Gold Miner In Need Of Help

Re: Gold Miner In Need Of Help

OK, we can give some estimates now...

• 4* 12 volt @ 100 AH batteries = 12 volts @ 400 AH storage.
• 15 Amp @ 12 volt pump
• 400 AH / 15 amps = 26.7 Hours

Now--The 100 AH capacity is at a C₂₀ discharge rate (100 AH battery /20 hours = 5 amps for 20 hours for from 100% to 0% state of charge). Now ~27 hour discharge rate is "close enough" for our needs (battery will appear to have slightly more than 100 AH capacity when discharged at less than a 20 hour rate).

Normally, for an off grid application, I would be suggesting that you discharge ~25% per day (2 days of stored power, 50% maximum discharge for longer battery life). You could discharge to 50% every day--But you may have problems getting back to 100% charge because there are not enough hours in the day of sun (it would be close in the desert--you may have enough hours of sun per day--just barely--Basically 10% rate of charge, ~5 hours to recharge the battery and another 4+ hours of "absorb" or holding voltage at ~14.8 volts to get from ~85% State of charge to 100% state of charge).

Now, to keep a battery bank "happy", we recommend around 5% to 13% rate of charge, and for a daily/heavy cycling, you will really need a 10% to 13% rate of charge:

• 400 AH * 14.8 volts charging * 1/0.77 panel+controller eff * 0.05 rate of charge = 384 Watt array minimum
• 400 AH * 14.8 volts charging * 1/0.77 panel+controller eff * 0.10 rate of charge = 769 Watt array nominal
• 400 AH * 14.8 volts charging * 1/0.77 panel+controller eff * 0.13 rate of charge = 999 Watt array "cost effective maximum"

Next, based on how much you want to use the pump and hours of sun per day, using PV Watts for Flagstaff AZ, fixed array mounted at 35 degrees from horizontal (you can move the rack a few times a year to get a bit better power):

Month    Solar Radiation (kWh/m 2/day)
1      5.19     
2      5.92     
3      6.27     
4      6.44     
5      6.56     
6      6.61     
7      5.95     
8      5.54     
9      6.59     
10      6.19     
11      5.47     
12      5.07     
Year      5.98

So, say a minimum of 5 hours of sun per day and assuming that you charge during the day and use power at night (all power is supplied by the battery bank, and all day time sun goes into charging) and you use 25% of the battery storage per day:

• 26.7 hours storage * 0.25 discharge per day = 6.675 hours per day usage
• You want to use 8 hours per day (still will probably be fine on your 100 AH)
• 15 amps * 14.8 volts charging * 8 hours of use * 1/0.77 panel+controller eff *1/0.80 battery charging eff * 1/5.0 hours of sun = 437 Watt array minimum

Now that is for 8 hours of pumping per "night". your application is probably going to be pumping during much of the daylight hours... That is going to help you a lot--The motor is going to draw a lot of its power directly from the solar array (no 80% battery efficiency issue), and the battery bank will not be discharged as deeply. However, 15 amps that was going to keep the battery bank "happy" during charging is now not available--So, ideally, you will want to account for that "loss" of charging energy:

• 15 amps * 14.8 volts charging * 1/0.77 panel+controller efficiency= 288 Watts from array direct to battery bank
• 384 Watt array minimum + 288 Watts to power pump = 672 Watt array minimum with day time pump load
• 769 Watt array nominal + 288 Watts to power pump = 1,057 Watt array nominal with day time pump load
• 999 Watt array nominal + 288 Watts to power pump = 1,287 Watt array cost effective maximum with day time pump load

So, I could see justifying a solar array of 672 to 1,287 Watts, with 1,057+ Watts being a "healthy sized array"--Plus, since you are using the pump during daylight hours, you could probably run camp lighting, radio, laptop computer, etc. at night with the "spare energy (remember, you only need ~437 Watts of the array to supply the actual pump load during "average" sun conditions in winter).

Obviously, there will be some times that you need to use a genset if you have more than 1-2 days of very dark/cloudy weather (or shut down/reduce your operation until sun returns). 400 AH battery bank with a ~45 amp 12 volt Iota charger + a Honda eu2000i (1,600 watt) genset or Yamaha equivalent inverter-generator would be fuel efficient and quiet backup power supply (when needed).

You will also need a hydrometer (this one from Midnite is well liked, rinse with distilled water after usage), a Battery Monitor (Victron another good brand), and a DC Current Clamp DMM, would all be handy.

Another off the wall suggestion--If you only pump during daylight hours, you can pump direct from solar with a Linear Current Booster:

http://www.solar-electric.com/dankoff-solar-pumps-controller-dsp200.html

Assuming:

• 15 amps * 12 volts * 1/0.77 panel derating * 1/0.80 LCB eff = 292 Watt array minimum

Since you will be pumping at other than the middle of the day, you can make the array larger to give you more hours a day of 15 amp @ 12 volt output. Using PV Watts for December, and the hourly data option, a 1,000 Watt array would look like:

1974, 12, 21, 08:00, 0
1974, 12, 21, 09:00, 139
1974, 12, 21, 10:00, 264
1974, 12, 21, 11:00, 450
1974, 12, 21, 12:00, 471
1974, 12, 21, 13:00, 449
1974, 12, 21, 14:00, 188
1974, 12, 21, 15:00, 188
1974, 12, 21, 16:00, 148
1974, 12, 21, 17:00, 4
1974, 12, 21, 18:00, 0

15amps * 12 volts = 180 watts

So, roughly, a 1,000 watt array on the shortest day of the year + LCB would (and 62% estimated efficiency) would give you 9:30 to 3:00pm pumping without any batteries (or solar charge controllers, etc.)... A possible option (batteries make the system very expensive, have to replace every ~3-5 years, etc.).

Your thoughts?

-Bill