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PostPosted: Apr 18th, '16, 19:47 
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I read that solar panels decrease in efficiency when the temperature is over 25. This would be fine for western countries, but for the tropics they would always be under performing.

I was wondering what research/new technologies are emerging for generating energy from the hot tropical sun? I imagine there would be possibilities but not much is being done as industrialized countries are generally temperate or cold.

In 40 (100+) heat, I imagine it wouldn't be too difficult to heat enough water for a small steam engine connected to a tiny pump?


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PostPosted: Apr 19th, '16, 06:40 
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Solar panels are rated at 25C, but the temperature coefficient of the cells means that as the temperature gets higher, the output gets lower. It's a continuous decrease, there is nothing magic about 25C, other than that was chosen as a convenient temperature for rating purposes. Output is higher when the cell temperature is below 25C.
40-50C air temperatures in summer are very common in large areas of the world, Australia, Africa, US etc- high temperatures are not confined to the tropics, and that translates to cells temperatures in the order of 65-85C, it depends somewhat on wind speed, humidity, solar radiation intensity etc. Panel output might be 20-30% down on rated in very high temperatures, but using a panel that has more output than the absolute minimum required easily solves that problem.

A steam powered pump will be vastly less efficient, less reliable and unable to operate at night than a solar panel + battery for powering a pump.

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PostPosted: Apr 19th, '16, 08:00 
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Thanks for the reply. I wasn't necessarily suggesting making a steam engine, just trying think outside the box and wondering if there weren't other options, especially for developing countries which struggle with the technology and govt support necessary to make it work.

In the summer it's 40 by early afternoon. Throughout the year we're lucky if a single day manages to remain below 30.


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PostPosted: Apr 19th, '16, 10:51 
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Plachon wrote:
In the summer it's 40 by early afternoon. Throughout the year we're lucky if a single day manages to remain below 30.

So you've got 3 choices really...

1. you can choose your plants and fish from those that do well in your environment,
2. you can change your environment to better fit your choices for fish and plants,
3. or you can try to get by with plants and/or fish unsuitable for your environment.

#1 is probably the least expensive and least stressful approach. #2 requires more resources and involves more complication. #3 will likely result in stressful failure.

So some research into what others do in a similar situation could provide secrets to success for you.

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PostPosted: Apr 19th, '16, 15:49 
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Thanks. I was thinking in terms of creating energy, rather than fish and vegs.


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PostPosted: Apr 19th, '16, 16:23 
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Plachon wrote:
I was thinking in terms of creating energy...


If only it were that simple ;)

The 1st Law of Thermodyamics says that energy can be neither created nor destroyed (conservation of energy).

Harvesting energy is another matter, and solar panels are likely to give you the best results and value of any of the available options. You can purchase PV panels for under $1 per watt these days.

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PostPosted: Apr 19th, '16, 16:51 
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OK, not 'create energy', but harvest it in ways other than solar electricity. For example solar hot water systems don't create electricity from the sun, they just use the heat. I know molten salt is used to store heat, then create electricity. So I'm wondering if their are other technologies that being researched?

I can't help but think that a lot of renewable energies are suited to cooler climates, because that's where their designed and that's where the market and money are. Some wealthy countries get hot, but it's relatively small compared to developing countries.


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PostPosted: Apr 19th, '16, 17:19 
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Producing molten salts is not a matter of hot ambient temperatures, and neither is producing hot water- they are both proportional to the intensity of the solar radiation. It is simple to produce boiling water with air temperatures near 0C. - it just requires clear sunny skies.

The tech for producing molten salts and steam via solar energy is not suitable for small scale energy production, such as you might need in a typical aquaponics system.

Wind power can be an economic solution if you live in a particularly windy area- unpleasantly windy to be outside in, but again, it is not really suitable for small scale energy production.

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PostPosted: Apr 20th, '16, 09:10 
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Thanks. It's more general than AP related. In Southeast Asia they are very slow to develop renewable systems. Solar is still way too expensive, there is not the awareness.

I see they are using the molten salts in warmer places (Nevada, Arizona, Spain), I wonder if they build them here? Southeast is probably well suited to these systems, but I don't see them being developed.

Another use of salt storage is by freezing and using it to cool, this would be interesting for AP and for the tropics. An Australian has won a prize for designing Low-Cost Molten Salt Energy Storage Solution. I wonder how much electricity is used to freeze the salt and how it compares with refrigeration methods?


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PostPosted: Apr 20th, '16, 10:51 
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Nevada, Spain etc are chosen for electricity production via concentrating the suns energy to produce molten salt because they are sunny, not because they are hot. Clear sky is what is important, not air temperature. The tropics tend to be fairly cloudy (in general, but varies depending on location), so are not really suited for the lowest cost of energy production vs somewhere sunny in the desert.

Saline solutions (salt itself is already "frozen" at room temperature) can have a freezing point down around -20C, (lowest is -21C at 23% salt) but you still have to use refigeration to get it there. I use plastic bottles full of frozen saline water when transporting frozen food, particularly trout, as it melts at ~-20C and keeps the contents colder than regular water ice blocks. Commercial ice blocks (usually blue plastic in Australia) probably have a saline or other similar low MP liquid in them too, rather than just water.

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PostPosted: Apr 20th, '16, 13:37 
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Its rather a shame more development hasn't gone into stirling engines (mechanical energy). They only require a temp differential not a phase change.
There again I like steam but the last time I remember it being done vaguely right (SAAB 9 cylinder wobble plate engine) the price of fuel went down and *frack* development (or something like that did it) :)
I have developed a large degree of cynicism when it comes to the industrial world developing alternate energy sources.


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PostPosted: Jul 17th, '16, 15:52 
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Hi Plachon,

That's a really unique perspective! And it sounds worthy of exploring - harnessing not just sunlight but the ever abundant heat in the tropics! I've just been getting to know more about solar power - actually more of its current limitations. I live in Singapore, a small Asian country in the tropics, and from what I learnt, current solar technology, even if placed in all the available land, is far from able to generate sufficient power for the country.

There is currently a method that taps on the non-visible range of light from the sun, but is still very new - bacteria photosynthesis which uses UV rays and infrared rays I think. http://www.binghamton.edu/inside/index. ... lar-panel/
Perhaps this helps us harness more than just the regular sunlight we see?

But what you said about heat - I don't know of any methods that retain heat from the sun. Hope to hear what you can find out! This might be very relevant in my region, where temperatures are always above 30 degrees celcius.


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PostPosted: Nov 9th, '16, 10:36 
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FF, that's an interesting perspective, as Singapore is by far the wealthiest country in SEA.

Below is a pic from a Thai army base, they are using hot water to create cool water, which is then used for cooling. I'm not sure how the system works, except that it's complicated. I was told to be feasible the system needs to be at least 30 tonnes - although I'm not sure what exactly they are weighing.
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solar-army.jpg [ 50.92 KiB | Viewed 2755 times ]


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PostPosted: Nov 9th, '16, 20:14 
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Not weighing anything, it's one of those crazy units they use in the USA, when taking about air conditioning capacity.

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PostPosted: Nov 9th, '16, 21:47 
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Gunagulla wrote:
Not weighing anything, it's one of those crazy units they use in the USA, when taking about air conditioning capacity.

Yep, this 30 ton Industrial Air Conditioner Unit weighs 4900 lbs (2223 kilos)...

Ohio Rental: 30 TON AIR CONDITIONER

Image

Why Is Air Conditioner Capacity Measured in Tons?
Quote:
A 4 ton air conditioner is one that can remove 48,000 BTUs of heat per hour from the house. For most people, though, 4 tons means 8000 pounds. (A BTU is a British Thermal Unit, approximately the amount of heat you get from burning one kitchen match all the way down.)

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