Does 100W power need 100W solar panel?

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Does 100W power need 100W solar panel?

Postby convict » Sun May 01, 2016 12:09 pm

I'm going to purchase a 12V 100W Air Pump for aerated purpose. I will have it running only when the sun is out via a solar panel. Can I use any solar panel or should I match it with its rated power.
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Re: Does 100W power need 100W solar panel?

Postby Gordon-Loomberah » Sun May 01, 2016 1:29 pm

That's quite large power for an aeration pump, unless you are using it for a really large tank of water. In my aquaponics systems the backup air pumps are 12V 25W, and they will pump up to 55litres per minute.

What is it that you want to aerate?

A 36 cell 12V solar panel will typically have an open circuit voltage somewhere around 22V, so your 12V pump better be able to handle the high voltage that may sometimes be across the motor or vibrator. Maximum power voltage will usually be around 17V. On partly cloudy days the pump will be going from flat out to stalled many times per day, which is likely to burn it out, unless it is designed for that sort of treatment. It would be much better to use a regulator and battery to deliver regulated power to the pump.

You might typically expect to see up to 75W from your 100W panel on a warm day when the panel is near face-on to the sun, and less at other times. Cloud edge effect periods might see up to 120W from the panel, especially in cooler weather.

If you want reliable aeration in sunny and cloudy weather then it would be best to use a battery and regulator, and probably 200W of PV, arranged as a virtual tracker, to give even output all day.
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Re: Does 100W power need 100W solar panel?

Postby APR » Sun May 01, 2016 8:31 pm

convict wrote:12V 100W Air Pump for aerated purpose. I will have it running only when the sun is out via a solar panel. Can I use any solar panel or should I....


As has been suggested, you would ideally have a battery in the system, however....

You will also need some way of connecting and disconnecting the pump from the battery at the start and end of solar generation otherwise the pump will continue to run until the battery is discharged.

Also, you may find the 100 watt rating is at the maximum pressure the pump can pump. If the aeration hose is discharging at say 600mm depth the pump will consume more power than if it is discharging at 300mm depth. To select as an example the following aeration pump...

http://www.ebay.com.au/itm/AU-STOCK-DC- ... 1904440446

... has a rated discharge pressure of 0.21 MPa. This is equivalent to the discharge hose being at a depth of 5.5 meters. If this pump had the discharge hose at 0.5 metres depth I would expect it to use significantly less wattage than it's 120 watt rating.

The best bet would be to select your pump and measure the wattage it is using when set up as you propose to use it. Then, from the number of hours you want to run the pump each day, you can size a battery and panel to suit as well as select a solar charge controller to handle the amperage and do the time switching required.

If I wanted a system to power a pump drawing 100 watt continuously for, say, 10 hours/day, and I wanted this system to contend with rainy and overcast days, I would be looking at 500 watt of panel power and 200 amp of 12 volt battery power, and even then a series of rainy days would drain the battery.

To do your exercise reliably is not going to be cheap.
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