Mike Lorrey wrote:
> Adrian Tymes wrote:
> > jeff davis wrote:
> > > I envision the dish as spin stabilized to keep it
> > > pointed at the sun, with steam generator, and dual,
> > > counter-rotating turbine/generator units axially
> > > mounted, and the waste heat radiator located in the
> > > shadow behind the dish.
> > Wouldn't direct photovoltaic be more efficient than a steam
> > generator?
> No. PV, even in multi layer/ multi spectrum cells, peaks out at about
> 35% efficiency. Thermal systems can be 80-90% efficient. This is
> efficiency in terms of energy conversion.
Not discounting thermal in general, but I thought steam engines in
practice tend to be about 30-35% efficient too. But that just makes
them equal (barring your data about power per mass), I guess...
> So, there, you are dealing with launch cost efficiency. Then you also
> have to consider maintenance and reliability. Generally, the rule is
> that the fewer moving parts, the more reliable and therefore the least
> cost in terms of maintenance. Since PV has no moving parts, it would
> seem to be the most reliable, while thermal systems generally require at
> least a turbine generator and a pump or two to function. This is fine if
> the actual MTBF is longer than the amount of time you expect between
> opportunities for maintenance inspections. This is not so great for a
> device which is not expected to return to human hands any time in
One could imagine RC maintenance bots, drifting from solar sat to solar
sat, skimming reaction mass from the atmosphere for ion engines powered
by its own PV system.
> As you can see, there are a lot of factors to consider.
This archive was generated by hypermail 2b30 : Sat May 11 2002 - 17:44:15 MDT