Solar thermal - collection and storage questions!

[adam_j_bradley]

I'm currently building up a 1kW Tesla Turbine and need some steam

Armed with very little knowledge about making a liquid hotter I come to you for advice!

I have the following requirements:
- I'm looking to generate about 80PSI steam, not sure about flow rate yet (and yes, as I typed this I realise this is a crucial element, I will loop back to this thread as soon as I know more)
- I would like to be able to storage surplus energy collected during the day to turn the turbine at night - "he who does not learn to store will have no power after 4"
- I want to use my roof for collection

My initial thoughts were to:
- Use a lot of evacuated glass tubes ($1-4$ wholesale)
- A working fluid other than water (to allow the system to, unpressurized, heat the working fluid above 100C/212F)
- Use a heat exchanger to make enough steam

Thoughts?

Thanks in advance!

[russ]

Not enough heat to do you any good with vacuum tube collectors.

You would most likely have to use concentrated solar - one method or another.

Then you have a storage problem - molten salt is used utility scale for limited storage but 6 hours or so is the longest period I have read about.

With the pressure this will be quite a system! Not easy

[Mike90250]

- I'm looking to generate about 80PSI steam, not sure about flow rate yet (and yes, as I typed this I realise this is a crucial element, I will loop back to this thread as soon as I know more)

Yikes ! I'm glad I'm not in your neighborhood. Best if you look up "steam boiler explosions" and what sort of insurance and inspections you will need.

Do you know what temperature you will need to get 80 PSI ?

http://www.unene.ca/un702-2005/text/section04.pdf

A regular household pressure cooker is only 2 or 3 PSI, and that's enough to mess up a kitchen.

Run away, run away....

[adam_j_bradley]

Not enough heat to do you any good with vacuum tube collectors.

You would most likely have to use concentrated solar - one method or another.

Then you have a storage problem - molten salt is used utility scale for limited storage but 6 hours or so is the longest period I have read about.

With the pressure this will be quite a system! Not easy

Trying to get my head around the numbers.

Aim/Background
- Aim to run turbogenerator 24 hours a day
- To heat 1 ml of water takes 4.18 Joules per degree C, the specific heat capacity. 1000 watts is 1000 Joules per second.

To drive the turbine (presumably with no energy left over) I need 6 m2 (64 sq/feet) @ 1kW/m2 = 6kW

I assume were raising the temperature of a small amount of water per second to 100C from about 20C, an 80C increase, quickly enough to drive the turbo-generator at a consistent pressure. With 6kW we have 6000 J/s over 100 ml/s (guess). I don't know the flow rate.

- 1ml. 4.18 * 80 (C) takes 334J
- 100ml. 4.18 * 80 * 100 takes 33,440J

So from "cold", we can start boiling in 5.5 seconds @ 6000J/s, and maintain a steady source of steam with 6kW of collectors giving us an efficiency of 16%. Not bad, but I'd prefer 30% (to find out why read on!)

If I wanted to make power 24 hours a day I'd need to collect a lot of energy to cover the 18.75 hours a day the sun isn't shining.

6000J/s for 67500 seconds gives 405,000,000 J/day which means I need to collection an additional 67kW!

Evacuated tubes do about 0.8 kW/m2 (I think) which means 83 m2 of collection area. I need a bigger house.

Thinking I might supplement with LPG

Sincerely,
Adam

[adam_j_bradley]

I'm beginning to think a "working fluid" (not water) and a heat exchanger to either water or a refridgerant of some description might be better.

Sincerely,
Adam

[netttech]

I'm beginning to think a "working fluid" (not water) and a heat exchanger to either water or a refridgerant of some description might be better.

Sincerely,
Adam

Seems like I read someplace (online), the Brits had a parabolic trough generating plant in the Middle East (1920s??). I believe it mentioned they heated oil to generate steam (I think).

Where you are finding Evacuted tubes for 1-$4? Since summer is winding down, I am back to pursuing my solar thermal project. Incorporating ETubes I may want to consider.

Thanks
Jeff

[adam_j_bradley]

Try http://www.alibaba.com/product-gs/30..._tube_for.html

Sincerely,
Adam