alt.energy.renewable

"Rob Dekker" schrieb im Newsbeitrag
news:QPyKj.524$%41.158@nlpi064.nbdc.sbc.com...
> Bill, you cover a lot of different things in one email.
> Let me just address one paragraph below.
>
> Rob
>
> "Bill" wrote in message
> news:585eca5e-bc8e-4950-8705-d6b29c4254e9@l28g2000prd.googlegroups.com...
>> In summary, we can make 100, 900, and 180,000 gallons an acre per year
>> of gasoline fuel equivalent using biodiesel, cellulosic ethanol, and
>> photovoltaics respectively.
>>
> ....
>> Now there are other energy sources wind and solar specifically
>> photovoltaics. In Spain wind accounts for about 30% of total
>> electricity, more than hydroelectric. But, assume the entire state of
>> Iowa was covered with photovoltaics. 17 watts per square foot (could
>> potentially be 35 watts per square foot with 40% efficient cells).
>> 43,560 square feet in a acre. 5 sun-hours a day (7 sun-hours a day in
>> Inyokern California).
>
> Most (regular/affordable) PV cells are less than 10% efficient.
> Assuming 72 Watt / square foot incoming radiant energy (level panels), you
> get 7 Watt per square foot.
> With 5 sun-hours per day, that is about 13 kWh/year per square foot.
> That is 556,000 kWh/year/acre (if you plaster every square foot with PV
> cells).
>
>> 250 WHrs/mile for a Prius. 30 miles in a
>> gallon. Do the math you get 493 gallons of equivalent gas in a DAY.
>> In a year, you get 180,000 equivalent gallons per acre.
>
> Gasoline has a heat of combustion of about 35 MJ/litre. That's 131
> MJ/gallon (US).
> That's about 36 kWh/gallon.
>
> Do the math and you get about 15,000 equivalent gallons per acre.
> So you are a factor 10x off if we look at the actual energy numbers.
>
> 15,000 gallons per acre is still very respectable, especially when
> compared to the abysmal numbers of regular biofuels.

You forget one thing in the comparsion.

The extrem low efficiency of a gasoline engine in average.

Maybe You heared in advertiging somethint like 30%,
but this is the efficiency under ideal conditions.

In city traffic, the efficiency of a gasoline engine is
most times below 10%

--
Roland Mösl
http://car.pege.org cars and traffic
http://live.pege.org building and live
http://www.pege.org