Running an Air Conditioner From The Sun - The Holy Grail

Discussion in 'Boat Design' started by CatBuilder, Mar 6, 2012.

  1. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Cat, I have to stand corrected here. Found several tech sheets for LiFePO4 batteries which claim 1500-2000 cycles @80% DoD. I see that several papers show big variation of that data with the temperature, so I'd take that into account to stay on the safe side.

    However, the real-life behaviour of my mobile phone (and my laptop too) remains an issue to consider, imo...

  2. CatBuilder

    CatBuilder Previous Member

    I definitely appreciate anyone helping me to keep from a 400% error or $11,000 mistake. :D

    Here are some links. See this LiFePO4 battery manufacturer:
    (scroll to "characteristics"),2129.0.html

    It's pretty much everywhere you look if you Google it. :D
  3. CatBuilder

    CatBuilder Previous Member

    You may be using something different in the iPhone or charging may not be ideal or something. Also, most laptops run on Lithium Ion batteries, not LiFePO4. I think the iPhone is also Lithium Ion. Those batteries are the ones that can catch fire. The LiFePO4 batteries are a different chemistry all together and were developed so electric cars did not just catch fire randomly. ha ha ha

    If they are used properly and carefully, like in the electric cars, they are incredible batteries.

    I dare say they change the game on those electric propulsion threads. People can get more power with less weight than ever out of these.

    I am very glad you are paying attention to the numbers and looking to correct them... much appreciated.
  4. CatBuilder

    CatBuilder Previous Member

    I don't think you understand my market. My clients will not do any work. They are on vacation and paying many thousands of dollars a week to be there. Also, if you read my posts, I don't dock the boat. This approach works for cruising, not for charters. Thank you though.
  5. Stumble
    Joined: Oct 2008
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    Location: New Orleans

    Stumble Senior Member


    I am not at home, and can't run the numbers, so no comment.

    But I am worried that your weight and power density numbers are for individual batteries, and do not take into account wiring, controllers, and the like. It would be interesting, and fruitful to see the size weight and power of large battery packs of this type.

    I would also be curious about the effect of a bad cell or two, and the failure rate of the individual cells.
  6. CatBuilder

    CatBuilder Previous Member

    Those are good points to consider. I will ask the experts (an electric car forum) about the practical hookup of the battery bank.

    Or... Just find a prius or volt or other similar car for sale at a dealership and have a look?
  7. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    You want AC and you want solar power, and want comfort. If you want it to work, you have to be on an energy budget. That includes lighting, refrigeration and then cooling. Something else to look at is propane powered Air conditioning and Refrigeration. It is more efficient than electrical because their is no conversion. People don't realize that when you take electricity from a solar panel DC, and then typically reduce to 12volt, then store it in a battery, then back to AC to power a motor, you are losing 20%-30% of the energy. If you use a diesel generator, there is still a sizable percentage lose because of all the conversion. Most efficient might be Compressor on a belt to small diesel generator. So a small diesel serves to heat water, run AC compressor, cold plate , and keep dc charged. This is an old technology, but it works and it is hard to beat. There are ready made system for sale, and are already soundproof.

    I personally have an 11,000 BTU AC hook to inverter, and I can run it for a few hours at night, but my two 180 watt solar panels can charge then up for the next night in one day. But honestly at anchor, not precluding mosquitoes, I have the ventilation of boat setup that is not a problem. I have box fans setup as ceiling fans over beds. Running these on Low is more than sufficient to keep us cool.

    How you design boat is very important to cooling. My bedroom are all below deck, below an area that receives very little sunlight. Something as silly as the color of your deck, can mean tremendous differences in cooling. I also have exhaust fans in bathrooms to keep humidity out of rest of boat. In other words I am looking at it from a Holistic approach because of limited power.
  8. CatBuilder

    CatBuilder Previous Member

    Please see my add on questions and comments below...

    Sort of. The proper direction would be cooling, then refrigeration, then lights, when designing the electric budget. We are starting in this thread with cooling. The rest will be 10%-20% max of the energy budget.

    Absolutely. I would love to run the entire boat on propane, including the outboards. However, propane isn't available dockside. Makes it problematic for filling and the tanks would be like the ones you see outside of a house. Not something you can refill without a truck.

    Can you show me a link to a propane air conditioner? I have been looking for a long time. If you could show me a link, it would be very helpful. That was what I was looking for in the first place.

    Right. Running a diesel generator or gasoline generator is the fall back plan. To listen to a diesel engine running all day and night all the time. It's not ideal, but it is the plan if nothing else works. Efficiency isn't an issue with solar. You don't need to be efficient, you just need to be able to keep up with demand, since there is no cost to running the system. You can have plenty of losses, but they don't actually matter. All that matters is the electricity coming out the end of the system is enough and the battery banks are not cycled to hard. That's why it's so much easier to use solar. Also, no labor spent running the diesel engine, doing oil changes, fixing the engine, etc... With the solar, as you know from your boat, it just works - all the time - no input from the crew.

    Yeah, that's about what I had on my last boat. Ran everything without any other power for years on end. I didn't use an air conditioner though. It ran refrigerator, freezer, lights, computer, phones, etc...

    But, you are talking about what, 360 watts of solar you are using and even that allows you to run the AC for a few hours? That's pretty cool. (no pun intended there!) :) I'm talking about 3,360 watts of solar, or roughly 10 of the systems you have installed on your boat. What's more important though, is the energy storage. Do you realize that on a sunny day, it will be like I would have a 3KW generator running all day, every day it's sunny out? That's the amount of power we're talking about here to put it in perspective. That, plus a 1,250AH battery bank if it were @12VDC that can also be discharged to 80% DOD. I'm running 24VDC to save weight on wires.

    Absolutely. This isn't my first boat. 6th, actually. The color of your deck isn't silly at all. There is no other color for decks and roofs of deckhouses than white. None. Not even a factor.

    12V fans and dorades will be plentiful. Exhaust fans will be plentiful.

    I am designing a holistic approach too. Same thing. I always do that.

    BUT... when someone feels hot, I will need to turn on an air conditioner. The setup in my post here gives 10 hours of cooling of the entire boat per day. If I am cooling on a hot, sunny day, the panels put out like a 3KW generator. The air conditioner takes 1.5KW to run. Nothing but extra energy to run other systems on days like that.

    On cloudy days, I have to watch my consumption, but could even run this thing for 10 hours at night, charging up the next day or over a day and a half. Or... if the guests need to be in 100% air conditioning the entire charter, we'll get docks each night for them.

    Also, when will the heat or AC actually be used? Heat few hours in the morning? A few hours on a hot evening to cool of for going to bed? The rest of the time, I now have a solar boat again. Solar slow cooker for the galley, solar microwave, solar hair dryers, solar hot water, you name it... all because I'm generating as much power as running a 3KW genset for 5 hours every day.

    Basically, I can't find a hole in this system at all and it looks like nobody else can either, though I welcome real challenges to the numbers if anyone can see anything wrong with them - like Daiquiri did.

    A second pair of eyes is very helpful with this kind of thing.
  9. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    I have to wonder if geothermal wouldn't be a more efficient option? However, in this case, instead of running geothermal lines into the earth, you would run them to a heat exchanger mounted to the boat hull below the waterline. This would be more efficient as long as the ambient water temperature is cooler than the ambient air temp for cooling, and warmer than ambient air temp for heating. Big question would be corrosion issues or barnacle build-up on the heat exchanger.
  10. CatBuilder

    CatBuilder Previous Member

    Ok, so this post is regarding the HVAC or air conditioning system only, correct? Not the power generation to run the compressors and stuff. I'll assume it is.

    I had definitely thought of doing this, but I didn't find anything off the shelf to make it happen. Do you know of any products off the shelf that are as efficient as a 23 SEER air cooled unit?

    The corrosion issues aren't a big deal on the heat exchanger with the seawater. All marine air conditioners use cupro nickel piping and those last 20 years+. Never had a problem with them. I'd use the same.

    Do you know of any off the shelf products that can reach 23 SEER or more and will allow me to use the seawater for heating and cooling?

    I'd be very interested in links.
  11. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Dude, you want him to drill into the core everytime he anchors?
  12. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    If you want a crazy idea. Only anchor in over 80 feet of water. Run a hose to those depths, the water will be plenty cold to cool your boat.
  13. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    As I mentioned in other thread. Oh,remember one thing... A big thing. The sun is a moving target. Unless you do something very mechanical/electronic moving of panel the best you get at any given time is about 50%, except when the sun is vertical. Any shadow or partial coverage greatly reduces output. So you really only get may be 50% of panel usage and only for about 6 hours a day. Make sure you figure these into yours calcs for solar. So you have 6 hours at 50% to provide electricity for 8-10 hours at full power. Try you numbers again for 1.5kw. By the way is what I have available on my boat with inverters, and I drive 11k btu ac, for 4 hours with it.
  14. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    I'd super insulate the boat. and what is water temp where it is being used?

    I've had good results using that cheap clear plastic film on house windows to make 'double pane' or even triple pane. Most of the heat exchange comes through the windows. They say it if for inside, but I've put in on outside where protected from rain and it is hanging tough, but I digress.

    In skylights in schools I was working on they put two layers of plastic in addition to the two roof and ceiling plexglass to block the solar heat but allow all the light. Really makes a diff. Once they forgot the two plastic sheets and the whole room was an oven by 11am.

    I guess it blocks the 'heat' wavelengths but not the visible light.

    I'd find some nice anti-heat plexiglass and figure out a way to block heat from the windows.

    Is this cat 'all windows' like most?

  15. CatBuilder

    CatBuilder Previous Member

    Yes, will be honing the numbers down a bit more as I get closer to the installation.

    I will consult with the solar suppliers about the system and the flat installation. They do make panels that can be shaded these days. I'll probably need to go for those just to be safe.

    Why are you asking me to try the numbers again at 1.5KW? I am looking at putting a 15KW system in. Not sure what you mean there... :?:
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