis, and the quantum requirements of the photosynthetic process. Only light within the wavelength range of 400 to 700 nm (photosynthetically active radiation, PAR) can be utilized by plants, effectively allowing only 45 % of total solar energy to be utilized for photosynthesis. Furthermore, fixation of one CO2 molecule during photosynthesis, necessitates a quantum requirement of ten (or more), which results in a maximum utilization of only 25% of the PAR absorbed by the photosynthetic system. On the basis of these limitations, the theoretical maximum efficiency of solar energy conversion is approximately 11%. In practice, however, the magnitude of photosynthetic efficiency observed in the field, is further decreased by factors such as poor absorption of sunlight due to its reflection, respiration requirements of photosynthesis and the need for optimal solar radiation levels. The net result being an overall photosynthetic efficiency of between 3% and 6% of total solar radiation.

http://www.fao.org/docrep/w7241e/w7241e05.htm#1.2.1

[tama]

6. The second law

http://en.wikipedia.org/wiki/Exergy

What really matters is not energy content but according to second law, exergy difference between forms of energy which is the amount of work that energy can do. Heat radiation has no exergy potential.

How much free solar photosynthesis exergy potential it has taken and takes to build a solar panel and how much exergy potential and usefull heat that solar panel produces? There is no comparison since a solar panel would not and could not exist without exergy potential from photysynthesis, it is never "more efficient" but totally dependent from biosphere.

[Nederland]

10. Incorrect

There is no comparison since a solar panel would not and could not exist without exergy potential from photysynthesis, it is never "more efficient" but totally dependent from biosphere.

This is incorrect. It is true that I need to make use of the exergy potential from photysynthesis to make my first solar panel. However, once I have that first solar panel, I can use it's energy to make a second, and a third, etc. I'm getting progressively better off because the solar panels are much more efficient than the plants were.

[Statistical]

5. The amount of energy is fissile material vastly exceeds hydrocarbons

Total energy stored in hydrocarbons is 0.3YJ (0.3*10^24).
Total energy in uranium is 2.4YJ roughly 10x as much.

Annual energy consumption is around 474 EJ (474 *10^16)

http://en.wikipedia.org/wiki/World_energy_resources_and_consumption

The accumulation of hydrocarbons has more to do with the millions of years of accumulated phtosynthesis rather than a high level of efficiency.

If I worked a minimum wage job but was able to do so for a couple billions years I would be rich.

[tama]

7. Again,

What matters is exergy and EROEI, not total energy sum. Total energy means nothing and it's very foolish to think it means anything else. Energy content and efficience is all about energy quality in terms of second law of thermodynamics and exergy and nothing to do with quantity of total energy.

[Statistical]

8. Well first of all that wasn't your claim.

Second as we deplete more and more stored hydrocarbons the EROEI drops.

Due to depletion EROEI is already higher for nuclear fission than for many forms of Hydrocarbons.

[tama]

9. EROEI

is a fuzzy concept, there is no objective way to draw a limit to what is considered energy or rather exergy invested and what is not. EROEI of nuclear fission can be made to look positive in EROEI only by drawing artificially manipulated limits to what is considered exergy invested.

[Statistical]

16. BS. The complete lifecycle of nuclear is EROEI postive. How much is debatable...

When you factor in construction, mining, enrichment, fuel fabrication, operating energy requirement, maintenance energy in terms of replacement, spent waste storage, and decommissioning nuclear is still positive EROEI.

http://www.world-nuclear.org/info/inf11.html

EROEI: 57:1

[tama]

18. World nuclear association

is hardly the place to look for non-partial evaluation. :)

And yes, that's a very myopic glance into very complex interdependent system of the whole ecosystem which includes human social system.

[Statistical]

19. "human social system" doesn't have jack shit to do with your false claim of negative EROEI

There are a lot of anti-nuclear folks on this forum. No problem with that.

The amount of positive EROEI is even debatable. There are studies that range from 15:1 to 50:1.

However even those who 100% oppose nuclear energy wouldn't be foolish enough to make a utterly ridiculous and easily verifiable claim as nuclear having an negative EROEI.

[tama]

20. Systemwise, the whole infrastructure is needed

So I cannot argue against this article:
http://design.antigov.org/txt/Lasse_Nordlund.htm
a small quote:

"Unlike it's generally presumed, we did not manage to make energy collection in primary production more efficient by the use of technology, or by a sophisticated division of labour. A tractor pulling a seven-bladed plough may look efficient, but it collects food energy a lot less efficiently than a person working by hand in a garden – when we take into account the energy and working time inputs more broadly than just for the individual farmer. To figure this out, we must assess how much energy it takes to collect primary energy indirectly, in a mechanized way. The results must be compared to the energy input that would have been necessary if had we collected the same amount of energy manually, using only simple tools.
During their lifespans, machines use energy as fuels and through maintenance, but also during the manufacturing process and eventually when they are disposed of. When a machine is manufactured, the more technologically advanced the machine is, the more energy will go into making it. This is because the energy needed to make a particular machine includes the energy it took to build all the machinery used to make it, and the energy used to build the machines that built that machinery as well.
In practice, we can trace the energy inputs in a manufacturing pyramid only to a limited extent, so the sum of energy inputs we get will always be less than what has really been used in the making of a machine. Even though, say a computer's dimensions are small, to manufacture one requires a large, energy consuming infrastructure from a network of roads to information networks.
This helps to explain in part why, despite "energy-saver machines" becoming more common, our energy consumption continues to grow explosively. With new machines, machine development promises us more saved energy, but at the same time it creates new ways to consume energy. The attempt to amend the energy deficit has become anunrelenting ascent into new energy consumption heights. Energy efficiency calculations in technical bulletins give a false idea about a machine's energy consumption by concentrating solely on the energy consumed when the machine is operating; for example, by concentrating on how long a distance can a vehicle travel with an amount of fuel. It's problematic to estimate a machine's utility entirely separately from the environment it is impacting. A heavy tractor compresses farmland, which then takes more energy to plough, which raises the energy needed to make a unit of food. The concept of energy efficiency leaves out the indirect energy needs that arise from having a machine in the first place, including ore mining, transportation, marketing, maintenance and changes in working technique. A car needs terrain cleared into a road to ride."

[OKIsItJustMe]

4. Did he not publish them, or did you simply not accept them?

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=234520&mesg_id=234557

[kristopher]

11. Your own link shows he hasn't published them.

[OKIsItJustMe]

12. Do, please explain

I gave you 3 citations, including one from Science.

In what way is that not published?

[kristopher]

13. Please quote the entire paragraph from the Science article with the efficiency numbers.

I'll wait.

[kristopher]

14. I stand corrected, he has published the data.

However as I noted before when I accepted the premise that he had achieved what you claimed, it doesn't change the overall picture nearly enough to make fuel cells attractive for most applications. Instead of the overall system efficiency being 3X+ less than electrochemical storage, it moves it to 2X+ less efficient.

[OKIsItJustMe]

15. In light of other developments, It's time for a new chart

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=234625&mesg_id=234625
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=234596&mesg_id=234646

[kristopher]

17. No, it isn't

The problem with the low efficiency of the fuel cell process is the extra generating infrastructure required. Since the Lh2 process is experimental we don't know the cost or practicality of its use. Does the experimental 'light > h2' (xLh2?) reduce the amount of infrastructure needed compared to batteries?

The answer is no, it doesn't. The proper comparison would be:
xLh2 = 100w > liquifaction = 85w > FC = 42.5w > vehicle = 38.25w

PV = 100w > battery charge/discharge = 95 > vehicle = 85.5w


You are conflating two areas of concern - cost of PV vs the xLh2 process, and the efficiency of the processes.

Now, if you can show that the xLh2 process can produce 100w of electricity for less than a PV (or wind turbine, or tidal generator etc)can produce about 220w, then you have a case to make.

The only other advantage the xLh2 process MIGHT offer is space, but not knowing what it actually required for the system, it would be premature to make that conclusion.