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15W solar powered system

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15W solar powered system
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Compulsive poster:)
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Joined: 11 Oct 2003
Posts: 142


Post 15W solar powered system Reply with quote
Hi guys,
you need to open a section that deal with the discussion on solar systems and operations.

ok, here `s my question.
how do you calculate battery drain time for a given load , example 15 watts system.
Tue Dec 22, 2009 3:28 pm View user's profile Send private message
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Joined: 18 Jan 2002
Posts: 3122
Location: Radio Land

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1. Establish voltage needed, say 12V
2. Establish battery capacity, say 1A of current for 24h = 24Ah battery for a system drawing 1A of current at 12V.

You need a battery that's at least 24Ah and 12V for the system to work 24/7 assuming you have 1 dark day from time to time.

Now assume you have 8 effective hours of sun per day and you need to fully charge that battery in this time.
If your solar panel is 12-15V as well and no inverters are used, you need to provide current of 24/8=3A at 12V
3A*12V=36W. You need 36W solar panel.

But since battery charging is not 100% efficient and you also don't get 36W of electrical power from 36W solar panel
due to angle of light, partial cloudiness etc it is better to take 2x more. Also while charging battery you are also powering
your transmitter so for those 8h you need 1A*12V additional power, which is another 8W. So you arrive at a figure of
80W, which is a good rough estimate.

Obviously if you are living in Norway this won't work very well due to low sunlight, exact calculation would take this
into account. Online calculators exist that will let you calculate exactly depending on your location.

So, to keep this simple, a system drawing 1A/12V would produce around 3-5W of RF power depending on design.
Using this analogy you need 3x more for 15W system, meaning you need 80Wx3= 240W solar panels and 24x3=
about 75Ah battery, better take 100Ah.

Best regards,
Marko - PCS Electronics
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Wed Dec 23, 2009 8:55 pm View user's profile Send private message Visit poster's website
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