Future Energy Sources 1.2 Solar Energy

3. Generate electricity by thermal means

Trough_Tower_&_Dish_System_Overview ...........And ...

I don't know what its called but Ive seen it on a sience program onnce. They covered a very large area with a black plastic sheet (apx 6' off the ground). In the centre of this "tent" the surface of the sheet was raised (like a funnel) ending in a tall tower.In this tower there was a turbine. As the air was heating up it created a drag towards the center and all of that air speeded up as it entered the tower spinning the turbine generating electricity. As the sun sets and the air cools down the whole process turned around and made the turbine spin the other way almost the whole night long. Problem with this you need a very large surface area to be covered.. The desert is a perfect location for a plant like this, but it is quite remote...

Hi Uncle Sarel, if there is one thing we have in S.A. its space. One just has to look at the Karoo. I agree with the fact that these areas are somewhat remote, but if one looks at the cost of piping crude from Durban to the Natref refinery, the refining process involved in generating H.F.O and the further shipment of FO 150 to the power stations one could look at the cost beginning to balance out somewhat. If one takes a look at Zim, and the inability of that country to supply power to it's major city and of course the productive farm land that is no longer productive ( we all know why, but I will not go into that right now) one would think that any one of the systems shown in the links could be viable to ease the power black outs that ZESA effects to reduce the energy bill.

There are plans to build a solar_tower like this near Mildura in Australia. I would however add that I have not heard of these plans prior to a week ago and since then have been unable to find anybody else that has heard of it.

The other thing is that to my knowledge nobody has ever built any structure this tall let alone a concrete one so I am somewhat skeptical of their claims.

This project was build as an experiment and shown on television a few (about 10 years ago) on a program called "beyond 2000" A large area (several Sq miles) was covered with a black plastic sheet. Gum poles were used to suspend the whole sheet (large greenhouses are build in a similar way) The footage was real, no scale models or computer generated graphics... It really made a huge impression on me, especially the fact that at night time the turbine slowed down, stopped and then started spinning the other way, lasting almost until sunset the next day... Although I am doubting this now just thinking about it...Can the cooling down of such a structure really suck enough air downwards through the chimney to power the generator the same way as day time, and if so, can it last for the whole night?

"Can the cooling down of such a structure really suck enough air downwards through the chimney to power the generator the same way as day time, and if so, can it last for the whole night?"

Initially my gut feeling was that the answer was NO! However I decided to think about it a bit more and here is what I came up with.

There are two parts to the operation of such a tower. Firstly there is there is the incoming solar radiation that powers it during the day and the radiation back to the atmosphere and ultimately into space that happens all the time. If you think about it the two must over a long period balance otherwise the temperature would not be stable as it is.

During the sunlit time the area under the covered portion will heat up while the incoming radiation is greater than the loss to the atmosphere and generate power proportionally to the difference between the incoming and outgoing radiation. This will happen some time after dawn until some time before sunset. On the other hand the system will work the other way for the remaining time.

Now the energy that is received during the sunlit hours must be equal to the energy that is reradiated over the whole day therefore we can say

Energy_Sun = Energy_Radiated

Power_Sun = Energy_Sun ÷ Hours_Daylight

Power_Radiated = Energy_Radiated ÷ 24 = Energy_Sun ÷ 24

Now the if the tower were 100% efficient the power we could get from it during the daylight and night would be

Power^_Day= Power_Sun – Power_Radiated

Power_Day = Energy_Sun ÷ Hours_{Daylight -} Energy_Sun ÷ 24

Power_Night = Energy_Radiated = Energy_Sun ÷ 24

Now over a year if you are at sea level the hours of daylight will be exactly the same as the hours of darkness therefore we can say that

Hours_Daylight = 12

And our equations now become

Power_Day = Energy_Sun ÷ 12 - Energy_Sun ÷ 24

Power_Day = Energy_Sun ÷ 24

Power_Night = Energy_Sun ÷ 24

Therefore in theory over a year with a 100% efficient collector it should theoretically be able to get the same amount of energy out of the system at night as it would during the day. However we are not talking about a 100% efficient system and the radiation back into the atmosphere isn't constant over the day as I have assumed but it would be possible to get somewhat similar amounts of energy from the thing at night as it would during the day.

I would suggest that remote power generation potential has great value in many areas not served by "the grid".

Yes, but what feeds the grid?

The real reason for the question is that the actual energy production system can't be extended till the end of time. It produces waste under different forms.

What Masu tries to build up is a decent list of energy producing and storage systems so that those who take the decisions have a choice.

Are PV cells energy effective?

I once got the remark that the amount of energy needed to make a PV cell is more than the energy that it will generate over it's lifespan.

When you look at the size of the installations, the amount of base material that goes in and work that needs to be done to get it working.

Has someone this calculation?

It is the same problem as with the H₂ hoax: first you must use an awful amount of energy to make H₂ from water and invest enormous amounts of money to store it. (look at the ugly $500000,- environmental "neutral" house) Then it can be used as a fuel in fucking expensive fuel cells (those membranes used are not comparable with kitchen foil).

Again a vote for CHP and thermal storage: keep on using traditional burning fuels to make your electricity but don't waste what Carnot can't use.

A lot of the ideas that are promoted now are a bigger problem than the oil and nuclear business.The amount of energy needed and nature consumed to create the installations is much more than the damage done when it would have been a traditional system.

Heat tubes should also be included under using 'Solar Energy'.

A heat tube is a sealed pipe that has a reduced atmosphere pressure. The pipe also has a medium that will boil at this reduced pressure at a relative low temperature. The medium might be water, glycol, alcohol, or even propane. The tube is mounted in such a manner that the hot end is lower than the cool end. The liquid is heated, changes into a vapor, rises to the cool end. It gives off the excess heat and changes back into a liquid. The liquid then runs back down the tube, is reheated and the cycle continues as long as the hot end is hot enough to boil the medium and the cool end is cool enough to condense the vapor.

Heat tubes are used to transfer heat from fireplaces, use excess heat from a boiler to preheat combustion air, as well as many other things.

The sun's heat could be concentrated on the hot end of a series of heat tubes using mirrors and then the heat harvested from the cool end.

The heat that is harvested could be stored in a large water tank, a large volume of cement or rocks and used at a later date.

Perhaps, using the correct liquid and a properly designed tube, the vapor could also be used to drive a turbine to turn a generator?

Use algae as the collector/converter mechanism for solar conversion (capturing/recycling) of CO₂ emissions, nutrients, heat (waste), water (recycled) to bio diesel, ethanol, and feed stock .

Reactor size per Mega watt of industrial emissions:
gas fired ~ 4-5 acres/Mega watt
coal fired ~ 10-12 acres/Mega watt (due to the higher emissions of coal)

Annual Yield/Acre estimates for closed reactor: biodiesel 8k gallons +plus+ ethanol 5k gallons +plus+ 70 tons feed/fertilizer (This is a mid range estimate … theoretically biodiesel yield might be as high as 15k gallons per acre year).

The yield for open solar ponds is about 20% of the yield of enclosed solar ponds (reactors) since the pedigree of the high yield algae can not be maintained.

Examples of enclosed reactor yields, a gas fired power plant (or other industrial application), on an annual per megawatt basis, could be about 32k gallons of biodiesel +plus+ 20k gallons of ethanol +plus+ 280 tons of feed/fertilizer stock … while …

a coal fire facility could be expected to be about 80k gallons of biodiesel +plus+ 50k gallons of ethanol +plus+ 700 tons of feed/fertilizer stock from per mega watt.

see:
http://cr4.globalspec.com/blogentry/1118/Future-Energy-Sources-3-2-Biofuels?frmtrk=CR4digest