The difficult part is getting the sun on it for 24 hours each day! ;-)
You might want to recompute with some more realistic daylight hours. Also
efficiency drops off a lot in morning and evening and I'm not sure your
"average" figures take that into account.
John

Daily, or continuously? There is no 'power daily', only energy daily.
But if you mean continuously, then the energy would be 400 gigawatts (400
GW in short) * 24 hours = 9600 Gigawatthour (9600 GWh in short) daily.
Now I wonder for which population you submit these figures.
If it is for the world's population of about 4 billion that you are
talking, then per head of the population you'd get an energy
consumption of 9600 GWh / 4 billion, or 9.6/4 = 2.4 kWh (kilowatthour)
daily.

It is not impossible to generate this energy on a daily basis by replacing
the roof materials of family houses by solar panels with a high efficiency.
In The Netherlands for instance, a 150 W peak power solar panel (about 1
m^2 in size, generates on average about 15 W power continuously.
So, for 2.4 kWh daily energy, which is equivalent to 2.4 kWh / 24 hours =
100 W continuous, one would need about 7 m^2 of solar panel on the roof.
It's not too difficult to do this.

In climates with more favourable solar conditions the area needed would
decrease accordingly, but if you talk of a much smaller population, then
the area needed should of course INcreasy accordingly.

shakiro

I do not know wether this is really true.

shakiro

[snip>

The problem with burning hydrogen is that solar panels can't make enough of
it. To replace today's vehicular use of oil, we'd need 230,000 tons of
hydrogen daily.  Solar cells to make that much hydrogen would cover about
20,000 square kilometers.  To get this much power -- 400 gigawatts daily --  
without carbon emissions, the only cost-effective solution is nuclear
plants. And that has its own political and ecological consequences.  See
http://www.world-nuclear.org/opinion/grant.htm

Seth

I think you're mostly right for short term, but long term belongs to
hydrogen.
The problem with solar is storing the energy. Stick a solar panel in your
back yard that converts water to hydrogen, and you can store as much as you
want.

I would like to present to you the (near) future of transportation...

Diesel hybrid cars (full two-mode plug-in hybrids)
Diesel for motorcycles
Diesel (probably 2-stroke) engines for general aviation (including
rotorcraft)
Extensive use of bio-diesel

Hybrid cars (gasoline)are in production
Diesel hybrid trucks and busses are in production
Diesel motorcycles are / will be in production soon
Diesel aviation engines are in production...more are coming

Very soon we will see the first diesel hybrid passenger car in
production

Diesel for aviation or motorcycles...they have been around for some
time. Think of Junkers "Jumo" 205. Decades ago there were several
Diesel aircraft engines built by Guiberson, Packard, Rolls-Royce,
Clerget, Fiat and others. Royal Enfield (India) has had a diesel
motorcycle in production for some time. I believe it is now
discontinued.

Some diesel hybrid car prototypes...

GM's Ope Astra diesel hybrid
Citroen Berlingo diesel hybrid
VW Golf diesel hybrid (so I hear)

Some diesel aviation engine prototypes...

SMA Morane Renault MR 200 www.smaengines.com
Teledyne Continental Motors CSD-283 www.teledyne.com (Nasa GAP)
DeltaHawk V-4 www.deltahawkengines.com
Zoche 01A www.zoche.de
Diesel Air Ltd. DAIR-100 www.dair.co.uk

Some (gasoline) hybrid cars in production...

Toyota's Prius and Lexus
Ford's Escape Hybrid

Some diesel motorcycle prototypes...

Diesel Kawasaki M1030 M1 (KLR 650) F1 Engineering / Hayes Diversified
Technologies (HDT)

For third world countries a diesel motorcycle could be ideal. It is
probably very dependable and durable and relatively easy to fix. It
could be bi-fuel, meaning it could use diesel, Jet A, light heater oil
and most importantly... bio-diesel and even straight vegetable oil
(SVO). It could ne equipped with a small (max 200kg) 2-wheel trailer
and a power take-out (PTO). The PTO would mostly be for a generator
and/or (water) pump.

Picture this. In a third world country, a motorcycle travels 100km @
80kmh with 2 litres vegetable oil that they have made themselves. It
then pumps (with a pump attached at the PTO) from a deep dwell 150
litres of fresh water into a tank that's on the trailer, drives back
and delivers the fresh water to the families in the village. Later at
night, it runs to provide electricity (with a generator attached to the
PTO) for many houses in the village and to recharge the batteries. This
motorcycle and its accessories the families in the village have bought
together, with some help from some organisation like the UN.

Of note: Of course the best way to produce electricity in these often
sunny third world countries is solar panels!!