Water cooler and solar panels

[Cudel]

Hi I am new to this and I have a question or two. I have 3- 100 watt 12v dc solar panels, I have a 35 amp controller, and a 4000 watt inverter I am connected to the grid. I built my lown home and I live in New Mexico. All I want is to be able to control my bigest energy consumer at the moment and that is my swamp cooler. It has a 3/4 HP motor, I thought I would use 12v Golf Cart Batt. the cooler circuit is seperate from the grid breaker panel. My wife will let me do anything I want as long as she stays cool. any help would be appreciated
Thanks

[cindynsg]

How much power does it use? I think you need a bigger battery. Golf cart deep cycle batteries are good for some small stuff but one may not crank out enough amps to sustain your cooler for very long after the sun goes down. tell me how many amp hours is the battery rated for?

[Cudel]

All the motor says it is 3/4 hp, I have not purchased any batteries yet, I have plenty of sun where I live and I am looking into the possibilty of installing a small wind mill as we have a good amout of wind year round.

[cindynsg]

you're going to want a battery(s) that is capable of storing enough power to run the cooler for at least 24 hours, more if you have bad weather for while unless you are willing to plug the cooler into an outlet when your battery isn't charged enough.

So, there's no sticker on the back of the cooler list how many amps volts watts it uses?

Well my medium sized refrigerator uses 1.4 Kw per day. I could probably get away with two 6 volt batteries each with a capacity of 350 amp hours, for about day and a half without having to charge them.

[Cudel]

I am disabled, my better half has a fit when I get up on a high roof (reason for being disabled in the first place) I had someone look and they could not see any other stickers, may have to go to a dealer of the same brand and get more information. That's in a different city and will take some time (I have lots of time )

Thanks for your help

[cindynsg]

come back tomorrow after more people read your post. There are guys like Mike could could tell you what 3/4 HP motor would need.

[Cudel]

OK, I have more information (I think) the motor is 3/4 hp two speed, draws 10 amps on high and 5 amps on low, that should be about 1150 watts on high and 575 watts on low. The batteries I am looking at are 6V 220VA. I don't ever remember the cooler being on all night, although it will start and stop once in a while during the night, depending on the temps. In the mornings it usually will start in low and eventually kick into high as the temp. rises. Of course everyday is different. So how do I figure out if I have enough solar panels and how many batteries I need?

[Mike90250]

Just back from a trip.

1 Hp is ~750 Watts, so a 3/4 HP motor should be about 600W, but nothing is perfect, and it will draw close to 700watts continuously. And swamp coolers have a 2nd motor to pump the water over the cooling pads, add another 150Watts for that one too.

Starting surge is about 10x running, so take that into account for your inverter size.

Mod sine inverters are cheap, but cause motors to run hot and sometimes overheat, Pure sine inverters are expensive, but are good power, just like the powerlines.

If you have regular powerlines to your house, I'd skip batteries, and consider a grid-tie system. Check your power company and see what's needed to get approval.

Battery systems are about 50% total efficiency, grid tie are about 85% efficient.

[Cudel]

Hi Mike, Sorry for the delay, I had to leave town for a couple of weeks. I have a friend that has a 5000/10000 pure signwave for sale, that I might consider. I do not want to connect to the grid at all. Thanks for your input, I appreciate the help.

Cudel

[Sunking]

Cudel Doesn't sound like you have enough to run the SWAMP COOLER. Typical single phase motors run about 85% effecient on the high end, so a rating of 3/4 HP = [746 W/hp x .75] / .85 = 660 watts. Question back at you is how many hours per day do you run the thing? Second question is which months will it operate.?

Here is some calculations based on running it 12 hours per day from April to October.

Daily power consumption = 660 watts x 12 hours per day = 7920 wh. Accounting for the efficiency, or lack of using a battery system of 66% means your panels will have to generate 7920 wh / .66 = 12 Kwh per day. That is a huge number for a battery system.

Looking at the Solar insolation tables for New Mexico using Albuquerque October has the least insolation of 6.5 hours. So the minimum size panel wattge = 12000 wh / 6.5 h = 1846 watts round up to 1900 watts is the minimum panel size required. Not too bad as your location is excellent solar insolation.

Now for the bad expensive news; Batteries. Assuming you want your batteries to last more than one year and get 5 years life out of them you do not want to discharge them more than 20% per day. That means your batteries will need a reserve capacity of 12000 wh x 5 days = 60 Kwh of capacity. To find th eAH capacity divide by the battery voltage. FWIW 12 volt is a poor choice for this system. 24 or 48 is more reasonable. Either way it takes the same amount of batteries.

12 volt = 64000 wh / 12 volts = 5333 AH
24 volt = 64000 wh / 24 volts = 2666 AH
48 volt = 64000 wh / 48 volts = 1333 AH

You are looking at about 10,000 pounds of lead at a cost of $120 per Kwh so 60 Kwh x $120 = $7200 just for the batteries using this example. Just the battery cost alone assuming they last 5 years means you will be paying $7200/14600 Kwh = 49-cents per Kwh. That is roughly 4 times more than buying from the utility. Are you sure that is what you want?

There is no way you can run the swamp cooler with a 300 watt solar panel array, well unless you just run it 3 hours per day.

[Cudel]

Well thank you for all the information, Reality sucks sometimes. Since I live in the very southern part of NM, and I have sunlight and good winds all the time, I thought there might be a way to accomplish the task. When the power goes off, it gets hot, when it gets hot, Mama's not happy. I have the thought of getting a wind mill and lowering the motor to 1/2 hp. when power goes off here, we have nothing, no water, no lighting, no cooling. Thanks to all who have responded.
Cudel

[Sunking]

Reality sucks sometimes. Since I live in the very southern part of NM, and I have sunlight and good winds all the time, I thought there might be a way to accomplish the task. When the power goes off, it gets hot, when it gets hot, Mama's not happy. I have the thought of getting a wind mill and lowering the motor to 1/2 hp.

Well by living in Southern NM helps a little because you have a little better insolation I think, not much, but a little better. Also lowering the HP of the motor will help. So in effect the solar panel wattage comes down from 1900 watts to maybe 1400 or 1500 watts (educated guess, did not run the numbers) and the battery AH capacity comes down around 30%. However it goes from the cost of your first born, to just an arm and a leg.

I have another idea, but still expensive. They do make very efficient 24 volt DC powered air conditioners. But to be perfectly honest if you have grid power, stay away from stand alone battery systems. In your area a grid tied system will pay off pretty quickly, especially if your state has rebates and incentives. But for emergency power your least expensive option is a generator. Good luck.