permaculture

["Laurence Gaffney" <lgaffney@bigpond.com>]

1.    Toby Hemenway wrote:-
"Doesn't that suggest that referring to total solar energy hitting the Earth 
is meaningless?"
 
I am not exactly sure what you mean here Toby but I don't think it is 
meaningless.
Doesn't the figure for total solar energy hitting the earth (per annum say) 
help provide the basis of an annual budget for sustainable energy use for 
humans and all other life as well as all earth processes?.

2.    Toby also wrote:-
"What matters is not how much energy reaches the planet, but how much can be 
usefully converted."

 Both matter,  and I think the Howard Odum approach which uses a concept of 
energy quality contributes to this discussion. Odum uses a term Solar 
Transformity which he describes as the solar energy calories(joules) required 
directly and indirectly to make one calorie(Joule) of a product, service or 
energy of another kind.
Some examples from page 69 of his 2001 book called "A Prosperous Way Down" 
are :-
(A)    It takes 1500 Calories of Sunlight energy to make 1 Calorie of wind 
energy.
(B)    It takes 50,000 Calories of sunlight energy to make 1 Calorie of 
fossil fuel energy 
(C)    It takes 170,000 Calories of sunlight energy to make1 Calorie of 
electric power.

Note that these are very generalized numbers and that it is the orders of 
magnitude that are significant here.
Note that wind energy is not additional to the earths annual solar energy 
budget as it is derivative.   
So one Joule of Electric Power is of much higher quality than one Joule of 
Sunlight Energy due to its "embedded" solar energy which Odum refers to as 
its Solar Emergy.

Question:- How does the current Solar Emergy consumption of humans in the USA 
per annum compare with the annual input of Solar Energy over its Land 
Mass/Boundaries?.  

Joules ain't Joules

Laurence Gaffney 

PS:-     What is the source of your figures Nathan? 

      

Date: Fri, 31 Aug 2007 08:45:19 -0700
From: Toby Hemenway <toby@patternliteracy.com>
Subject: Re: [permaculture] energy/ethanol
To: permaculture <permaculture@lists.ibiblio.org>
Message-ID: <46D8378F.8000700@patternliteracy.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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