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Well we started off 2015 with our first solar site. Learned a number of things that should of been looked into more and I find that I am still learning on much. The problem is that the winter has proven to be a bit of pain to keep everything going. We just went thought 3 (yes 3) weeks of overcast, fog, rain, and snow. Yesterday was the first full day of sun so it was a very welcome sign of relief. We are looking at adding some wind power as we generally have plenty of it especially during the winter.

What I would like to know from other solar users or anyone that knows about this subject is what would be the most ideal battery bank voltage to use? I current have it setup as a 12v bank but I am thinking about moving to 24v as I believe the conversion from 12v to 48v on the Netonix creates less efficiency compared to the 24v bank.

The other question that I have is if I move to a 24v system should the overall run time stay roughly the same? So say I would take 4 12v batteries that is currently setup as 400AH and change this to a 24v battary bank it would then reduce to 200AH. But on the other hand if I am thinking of this correctly changing the load voltage to 24v to the Netonix should basically cut the amps used in half compared to the 12V system. That would then basically make the run time identical if not longer a bit longer as the conversion to 48v should be more efficient.

Yes, 24V is much better than 12V

Also if running 24V or 48V you have the option in an emergency to drain the batteries much further and stay up longer!

Higher voltage is going to be better most of the time. As long as your panels produce a higher voltage than your battery bank. That usually ends up as 24v.

If I were you, I'd do the math on how short on solar you are and consider just oversizing your array to compensate. Wind is great, but getting a good turbine can be a serious challenge. We've been through a number of them and had a few catastrophic failures. by catastrophic, I mean they exploded and we never found the blades.... If you do go with wind, look for a unit that can be electronically braked and actually keep the thing stopped until needed.

Look at a VAWT, they can operate at slower wind speeds and don't fail so hard.

A small unit like so:
http://www.ebay.com/itm/30W-24V-ALEKO-V ... SwUdlWhDD8
or
http://www.ebay.com/itm/ALEKO-WGV75-50W ... SwyQtVxUcK

might do the job for you.

No matter what voltage you use, you should use a DC-DC converter. Or even better, use a WS-12-250-DC to run all your equipment off of. If you try running a 24 VDC system without a DC-DC converter, you will have problems. The charge voltage on a 24 system is 29 volts. That is above the 28 volt limit of AirMax equipment. The radios will cut out when the batteries go into charge.

Any new sites I build will be 48VDC and will use a Netonix Smart DC switch!

sirhc wrote:Yes, 24V is much better than 12V

Also if running 24V or 48V you have the option in an emergency to drain the batteries much further and stay up longer!

This is very old, but my thought has always been. 12volt is better because in an OMG it's down because of voltage emergency, you can always hookup jumper cables between your truck, snow cat, side-by-side, or whatever and the batteries to charge. If it comes to down to needing to put charge into a dead or low bank it's much harder to field charge a 24 or 48 volt bank.

If you use 12 volt and the DC WISP switches you need to engineer your site so that each switch's radio load stays below 120watts to ensure you can power everything if the batteries get low.

At present we have 6 DC sites. All are solar fed and a few have wind as well. We use NeverWet on the wind turbine blades to prevent ice and we use RainX on the solar panels to reduce ice as well.

The more batteries the better and monitor your voltage so you know at least 24 hours before the site goes down because of voltage.

LRL wrote:12volt is better because in an OMG it's down because of voltage emergency, you can always hookup jumper cables between your truck, snow cat, side-by-side, or whatever and the batteries to charge. If it comes to down to needing to put charge into a dead or low bank it's much harder to field charge a 24 or 48 volt bank.

A boost converter is *cheap* and can get you up to 26v to charge your 24v array easily with minimal losses. Feeding your Netonix switches with 24v allows much more deep-discharge option when times get tough (weeks of overcast)

LRL wrote:If you use 12 volt and the DC WISP switches you need to engineer your site so that each switch's radio load stays below 120watts to ensure you can power everything if the batteries get low.

which is why 24v is good, keeps the amps down. If you have 120W in equipment, you should probably have 2 switches, one on each side of your ring or on the two primary links... Really, just full AF or carrier links would get you up there, AFX and PtMP gear doesn't use that much power.

LRL wrote:The more batteries the better and monitor your voltage so you know at least 24 hours before the site goes down because of voltage.

If you over-bank, you could be unable to bring them up to a satisfactory charge. You should always plan your battery bank properly so that your power source can actually keep them charged. A simpler way to put it is that you should not have more power than you can charge...

If there is anything to over-buy, it's solar. do a full 55-60 degree tilt (or whatever your latitude suggests for winter) and add extra panels. Wind has been a major headache for us. Losing blades, seized motors, general mayhem from strong gusts. We had a rotor 'explode' so thoroughly that only the axel was left on the pole and the blades evaporated...

We've been looking at auto-start generators with contact trigger and then a small zenner diode relay combo to trigger under a given voltage. That would buy time to get out to the site and gas up, wipe the panels, and fix whatever might need fixing.

I'm also building a pretty serious li-ion battery pack from recycled 18650 cells (up to 3.3kWh) as a carry-in booster pack. If it was overcast for a long period and the over-built solar setup didn't cut it, I could haul in 2 days of pre-charged power, charge the on-site batteries with the portable generator, and get some sleep.

really, you can't completely eliminate a solar site's power issues. better to have a good buffer and plan of action so you don't have to ride your quad into the woods at 3:30am in december... That ride can wait until daylight.

I'd love to see a "cheap" boost converter that touts enough amps to make it feasible to to employ in these scenarios. I haven't see any over 30-40 amps. The 250amp alternator in the truck is pretty bullet proof and I can send my greeny tech to babysit it.

I have a homebrew gasoline DC generator I'm looking to employ on our toughest site this winter. The engine is electric start and with a programmable relay board I have high hopes. Too bad after it was built I found this http://www.altendc.com/p1-propane-batte ... -generator My homebrew was easily 4k cheaper though :/

Charge controller depending, too much solar can be bad as well. We plan our sites for 7 days of power just on battery without input and we plan for on the worse day (shortest in winter) if full sun we'll recoup 3 days. We usually have 2-3 days left when we make a charge trip.

The biggest hurdle we run up against is temperature. It's not uncommon to see -30f at most of our sites during the winter. This is my biggest reason for not dragging batteries down like you could do with a 24v or 48v system.

We run an AF24 ring and AFX as backups. Thanks to the DC switches it's made it easy to drop the AF24's at night. No more custom scripting for me to do that!

We've lost two wind generators in the last 5 years, I'm okay with that ratio. For us they are the saving grace. You might look into some auto-furling options. In my experience the spring loaded tail works the best.

How many 18650 cells we talking here? I've looked at lithium options but our temps rule them out.

Thanks to the DC switches it's made it easy to drop the AF24's at night.

Would be nice to be able to trigger this by monitoring battery capacity and sending an API call to the switch. This about a scenario where you have a ring/meshed distribution network and one hop on the path has a power issue. It would be nice to power down all non-critial radios to keep the customers on the site up but take it out of the ring. Sure, the network now has a single path if it's a ring, but this path was definitely going down anyway. Much easier to power a switch and a few APs than the same with 2-3 full AF radios and other higher draw radios for the ring.

Where just a few AF radios needs a significant power bank, a single 12v battery can power a couple APs through the night in a pinch.


As far as 'too much solar', no such thing. If you open the circuit, solar panels can just sit in the sun and they don't produce. The only concern is if you do close the circuit you might have too much draw, but if you partition the panels into groups and have separate solar controllers for the groups feed a single battery charger, no problem.

rebelwireless wrote:Would be nice to be able to trigger this by monitoring battery capacity and sending an API call to the switch.

The SMART DC switches allow ports to be shut down based on time or input voltage level?

My only suggestion for the shutdown options, would be a logical way of powering off links after bandwidth falls below or above. The below is easy as you'll be monitoring the same link as you're dropping. It would be more difficult to activate an already shutdown link when the backup is over x amount.

Currently I've programed this feature into some dude scripts and CLI.