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#31473 06/26/06 11:35 PM
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I've been reading through the forum for homemade aeration systems trying to get some good ideas for my pond that's about 3/4 acre with a max depth of 7'. Running electricity to it is out of the question and I'm not paying an arm and a leg for a commercial solar system. My idea that I've come up with is to utilize a 1/4 hp gast pump rigged to a 30-45 watt solar panel, battery, and 75 watt inverter. Through some quick internet search schooling I've come up with these calculations (please correct/advise/tell me I'm stupid if I'm totally wrong). Wattage for the pump equates to 63.25w (115 x .55) totaling 13.2 amps per day (.55x24). A 75 watt inverter (thinking this is sufficient) would draw .625 amps (75/120) and 15 amps per day (.625x24). Searching solar panels I've found a site stating a rule of thumb for expected daily amp yield to be rated wattage divided by 3 for southern U.S. areas. Therefore a 45 watt panel would yield an avg 15 amps per day. My first question is whether to include both the pump and the inverter's power draw or solely the inverter in calculating total draw on the battery. I would think the inverter is simply drawing and converting power while passing most of it along to the pump but my ignorance has got me stuck on this question. If I only account for the inverter's draw of 15 amps per day that would mean a 45w solar panel can supply just enough maintaining power. If I have to account for both the pump and inverter then I'd need to increase my solar wattage i.e. more money that I'm trying to avoid. Does anyone have any suggestions on this? I'll take any advice both good or bad but I'd like to think I can make this work.

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Alan

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1) Total draw would be what the pump uses plus some loss in the inverter (inefficiencies of conversion). IIRC the "75 watt" rating on the inverter is the max power it will supply, not the loss from the inverter itself.

2) I think the power budget calculation is more complicated than it needs to be by the conversion to amps - you should be able to double check with Watts in vs. Watts out. Assuming your solar panel "rated power divided by 3" rule of thumb is good, a 45 watt panel would deliver 15 Watts power averaged over 24 hours, not (I believe) 15 Amps. So to run a system pulling 75W (for argument, let's assume the Inverter max power is also the total load), I think you would need 5 45 Watt Solar panels (5x15W average delivered powered = 75Watts power used 24/7).

3) Would it make sense to run the figures ($ and power consumption) for a timer to aerate part time? If you only ran the pump at night, that would give you aeration benefits when needed the most, but reduce the total daily power draw. This would cut the number of panels needed and possibly battery size, but of course you would have to run the timer 24/7. It's something to consider which might miake sense depending on prices and the power budget.

I'm just discussing all this using a general electrical engineering education, not specific knowledge of solar power systems, aeration or otherwise. So maybe I'm full of fertilizer.


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Welcome to the PB forum. We are lucky to have several electrical engineering types here including Theo. Good luck with the project.

Here is a link to the same topic solar aeration by others here.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=12;t=000063#000001

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=002321;p=2
















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 Quote:
Originally posted by BassAsassin:
Wattage for the pump equates to 63.25w (115 x .55) totaling 13.2 amps per day (.55x24). A 75 watt inverter (thinking this is sufficient) would draw .625 amps (75/120) and 15 amps per day (.625x24).
Thanks

Alan
Hey Alan,

I hate to tell you this, but pumps require very large solar panels.

For example, a 45w panel produces ~4a. Subtract 25% for inverter inefficiency, occasional clouds, and sun angle, and it really starts to look bad.

If you eliminate the inverter and use 12v equimpent, you come out a bit better. But still, a 4a pump isn't going to move much air.

Going to solar-charged battery power is even less efficient, and presents a whole new set of problems.

I have been kicking around a lot of things looking for the best way to help aerate my pond with solar, and came up with a water circulation system. It involves a trolling motor head, and a large PVC pipe a tad larger in ID than the prop diameter. A 100W solar panel should turn the prop fast enough to circulate a lot of water, and get some pretty decent surface aeration. I know the aeration is poorest when you need it the most, but it's far better than nothing.

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Bassasassin, whew, that name has too many "ass's" in it to type quickly. No insult intended. If there is power available somewhere in the area why not just run an electric pump near the power and run air lines to the pond. Many threads on here discuss running air line for some distance. I currently run my air 500 feet. But I think you could run air lines a half mile if you had to. Just need to be the right size. Here is a calculator you can use to determine pressure drop.

http://us.kaeser.com/Online_Services/Toolbox/Pressure_drop/default.asp#0

You can run a 1 inch pipe a half mile and pump 5 cfm through it at 10 psi while only losing a little over 3 psi. You will need something like a rotary vane pump capable of 15 psi tops because you will be pushing the 3 psi pressure loss plus 3 psi to get down to 7 feet plus whatever your aerator back pressure is, so figure the pump will probably run at no higher than 10 psi. to move air a half mile! 1 inch irrigation pipe is relatively cheap.


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If you MUST use solar aeration, bobad makes some points, but may be a little too pessimistic. The new smaller DC-AC inverters are quite efficient; in the order of 90-95% and draw very little current with the load turned off. If you do use an inverter you will need one rated at least twice the continuous duty rating..ie. with your 75 watt load, get a 150 watt continuous duty rated inverter. They are very inexpensive. With 45 watt panels and 75 watt load, you should be able to aerate at night for 4 to 5 hrs in summer. If you can swap out the batteries weekly, you can get a couple more hrs a night. I would suggest cycling 2 hrs on and 1 off which will help with the battery efficiency. Hope this helps.


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Hey Burg, I meant inverter, clouds, and everything combined will give you a 25% efficiency hit. I have a new, small (1500w)inverter, and it supposedly gets me ~90% efficiency. \:\)

Just a warning about Batteries. When choosing battery capacity, figure 5X more capacity (in Ah) than needed for your planned running hours. That's because batteries die quickly if ran down below 80% of their capacity. Golf car batteries will hold up pretty good down to 50%, but will last 3x longer if not discharged below 80%. I guess a common trolling motor battery will last about a month if it's drawn down below 25% every night, and about 2 years if drawn down no lower than 80%.

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bobad, I edited out the memory lapse. As I said, bobad has a new smallish inverter. He makes good points about clouds and such. Some panels such as ICP from Canada work well with very low light levels. As he mentioned, Trojan golf cart batteries are made for heavy duty cycling. They also make the Minn Kota brand of AGM(absorbed glass mat) newer gel cell type batteries.
Just do some experimenting, get a digital volt meter, they are cheap now days. Dont let the battery get below 12 volts under load.


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Actually open circuit voltage on a 12 volt that has been off charge for a hour should be around 12.72 volts 2.12 vdc per cell and on charge fully charged the vdc will be between 14.75-15. vdc good way to check to see if your charger is working properly

Depending on the equipment and if it has a kick out voltage most things will run to 10vdc which is 1.66 vpc Things have changed abit since I was in the battery field with the gel cells and the AGM batteries. But regular flooded cells and motive power batteries (forklift) would discharge to 80% which is 1.37 vdc but that was for dc motors so I dont know what the inverters are design to accept.
When you charge your batteries is when they wear out, if you charge it for a hour is the same as a 8 hr. charge the same amount of materials falls from the plates and settles on the bottom(flooded type) glass mat and gel are a different make up of sulfuric acids and calciums usally a higher specific gravity around 1300-1310 much higher ah capacity and run time but a shorter life span...Sorry been A while since I was talking batteries and I am rambling


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