[ RadSafe ] SOLAR as a replacement for fossil fuel?

[Ted de Castro]

Sorry folks - my calculator an I just aren't getting along today - my 
previous numbers were wrong - too low.  Here's the whole thing redone 
and triple checked.

I welcome comment/correction - there ARE assumptions in here!  BUT 
bottom line - whatever form of prompt (solar cells or focusing for steam 
generation) or near prompt (bio fuel or wind or wave or hydro - yes 
hydro is solar powered too) - it would take harvesting ALL the solar 
radiation from just too much of the earth's surface area (6.4% if by 
land - 1.6% if by sea too for bio fuel - the cheapest way to cover the 
most area) and thus would be also too costly.  Its just not practical.

I found this an interesting exercise to assess potential.

Here are ALL the calcs:

Consumption:

ref 1:
Oil 85,000  thousand barrels per day

ref 2:
160 e15 btu/yr
coal 95e15 btu/yr
gas  95e15 btu/yr

Oil energy equivalent /barrel (42 gal crude 44 gal processed)
1.7 MWh
5.8 e6 BTU
6.1178632e9 J

surface of earth

50.25 e6 sq mi
1.396 e14 sqm

oil usage:

6.8 of 44 gal barrel NOT used as fuel

((44-6.8)/44) used as fuel = 0.8454545455

Solar

1.4 kw/sqm at noon at the equator at the summer solstice
avg sun 12 hr/day.

So - fossil fuel

85,000*1000*5.8 e6*0.8454545455*365.25 = 1.52 e17 btu.yr
or 160 e15 = 1.6 e17 as stated in the other reference
so data is consistent


Or using the the 1.7 MWhr number (1.7e3 KWhr)

1.7e3*0.8454545455*8.5e7*365.25 = 4.46e13 kWhr/yr for oil
PLUS 95/160*4.46e13 = 2.649e13 for coal
PLUS 95/160*4.46e13 = 2.649e13 for gas

= 9.76e13 kWhr/yr total fossil fuel

Solar

use 1.4 kW/sqM at noon solstice
Assume 12 hr/day
Assume AVG sunlight through day through latitudes ~ 1/3 max constant use .5
(requires ALL tracking solar collectors)
.5*1.396e14*12*365.25 = 3.059e17 kWhr/yr

THUS

3.19 e-4 (.0319%) of earth surface required at 100% efficiency
0.319% @ 10% - (1.276% of land only) (best solar cells currently 10%)
1.595% @ 2% (bio fuel grass) - (6.38% of land only)