Australian Solar Thermal ideas get to 2020 summit

[LMagic007]

Originally Posted by SgtThursday

Guys,

Work out the required overall system efficiency to deliver 5 kWh of electricity 24/7, PLUS air con, PLUS hot water from 7 tube arrays measuring 2m * 2.4 m each in Brisbane (avg insolation 5.25 PSH).

Compare with published efficiencies for other solar thermal systems (eg. parabolic trough concentrators).

Then decide whether the kW vs kWh question is even worth quibbling about.

SgtThursday

Hi Sgt , Welcome to the forum.

Don't you mean 5 kw 24/7 and not 5 kwh 24/7 ?

As I understand from the web site, the system generator is rated at 5 kWe and is said to produce 120 kwh per day, presumably from the captured thermal energy.

As discussed, the site though appears a bit sloppy and inconsistent in its use of terminology. That's the main point raised.

I might say though, that efficiency alone, is not the only factor that needs to be considered when implementing a design. Ease of operation, reliability and cost of maintenance and repairs etc.. are also key factors.

I can't comment further on the system itself because I am not privy to its specs. I understand they are releasing the product to the market this year.

It's not really my area and I might add though, that I do think their figures appear very optimistic, but without knowing all relevant information, it's difficult for me to draw a firm conclusion.

With that said, I'm not sure where you got your figures from. I could not see reference to them on the web site.

Can you please elaborate more specifically what you are trying to convey.

Thanks

[SgtThursday]

Oops, I made the kW / kWh mistake myself!

Of course I meant 5 kW * 24 h, or 120 kWh/d as they claim.

Their website suggests a 5 kW system needs 7 banks of tubes, each measuring 4.8 sqm, so 33.6 sqm in total. Brisbane gets an average of 5.25 peak sun hours a day. One peak sun hour is equivalent to 1 kWh per sqm of sunlight. So that 33.6 sqm footprint should collect 33.6 * 5.25 * 1 = 176.4 kWh/day. To achieve the claimed export of electricity alone, the whole cycle efficiency (sunlight energy in to usable energy out) must be 68% - about 2-3 times what the most efficient parabolic trough solar thermal collectors can deliver. That's before you even consider the promised additional benefits of air con and hot water... so let's do that as well. The website distinctly shows a Rotartica absorptive chiller for air con (really only half an AC but let's press on), checking the Rotartica website shows that one unit needs a further 7.2 kW of thermal energy input. If we ran that unit for 8 hours that would then be an additional 57.6 kWh per day... add that to the promised 120 kWh electrical output and you get 177.6 kWh. Hot water? 200 L a day will chew up another 5.8 kWh to heat by 25 degrees (in a perfect heater) so now we're up to 183.4 kWh per day... enough?

Earlier I compared the Thermogen efficiency to the best possible parabolic trough generation efficiency, which is about 25%. These concentrate sunlight into a central column which reaches a high working temperature (400+ degC). Evac tubes have a much lower maximum temperature (stagnation temperature ~ 250 degC but water can't get that hot without boiling, at 10 bar (pressure rating of most mains pressure tanks) it only reaches 180 deg. This is low-temperature stuff and thermal efficiencies for a heat engine decrease with operating temperature. A more realistic full cycle efficiency for this type of application would be 7-10%. Maybe 15% if everything works well but beyond that I think we're in dreamland.

The long and the short of it is:

I think the claims of the Thermogen website are at best hopelessly optimistic, and at worst fraudulent.

[LMagic007]

Yes the web sites figures are concerning. Having said that it may depend on how you interpret the information.

This heated water is then stored in 1000 litre insulated tanks at 150-200°C. These tanks are a solar energy storage system designed to store enough energy to provide the following services for up to three days without sunshine:

Thermogen - Home

i.e. 3 days of energy storage to provide the services mentioned. But the article could be more clearly explained I think. Anyway I'm not committing myself to a firm view at this stage, until I have more detail.

[SgtThursday]

Hmm, I didn't even look at the storage claim... so let's do so.

1000 L of water = 1000 kg
Heat capacity of water = 4.18 kJ/kg.degC
Max temperature 200 deg C
Ambient temperature 20 deg C (let's say ~ avg for Brisbane?)
Temperature difference = 180 deg C
Max stored heat = 1000 * 4.18 * 180 = 752400 kJ = 209 kWh
209 kWh / 3 days = 69.7 kWh/d
Promises made ~ 180 kWh/d (electricity + AC + hot water)

Even ignoring the AC and hot water and using the "bankable" 120 kWh/d electricity we'd be at a substantial deficit... and that's if we could assume 100% efficiency converting the stored heat energy into the other useful forms... which is also impossible if we want to obey the laws of thermodynamics.

Let me know when you're ready to commit to a firm view.

[LMagic007]

Originally Posted by SgtThursday

Hmm, I didn't even look at the storage claim... so let's do so.

1000 L of water = 1000 kg
Heat capacity of water = 4.18 kJ/kg.degC
Max temperature 200 deg C
Ambient temperature 20 deg C (let's say ~ avg for Brisbane?)
Temperature difference = 180 deg C
Max stored heat = 1000 * 4.18 * 180 = 752400 kJ = 209 kWh
209 kWh / 3 days = 69.7 kWh/d
Promises made ~ 180 kWh/d (electricity + AC + hot water)
Even ignoring the AC and hot water and using the "bankable" 120 kWh/d electricity we'd be at a substantial deficit... and that's if we could assume 100% efficiency converting the stored heat energy into the other useful forms... which is also impossible if we want to obey the laws of thermodynamics.

Let me know when you're ready to commit to a firm view.

On the surface and in respect of some basic calculations, as indicated it does look rather impressive, to a point of almost too good to believe. Beyond that however rather than bandy about hypothesis ad infinitum, I suggest the only real way you will have absolute certainty, is knowing exactly what they are proposing. I haven't been back to review their site since my initial brief overview. Other things to do I'm afraid.

The information on their site seems to me to be somewhat ambiguous and the use English on the web site to me at least, makes interpretation subjective in some areas. This aspect also raises some concern, thus I would equally not want to be too presumptuous about their intended meaning in every aspect conveyed. Further more, the errors on the site make it difficult to have great confidence in the information presented, thus even deriving calculations from potentially erroneous and poorly written information, might likely yield misinterpretation and error. I would not want to make any assumptions about their intended meaning. We sited examples of basic errors and that weakens ones confidence in the information and how best to interpret it.

I do sometimes wonder if the site was typed up by the office clerk or someone. Another example, they refer to "SSHCMV" when I wonder if they meant SHCMV ( Super Heat Conduction Metal Vacuum ) i.e. with one less "S". I guess it might be a super super version.

I also note they use the word "tanks" in their description, although you only factored in 1 tank in your calcs. Again an example of interpretation of their language. It could be, that they mean more than one tank. I just dont want to jump to conclusions at this stage.

Thus in respect of this, I would not see a great deal of sense committing to a view, until they have released the product and the real world results are in. I'm happy to watch and see for the time being, but by all means follow it up further, perhaps with the developers, if interested.

[SgtThursday]

I don't think there is much room for assumptions about the intended meaning of several claims. This one in particular is pretty unambiguous (except for maybe the words "up to"?):

"Property valuers have estimated that the Thermogen system will add up to $180,000 to the value of a home and the extra income from power generated will supply a revenue stream of up to $20,000 per annum at current rates which will pay the mortgage on most homes in Australia."

I am not talking about small errors of assumption. I am talking about huge errors of concept. In every calculation I've applied the benefit of the doubt thickly with a trowel and even then I think the claimed performance is still an order of magnitude away from reality. It is simply not fair to lure the Australian public with $x0000s and $x00000s like this.

You are right, though - much better to approach the manufacturers than continue this discussion here. I shall continue to conduct my own research and investigations to help satisfy my own judgement elsewhere.

[Windguy]

I do see some minor faults as well where they have some similar ideas to mine, but my ideas were based upon them being large to massive otherwise the mechanical resistance will be a big killer in efficiencies.

Solar thermal is already established as big plants. But there is a reason we use P.V's instead on a house.

Why build it small though is because the general public is not as scrutineering as major companies and governments.

[LMagic007]

Yes though its clear from the site the use the word tanks plural and not just one tank and if you have enough tanks and enough collector area you can store much more energy than would be provided for in calculations made thus far in this thread. It really does seem to be a question of how you choose to interpret their language. I'm not going to comment on financial claims, but it does all sound rather impressive to a point of questioning its authenticity. Beyond that though I doubt we will find the true answer here, though in the final analysis, I doubt it would get past the eyes of experts, when it hits the ground running.

This heated water is then stored in 1000litre insulated tanks at 150-200°C. These tanks are a solar energy storage system designed to store enough energy to provide the following services for up to three days without sunshine:

Thermogen - Home

[SgtThursday]

Originally Posted by Windguy

Why build it small though is because the general public is not as scrutineering as major companies and governments.

I think if someone promised to pay off my mortgage, but actually struggled to pay my electricity bill, I'd be pretty scrutineering.

Particularly if I paid tens of thousands of dollars for the privilege. A bank of 18 CPC Sunplus tubes is currently $2400, so seven of these is almost $17k - without any other miraculous machinery.

Big Solar Thermal works and works well. Small PV works and works well. Yes, push the envelope, but as Judge Judy says "don't p*** on my leg and tell me it's raining".

[SgtThursday]

[quote=LMagic007;241802]... and if you have enough tanks and enough collector area you can store much more energy than would be provided for in calculations made thus far in this thread

Of course you can. But the site is clear on what it promises - all that from 7 tube banks.

No more oxygen to this. I'm out.