small telcom project - need advise

System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
Hi Everyone!

I have been trying to figure this out on my own, but I just can't get it.

I have some small telcom units that I'd like to solar power. I don't have many details but here it goes.

Unit #1 12VDC 7.5 watts
Unit #2 12VDC 4 watts

This is just according to the manufacturer. I'm not sure how to measure the exact usage, but would like to know how.

I just need a system that will run these units everyday all day. The project is near Denver, CO.

I REALLY appreciate any thoughts and help you all may have.

Thanks a bunch!
Eric
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Comments

  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #2
    Re: small telcom project - need advise

    Eric,

    Based on the specs provided, your energy requirement will be (7.5 W + 4 W) x 24 hours = 276 Wh/day. From a nominal 12 V battery, that would be 276 Wh/day / 12 V = 23 Ah/day. However, the coulombic efficiency (Ah out / Ah in) of a flooded-cell lead-acid deep-cycle battery is only ~90%, so you’d need to generate 25.6 Ah/day

    Lowest insolation on a south-facing PV module tilted up at latitude + 15 degrees (~55 degrees) in the Boulder/Denver area averages 4.5 hours/day in December. This suggests that you’d need a PV module rated at 25.6 Ah/day / 4.5 hours/day = 5.7 A (STC Imp). The probably means a PV module rated for ~100 W STC. Something in the 120 W ~ 130 W arrange would provide some cushion for a 24/7 system.

    Allowing for three days of autonomy (virtually no Sun during a long storm event) and limiting battery discharge to 50%, you’d need a battery rated at 23 Ah/day x 3 days / 50% = 138 Ah. This would be something like a Group 31 size 12 V battery.

    If you go with a flooded-cell battery, you’ll probably need something like the Morningstar ProStar 15M controller to properly charge and maintain the battery. If you go with an AGM battery (more expensive but more efficient and less maintenance), then you could get by with a Morningstar Sunsaver 10 controller with low voltage disconnect (LVD).

    These are the basics. Many of the items described are available from this site’s store. Is this what you had in mind?

    Regards,
    Jim / crewzer
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: small telcom project - need advise

    Thank you for the response. That's exactly what I was looking for. I had no idea this tiny equipment would require such a large panel. Sounds like I need to find some new equipment to use that requires less watts. We just don't have the room for such a large panel.

    I'm curious the size panel needed for 12VDC @ 5 watts? I have a few equipment options available.

    I really appreciate your help!

    Eric
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #4
    Re: small telcom project - need advise

    Eric,

    The system sizes generally scale proportionally. If an 11.5 W 24/7 load needs a minimum 100 W PV module, then a 5 W 24/7 load will need a....

    One thing to bear in mind is that the charging voltage for the "12 V" battery will likely be at least 14.1 V, and could approach 16 V for cold temperature equalization of a flooded-cell battery. You'll need to verify that your 12 V loads can handle that high a voltage. If not, you'll have to consider a DC-DC converter, and its loss will have to be factored into your energy requirement.

    HTH,
    Jim / crewzer
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: small telcom project - need advise

    i'll throw an extra wrench into this by asking if that wattage you state is rf watts or dc watts? if it is rf power it takes much more power in dc watts to produce the rf wattage and i might add that rf transmitters are not all that efficient.
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: small telcom project - need advise

    @crewzer - thanks for the input. The equipment should be able to handle the flux in power I think. The manual states 12-24VDC.

    @niel - these are DC watts not RF watts.

    Thanks again for all your help!!
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