Need help with small system

[jagjohn2000]

We are doing a wireless point to point system for a customer. We have power at one side but at the other we do not. Have a clear view of sky without any obstructions. Trying to get a system sized. We are in southern Kentucky and will be using two pieces of equipment with a total max consumption of 17 watts @ 2 amps. Probably will never pull full draw out of modem or ptp equipment. Need to be powered on 24/7 365. Cost isnt a huge factor but the cheaper the better. Seen some systems with 100 watt panel and charge controller and add a 100 ah battery. Hope this will work or can i go with less or will i need more?

[Amy@altE]

What's the voltage of the equipment? Is it 9VDC? (17W / 2A= 8.5 volts). If so, you'll need a DC/DC converter to bring the 12V battery down to 9V.
17W x 24 hours = 408 watt hours (Wh) / 3.6 sun hours (winter in KY) / .6 system losses = 188 watts, round up to 200W solar needed / 12V = 20A charge controller.

408Wh / .9 efficiency for DC/DC converter (guess) x 4 days without sun x 1.4 temperature compensation (30F) x 2 (50% DoD) / 12V = 423Ah 12V battery bank.

[jflorey2]

Need to be powered on 24/7 365. Cost isnt a huge factor but the cheaper the better.

Those two statements don't really go together. For reliable 24/7/365 power you need a battery bank, two high quality generators, a good transfer switch/controller and an inverter. Solar (being unreliable) can extend the time between fuelings but can't do the job itself.

If you want a 95% (or even 99%) availability now you are moving into solar territory. If there is some synchrony between use and daylight hours (i.e. power only used during the day) then you'll save a bit on battery size as well. Amy's numbers above are a good starting point. I would also consider a LiFePO4 battery instead of a lead acid if this will be in a remote location; less weight to move and fewer service calls. Much higher initial cost but lower overall cost.

[Amy@altE]

I would also consider a LiFePO4 battery instead of a lead acid if this will be in a remote location; less weight to move and fewer service calls. Much higher initial cost but lower overall cost.

If you did go with lithium, you could also use a smaller battery bank, because you can use a lot more of the energy stored in the battery, you could plan on a 80% depth of discharge (DoD), and depending on the battery used, don't need temperature compensation. 408Wh / .9 efficiency for DC/DC converter (guess) x 4 days without sun / 80% DoD / 12V = 188Ah 12V lithium battery bank.

[jagjohn2000]

This is not a critical system, so 24/7 365 is a stretch. They currently subscribe to satellite internet so they are used to getting terrible performance already. If there was a day or two down time here and there that would be ok. I just meant that the equipment will be powered on continuously. I haven't looked at the Lithium but I will sure check it out. Is there a longer life expectancy out of those as well? System is actually all 110v so I would have to invert to 110 so there will be loss there too. Unless there is an easy way to run modem at 12v 1.5amp and a ubiquiti LBE at 24v @ .3 amp.

[jflorey2]

This is not a critical system, so 24/7 365 is a stretch. They currently subscribe to satellite internet so they are used to getting terrible performance already. If there was a day or two down time here and there that would be ok.

Then it sounds like a solar solution would be reasonable. You will effectively pay for reliability, quickly reaching a point of diminishing returns (i.e. it's easy to go from 95 to 97% availability, a lot harder to to from 97 to 99%.)

I just meant that the equipment will be powered on continuously. I haven't looked at the Lithium but I will sure check it out. Is there a longer life expectancy out of those as well?

Yes, much longer. If you treat them like a lead-acid (i.e. 50% maximum depth of discharge) then you'll see ~10X longer lifetimes. As Amy mentioned, you could also plan for 80% DOD to save some money, although then your cycle life goes down.

System is actually all 110v so I would have to invert to 110 so there will be loss there too. Unless there is an easy way to run modem at 12v 1.5amp and a ubiquiti LBE at 24v @ .3 amp.

Sure; run a 24V system and use a 24 to 12V buck converter or halver.

[Mike90250]

Many lithium's have a thermal Low Temp limit. If these are going outdoors, they need frost protection ! Or put them indoors.