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Energy

(just did some reading on means for capturing sunlight and how efficient they are; it challenged some of my preconceptions of where the solution might lie, so I though I’d share it with you guys too. I omit energy sources that are many thermodynamic steps removed from incident solar radiation, like hydroelectric, wind and waves – I *assume* these are extremely inefficient converters).

Chlorophyll (in plants, converts sunrays into ‘redox potential’ – useful chemical energy that can smash carbon dioxide and water together to form hydrocarbons – like sugar or biodiesel): ~100%

Conversion of chlorophyll-derived energy to useful molecules, like sugars: 50%

Factor in the energy spent by the plant so that it can live, and the sunlight reflected off the leaves, and your big green plant could theoretically convert just 11% (other sources quote 34%). Sugar cane is at the top end of the ones that have been measured: 4%; corn is 0.5% (corn is a major crop being used for bioethanol); wheat is 0.3%

Solar panels: 20%

Algae: 13%

I’d also like to know what the energy efficiency of a snickers bar or a sausage is (in terms of energy used by plants to make the individual components, energy to make the bar, energy to transport it to me, versus the energy it refuels my body with); my (largely baseless) guess is that it must be anywhere in the 0.000x – 0.0000000x% range. What a waste of sunrays!

UPDATE: http://venturebeat.com/2008/05/29/sapphire-energy-gets-open-checkbook-from-investors-for-algae-based-gasoline/ “Green crude” project putting bacteria in dirty water or seawater and extracting petroleum gets ‘blank cheque’ to make it happen, and quick. The Wellcome Trust is getting in on this, which is interesting – and probably a good sign for the viability of the technology

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This entry was posted on Sunday, May 25th, 2008 at 11:04 pm and is filed under Musings, New science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

gregory

lovely bit about the snickers bar and the sausage .... and brings up a point about what we can so far measure .... the snickers bar has caloies, and cool, we can measure that, but it has no life-force, a completely unquantifiable concept, but one which is quite real, and why fresh juice is better than processed, though it is "the same thing"
crosbie

What might also be interesting would be to compare the cost of any product with what it's cost would have been had all the fossil fuel use been substituted with renewable fuel use (throughout its production lifecycle).
There isn't necessarily a problem with wasted sunrays (given that the energy reaches the earth no matter what we do with it), but with wasted fossil/nuclear fuel (or indeed, use of any fuel that produces or releases energy as opposed to harnessing solar energy).

If you're interested in saving solar energy, it might be interesting to compute how much of the surface of the Sahara desert would need to be covered by a good mirror in order to reflect back into space the world's daily production/release of energy (i.e. excluding hydro/wind/solar power). That might be a fun measure of man's impact on the planet's energy budget (thus global warming due to energy as opposed to deforestation, pollution, etc.).
crosbie

I should add that the mirror won't be vastly superior to sand, and the atmosphere will still capture a fair bit of reflected sunlight (via absorption, reflection, refraction), but this calculation would still be interesting.
gregory

another huge can of worms, measuring the external or hidden or social costs, yet the real costs, of many things .... we buy tyres, tires, never pay for the cleaning up of all the particles inhaled by city kids, or for the disposal, on and on

economics has a long way to go
Philippe Bradley

Ah, the problem of externalities. Turns out economics does have the answer, but politics is lagging. Putting taxes on tires or road users comes across as "yet another stealth tax"... when really all it's doing is forcing people to compensate society for the bad effects of their behaviour. Sadly politicians don't have the willpower to make that happen.
Philippe Bradley

A problem with 'going solar' is that datacenters (perfect converters of electricity into heat, plus a bit of noise and airflow) increasingly need to be located in cold environments (Siberia, Greenland, Alaska), though solar intensity in those regions is low. Unless the energy can be transported between the two zones (by wire or as a fuel), solar may be out of the question for powering the 'net.