>

I did not say biomass---which does release greenhouse

> > ... biogas (the ONLY energy source that

> contributes zero

> > greenhouse gas emissions ...

>

> =v= Sorry, but this is also bogus wording. Biomass

> still adds

> carbon to an atmosphere already overburdened with

> it, and it

> stays there and has an impact for a lag time. It

> definitely

> has a distinct advantage over fossil fuels in that

> its lag time

> is much shorter, but tallying it up as "zero" is

> inaccurate.

> <_Jym_>

gases, since it is not covered and captured---but

instead work with biogas, or natural fuel gas, which

does not contribute any net greenhouse gas emissions,

since it relies on an anaerobic environment that

prevents gases from escaping---and creates better

fertilizer by trapping the nitrogen, too. Since the

methane is burned during combustion and the CO2

released is the same amount released during natural

decomposition, it is more than offset by the plant

matter growing in the first place. Meaning I am

perfectly accurate in using the word "zero". Your

skepticism is defying science.

____________________________________________________________________________________

Take the Internet to Go: Yahoo!Go puts the Internet in your pocket: mail, news, photos & more.

http://mobile.yahoo.com/go?refer=1GNXIC- Hi All,

A recent post claimed that:

>... rainwater dropping off the living roof

First of all, 8 MW is power, not energy. Energy is

>will generate electricity in the winter. Might not

>sound like much, but 1" of rainfall over a 5000 sq.ft.

>roof will produce 250 cu.m. of water, dropping 13.5 m.

>will potentially generate 30 MJ or 8 MW of power.

>Enough to light 4,000 homes.

power * time, so 8 MW for one hour is 8 MWh.

5000 s.f. x 1 inch = 417 ft3, which is about 26,000 lbs.

13.5 m is about 45 feet. 26,000 lbs falling 45 feet

does 1,170,000 ft-lbs of work. At 33,000 ft-lbs/min

for one horsepower, this is 35.5 HP-minutes. One

HP is 746 watts, so this is 26,500 watt-minutes or

440 watt-hours or .44 kWh. If it rains 40 inches a

year, you get 18 kWh per year, or about enough to

power .002 of a house for a year at the once-commonly-used

value of 1 kW continuous will power one house. (I think

maybe 2 kW is the new number, but I'm not sure.)

So, this calculation is off by a factor of 4000/.002

or 1,986,704, give or take a few gnats' whiskers.

We really have to be numerate in these discussions.

What this really highlights, though, is that people

have NO conception of the amount of energy we are

using. The notion that a little rainwater falling off

a roof could power 4000 homes is truly discouraging.

And doesn't anyone study physics any more?

Regards,

Joel

----- ### -----

J.H. Crawford Carfree Cities

mailbox@... http://www.carfree.com - I was about to ask for more information about that system: thanks for

saving me the trouble!

I was slightly sceptical, because one of the great advantages of a

living roof is the cooling effect of plant transpiration,

particularly useful in hot, moist climates. This tends to reduce the

volume of water that comes off the roof as stormwater considerably.

Because I live in a warm, dryish climate my own plans limit living

roofs to those that are readily accessible, and include a

considerable area of steeply-pitched conventional roof for the

purpose of gathering rainwater. Even so, at the annual rainfall of

750mm the site area is not great enough to supply the entire water

needs of the occupants at the projected density, but such things as

using grey water to flush the toilets can reduce mains water

consumption considerably.

Indeed the calculations required to project the power consumed by an

electric pump to pump grey water to a roof-mounted cistern, which

delivered a surprisingly low figure, only reinforced my suspicions.

I've been considering supplemental wind power for the same project,

notwithstanding the losses in efficiency due to a turbulent, truly

urban roofscape. Here's a useful resource for this sort of thing:

http://www.otherpower.com I enjoy their combination of common sense

and dogged low-tech independence.

The figure of 9000kWh per year is mentioned somewhere on that site as

being slightly profligate. It corresponds to about 1.22kW continuous.

My own calculations produce a slightly lower figure if one excludes

electric cooking, so I suspect that 1kW continuous is not unrealistic

if one steers clear of silly things like water taps that need

electrical connections that allow them to change colour (they're

actually made!), or the facility of running a bath over the internet

from another country.

Best regards

Dawie Coetzee

--- In carfree_cities@yahoogroups.com, "J.H. Crawford" <mailbox@...>

wrote:>

>

> Hi All,

>

> A recent post claimed that:

>

> >... rainwater dropping off the living roof

> >will generate electricity in the winter. Might not

> >sound like much, but 1" of rainfall over a 5000 sq.ft.

> >roof will produce 250 cu.m. of water, dropping 13.5 m.

> >will potentially generate 30 MJ or 8 MW of power.

> >Enough to light 4,000 homes.

>

> First of all, 8 MW is power, not energy. Energy is

> power * time, so 8 MW for one hour is 8 MWh.

>

> 5000 s.f. x 1 inch = 417 ft3, which is about 26,000 lbs.

> 13.5 m is about 45 feet. 26,000 lbs falling 45 feet

> does 1,170,000 ft-lbs of work. At 33,000 ft-lbs/min

> for one horsepower, this is 35.5 HP-minutes. One

> HP is 746 watts, so this is 26,500 watt-minutes or

> 440 watt-hours or .44 kWh. If it rains 40 inches a

> year, you get 18 kWh per year, or about enough to

> power .002 of a house for a year at the once-commonly-used

> value of 1 kW continuous will power one house. (I think

> maybe 2 kW is the new number, but I'm not sure.)

>

> So, this calculation is off by a factor of 4000/.002

> or 1,986,704, give or take a few gnats' whiskers.

>

> We really have to be numerate in these discussions.

> What this really highlights, though, is that people

> have NO conception of the amount of energy we are

> using. The notion that a little rainwater falling off

> a roof could power 4000 homes is truly discouraging.

>

> And doesn't anyone study physics any more?

>

> Regards,

>

> Joel

>

>

>

>

>

>

>

>

> ----- ### -----

> J.H. Crawford Carfree Cities

> mailbox@... http://www.carfree.com

> - OK.

Lance Armstrong pedalling a bike-driven generator can

produce about 350 watts and he can probably keep this

up for about 3 hours. That is, roughly, 1 kilowatt-hour.

If Lance drives to the gym in a Prius and he travels

10 miles round trip, he uses an average of about 10 HP

for a period of 10 minutes (assuming an unlikely average

speed of 60 MPH). At 746 watts/HP, this is 74,600 watt-min:

10 min * 10 HP * 746 watts

74,600 watt-min is 1243 watt-hours or 1.243 kWh

So, in ten minutes of driving, Lance uses more energy than

he can produce in 3 hours of pedalling.

Now, if it's YOU on the treadmill, how many watts continuous

can you produced for three hours?

If you power your car by pedalling a generator to charge

its batteries, you're going to have to pedal for, say,

one working shift in order to drive 10 miles back and

forth to work. Or, you could ride your bike for, say,

40 minutes each way.

We MUST get our heads around the notion of just how much

energy we are consuming. It's truly incredible. Think in

terms of reducing your energy consumption 10-fold in

your lifetime. Even THAT is probably not sustainable.

The fix we're in is so much worse than people think it is,

simply because they think it's quite normal to put 10 gallons

of gasoline in the car once or twice a week. The energy

content of that gasoline is just incredible; only since

the start of the industrial era have people been able to

consume energy at this rate. This has only been possible

because we have been burning fossil fuels created over a

span of millions of years during the course of a century.

Rainwater falling off the roof is not going to power your

next flight to Disneyworld. It's not going to get you to

the airport. In fact, it's barely going to get you out

of the driveway.

Life is going to change. Get used to it. Then figure out

how to enjoy it. That's not hard. Just imagine carfree cities.

Joel

----- ### -----

J.H. Crawford Carfree Cities

mailbox@... http://www.carfree.com - Joel's post is an extraordinarily elegant explanation of the brutally

simple math that underlies our inescapable energy crisis - and gives

the lie to so many facile and fantastic claims about "solutions" thereto.

If anyone here is unfamiliar with such calculations, PLEASE correct

that deficiency. Truly understanding the magnitude of the fix we are

in is essential, if there is to be any chance of survival for our

civilization.

-Doug

--- In carfree_cities@yahoogroups.com, "J.H. Crawford" <mailbox@...>

wrote:>

>

> OK.

>

> Lance Armstrong pedalling a bike-driven generator can

> produce about 350 watts and he can probably keep this

> up for about 3 hours. That is, roughly, 1 kilowatt-hour.