# The Naked Scientists Forum

### Author Topic: Creating electricity from global warming  (Read 9130 times)

#### lyner

• Guest
##### Creating electricity from global warming
« Reply #25 on: 23/05/2008 22:29:08 »
In any case, where is this thread going?
Are we discussing
1.how a tree gets enough energy to supply what is needed for self irrigation (it clearly gets enough energy)
or
2. whether this is a system which could be looked upon as a possible Energy Resource for electricity generation (not in a million years - there just isn't enough power input)?

It isn't clear.

#### YourUncleBob

• Jr. Member
• Posts: 23
##### Creating electricity from global warming
« Reply #26 on: 29/05/2008 10:32:34 »
Sophie Dave,

I wish I could devote more time on here, hopefully soon, in the meantime let me clarify where this thread is hopefully going.

Two questions need to be addressed.

1) How much power can be generated from the falling water 800,000 liters falling 250 meters through a 20 cm diameter pipe?

2) Can our Artificial Trees lift that much water?

We have a lot of confidence in our Artificial tree's ability to lift the water. Which as I alluded to earlier has to do with the apparatus used in the experiments to measure the energy required to evaporate 1 kg of water. Did any of you check it out? (remember water is not a good conductor of heat)

Question 1 has been very confusing, have you guys checked the link I gave for the formula I used? If not please check their example, I'll copy and paste it below.

If you could kindly point out the errors I made when working through the formula with our numbers I would be very grateful.

Power = (10 feet) x (500 cubic feet per second) x (0.80) / 11.8 = 339 kilowatts

To get an idea what 339 kilowatts means, let's see how much electric energy we can make in a year.

Since electric energy is normally measured in kilowatt-hours, we multiply the power from our dam by the number of hours in a year.

Electric Energy = (339 kilowatts) x (24 hours per day) x (365 days per year) = 2,969,000 kilowatt hours.

The average annual residential energy use in the U.S. is about 3,000 kilowatt-hours for each person. So we can figure out how many people our dam could serve by dividing the annual energy production by 3,000.

People Served = 2,969,000 kilowatts-hours / 3,000 kilowatt-hours per person) = 990 people

Kind Regards
Blaine

#### daveshorts

• Moderator
• Neilep Level Member
• Posts: 2583
• Physics, Experiments
##### Creating electricity from global warming
« Reply #27 on: 29/05/2008 10:48:44 »
Question 1 is not confusing, it is trivial to put an upper bound on.

800 000kg of water raised by 250m by mgh has about

800 000kg * 10kgm/s2 * 250m
2GJ of energy
which is 555kWhr of energy.

assuming this is  what your system can lift in a day (which will mean it has an area of about 8 hectares)

you will be producing an average of 23kW

about 50ish people assuming a 100% efficient conversion from potential to electrical energy, this is probably nearer 80% so you are talking about 18kW average.

#### lyner

• Guest
##### Creating electricity from global warming
« Reply #28 on: 29/05/2008 15:18:48 »
Yes, Y U B, question 1 is triv.
This system works on evaporation of some of the water to provide energy for lifting all of it.
I have a suspicion that all this energy transfer could produce a significant modification to the microclimate. The air would be full of evaporated water and it could mean an increase in rainfall (admittedly, some of this rainfall would find itself back in the system again.)
This process is not unlike the normal water cycle, which uses the GPE of water which has been lifted there by solar energy via the clouds.
I would need some more information before accepting that an area of artificial tree covering 8 hectares would produce the quoted level of power output. It would depend, greatly, upon the actual location on the Earth and the existing climate. A cold Northerly wind would put the mockers on it, I feel.

#### daveshorts

• Moderator
• Neilep Level Member
• Posts: 2583
• Physics, Experiments
##### Creating electricity from global warming
« Reply #29 on: 29/05/2008 15:43:46 »
The 8.5ha is the minimum possible area at the equator if all the sun's energy falling onto those 8ha was used to evaporate water and then all the water was condensed again (with some mysterious immense heat sink) 250m up.

As a comparison 8ha of 12.5% efficient solar cells on the equator would produce nearer 80 000*30W/m2 2.4MW - I think rather better than 20kw, and probably also far cheaper to build as they don't involve thousands of 205m tall 'trees', with giant glass domes at the top, and huge pumps to move cold seawater in order to cool your condensing surfaces which would probably use more energy than your turbines produce.

#### lyner

• Guest
##### Creating electricity from global warming
« Reply #30 on: 30/05/2008 11:51:14 »
My original point about the system that trees use is that it does a particular job excellently. The available power just suits the requirement and doesn't allow for TV, heating or lighting.

#### The Naked Scientists Forum

##### Creating electricity from global warming
« Reply #30 on: 30/05/2008 11:51:14 »