Solar PV direct Pumping system. What size solar panel do I need?

[Mike90250]

How did you solve this problem? I wish to do the same.

Which is the problem you wish to solve? One small difference in YOUR install, will make a difference in the solution.

[PCH]

How did you solve this problem? I wish to do the same.

[LETitROLL]

Hello! I am working on a project where I need to pump water from one tank to another one. I am located in Rockford, IL and need to pump this system for a few hours. The pump that I am looking at using is a Shurflo 12 VDC pump (Model # 2088-514-145). I need 10 PSI and 2.90 GPM and the current needed for the pump is 5.6. I am not going to use any batteries as they are expensive, but I am wanting to use a Shurflo pump controller, 902-200 9300 series 12/24 V, to get a better performance from the pump. The one thing I am not sure of is what size solar panel do I need to run this pump? I calculated that I would need a 100 Watt pump, but I am not sure if this is correct.

Batteries are only expensive when you use them to store energy and then use that energy at a later time over and over, It would be much simpler and cheaper in most cases like yours to just use a used car battery to satisfy the circuit and use a Cheap PWM controller, you don't need to store energy, if you are only going to use the system while the sun is up, the battery will just float most of the time, with the bonus of your system still working when a cloud passes by. Most cheap controllers can handle that kind of current on the load outputs and they usually have a timer and LVD to keep things happy, you just have to make sure and use a timer or manually control the system, but you are only going to get a working pump limited time your other way anyhow.

[PNPmacnab]

What is the intended use of this pump? Are you charging a tank or just using this for watering? Have you bought the panel already, buying a battery voltage panel is a big mistake cost and performance wise. If you can operate the pump at a lower voltage like 9-10V, I would do that. Solar is a lot like a puppy or wife, it seems like a good idea at first.

[J.P.M.]

I agree, but my group wants to do this without batteries.

Is your group aware of the technical, maintenance and financial consequences of their perhaps ill-informed desires ? Or are they more of a "I saw this on U-tube so it must be a snap" type of mentality ?

[ERIC5249]

I agree, but my group wants to do this without batteries.

[littleharbor]

This project would really be much simpler if you just went with a small sealed 12 volt battery and a small inexpensive controller.

[ERIC5249]

It appears the pump controller needs higher voltage than a single 12 volt panel puts out. If you add another 100 watt 12 volt panel you need to series wire them.

Alright, well I was planning on using a dc-dc buck converter instead of a pump controller. I was not able to find a pump controller for this specific pump.

[littleharbor]

It appears the pump controller needs higher voltage than a single 12 volt panel puts out. If you add another 100 watt 12 volt panel you need to series wire them.

[ERIC5249]

The numbers you are giving are incorrect, as is your terminology. They would make your panel over 207 watts. Your first number would be Voc. or open circuit voltage.The number you want is Vmp. or voltage @ maximum power and should be in the 18.5 volt range The second number is short circuit voltage but the number you want is Imp. and should be around 8.1 amps. These numbers wont likely be seen in real world situations unless you are in cold, clear noontime, sunny situations.

Alright, I see what you are saying and I see how I am off. If these numbers are unlikely unless I am in good conditions like you said, then how would I go about getting these numbers? Would I need to combine solar panels in series or parallel to get what I need?

[littleharbor]

[QUOTE=ERIC5249;n373587]

Alright. I have a 150 W solar panel that has an optimum operating voltage of 22.9 V and an short circuit voltage of 9.05 A.

The numbers you are giving are incorrect, as is your terminology. They would make your panel over 207 watts. Your first number would be Voc. or open circuit voltage.The number you want is Vmp. or voltage @ maximum power and should be in the 18.5 volt range The second number is short circuit voltage but the number you want is Imp. and should be around 8.1 amps. These numbers wont likely be seen in real world situations unless you are in cold, clear noontime, sunny situations.

[PNPmacnab]

Your math is a little off and your panel specs don't add up. Lets say for example power point is 9A @18V. 18V/12V X 9A = 13.5A due to current boost, so half power would be 6.75A X 85% = 5.7A. They specify a smaller panel when direct connecting because solar is a current source. With a larger panel the voltage on the motor could exceed 20V and a lot more current. In motors generally all you care about is current and you will never exceed the short circuit current of a panel. in direct connect A LCB will have either a current or voltage limit built in so that is controlled.

I have 560W of panels in my test set up and some days I am lucky to get 40W.

[bcroe]

No, I do not plan on using a line of power.

So what will you do those cloudy days?

[ERIC5249]

The sun may be shining today here in Rockford, but there are plenty of days it is not. Are
you going to use line power then? Bruce Roe

No, I do not plan on using a line of power.

[ERIC5249]

Watts in X 85% = potential watts out. Lower the voltage and it will be capable of more current. It is the voltage and load on the motor which determines the current. Throught most of the day expect less than 50% of panels output. I would lay the panels almost flat if I had sufficient panel power. E and W also works. Crappy output but more consistent throughout the day. Check open circuit voltage of panels. Converter has to be rated for more than that voltage.

Alright. I have a 150 W solar panel that has an optimum operating voltage of 22.9 V and an short circuit voltage of 9.05 A. I am thinking I would need a bigger solar panel to run this pump based off what you said. Half of the optimum operating voltage would give me 9 V. The solar panel that Shurflo recommended for the motor was a 75 W solar panel, but I think that would be insufficient to run this pump. I can see why they would recommend this as the pump can only handle 80 W. Unless I am wrong, I think this 150 W solar panel should be good enough for this pump.

Thank you for your input on buck converters, it is helpful.