Design Project

[Huntington]

Hello good people of SolarPanels. My name is Nicholas and I have a project Im working on. This is a school project for my Engineering Club. No worries,this is not a class so we are allowed to get help and advice.

Details are still coming in on what we need to accomplish but the basic of the system is to convert one of the campus greenhouses to "off the grid" solar. We have one panel installed already. The output of the panel is unknown at this time but I would guess its about 60w. Its mounted on a pole and we have another pole to use or the roofs of the adjacent greenhouses. The panel was already installed before we got this project. Currently it powers a pump for the pound.

The greenhouse is about 25' X 15' with one exhaust fan and automatic vents. (The fan will need to be replaced with DC, currently it is 110v 1/4hp @ 2a)


The power requirements for this system:

Need to run the pound pump 24/7. (possibility of a 2nd pump for interrogation) I think the current one is 12vdc 60a

Need to buy and install lights, they will be used for approx 3 hours a night.
(Im thinking shop lights, total of 4, 2 on each side)

Need to install a new exhaust fan, 12v system, it is controlled by a thermostat, 80*F it turns on and vents open. Already have the thermostat and vents. (Although the vents need some work)

Solar cells. we have the one but I know we need more, just dont know how many more we need and @ what watt.

Being off the grid we need a battery and charger. Battery needs to be able to support the above in case of power failure and night time operation.

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There really are no other requirements and nothing is set in stone. The budget is $3000, we have all the labor and electricians/contractors free. Just need to buy parts, and maybe get some stuff donated.


I hope I didn't bore you, any help would be appreciated and I hope you find this project interesting. I will be doing my homework and reading all your threads but I wanted to post and try to generate some feedback.

[Sunking]

Nope you did not bore me to say the least, but it is time for you to get a lesson in economics.

Here is what I have for your power requirements:

• Pump requires 12 volts x 60 amps = 720 watts x 24 hours = 17.3 Kwh per day
• Shop Light you did not really specify, does not matter, I will not use them in a calculations because there is no point
• Exhaust fan, same as light no details, no point

So we will just use the pump, and assume you live in some place like say Tulsa OK where you get pretty good solar insolation in winter of 4 hours.

Panel size = [17,300 watts x 1.5 efficiency factor] / Tulsa Sun Hours of 4 = 6487 watts, round up to 6500 watt solar panel array at $3 per watt = 6500 x 3 = $19,500. You said you have a 60 watt panel already and a $3000 budget right?

Next is a battery bank at 12 volts. Well that will take a 10,800 AH battery stack, a new building to hold all the batteries which is not included in the cost but the batteries will cost $15,600 plus a building to hold them.

You will need 7 80 amp MPPT Charge Controllers at $500 per unit so 7 x $500 = $3500

Lastly around another $4000 in misc material.

Total cost estimate = $42,600 just to run the pump. Care to add on the cost of the lights and exhaust fan? If you live where the solar insolation is not as good as Tulsa, the cost will go up because you will need a larger solar panel array wattage.

Here is the deal if you buy electricity from the power company and pay the national average of 11.2 cents per Kwh will cost you 17.3 kwh x 11.2 cents per Kwh = $1.98 per day to run the pump. Since the batteries have to be replaced every 5 years your kwh cost for the first 5 years to run the pump will cost you 17.3 Kwh per day x 1825 days = 31,573 Kwh's. So $42,600 / 31,573 Kwh = $1.35 per Kwh. You will be paying 12 times more than you do now using an off-grid battery system.

[Huntington]

Thankyou for the advice and numbers but I think your missing the point of this project. We need to keep a $3000 budget and I dont think we need such a large system. The pump is already running on solar, we just need a way to keep it going at nigh. Im sorry for the limited details, more are on the way.

I didnt mention the lighting specs or the fan because I have not bought any so anything is doable.

I am a noob at all this solar stuff but I know our project is doable within our budget. Just got to think outside the box.

Maybe a stand alone solar panel for battery charging, stand alone for pump, stand alone for fan. And battery backup for cloudy and night time use.

I could be wrong about the pump amps. 60 seems high to me, Im just going off what I was told.

Oh ya, our location is Irvine CA. Its for Irvine Vally College. So Cali.

[Huntington]

http://www.rewci.com/solar-8-watt-water-pump.html

just a thought, this system is a solar water pump and battery. The runs off solar during the day and charges an SLA for night time use. Only about 4 hours of battery run time. All for only $160. I bet a bigger battery and larger solar cell can extend the night time run time. Something like that could take care of the water pump and its not all that $$$

[Mike90250]

You are wanting a lot, for only $3,000 I don't know if it can be done. As soon as you add batteries to the system, you now need almost 4x the original solar panel to recharge the daes battery, and still run everything (fan & pump) I'll look back in later when I have time to look up the stuff you need,

[Sunking]

Thankyou for the advice and numbers but I think your missing the point of this project.

No I did not miss the point that is why I said you need a lesson in economics, you cannot do what you want to do for $3000. For $3000 you might be able to run the lights, but based on the power you stated you are not going to touch the pump or fans for $3000.

We need to keep a $3000 budget and I dont think we need such a large system. The pump is already running on solar, we just need a way to keep it going at nigh. Im sorry for the limited details, more are on the way.

I understand that but you are fighting pure physics and unlike human laws you can not violate the Law of Physics.

My numbers are correct based on what information you provided and my assumed location of Tulsa OK. I knew you were in trouble right from the start because you said the current motor is 110 volts @ 1/4 hp. Ok a 1/4 hp motor at a PF of .85 requires [742 watts per hp x .25] /.85 = 218 watts. Now if you want to run that motor for 24 hours that is 24 hours x 218 watts = 5232 watt-hours. Ok to power that with solar you have to account for the inefficiency of a battery system. If you use a quality MPPT controller the absolute best is 66% period. In reality more like 50%. But for a constant load and careful design we can use 66%. That means you solar panel has to generate 5232 wh / .66 = 7927 wh each and every day to keep up.

Ok with you being in Irvine makes things a little better because that area has a higher radiance than Tulsa. For Irvine you winter Sun hours = 5 hours. So to calculate the solar panel wattage required to run your motor 24 hours we take the watt-hours needed in a day, and factor out the watts by dividing by the hours. so 7927 wh / 5 h = 1459 watts, round up to 1500 watts of solar panel wattage are needed to run that motor 24 hours per day. FWIW a 60 watt solar panel was not running your motor based on the information you provided., it is physically impossible because your motor needs almost 8000 watt hours per day and your solar panel can only make 300 to 500 wh in the summer months. Does not compute.

But guess what you did? You decided to switch motors to a very inefficient 12 volt motor that requires 60 amps. Watts = Voltage x Amps. 12 volts x 60 amps = 720 watts. You increased your power demand 3 times. Instead of using the AC motor that requires a 1500 watt solar array, you now need a 4500 watt array to do the job. We have not even discussed lights and fans because there is no point, you do not have the budget to touch it.

I know that is not what you want to hear and sounds like I am trying to discourage you but I am not. I am trying to get you to think this through in realistic terms If you are an engineering student, look at the numbers, they do not lie . Now if you gave me the wrong numbers, well what can I say other than don't shoot the computer for entering the wrong data? So you need to hammer out the real power requirements to do this. First step is to nail down your daily watt hour requirements. Otherwise in a competitive market if your green house is growing roses and it cost you $2 to grow a rose, and your competitor sells them for $1, you are out of biz.

[Sunking]

http://www.rewci.com/solar-8-watt-water-pump.htmljust a thought, this system is a solar water pump and battery.

Have you run any numbers on this pump? Something is very wrong with their specs:
Power = 8 watts
Max intake = 2 gpm
Max lift = 6 feet @ 3.5 gpm

Both numbers are not even physically possible at 8 watts.

[Huntington]

Sunking;

Thanks for the advice but I dont want to hear it cant be done. In my world anything is possible. Our budget is small but so is our need.

All the numbers you throw out are worthless. The current fan and pump can be replaced. The pump is running off solar only right now, possible or not. All I want to do is add a battery for night time use and solar to charge the battery.

The fan can be eliminated, when I saw it was 110v I had doubts but though we should give it a try.

The point of the project is to demonstrate an off the grid approach at power, not to make a kick ass all inclusive system.

I do appreciate your interest in this project but if your opinion is, it cant be done.. I have no need for your input. What I do need is suggestions, off the wall and outside the box.

[Mike90250]

Your only chance to do what you are asking, for $3000, is to contact some solar PV mfg's and ask if they would donate some solar PV panels.

First, we need what what has to happen,
Air flow, in CFM
Water flow, in GPM and head
Lighting, how many lumens, how many hours.
Manual controls or automatic
Is Grid power avaib if there is a 2 day rainstorm?
Who will add distilled water to the batteries, or do you need sealed batteries (more $$)
Do you need to buy racks for the PV, or will the maintainaince dept build them?
What's the required lifetime? 2 years, 6 years, 15 years?
Does it need to pass city inspection?
Do you have a local vendor, or will stuff be shipped from another state?
Using high efficiency AC motors is way better than brushed DC motors that will not last 1 year.
For 5,000 lumens of light, you could use pricey LED's (30Watts), or metal halide bulbs(300W). If metal halide, you need 10x the solar power. Lots of trade offs needed to be considered.

[Jason]

Sunking;

Thanks for the advice but I dont want to hear it cant be done. In my world anything is possible. Our budget is small but so is our need.

All the numbers you throw out are worthless. The current fan and pump can be replaced. The pump is running off solar only right now, possible or not. All I want to do is add a battery for night time use and solar to charge the battery.

The fan can be eliminated, when I saw it was 110v I had doubts but though we should give it a try.

The point of the project is to demonstrate an off the grid approach at power, not to make a kick ass all inclusive system.

I do appreciate your interest in this project but if your opinion is, it cant be done.. I have no need for your input. What I do need is suggestions, off the wall and outside the box.

why not just provide more solid details rather than automatically doubting the people trying to help you?

you acknowledged yourself your short on details. find them out and you can get exact answers to your situation.

[Huntington]

The problem with providing details is, there are none.

All we know is, they would like some light to work at night for a few hours. We have a pound that has a pump, the pump is run by solar, an unknown panel and pump watts. The pump needs to run at night too. The fan is an ac fan running off the grid. It was brought up that it would be nice to be able to have a back up system for the fan when there is power failure.


The lighting will be controlled by a switch. The fan is already on an automatic system. We do have maint persons to look after the system but as always with any project, we need to keep maint to a min, spend more on battery's to eliminate the need for water.

The amount of light should not be much, LED are an idea but they are pricey and not very bright.

One solar panel is mounted on a pole, we have another pole to use as well as the roofs on other buildings.

...Im only saying dont post that it cant be done, no need for a negative post like that.

[Jarod]

you may give us the wrong current of the pump
720W pump is huge for your 25'

[Huntington]

The pump is for a small pound outside the green house, I think it is the wrong spec though. I am just going by what I was told. I will check out the site monday and double check everything. I can change out the pump to anything though. The pound is very small, only about 12' across and not very deep. It promotes wildlife and the pump is just to cycle the water. Nothing set in stone regarding how much water needs to be cycled.

[Sunking]

The problem with providing details is, there are none.

Sorry you do not like my answers; but how do you expect anyone to help you without details?

Good Luck

[russ]

First thing to learn about engineering - you deal with facts! Wishes and the bosses demands mean little or nothing.

İf you think you have the wrong facts such as the pump details then you get them yourself.