School project solar panel, help!

[akkiano]

Hello all, I am an undergraduate student working on a sustainable food growth project for the research laboratory I work in. We are going to try to harvest fish as food in a sustainable way. My lab colleagues and I are trying to build an 18 volt solar panel to power a 12 volt water pump which will be pumping water from the fish tank into a solar water heater we will be constructing next. None of us have a lot of electrical background (biology/biochemistry majors, haha) so we are currently lost when it comes to figuring out if a charge controller is needed for our setup.

We want to avoid using a battery with our panel because we are trying to stay environmentally friendly and batteries have toxic components. We plan on hooking up the panel directly to the pump. My concern is that the panel could possibly over-power the pump and fry it. To which my question is: could I use a charge controller to protect the pump from getting fried? I know charge controllers are supposed to be used to protect batteries. And if I can use a charge controller, which type would be adequate? Is there something else that I could use to protect the pump from the panel??

These are the water pumps we are currently considering:

http://www.swiftech.com/mcp35512vdcpump.aspx

http://www.swiftech.com/MCP35x2PUMP.aspx#tab3

They were recommended by this page on DIY solar water heaters which we are using as reference:

http://www.builditsolar.com/Experimental/PEXColDHW/Pump.htm

Any helpful information will be very much appreciated!!

[Sunking]

Will not work. Charge controllers need a battery to operate correctly. Best bet to to way oversize the panel and then build a simple series or shunt voltage regulator.

[bonaire]

Hello teacher.
Well, sometimes teachers get it wrong.
Let's teach the kids real-world when it comes to environmentally sound, friendly ideas.

Batteries are one of the most recycled products on the planet (well, at least in North America). A battery system is needed to power the pumps at night and if you want fish to live more than one day, they need power at night to power the pumps.

So, please integrate batteries into your teaching. The kids don't need to be afraid of using batteries for renewable projects. In years to come, batteries will become more commonplace with longer-life Lithium-Ion types of battery systems which themselves will also be recycleable. The only way to use renewables "off grid" at night is through batteries. Or use a solar grid-tied system but to do that, you will need a hybrid design where you do something with a grid plug at night and solar during the day. Also, solar is not uniformly power productive. It produces its better power from 11am to 1pm on a sunny day. Will you have clouds there on some days? Will you have other issues that the students should learn about in terms of solar pv? Sure, so batteries are needed.

[akkiano]

Will not work. Charge controllers need a battery to operate correctly. Best bet to to way oversize the panel and then build a simple series or shunt voltage regulator.

Can you elaborate on what you mean by oversizing and building a simple series or shunt voltage regulator?? I have never worked with anything electrical and have very limited knowledge :/ Is it even possible for the panel to over-power the pump and fry it?? Is that a logical concern that I have or no?

Hello teacher.
Well, sometimes teachers get it wrong.
Let's teach the kids real-world when it comes to environmentally sound, friendly ideas.

Batteries are one of the most recycled products on the planet (well, at least in North America). A battery system is needed to power the pumps at night and if you want fish to live more than one day, they need power at night to power the pumps.

So, please integrate batteries into your teaching. The kids don't need to be afraid of using batteries for renewable projects. In years to come, batteries will become more commonplace with longer-life Lithium-Ion types of battery systems which themselves will also be recycleable. The only way to use renewables "off grid" at night is through batteries. Or use a solar grid-tied system but to do that, you will need a hybrid design where you do something with a grid plug at night and solar during the day. Also, solar is not uniformly power productive. It produces its better power from 11am to 1pm on a sunny day. Will you have clouds there on some days? Will you have other issues that the students should learn about in terms of solar pv? Sure, so batteries are needed.

Haha, I'm just the student actually But the professor in charge of the lab and serving as our adviser on this project was indeed the one that opposed the use of the battery because of their toxicity. I agree with the things you said though. I will bring these points up to him. I think maybe he believes we can do without the battery because this panel will be used to pump water into the solar water heater. No need to pump water in there at night, so no need for the pump to be on, hence no need for a battery.

[inetdog]

No need to pump water in there at night, so no need for the pump to be on, hence no need for a battery.

But the output of the solar panels will be at a particular voltage (Vmp) for greatest power output, but the current will vary with the amount of sunlight striking the panels. Leaving out for the moment the whole idea of long term energy storage, since the time of use will match the solar hours for this application, a motor such as the one on a DC pump will expect to see different amounts of current depending on the voltage and the load. Not a good match. The batteries assist in that matching.
A MPPT Charge Controller will take the maximum available power, at the best combination of current and voltage for the current light level, and convert it to the maximum possible current to the battery and the pump.

If all you are doing is heating the water, then you only need the pump during those hours, but the amount of heat available will not necessarily match the amount of PV available. Again, the batteries allow that to be evened out.
And it gives you the opportunity to use energy for a filter pump, etc. the rest of the 24 hour period.

Using solar for the heater and grid AC for the filter/aerator is cheating when prototyping a practical third world tool. (Extra credit for seeing that....)

If you do not use batteries, you will at least want to use a device called a linear current booster which will better match the panel output to the pump. That will cost about as much as a CC and batteries.

[Naptown]

Instead of trying to invent the wheel try a google search for solar pump. there are a wide variety out there that do not use batteries.

[akkiano]

But the output of the solar panels will be at a particular voltage (Vmp) for greatest power output, but the current will vary with the amount of sunlight striking the panels. Leaving out for the moment the whole idea of long term energy storage, since the time of use will match the solar hours for this application, a motor such as the one on a DC pump will expect to see different amounts of current depending on the voltage and the load. Not a good match. The batteries assist in that matching.
A MPPT Charge Controller will take the maximum available power, at the best combination of current and voltage for the current light level, and convert it to the maximum possible current to the battery and the pump.

If all you are doing is heating the water, then you only need the pump during those hours, but the amount of heat available will not necessarily match the amount of PV available. Again, the batteries allow that to be evened out.
And it gives you the opportunity to use energy for a filter pump, etc. the rest of the 24 hour period.

Using solar for the heater and grid AC for the filter/aerator is cheating when prototyping a practical third world tool. (Extra credit for seeing that....)

If you do not use batteries, you will at least want to use a device called a linear current booster which will better match the panel output to the pump. That will cost about as much as a CC and batteries.

Thanks for all that info. I will definitely look into those linear current boosters more. In the instance that I can convince my adviser to go with hooking the pump to a battery, is there a way to turn off power to the pump at night when the solar heater is not in use??

Instead of trying to invent the wheel try a google search for solar pump. there are a wide variety out there that do not use batteries.

The idea of the project is to be as hands-on as possible in order to maximize the experience and knowledge derived. Yes, probably infinitely easier to buy a solar water pump than to have a of couple inexperienced students try to build one, but we wouldn't be learning or accomplishing much and we certainly wouldn't get the gratification that comes when building something.

[inetdog]

The idea of the project is to be as hands-on as possible in order to maximize the experience and knowledge derived. Yes, probably infinitely easier to buy a solar water pump than to have a of couple inexperienced students try to build one, but we wouldn't be learning or accomplishing much and we certainly wouldn't get the gratification that comes when building something.

I think you may have missed the point that Naptown was making.
You will by buying a pump/motor combination in any case, rather than building it. If you buy a pump/motor combination that has been designed for direct connection to a solar panel, there is not a big difference (except in cost!) and you will still have to wire up the panels, handle the solar thermal collector, etc.
A solar water pump is just that, a pump, rather than a complete assembly of all of the needed parts

[akkiano]

I think you may have missed the point that Naptown was making.
You will by buying a pump/motor combination in any case, rather than building it. If you buy a pump/motor combination that has been designed for direct connection to a solar panel, there is not a big difference (except in cost!) and you will still have to wire up the panels, handle the solar thermal collector, etc.
A solar water pump is just that, a pump, rather than a complete assembly of all of the needed parts

Ahh, yes totally missed it, haha I assumed that the solar water pumps were pump/panel assembly, didn't realize that they were also pumps on their own designed to be used with a solar panel. We've already started building our panel that's why this didn't seem to make sense to me. So I wouldn't have to worry about the panel frying the pump with one of these solar water pumps since they are designed to work with panels??

[Sunking]

Can you elaborate on what you mean by oversizing and building a simple series or shunt voltage regulator??

I will try, but it is going to take a electronic engineering student to help you out. Not sure you are going to be able to understand what I am about to say.

A solar panel is a current source not a voltage source like a battery. A DC motor is rated at a specified voltage like 12 volts for example. So let's say we have DC motor rated at 12 volts @ 8.33 amps or 100 watts when 12 volts is applied. You could not use a 100 watt solar panel made for a 12 volt battery system because all 12 volt battery panels operate at a Vmp of about 18 volts. So a 100 watt solar panel would have a Vmp of 18 volts at a maximum current of 5.5 amps. 8.3 amps is greater than 5.5 amps. If you were to connect that panel directly to the motor, the motor would be running at a very low speed if at all. It would draw the full 5.5 amps, but the voltage would collapse to 7.9 volts because the panel is a current source, not a voltage source. The motor needs a fixed 12 volts. Will really 13 volts but who is counting.

So what you have to do is select a panel that is significantly larger than what the motor requires to operate. For example if you had a 500 watt standard battery panel its max output is 18 volts @ 27 amps. Notice I said maximum is up to 27 amps. That does not mean you have to use all of it. With a simple 3 terminal series voltage regulator it changes the solar panel from a current source to a voltage source which you fix @ 13 volts output to the motor. At 13 volts the motor will only draw 8.3 amps from the panel.

Now here is the big advantage of using an over sized panel. As I stated a solar panel is a current source, and the current is directly proportional to the amount of sunlight it receives. If you were to take a solar panel out, short the leads out and measure the current during the course of a day assuming a nice bright cloudless day, you would only see the specified rated current for a very brief hour or so around solar noon. If you were to use say a 150 watt panel with an output of 18 volts @ 8.33 amps, it would only run the motor about 1 hour during the day at solar noon. Oversize it like to 500 watts with a panel rating of 18 volts @ 27 amps, and you should get 5 or 6 hours run time during the day assuming it is a bright sunny day.

So what you want to do is find you an EE Student and have him design build you a 3-terminal voltage regulator capable of 25 volt max input, 13 volt output, with a current rating at 50% more than the motor requires. So if that motor was the one I used in my example up to 25 volt input, 13 volts Output with a maximum current rating of 12 amps. Connect the regulator between the honking over sized panel and motor

Hope that helps.

[inetdog]

So I wouldn't have to worry about the panel frying the pump with one of these solar water pumps since they are designed to work with panels??

Exactly. As long as the panel voltage is within the input range of the pump. You should check the pump specifications online. Also, how did you decide what voltage to build the panel to (number of cells in series) without knowing what it was going to power???

[akkiano]

I will try, but it is going to take a electronic engineering student to help you out. Not sure you are going to be able to understand what I am about to say.

Thank you very much for trying to explain all that for me. Haha, yes it was a lot to comprehend... probably didn't get most of it (I really am a noob at all this, I admit). But you bring up a good point that maybe I should get in touch with someone in the electrical engineering department on campus. I personally don't know any EE students but I will try to contact some faculty members to see if I have any luck.

Exactly. As long as the panel voltage is within the input range of the pump. You should check the pump specifications online. Also, how did you decide what voltage to build the panel to (number of cells in series) without knowing what it was going to power???

We decided on building a 36 cell, 18 volt panel based on the DIY guides and videos we've been watching which all say that is how big a panel needs to be to power a 12 volt battery and we were looking at using a 12 volt pump for our water heater recommended from a DIY site so we thought that panel size would be appropriate.

[Naptown]

and what will be the watt rating on the panel you are building. that will be the limiting factor on the pump. You have made the classic solar mistake of putting the cart in front of the horse and started on a panel before identifying what precisely it will power. You may find yourself building more than one.

[akkiano]

and what will be the watt rating on the panel you are building. that will be the limiting factor on the pump. You have made the classic solar mistake of putting the cart in front of the horse and started on a panel before identifying what precisely it will power. You may find yourself building more than one.

Well the cells that we are using are 3" x 6", 0.5 volt, 3.6 amps, 1.8 watts each, and we planed on wiring 36 serially so the panel would be 18 volts, 3.6 amps, which would be 64.8 watts then... did I do that right?? Well we actually started looking into the water heater first and then found this pump which we were heavily leaning towards:

http://www.builditsolar.com/Experimental/PEXColDHW/Pump.htm

After we identified that pump, we went ahead and started looking into the panel and, like I mentioned, found that an 18 volt panel powered a 12 volt battery and since our pump is 12 volts, we thought making such a panel would be adequate and so we began our panel making process. None of us know much on electrical systems though, so we didn't realize it was going to be more complicated than that (especially without the planned use of a battery). I guess that's the whole point of throwing us onto this with so little experience and background knowledge, to make us learn.