Question About Solar Power

axim

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Mar 16, 2006
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Pardon my ignorance, but I can't figure out how to post a new thread. I have a similar question. I want to use a 30W 2AMP solar panel to charge a 12V 60AMP battery connected to a 1200W power inverter. This solar generator will power a 400W water pump several times a day for a few minutes. Total pump activity should not exceed 1-2 hour a day. In addition the generator would power a camping trailer with a built an on board 12V battery and charger. My question is, would the 30W solar panel be enough to charge the 12V battery and how long would it take to charge on both sunny and cloudy days?

Thanks
 
Last edited:

Keith R

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Jan 1, 2002
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Axim, I moved your post into its own thread, so it gets more attention.

In the future, look to the button on the top left of any forum you're in that says "New Thread." Click it and follow steps from there.
 

axim

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Mar 16, 2006
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Keith R said:
Axim, I moved your post into its own thread, so it gets more attention.

In the future, look to the button on the top left of any forum you're in that says "New Thread." Click it and follow steps from there.

Grately appreciated!

Axim
 

NotLurking

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Jul 21, 2003
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Axim, the answer to your question is: YES, the solar panel can charge the 12v battery under the right conditions. The time needed to charge the battery to full capacity depend on many factors. In short, what I'm trying to tell you is:

  • you are not asking the proper questions
  • you need to provide MORE information to get a better answer
  • and...the system you suggest is marginal, at best, for the job

A clear indication that the system is inadequate is the reserve power capacity of ONLY 720 watt-hours. The 720 w/h battery capacity, for all intent and purposes, is really 360 w/h or 50% of total rating, not even allowing 1 hour of use per day in cloudy weather.

The inverter clearly needs at least another 12v - 60A battery. The inverter is a 1200w unit that needs as input 1200w + (~12%) = ~1344w to output the full 1200w of power. If the pump is for a pool, the motor will probably be an induction type requiring 2-3 times its rated consumption at startup - or 800-1200w the first few seconds of startup, pushing the inverter to its maximum rated power, requiring 112A at 12v for a few seconds. Although the lonely 12v-60A batt will, in a pinch, and if fully charged, provide the needed 112A for a couple of seconds, I would not recommend this type of use for deep cycle batteries.

Have you considered using a 12v DC pump motor and dispensing with the inverter altogether?

When considering any solution that includes solar cells (panels, PV) remember that the cells will provide the rated output when the sun is perpendicular to the cells. This makes the average 'solar' day 5-6 hours long.

Calculating what would be needed in terms of PV (solar panels) and storage (batteries) is not too difficult. Lets consider your situation....
  • induction pool pump 400w (120AC -3.33 Amps -- apparent power - assuming perfect power factor)
  • pump startup 3x400 = 1200w
  • If and only if, only the pump will run off the inverter 1200w unit would work but I prefer 1500w.
  • Assuming inverter efficiency at 88%, 1344w of input is needed to get 1200w output.
  • Allowing for 2 days of backup with no sun and a typical 2 hour day pump use.
  • Finally assume 6 hours of sun per day.

pump uses 400w per hour for 2 hours = 800w per day
800w x 2 = 1600w for 2 day reserve.

1600w x 2 = 3200w Total battery capacity needed.

You'll need one battery bank of 12v - 267Amps.

Since maximum (normal) battery discharge will be at 50% total capacity, or 1600w, will need to be replaced in 6 hours, 2 PV panels of 120w (actually 130w) should work nicely.

In the event that you don't care for backup reserves, don't plan to use the pump on cloudy/rainy days, will be discharging your batteries over 50% (not recommended) or don't care if you don't fully charge your batteries in one day (6 hours of sun), you can have a MUCH cheaper and less sophisticated system.

As and example.... same pump with no backup capacity, batts 75% discharge allowed.

One batt bank 12v - 100Amps = 1200w
One 130w PV panel 6 Hours charge time for 1-3/4 hour of pump use (6 hours of good sun per day)

NotLurking
 

axim

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Mar 16, 2006
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NotLurking said:
Axim, the answer to your question is: YES, the solar panel can charge the 12v battery under the right conditions. The time needed to charge the battery to full capacity depend on many factors. In short, what I'm trying to tell you is:

  • you are not asking the proper questions
  • you need to provide MORE information to get a better answer
  • and...the system you suggest is marginal, at best, for the job

NotLurking

Thanks for a quick reply. Let me try and provide more information. The generator consist of a power box (see link)
http://www.canadiantire.ca/assortme...4443271702&assortment=primary&fromSearch=true

and two 15W solar panes (see link)
http://www.canadiantiresolar.ca/english/15w.htm

The pump is a 1/2 Horsepower shallow well with a 5 gallon reservoir attached to draw water from a lake into the trailer. The power box needs also to supply power to the trailer.

Besides 130W panel and battery banks, what else would you recommend?

Thanks again,

Axim