system sizing

jmtheman28

How do I size solar panels to charge the batteries I need. I have a pump that operates at 230V and 10 Amps for 8.5 hours/day. My assumption is that I need solar panels capable of 2300 watts (230x10), and batteries that are wired to have 24V, so 2300W x 8.5 hr / (24 V * 80% efficient) = 1020 AH capacity? So I could use 11-210Watt solar panels and 10-212AH batteries with 5-5 battery wiring. Am I looking at this right?

icarus

Re: system sizing

Whoa,, take a deep breath!

You pump use translates to ~ 19 kwh/day. That is a huge draw for any battery based system.

The simple rule of thumb is you can take the name plate rating of a solar panel (in watts)
divide that in 1/2 to account for total system loses, then multiply that number by 4 (the average number of hours of "good" sun.

So for example, 2300 watts of panel might produce net/net 2300/2*4=~4600 wh/day

So in reality you might need nearer 9000 watts of PV.

Now, these numbers are a bit nebulous for water pumping, but you will have considerable losses to consider,, even if you pump directly from the PV with no batteries and inverters. (The numbers get better, but you still need to find ~19kwh of power per day) 19 kwh just to pump,, call it 35 (or more) if you pump using a battery,, and that is no reserve.

It is important to realize that no matter how you cut it, there are many loses that people over look. You start out right, realizing that your panels will only yield ~80% of rated on any regular basis. Next, you have wiring loses between the Pv and the controller, controller conversion loses, more wiring loses to the battery, basic battery charging efficiency (In rough numbers it takes ~125 ah of charge to replace 100 ah of draw), more wiring loses to an inverter, basic inverter conversion loses, and finally more wiring loses to the pump.

I suggest that you first read and understand the following:http://www.batteryfaq.org/
Followed by the water pumping threads on this forum.

There were some threads just recently that address this very issue,, that of large pumping needs. The hard reality is water pumping is takes a lot of power. (Just carry a 5 gallon bucket up the stairs and one will find out real quick!)

Good luck and welcome to the forum.

mike95490

Re: system sizing

Can the pumps run daytimes, or all at night? If you can use daylight to run them for 6 hours, that's 6 hour s of battery you dont have to store.

Whats the penalty if there is 4 cloudy days, and not enough power to charge or pump? Cattle die off or you just don't do laundry?

230V @ 10 A is a REAL HEAVY LOAD (2,300 watts run, and 10x that to start) I'll assume it's 3 phase? Do you have a phase controller to take single phase 230V and create 3 phase, or would you need a 3 phase inverter?

jmtheman28

Re: system sizing

The pump is 3 phase but I am not sure which inverter to use for 3 phase?

Cariboocoot

Re: system sizing

jmtheman28 wrote: »

The pump is 3 phase but I am not sure which inverter to use for 3 phase?

This is so "not the place to start" for getting your feet wet in solar! (Mixed metaphor of the year award!)

Three phase requires some fancy wiring to get from solar. Like three Outback FX's. Read that as $6,000 worth of inverter, just for starters. There are some 'transformers' (can't think of the right word) that allow the operation of 3-phase motors from single phase current. Again; money. Chances are this is not going to be an economical solution no matter how you solve it.

As Tony has already mentioned, your power requirements are massive. Way too much to be practical in solar terms. 9kW of panels would run another $8,000.

My opinion is that you should look into a different power source (what's wrong with the grid? Unavailable? Undependable?) or a different pump that's designed to run from solar: http://store.solar-electric.com/sun-pumps.html
That may require some rethinking of your pumping operations (big storage tank, etc).

BB.

Re: system sizing

There is a way of running 3 phase pumps from single phase--Look up VFD (Variable Frequency Drives)... They are pretty cool devices and can be very nice for the job... But, in the end, a large motor / load on solar will result in an expensive off grid solution.

-Bill

solar_dave

Re: system sizing

Cariboocoot wrote: »

Three phase requires some fancy wiring to get from solar. Like three Outback FX's. Read that as $6,000 worth of inverter, just for starters. There are some 'transformers' (can't think of the right word) that allow the operation of 3-phase motors from single phase current. Again; money. Chances are this is not going to be an economical solution no matter how you solve it.

.

The acronym is VFD
http://en.wikipedia.org/wiki/Variable-frequency_drive

Cariboocoot

Re: system sizing

BB. wrote: »

There is a way of running 3 phase pumps from single phase--Look up VFD (Variable Frequency Drives)... They are pretty cool devices and can be very nice for the job... But, in the end, a large motor / load on solar will result in an expensive off grid solution.

-Bill

Thanks, Bill! VFD is what I couldn't think of!

jmtheman28

Re: system sizing

What would you suggest is the max watt-hr/day to run on a day-to-day off grid PV system? 2000 WH/day?

Cariboocoot

Re: system sizing

jmtheman28 wrote: »

What would you suggest is the max watt-hr/day to run on a day-to-day off grid PV system? 2000 WH/day?

There isn't any maximum per se, it's a matter of practicality. My system produces about 2.2 kWhrs per day and it cost roughly $8,000 with me doing the install. I have in fact sized systems as large as 19 kW - it would be about $64,000 just for the panels. You probably don't want to spend that, eh? Your need for 3-phase automatically ups the price because of having to get either the VFD (and thanks solar_dave but Bill got in ahead of you ) or three inverters just to supply the type of power.

And that's what it comes down to; is there a less expensive way to accomplish the same end goal?

In general, you try to find the compromise between expense and "most bases covered" for supplying power. If that means a generator to pump water then you have to decided if that is acceptable. The first step for off-grid is always get the load requirements down to an absolute minimum.

And since I've already been chastised for not answering peoples' questions elsewhere today ...

Basic charging formula calculation:

Total Amp/hrs of battery bank (@ '20 hr' rate) * 10% (5-13 is the range for FLA's) = Target Charging Current.
TCC * Charge Voltage (higher than System Voltage = Absorb set point) = Usable Watts needed.
(UW * 100) / 80 (usual expected panel efficiency) = total panel Watts needed to charge the bank.
(If this is all right the replacing of the Amp hours used usually takes care of itself.)

icarus

Re: system sizing

Marc has it dialed. I would only add, that in addition to giving you loads careful consideration, see what you can slough off on other power/fuel sources
We live just fine on less than a KWH/day, but the only resistance heating appliance we have is a soldering iron! We cook with gas, have a propane toaster, heat water with gas etc. We load shift as much as possible so that as many loads can be powered during daylight hours etc. We then use generators for the shops and other large loads,, including the vacuum cleaner. A few gallons of gasoline per month saves tons of PV costs.

Build the biggest system you can afford, that fits your needs as closely as possible, with some head room to grow as you budget allows. (remember, you can easily add PV, not as easily add batteries.

Tony