permaculture

[Toby Hemenway <toby@patternliteracy.com>]

Nathan Czuba wrote:
> The total solar energy available to the earth is approximately 3850 ZJ (zettajoules) per year. 
> Oceans absorb approximately 285 ZJ of solar energy per year.
> Winds can theoretically supply 6 ZJ of energy per year. 
> Biomass captures approximately 1.8 ZJ of solar energy per year.
> Worldwide energy consumption was 0.471 ZJ in 2004.
>   
It's those last two numbers that are the most revealing. All the life on 
Earth, after about 3 billion years of evolution, blanketing nearly the 
whole land surface and much of the ocean, can capture 0.05% of the 
sunlight that hits the planet. So how much do you think humans can 
capture? Doesn't that suggest that referring to total solar energy 
hitting the Earth is meaningless? What matters is not how much energy 
reaches the planet, but how much can be usefully converted. All of life, 
all over the planet, can only capture about 4 times more solar energy 
than the energy humans use in the form of petroleum. That gives you an 
idea of how much hardware we'd need to keep up the current rate without 
oil. We already redirect for our needs about 40% of current biomass 
produced on the planet, according to some figures. So it's going to be 
tough to increase that amount without even more seriously disrupting 
ecosystem function.

I'm curious about the figure for wind. Is that how much energy all the 
winds on the whole planet produce? If so, it's meaningless. Remember, 
you have to build the hardware, and keep it running, to catch energy, 
which drops the EROI. That's why plants are only about 7% efficient. PV 
panels themselves are more efficient, but once you add in embedded 
energy costs, transmission and conversion costs, etc., PV drops to worse 
than plants. PV panels take years just to pay back their embedded 
energy, while plants pay as they go.

Here's a thought problem: if a PV panel takes years to pay off its cost 
of construction, how many PV panels will it take to build one PV panel? 
I think if we used most of the petroleum left to build PV panels and 
wind generators, we could keep up our current lifestyle for a while 
after oil gets scarce. But we're not doing that.

Toby

http://patternliteracy.com