System recommendations for PV Newbie

System · March 2008

Hi Folks,

I am in process of putting up some WiFi/Radio internet line of Sight towers to provide internet for a small rural setting.

I am now at a point in my tower placements that I require a remote tower or two in order to complete the service to this community.

Each tower that i have hooked into AC, uses only about 8 watts (registered with a kill-a-watt pro).

The area that these will be in get about 4 or 5 hours minimum of direct sunlight (Northern Idaho/British Columbia Border)

I would like any recommendations that you all might have regarding size, brand for the equipment.

Thanks!

mike95490 · March 2008

Re: System recommendations for PV Newbie

So a real quick calculation is only going to be in watts, as you did not assign a system voltage.

8 watts for ease, and margin, rounded up to 10 watts 24/7. 240WH / daily

Since this is a "high reliable link" you would likely like it to run for 4 or 5 days of bad weather. (What's the longest stretch of bad weather do you want to endure?)

5 days x 240KWH = 1250 KW capacity needed
( @ 12.5V this would be 100AH, requiring a 200AH battery to not get discharged below 50% for long battery life )

Now a panel that can recharge a flat battery in one, or 2 days ??? figure 4 hours of sun in the winter (on the completely cloudless days before and after your 4 day storm) That would be a big panel (100AH in 4 hours) Call it 2 sunny days to recharge - so 8 hours of light 1.25KW would be about 156Watt panel, under perfect conditions, and no system losses or un-equal battery charge times factored in.

A MPPT controller would be nice, to get the extra power from the cold winters sun, but about 500W is the equilibrium point of it's own internal losses, and your system is smaller than that.

What's the coldest the battery pack will get, any chance for heat - frozen batteries are useless.

How will the radio and router handle the shutdown and restart if the voltage fluctuates at end of charge, and will they start as voltage slowly ramps up - sometimes a soft power application never hits the reboot circuit.

System2 · April 2008

Re: System recommendations for PV Newbie

Wow, thanks for the deatiled response. I appreciate it.

The repeater equipment can all be run on either 12 volt or 24 volt, So that is why I did not specifiy. I thought I would find out what people had to say on the topic before I decided.

As for your calculatipons on Worst Case Scenario, you are correct in applying a 4 or 5 day window to a bad storm moving throughout this area of the country.

So, If I read you correctly:

1) Assuming 12 volt subsystem
a) 160 watt plus panel is adequate
b) either 2x100 amp hour deep cycle batteries in Parralel or 1 gigantic 200 amp hour battery is adequate
c) A maximum Power Point Tracker is recommended but not necessarily required for this application.

So would 2 80watt panels actually be better or keep it simple with one panel ?

You seem to know your stuff, would you recommend any specific equipment or dealers to purchase this equipment?

Thanks again for your help!

Mike Kietzman

Solar Guppy · April 2008

Re: System recommendations for PV Newbie

Also, the new ( soon to be shipping? ) MorningStar Mppt would be a perfect fit for your type of application

http://www.morningstarcorp.com/products/SunSaverMPPT/SunSaverMPPT.shtml

mike95490 · April 2008

Re: System recommendations for PV Newbie

mkietzma wrote: »

So would 2 80watt panels actually be better or keep it simple with one panel ?

I'd go with a single panel. I'd look at something in the 200W range w/ a MPPT controller.

Run one in your back yard for a couple days, lat it charge, run radio, and cover with a tarp for a day, and see what the battery drop is, to confirm it will work as long as you need it to.

I'd also look at AGM batteries, you won't be doing fast charges, and they don't need water monthly. Hopefully, the new SunSaver MPPT will work with it (link was down when I went to look)

niel · April 2008

Re: System recommendations for PV Newbie

you should note that your continuous operation should be designed against the worst case conditions. part of that was addressed with the 5 day outage possibility and the reserve battery capacity, but you will not get 4-5hrs of full sun in january. for that worst month scenario you will get at best 2.9hrs for a flat plate collector aimed south and at latitiude +15degrees tilt based on boise, idaho. http://rredc.nrel.gov/solar/pubs/redbook/PDFs/ID.PDF
this changes your pv requirements with less full sun available. figuring the 8 hours you needed between 2 days before for charging you now will need 8/5.8=1.38 times as much power from the pvs to deliver that same charge in that 2 day span. 156w x 1.38=215w. one must go minimumly with 215w and maybe an agm battery of around 200ah.
this will work in most cases in the winter, but there's always a small percentage of times it will be worse so some kind of provision to be able to feed a charge to the system from another source may be needed. this could be an ac charger fed from a generator with a tap running up to the battery with accessibility in mind. if the site is inaccessible for very long periods of time you may not come to its rescue in time before the battery is killed and service is disrupted.
this also brings up the fact that most batteries will not be mounted near the transmitter's height so care must be taken to observe wire resistive losses and that can be done with the voltage drop calculator in the sticky in general solar topics.

System recommendations for PV Newbie

Comments

Categories