Running an Air Conditioner From The Sun - The Holy Grail

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

  1. CatBuilder

    CatBuilder Previous Member

    Where do you find heat blocking plexiglass? Is it just infrared blocking, or is it actually a better insulator than regular plexiglass? I don't want to block infrared because it will cause me to have to use the system more often when it's cold out. No gain there, just trading running it when it's hot for running it when it's cold.

    The boat is made of R4.16 foam plus fiberglass skins. That's my insulation.
  2. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    How many solar panels are you going to need to put out 15,000 watts?

    That is what you inverters are going to put out, put if you don't similar amounts coming in, you won't be able to recharge.

    When most boat I have seen have about 500 watt of solar feeding a 400-800 watt inverter. I know of some with 3000 watt inverters but they run generators for a couple of hours a day to charge the batteries of a quite night sleep. Most yachts that take AC religiously run of generators all the time since they leave port till they dock again. The Luxury of house type AC requires a generator.

    It is the same problem you have with electric marine propulsion the numbers just don't add up unless you are willing to sacrifice something.

    Oh, and forget about running hairdryers on inverters, they just drain the batteries too quickly.
  3. CatBuilder

    CatBuilder Previous Member

    I think we are having a miscommunication or I may have typed something wrong.

    I think we got bogged down in a KW vs KWh thing again. :D

    It is a 3KW solar array with a 15KWh battery bank. Sorry if I wasn't clear.

    You know people who run the generator a couple hours a day to charge up and get a good night's sleep, right? What size generator is it? How many hours do they run it?
  4. Stumble
    Joined: Oct 2008
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    Stumble Senior Member


    Take a look at they sell the geothermal units that were mentioned. I have never heard of them being installed on a boat, and have no idea how they would work, but they are the experts.

    Personally I would think that going this far from typical could be a huge cluster. It might work, and work well, but being the first person to install such a unit could result in massive R&D costs to get it right. If the manufacturer is interested in covering this cost it might be a cheap way to get AC installed, but if not it could quickly drain your pocket before it ever works right.

    The other issue I see is that I think these systems assume a constant ground temprature, by drilling deep into the earth, I have no idea how this would work in water where the water temprature would be constantly changing.
  5. Timothy
    Joined: Oct 2004
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    Timothy Senior Member

    I had a ground loop system at a cottage on Lake of Bays . It worked but not as well as claimed. On my boat I have separate compressors for my fridge and freezer. On the fridge I had the optional sea water pump and coil installed but never use, as unless the water temperature is very low I don't think the energy saved is enough to offset that used by the pump.
  6. hoytedow
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    hoytedow Carbon Based Life Form

  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The problem with solar is you have to pay dearly per watt up front, essentially paying for your electricity usage, across the amortization period initially, which typically takes up 1/2 or more of the panel(s) life span. After this, you're getting free energy, but again, you have to pay for this convenience up front.

    The math isn't hard to do; figure out what your average daily KWH needs are, assemble an array that can provide this number or better, across the amount of time you have good production.

    My house uses an average of about 55 KWH per day annually. Assuming 6 complete hours of full production from PV panels, means I need a little over 9 KW of capacity to become energy grid neutral. This of course assumes I suck off the grid during non-production hours (18 hours per day), but I generate enough to pay this off, leaving no real electric bill. At $4 to $5 per watt for retail prices on panels, the math is simple and a fundamental reason PV's haven't taken off in this country.

    The only way I've seen to reduce these up front cost is to make your own panels, by purchasing damaged and broken PV segments. The work is fairly easy, though tedious. If I had a good source for damaged and broken PV segments, I'll buy as many as I could and start soldering them up.
  8. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    a problem with marine instalation solar panels is overheating and effeciency loss. Air must circulate behind the panel to cool them . This is difficult to achieve when the panels are set into cabin tops or sheer clamps. Better add this heat loss into your overall solar oputput budget.
  9. Mick@itc
    Joined: Jan 2011
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    Location: Melbourne

    Mick@itc Junior Member

    Focusing on cooling for a moment rather than ac. Have you considered evaporative cooling? It's more like a breeze under a tree than a cold air blast but it is comfortable.
    1 person likes this.
  10. CatBuilder

    CatBuilder Previous Member

    I agree with this post. People are very short sighted in this country and can only think about the cost over the first year or two. One reason I am able to afford to build a boat is that I look at costs over a lifetime. Invariably I spend more up front on everything, but over time, I spend less.

    You can buy a $200 pair of Prada dress shoes or a $20 pair at Walmart. Over 15 years, you end up spending more at Walmart.

    Solar is cheaper than an air cooled diesel generator at the 10 year mark in a usage scenario I did about 7 years ago. Naturally, I've done this math to find which of the options is the best deal.

    War involving Iran? No contest even in 5 years if diesel and gas go to $5/gal.

    The problem of people without enough capital wanting solar on their homes is easily solved by loans or leases on the panels. There are a lot of companies doing this now for residential homes and for large businesses. You'd be surprised how many people have PV solar now that the cost has come down and there is financing available for those who can't afford it up front.
  11. CatBuilder

    CatBuilder Previous Member

    Mick, I have a system that works here. Why would I want to experiment with evaporative cooling? Evaporative cooling doesn't work where I live since things barely evaporate at all in high humidity.
  12. CatBuilder

    CatBuilder Previous Member

    Yes, this is important. Like anything on a boat, they must be installed properly to work.
  13. CatBuilder

    CatBuilder Previous Member

    It was late, but I was confused. I kept looking for info on infrared on that link but didn't see it.
  14. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    How do you propose to mount this large surface area of solar cells ?

  15. CatBuilder

    CatBuilder Previous Member

    PAR, there is a mistake in your math. Panels are no longer $4 or $5 per watt. They are $1.26 per watt in the specific example I used. That is part of what makes this economical.

    For the equivalent of a 3kw generator running 5 hours per day, every day, for 20 years, I am paying $4256. That is less than the cost of a marine diesel generator and I don't even need to put fuel in it or do any maintenance. In fact, all I have to do is watch my battery monitor. Otherwise, it'll be just like the power on land in a house - except there is no bill each month.

    That's what I really love. No daily chores. Just enjoy free power once you've paid your $4K.

    With the drop in prices from years ago when both you and i looked at this stuff, it is now much less than 10 years to break even and start enjoying free power.

    Using a good solar setup is a lot like buying a car in cash vs. leasing. Like buying a car, solar is quite expensive up front. Like a lease, when you use a generator, you pay a similar amount up front, but then you have monthly payments to worry about.

    I like buying things outright, because it saves money in the long run. Yes, despite the fact that I just leased a new car.. ha ha ha. I had to do that because I'm 1000 miles away from home and can't keep up with car repairs and stuff.

    But still, same principle. Pay now, spend less over the lifetime. It's how I save money.
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