Pond Waterfall and Aeration Power Sizing - New to solar

[tjroufs2007]

My wife and I are putting in a pond with a waterfall and aeration pumps in an area that doesn't have access to power. I am having issues spec'ing out a solar system to run these for 12hrs a day (ideally, we would like 24hr, but that might not be economical). We live in MN, so the pumps would only run for about 6-8 months out of the year. The specs on the equipment are as follows:

- Air pump: 120 VAC, 1.4 amp, 85W
- Water pump: 120 VAC, 1.8 amp, 219W

My calculations show me that to run these for 12 hrs a day, I would need 3.6 kwh of power. If I divide by 4 hr (assuming only 4 hrs of strong sunlight even though I get great sun from 10am - 7pm), I would need 912 watts of solar paneling. That seems like a lot of power for just two pumps. I also don't know how to spec out the appropriate controller, inverter, wire, and batteries. I have tried, but I'm getting overwhelmed with all of the information out there, and would like some help/guidance in creating the appropriate system. Thank you for taking the time to read this, and I look forward to any help.

 

[Brewman]

Look for DC pumps, it I'll make your life much easier.

 

[svetz]

Hi tjroufs2007!

Welcome to the forums!

Sure hope you're getting a man-cave or equally desirable thing in return for putting in her fountain!

Let's walk you through the math so you can play around with the numbers.

9 hrs a day (10 AM to 7 PM), air pump, Only 6 months around summer, somewhere in MN

- Air pump: 120 VAC, 1.4 amp, 85W (168W inrush?) = 765 wH
- Water pump: 120 VAC, 1.8 amp, 219W = 9h x 219W = 1971 Wh

So, probably a 500W inverter to handle inrush needs. I'm guessing on these, someone else might have a better feel or you can find actual numbers from the manufacturer.

1971 + 765 = 2736 Wh (AC)
AC Inverter 80% efficient, 2736 / .8 = 3420 Wh/d (you see why @Brewman suggested going DC, save money with no inverter and reduces everything else as you won't have a 20% power loss, I boat's bilge pump might work).

Lead Acid, DoD 50%, 3420 / .5 = 6,840 Wh/d Battery
LiFePO4, DoD 80%, 3420 / .8 = 4,275 Wh/d Battery

Those numbers are per day... if you want battery backup for 3 days with no sun then multiply by 3.

You need 3420 Wh/d of battery power, so let's assume your SCC is 80% efficient, that means you need 3420 / .8 = 4275 Wh/d solar.

If only you had a value that told you how to convert that in how many watts of solar panels you need! That's what your local insolation number does.

You can get monthly insolation values for your area from this url http://www.solarelectricityhandbook.com/solar-irradiance.html

For example, using the calculator above for Coons Rapids, the lowest insolation is 3.82 in September.

4275 Wh/d of solar needed / 3.82 insolation = 1120W solar Array!

Hope that helps! From there, these threads should help you out with example calculations:

• What does it mean to have solar panels in parallel and series?
• How to figure out how much Solar and inverter wattage is needed to charge a battery
• Figuring out how many panels in series and parallel based on your MPPT

The FAQ has a number of other helpful threads you might enjoy.

Let us know if you still have questions.

 

[svetz]

If you don't care about powering when the sun isn't shining, you can save a ton of $ by minimizing batteries. In this post, the battery is only used as a buffer which will minimize your costs.

For simplicity lets assume you switch to DC pumps and the whole thing is taking 300 watts.

The lower the sun is in the sky, the more the atmosphere absorbs the solar rays. At solar noon on a day matching Standard Test Conditions, there's 1000 W/m^s. When you see solar panels for sale they're rated in the watts you'd get on that perfect day. Since you'll probably never be at ideal conditions, let's assume you'll see 80% of that. So a 100W panel at solar noon will generate 80W. Let's say you want the pond to kick on 2 hours before solar noon (roughly 10 AM). Each hour the sun moves 15 degrees in the sky. So 12-10 = 2 hours, 2 x 15 = 30 degrees. 90-30 =60, and if you look at the chart to the right you'll see at 60 degrees elevation you can expect 85% of your max. Since your max is 80, that 80 x .85 = 68W.

Your pond needs 300W (plus inrush) to start, so for it to start at 10:00 that would be 300/68 = 5 (rounded up) 100 Watt solar watt panels.

The battery only needs to be a few amp hours now to cover the in-rush. Or, if you want the fountain to run for at least 30 min without sunlight, then that's 300 x 30min/ (60 min/hour) = 150 Wh. 150 Wh / 12 V = 21.5 Ah battery.

So, while the previous post would cost a lot of moolah, now you only need 5 x 100 W panels, (or two 300 W which might be cheaper), a cheap AGM battery, an SCC, and a low-voltage cutoff switch. The low voltage cutoff switch prevents the battery from discharging too far (see the battery FAQ).

Did I mention there was a test? Yep! So, now that you know the math... what time of day will the fountain stop with the above data? How many panels to get it to start at 9 A.M. and how long would it run to?

Okay, one last quick trick. At 10 A.M. you have just enough power to run the fountain. But at noon you're making excess power that could be used to charge the battery. So, you can increase the battery and panels to charge the battery and run the fountain...then as the solar wains the battery can supply the rest of the power to make the fountain run longer.

Good luck! Also, please post pictures ... would love to see what you do!

 

[Brewman]

What size water pump are you looking for?

 

[tjroufs2007]

Thank you Brewman and svetz for your quick responses. You

Brewman - The water pump I currently have pushes about 4000 gph. It is part of an aquascapes waterfall and skimmer setup I got for almost nothing. I would like the flow near the 4000 gph as I'm using it to agitate my pond in order to avoid algae blooms.

 

[svetz]

No clue if they're any good....

4000 GPH DC pump, 180W, 12V, $135
4700 GPH DC pump, 204W, 12V $99 (4 yr warranty)

 

[Fred S]

Fun project!
Svetz, also a LVD of some sort would be needed to stop at 50% DOD.

 

[Brewman]

If you get DC pumps you could just use the SCC load output, it would have its own LVD and it's timer for the off and on of the pumps.