The absorbtion cycle also operates at a COP of about .8 to 1.0 tops. Given the temperatures needed to drive the absorbtion cycle, your thermal collector will only be operating in the 20-30% efficiency range at best and that's using a vaccum tube, flat plate technology won't even work. Also, it would be nearly imposibble to store the necessary thermal energy to drive the system when the sun isn't shining although gas is an excellent backup. You could also build what is often referred to as an "ice battery" where you store your cooling capacity in some form of phase change material, typically a water/brine or water alcohol mixture to lower the freezing point. There is a lot of promise for this approach but it still works better with vapor compression cycle refrigeration.
As an engineer who specializes in both refrigeration and solar I have been working on this problem for years. I've even built both Peltier and absorbtion systems for experimentation and none of them worked very well.
When you consider a vapor compression systems typically provide a COP of 3.0 right out of the box and can be easily tricked out to deliver COPs as high as 5.0 and modern photovoltaics have efficiencies in the 15-20% range with electricity realively easy to store,(as compared to thermal energy), I have concluded that photovoltaically driven vapor compression is hands down the easiest, most efficient approach to the problem of refrigeration and have built numerous systems that worked well.
While driving your compressor with DC does take out some of the losses associated with DC-AC inversion, the DC systems are much more expensive and it is a lot easier and more versitile to built a 120V micro power system. Once you have constructed a small photovoltaic micro power system you can also plug other things into it besides your refrigerator if you build it with some latent capacity. That's pretty much what I have on the Arc and it works very good. I have more than enough power storage for refrigeration and other house power requirements but can't quite run my A/C all night,(yet). However all I need is more money for batteries. Storing the energy for when the sun is not shining is still the big challenge and that's where the "ice battery" approach holds a lot of promise in my opinion.
Carter Quillen
From: Kevin Pemberton <pembertonkevin@gmail.com>
To: electricboats@yahoogroups.com
Sent: Thursday, October 18, 2012 4:03 PM
Subject: Re: [Electric Boats] Re: O/B Gear Ratios? + 12V Accessories
To: electricboats@yahoogroups.com
Sent: Thursday, October 18, 2012 4:03 PM
Subject: Re: [Electric Boats] Re: O/B Gear Ratios? + 12V Accessories
For the experimenter a look at adsorption refrigeration using activated
carbon fibre and methanol may be an option on an electric boat. The main
reason this is so is a solar panel (not PV) a meter square would be all
that is needed to keep your food cold. At this time I think that it is
a DIY project though.
Kevin Pemberton
On 10/16/2012 02:32 PM, Carter Quillen wrote:
> A vapor compression refrigeration cycle has a coefficient of performance in the 3-5.0 range. That means for every Watt you put in, you will move between 3-5.0 Watts of energy out of the control volume, (refrigerated space).
>
> A Peltier device has a COP between .5-.9. Clearly the vapor compression system is the better choice for efficiency.
>
>
> ________________________________
> From: mattelderca <mattelderca@yahoo.ca>
> To: electricboats@yahoogroups.com
> Sent: Tuesday, October 16, 2012 8:49 AM
> Subject: [Electric Boats] Re: O/B Gear Ratios? + 12V Accessories
>
> In regards to refrigeration, lots of people have made their own.
> There are some very efficient DC compressors out there to employ in this. 12 to 24 volt BLDC compressors are available that can be used in just about any size refrigerator/ freezer. Commercially available ones are usually around 14 cubic feet. These refrigerators will run 24/7/365 off of any 150 watt solar panel and matching battery. Current consumption at 12 volts is only around 2.4 amps at full load.
> In a well insulated enclosure these would be much more efficient than a junction device. And they are available for alternative/HC refrigerants as well.
> More info below,
>
> http://www.danfoss.com/Products/Categories/Group/RA/Compressors/Direct-Current-Compressors/b44e7573-473b-4dba-90c2-431ffccf0b9c.html
>
> http://www.masterflux.com/products/cascade/
>
> --- In electricboats@yahoogroups.com, Craig Carmichael <craig@...> wrote:
>> Thanks for the responses!
>>
> SNIP
> I'm really in this to create renewable energy things myself*,
>
> SNIP
>> Cheers,
>> Craig
>>
>> * As an example of how one thing can lead to others... people told me
>> that Peltier elements were too inefficient for anything more than a
>> small camping cooler -- not worth thinking about for a fridge. If I'd
>> taken that advise, nothing would have been achieved. But here's three
>> things that have arisen from the experiment:
>>
>> -- I'm the only person I know who has ever made a home made fridge.
>> It does use 1/2 as much electricity for only 1/3 the cubic space of
>> my regular fridge in spite of 3" of foam insulation - but it works
>> and it's 12 volts. And with a freezing/melting ice chest to store and
>> release coldness, plus when I've done the "smart control", it'll run
>> mainly in the day when the solar panels are making the electricity.
>> If I hadn't explored it, the ideas for making it practical and for
>> reducing battery energy storage requirements to run a fridge wouldn't
>> have come to light.
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
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