Solar Options for Tower

[Adina]

I've recently determined I am grossly undersized in my solar deployment on a new tower. I'm sure it is due to not having enough panels, and possibly my choice of 24V instead of 12V. I need help getting this sized properly, as my math and my references are all frazzled.

To describe it:

4 mikrotik 411A units (3W max)

3 XR2 and one XR5 cards in this array. (1.3A Max)

1 mikrotik RB150 (3W max?)

1 SR9 (1.2A Max)
1 R52H (.8A Max)

1 mikrotik RB750 (3W Max)

MorningStar SS-10 charge controller (10A/24V)

2 35Ah sealed batteries @ 24V

I currently have an 80W array at 24V, and have another 40W panel to patch in today. I am sure I am undersized, but am coming up with numbers that scare the numbness out of me. Thoughts/suggestions?

Thanks,

Taylor

[knightshade]

do you have a controller for charging

[Dave-D]

Taylor, first you need to convert all the
loads to watts; you have a mixture of
watts and amps; they're not the same.

Add the watts up and multiply by 24;
that's the watt-hours [W/hr] you
need to supply equipment each day.

If there's no sun, the battery must
provide this power. A battery should
never be discharged below 50%; your
batteries have 2*35x24*50% or
840W-hr storage.

Divide 840 by your load in watts to
determine the number of hours your
battery bank can supply power in
the absence of sunlight.

When the sun does shine, solar
panels will produce rated output
only during mid-day; output is
also seasonal; for your panels, it
ranges between about 500 to 1100
W/hr each clear day. On a heavily
overcast day, it could be zero.

The panels must supply both the
needs of your equipment and the
ability to recharge the battery.
So you need to calculate the
total budget for worst-case.

Ubiquiti has an app note on solar
power; take a look:
http://www.ubnt.com/wiki/index.php/Planning_a_wisp_solar_powered_tower

Have fun! Dave

[Adina]

Dave,

Thanks for your reply, and the link! I really appreciate any help in getting my numbers right, I am way under...

Corrections:

My batteries are 35Ah 12V batteries wired in series.

The reason for the mixture of amps and watts is the ratings I can find online. I am unsure how to properly calculate watts for the MiniPCI cards, is the voltage 3.3V when in use? Would that make it:

1.3A x 3.3V = 4.29W

That would give me:

8.5W per 411 AP
10W for RB150 AP
3W for core switch/router

Totals now in watts are:

8.5x4 = 34W + 10W +3W = 47W*24=1128W/hr

1128W/hr needs 282W of panel in my 4hr winter zone.

4 days of power = 4512W/hr

Converted to A/hr - 188A/hr battery bank @ 24V - Currently have 35A/hr

I plan on solving this problem immediately, with an AC circuit as primary until this is fixed.

Thanks,

Taylor

[Dave-D]

That 3.3V figure will give you about
the right wattage; add at least 10%
for power supply losses.

Batteries are now: 2X35X12 X50%,
or 420W/hr. If you want to keep your
load alive four days with no charge,
that's 4512/420, or 10.75 times as
much battery storage. Ouch! Dave

[Adina]

YEOW! Batteries for this tower could quickly hit another $600, and I simply don't have it right now. Not to mention another pair of panels....

Question:

Would running 12V make ANY difference? Seems not.

Thanks,

Sad Taylor

[Dave-D]

Typically, running higher voltage
gives higher efficiency because
there is less loss in cabling.

The only time 12V might make
better sense is if you are able
to run the devices directly from
12V, eliminating power supplies. Dave