Solar garden pump problem

SolarWally · March 2012

A couple of years ago a local solar company set up a solar powered pump system for my garden (I have zero knowledge in this area). Rainwater is collected in an underground tank, then pumped to an above ground holding tank for gravity-feed watering of the garden. There’s a float switch in the above ground tank to turn the system off when the tank is full and a sensor in the underground tank to turn it off if that water level runs low. The system featured a 20 watt solar panel, 12 volt battery, 6 amp charge controller.

The first year it worked great, except after a couple of months the battery failed. A new battery suffered the same fate early last year. Since I had not really wanted a battery in the system in the first place (I don’t water a lot so the tank doesn’t have to fill in a hurry) the guy came up with a new battery-free setup. However, at this point we had an acrimonious falling out because, having charged me three times his estimate for the original system, he now planned on charging me again for the new setup.

Long story short, I returned the original setup, took the new setup in return and installed it myself. Needless to say, it too doesn’t quite work. It pumps water, but the water falls a few feet short of reaching the above ground tank. The pump is about 7 feet below ground and the inlet of the above ground tank is about 10 feet above that ground level. However, the total length of pipe is about 60 feet. The pump is an LVM105, which worked fine when there was a battery in the equation so I’m assuming it has enough umph though it does say its head rating is 32 feet. Also in the current setup is a ‘PV direct pump controller’ and the same ‘20 watt high efficiency solar panel.’ I have no specs or other information for these two.

My question is what do I need to do now to make it work? Another panel? Different pump? Any help would be appreciated. Thanks.

niel · March 2012

Re: Solar garden pump problem

welcome,
this does make it more difficult to nail down when you aren't very familiar with the stuff, but it sounds to me like the pv is insufficient to keep the battery charged enough to properly run the pump. you might try temporarily using another battery with a full charge on it to confirm the pump will run correctly and be sufficient for your needs. if it works then you have confirmed the batteries weren't being kept up enough with a proper charge and more pv would be needed, but how much i can't say without more pertinent info on the pump's current draw rating and how long it will typically run for in a day.

Windsun · March 2012

Re: Solar garden pump problem

LVM 105 comes with battery clips. These pumps are designed for 12-volt operation and will be damaged by array-direct operation if voltage goes above 15 volts.

Model Number________________ LVM105
Current (amps)________________ 4.5
Flow rate (gpm) at 0 psi_________4
Pressure (max psi) at 0 flow_____14
Maximum head (feet)___________ 32
Dimensions (inches)___________ 1.5 x 6.54
Weight (lb)___________________ 1.1
Cable length__________________12 ft

As there is no possible way that a 20 watt panel could supply even 1/3 of the stated 4.5 amps, that is probably your problem. It is probably a 15 volt panel, so 20/15 = about 1.3 amps max.

I am curious what you paid for that setup - the pump sells for around $30, and we sell the 20 watt panels for about $91.

niel · March 2012

Re: Solar garden pump problem

don't forget about the batteries he had to buy too. you will need to tell us how long you intend to operate it in a 24hr period and then we can talk of a proper sized battery, controller, and pv. do tell us what battery was initially supplied for this and what its amp hour rating was.

imho, that company took advantage of you.

SolarWally · March 2012

Re: Solar garden pump problem

You are correct that I got screwed in this deal. I should have picked up on the problems much sooner, but as the original setup worked fine I was prepared to bite the bullet – until the battery died. The garden, which is not that big, was new so I was watering daily, but not using a huge amount, probably no more than 50 gallons a time. I doubt the pump ran for more than half an hour any given day with the exception of its initial use when I first filled the above ground tank. Since I empty the tank for the winter to avoid freezing I have to fill it each spring, but that doesn’t have to happen at one go.
One point is that I watered, and therefore the pump ran, in the late afternoon when there was no sun on the panel. So I think the pump was running off the battery, which was not being recharged until the next morning. The pump definitely worked fine when the battery was charged.
The info I have for that battery is “AGM 7 AH 12V.” I don’t remember what the brand was but, as I mentioned I no longer have a battery in the setup and would prefer not to have one.
I hope that helps clarify things.

Windsun · March 2012

Re: Solar garden pump problem

The battery you had was pretty small - 7 AH is about the size of a small motorcycle battery. At this point it seems like you have two options - get a bigger or another solar panel, or get a small battery. We do not sell any batteries that small, the smallest we go is 34 AH - http://www.solar-electric.com/sunxtenagmse.html You could probably pick up a small battery in the 7 to 15 AH size locally for around $60 or less, but eventually it will need to be replaced also and you would need a charge controller.

So your best option might be to just get a 2nd panel to add to what you have, but it looks like you would need at least 50 watts of panel total.

BB. · March 2012

Re: Solar garden pump problem

If you do not need a battery to run the pump after dark/during bad weather--You might look at a:

7 amp Linear Current Booster/Pump Driver

They are not cheap (this is around $140)--But they can help you.

A solar panel, ideally, outputs at ~Vmp (say ~17.5 volts) from zero to rated current. A DC motor would really like to see maximum amperage at lower voltages--The LCB does that electrical transformation (like a MPPT charge controller does--sort of equivalent of a transmission between the engine and the wheels).

Used to control and power a DC motor from a solar panel. The unit prevents stalling of the motor under less than full sun condition. The power of the sun is transformed to the motor running conditions so as the sun goes down the motor slows down instead of stalling. Conversely, or as the sun comes up the motor starts running much earlier instead of staying stalled for hours when it could be running. This translates into more running time of the motor where it spends a lot of time working instead of stalled doing no work.

With the price of solar panels dropping so much right now--I am not sure if getting more solar panels or purchasing LCB is the better idea...

Perhaps Windsun can help (or you can call NAWS directly for their recommendations).

-Bill

niel · March 2012

Re: Solar garden pump problem

if bb's idea of no battery needed due to daylight operations is feasable you may want even far more in pv to cover the overcast days with some current ability to cover some pumping. luckily though overcast days need less water for a garden.

seeing what your location is and how little sun you get it may be a good idea to get a bit more capacity for the battery just to insure on those long stretches of sunless days that you are less likely to drain the battery down too far. i also agree with the larger pv wattage and if you can go a tad more than 50w it certainly wouldn't hurt excepting the extra cost. the higher wattage would help to bring the battery back up a bit faster after a slump of poor to no sun. do stick with the agm style battery though as they can take higher charge rates better that standard flooded lead acid types.

34ah battery capacity may be allot of capacity overkill, but it can work well with about 50w or more of pv.

Shadowcatcher · March 2012

Re: Solar garden pump problem

As a possible alternative is a water pumping wind mill. http://airliftech.com

SolarWally · March 2012

Re: Solar garden pump problem

Thanks for the responses. I didn’t mention it before but my above ground tank holds about 250 gallons so I can operate off it for a week or more without filling it. I’ve found that’s plenty to carry me through cloudy stretches, even here in the Pacific Northwest! Plus, if it is cloudy, I water less so it lasts longer. Also, the solar panel gets good sun exposure from early morning through mid afternoon.
I definitely prefer not to put a battery back into the system, so adding another panel would be the preferred way to go. I might be able to borrow one and add it to the system temporarily to make sure it will do the job, that is assuming the sun comes out here again sometime soon!
One thing I’m not sure of is the “PV direct pump controller” that is in the system now. There’s no marking on it to identify it further. I’m not sure if this is something along the lines of what BB is referring to, but it sounds like I need a controller to ensure the pump doesn’t get fried.
I think I’ll go back to the guy who sold me the unit and at least try to find out some specifics Chances are, like everything else, it’s inadequate for what I need but there’s no harm in finding out.

Solar garden pump problem

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