# small telcom project - need advise

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.

Thanks a bunch!
Eric

• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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
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.

Eric
• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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
• Solar Expert Posts: 10,300 ✭✭✭✭
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.