Can My Solar Array Run My AC?

[Skuzzlebutt]

One last thought. How new is your a/c. The latest models might run fine where a unit a couple years old will trip the inverter every time.

And don't expect a 750 watt inverter to work.

The above is in addition to the "no" in the above posts. Rather, if you need an hour or so of cool you might be OK. Or have a bank of ten or more batteries and a few more solar panels, and dock where you get max sun all day, and can plug into shore power overnight. Not practical!

[StuM]

Originally Posted by Dave22q

Assume 50% average production for a 10 hour day. That's 2100 W if your batteries accept every bit and that is a gross overestimate because the rate of acceptance decreases dramatically as the batteries approach full charge. Your AC eats about 495 W every hour. At an inverter efficiency of 90% you need to draw 550 A/hr to run the machine. ...

Sigh! What a horrible abuse of electrical units, resulting in an incomprehensible statement!

Please take a look at the following link before offering your advise:
http://www.cruisersforum.com/forums/...ml#post1933764

[baycruiser]

Firstly my experience is 30years living with primitve solar systems .now tho I use a very simple simplicity is key and good wiring over short distance and real good connections so stress good wires short as pos. and real good connections and do not use 240 when sun is not out if pos.if you do these things you will do what you want but I have never neededA.C. anchor in breeze or use fans see large range 12v now .also I dont have women on board who cant live as I do I live near tropic of capricorn I now use 240 freezer on timer and toaster and small 240 water heater and battery charger as necassary thru 24v.1500w pure sw inverter thru 2 n70s. wired to 24v never am short of power and nevr use geny o yeh I now carry about 550 w solar and my 24v batterys are on float most days by 8am. now considering water maker to use more power during the day as I have PLENTY My policy listen to few and dont use domestic electrician .Good luk and dont give up

[timbenner]

Originally Posted by Gone2long

Pardon my ignorance as I am a newbie in all this solar stuff, but what I guess you mean is that, when the inverter draws 495 Watts from a 12V system, that ends up being 41.25 or so Amps per hour, instead of the 2.15A when I use the AC on a 230 AC line. Correct?

That being the case, I would be using 40+ amp hours per hour. Demand on the system other than the AC would be extremely negligible, or, if I turn everything else off, non-existent. So, if I had 420 amp hours of battery storage, perfect sunlight, a 100% operative system, and ran nothing but the AC, I would run my batteries to zero in about 10 hours. Make sense?

I usually have perfect sunlight, but I understand that the batts should never go that low and that sytems usually get no where near 100% functionality, so we are just talking theory here. But the theory, or lets say, hypothetical capabilities of the system under optimum performance, is what I (as a complete novice) am trying to understand.

Thanks for your help,

G2l

drawn Maybe this is my ignorance talking here, but I don't get how

I think if you have 420 amp hours of battery storage, you can only use half that or 210 amps. Every boat I've seen with a/c (I have 3 a/c units on board) has a generator to run them. I have a 5kw generator on board to run my 3 units.

[svlamorocha]

Originally Posted by timbenner

Every boat I've seen with a/c (I have 3 a/c units on board) has a generator to run them. I have a 5kw generator on board to run my 3 units.

That is all fine and dandy, but I have seen more than one cat that stopped usingh the genset after installing 1+ KW of solar and lithium batteries...

[DotDun]

Originally Posted by svlamorocha

That is all fine and dandy, but I have seen more than one cat that stopped usingh the genset after installing 1+ KW of solar and lithium batteries...

I doubt they are running AC.....at least for not more than 1 hour/day.

1kw solar @ 5 hours = ~300ah back into the batteries. Normal house is probably 200-250ah/day.

[leftbrainstuff]

Originally Posted by tkeithlu

You're right that inverters don't like spikes, and compressors give out whoppers. When your inverter flips, it stays flipped, squealing at you in the middle of the night even though there is plenty of residual battery capacity to do the job. I appreciate your desire to know the details of "no" to a question for which you wanted a "yes." Now I think it's time to dig into the books some more. From a practical standpoint, I learned that the answer was "no" from trying to run an apartment sized refrigerator overnight off a much bigger battery bank and a larger inverter than you propose. Refrigerators are, after all, air conditioning units cooling very small rooms. If you want air conditioning, run the genset.

+1

The math and science don't lie. Marketing, opinion and wanting something to work are not helpful.

[leftbrainstuff]

Originally Posted by valhalla360

Let's say your 420w of solar panels puts out 4hrs worth of it's rated output (taking into account lower output in morning and late afternoon for an average).

That gives you: 1680wh of generated power per day to play with.

Assuming 100% EFFICENCY AND ZERO OTHER ELECTRICAL LOADS, you have a little over 3hrs of run time. Reality is with system losses and other minor loads, you will be lucky to get 2.5hrs worth of energy for the air/con unit.

Based on the draw, that unit must be on the order of 4000btu which is tiny. Running such a small unit during the day, it wouldn't stand a chance keeping up with solar heat gain for even a small cabin, so I will assume the plan is to run it in the evening before bed to cool just the sleeping cabin. It will probably take the full 2.5hrs just to get the cabin down to a comfortable temp but then you run out of power and on a hot night, the cabin will quickly become hot and stuffy forcing you to open a hatch and blowing the cooled air out of the cabin.

Now you need a battery bank to store that energy because you will be using the air/con when the sun isn't shining. 1680wh is about 140amp-hr but realistically you need about 3 times that in storage (assuming lead acid batteries) because it's really tough to fill the last 10% as the batteries accept less charge the closer they get to full and you shouldn't take them below 50% if you want them to last, you need around 420amp-hr of batteries.

Inverter is actually one of the easier items. Get a decent sine wave inverter but to handle start up loads, you are probably looking at a 1500w unit to handle the spike.


So while it is technically possible, it's very impractical.

+1. Lots of common sense ald logic is now appearing in this post.

[leftbrainstuff]

Originally Posted by StuM

Sigh! What a horrible abuse of electrical units, resulting in an incomprehensible statement!

Please take a look at the following link before offering your advise:
http://www.cruisersforum.com/forums/...ml#post1933764

As an engineer I cringe whenever I read the solar / battery / electrical posts.

This is why we engineers harp on about first principles, math and test results.

[Paul54]

After dealing with solar power systems for many years now, I must confirm what several other posters have said. You have got to learn the math to design a system that will work. If you do not want to learn the math, then find someone trustworthy to do it for you.

What you want, what you think should happen will not get you a system that works. You will be disappointed.

Based on no information, I would say that, no, you can not run your AC unit for any effective amount of time off of your current system.

[tkeithlu]

Gone2Long, AC power on boats brings out more real experts (not me) faster than any other area of expertise on this forum, to the point that I'm very hesitant to comment in the area, despite an electrical engineering class 50 years ago and having wired my own boat. They can be dazzling and adamant. Don't take it personally. You are valued on the forum, and if you don't like the answers, go hook up an air conditioner to your solar/battery/inverter system and see what happens. It's your boat and your money.

[tstano]

Think of it this way. What would it take to run a refrigerator by solar alone. Then leave the door open and add a fan. Yikes you don't need an engineers degree to sum that up.


All U Get

[tkeithlu]

Beautiful answer, tstano. Makes the point without dragging a person who is not adept with the physics of electricity through a bunch of numbers and units he doesn't understand.

[svlamorocha]

Originally Posted by DotDun

I doubt they are running AC.....at least for not more than 1 hour/day.

1kw solar @ 5 hours = ~300ah back into the batteries. Normal house is probably 200-250ah/day.

I presume use of one 8kbtu unit AC use at siesta time, when panels are producing rated capacity. A good 8kbtu unit running at 60% duty cycle will on average consume about 700 watts x 0.6 = 420 watts, or 1.46 kWh while you enjoy your three-hour siesta. That is about half of what the panels will produce during the siesta. Assume 4 hours per day of rated solar capacity, deduct inverter losses of 15% on the AC load (say 0.22 kWh) and you have 2.32kWh per day left for other loads and battery/cjarging inefficiency. This falls short of your 250Ah for other loads but wil keep up with my 150Ah.

Have 1.5kW of cheap Chinese flexible solar at 1 buck per W and you are way ahead.

I also presume lithium batteries that will waste little energy (Peukert, float, hydrogen bubbling, etc); lead is a different story altogether.

Granted, this is for those of us who think that if you need A/C at a time that is not siesta time or you do not get 4 hours of rated capacity per day from the panels then you are in the wrong place for the time of the year

[DotDun]

Originally Posted by svlamorocha

I presume use of one 8kbtu unit AC use at siesta time, when panels are producing rated capacity. A good 8kbtu unit running at 60% duty cycle will on average consume about 700 watts x 0.6 = 420 watts, or 1.46 kWh while you enjoy your three-hour siesta. That is about half of what the panels will produce during the siesta. Assume 4 hours per day of rated solar capacity, deduct inverter losses of 15% on the AC load (say 0.22 kWh) and you have 2.32kWh per day left for other loads and battery/cjarging inefficiency. This falls short of your 250Ah for other loads but wil keep up with my 150Ah.

Have 1.5kW of cheap Chinese flexible solar at 1 buck per W and you are way ahead.

I also presume lithium batteries that will waste little energy (Peukert, float, hydrogen bubbling, etc); lead is a different story altogether.

Granted, this is for those of us who think that if you need A/C at a time that is not siesta time or you do not get 4 hours of rated capacity per day from the panels then you are in the wrong place for the time of the year

I won't argue your math, in fact, won't even try to calculate it. But I will state that a catamaran big enough to hold 1kw of solar, a 8kbtu AC won't even make a dent in the temp if run during siesta time. It would take >32kbtu which is not solar friendly.