Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Paul Anderson on 13/01/2009 09:09:17

Title: How efficient is chlorophyll at converting energy from the sun?
Post by: Paul Anderson on 13/01/2009 09:09:17

Paul Anderson  asked the Naked Scientists:

Hi Chris and team,

How efficient is chlorophyll at converting energy from the sun and how do you measure that efficiency?

If it is efficient, is anyone trying to exploit that as a substitute for the current photovoltaic systems?
 
Regards
Paul
NZ

What do you think?

Title: How efficient is chlorophyll at converting energy from the sun?
Post by: acidflask on 14/01/2009 07:28:30

Hello Paul,

The answer is somewhere between 10% and 99.9999%, depending on what exactly you mean by "converting energy from the sun". This involves many steps in chlorophyll-containing organisms, which can be roughly summarized by

light energy --> chemical energy within chlorophyll --> chemical energy in ATP or other energy transporter molecule --> chemical energy stored in edible plant parts

If you are interested in the most elementary step of light harvesting, i.e. converting light energy into chemical energy within chlorophyll (as an electronically excited state), the proteins that contain chlorophyll do so with staggering efficiency, with a loss estimated at about 1 in 1 million. The other elementary steps involving electron transport (basically the protein version of wires) are also extremely efficient, in the range of 99% or higher.

However, these processes are TOO efficient, which is bad because too much trapped energy within the chlorophyll can destroy it (a process called photobleaching or photodegradation) and/or can overload the electron transport chain. To counteract this, chlorophyll-containing systems have developed all sorts of mechanisms to dump excess energy. When you take into account the effects of regulation, the estimated efficiency drops to 40 - 60%, i.e. about half the energy received as light ends up as ATP or some other energy carrier at the receiving end of the light harvesting and electron transport chains.

When you further account for maintenance requirements, like replacing burnt-out chlorophyll (which lasts on average 500 - 1000 photons before it degrades), respiration, the cost of maintaining regulation and so on, the net efficiency going from light to consumable energy (like potatoes or onion bulbs) is estimated at around 10%.

Title: How efficient is chlorophyll at converting energy from the sun?
Post by: lyner on 15/01/2009 21:10:38

Quote

If it is efficient, is anyone trying to exploit that as a substitute for the current photovoltaic systems?
 

Sounds like a wood burning power station is what you're after!