Solar powered WiFi link?

The Continental Op · 13-11-2020 4:51pm #1

I've a plan in mind for a solar power WiFi link and this seems to be the best place to ask some questions.

I'd like to power two Ubiquti nanostations which have a max power requirement of 8 Watts each so need a continuous supply capable of 16 Watts. The nanostations should operate at 12V. To err on the safe side I'd say the supply needs to be 1.5 Amps at 12V although I suspect it will be much less (ubiquiti forums indicate it may be much less probably half that with no data).

So my calculation is that a 15 Amp hour battery would last 10 hours a 60 Amp hour battery would run for 40 hours. I know that would kill the battery but have to start my calculations somewhere. Giving a 100 Amp leisure battery a 65 hour life (before death). Assuming power consumption would be much less than the maximum I think the 100 Amp battery would be OK for at least 3 days without discharging to a state that its useless, but hopefully a decent charge controller or additional circuitry could switch it all off long before the battery is ruined.

My big question is if I go with a 100 Amp leisure battery what sort of size solar panel or panels do I need to keep it charged year round and is it even feasible to keep the system running on solar during the winter?

I was hoping and really thats more hope than anything that a 100W panel and a 10 Amp charge controller would do the job but is that just wishful thinking?

There is plenty of space (its unused farmland on the side of a steep hill) to put in more panels but I'd like to minimise the footprint to try and stop people investigating that funny looking thing on the side of the hill and walking off with it. Also if it needed multiple panels and more batteries it would be a less economic proposition. I have permission to use the location and might have permission for another slightly better LOS location so a reliable solar system could be moved later if required. I'm not doing this for myself I'm looking at it for a neighbor, if it was me I'd just go for it with a suck it and see approach but I'd like to spec it all out with some prices for something that should work before going ahead. Its one of those getting the internet where there is no fixed line broadband and at the edge of 3/4G coverage with no LOS to any 3/4G mast.

unkel · 13-11-2020 10:33pm

Lots of issues. A 100Ah battery will not do the trick if you get a bad few days in winter. If it's a lead acid battery, you can only use 50Ah of that anyway. And the battery won't even make it through the winter, even if we have the best winter ever, as lead acid needs to be fully charged at least once a week or it will die a quick death

Unless you hook up several full size (300W) panels. And even then it'd be tricky

Unless you go lithium battery. Spec it such that it can last a week without PV. And get a PV panel far bigger than you think you would need. I'd go at least one full size (300W) panel

But this is just guessing and it depends quite alot on where in Ireland you are

You will have to just take the plunge and go for a system based on considerations like above and hope for the best. Or measure PV production over winter before deploying a system next year, but I certainly wouldn't have the patience for that

The Continental Op · 13-11-2020 10:59pm

You summed up my big problem measuring PV production. Location is both good and bad, South coast facing south nothing to shade it but plenty of rain and fog comes in off the sea.

Charging off site wouldn't be too much of a problem and something I'd thought about. Two batteries wouldn't add much to the cost. People will put a lot of effort into getting their netflix

I've already got some of the ubiquiti radios in use so really think I'll have to try and measure how much power they really use so I can make some good rather than guessed calculations.

unkel · 13-11-2020 11:38pm

The Continental Op wrote: »

Charging off site wouldn't be too much of a problem

OK I presumed that would be a problem. If you can charge off site, it will make a big difference. Easiest is to just have two batteries then and swap them out when you've had a few bad days, then charge the depleted one at home and bring it over after the next few bad days, etc.

Very doable all of a sudden. A 100W panel would probably do the job, but I would just use a full size panel as they barely cost any more. A cheap chinese solar charge controller is probably all you need. Is the location secure / remote or is there a chance of theft of equipment?

The Continental Op · 14-11-2020 12:26am

Site isn't remote, very near a main road but not actually overlooked by it so I don't see much of a security problem access is quite tricky but changing a battery regularly could make a well worn track, its not a great distance but battery would need lugging up a bit of a hill. There is a better location nearby which is much more secure so I'm holding out for that.

I'm looking for the cheapest simplest method of testing and I think I've found it. I have two of the radio's working at home one is important the other is just for convenience so I can just see how long I can power one from a known size battery. All I need to do is get a solar charge controller so I won't completely wreak and old car battery (I've a nearly new 70 Amp hour one from a car I scrapped recently). I can power the radio from the battery and monitor it from a Windows 10 laptop when the internet goes off in the event log will be when the battery gets down to 50% or whatever the controller is set at.

As you can see I'm thinking this out as I go.

kanuseeme · 14-11-2020 1:37pm

Give a look at these, one is a water pump, the other a electric fence, I would think the water pump would be a better fit just tear out the pump part maybe add more batteries.

https://www.donedeal.ie/farmtools-for-sale/solar-water-system/26172274
https://www.donedeal.ie/fencingequipment-for-sale/solar-mains-fencers/22379836

I think the last thing you want is to haul batteries cross country on a crappy day like today.

ED E · 14-11-2020 1:46pm

If they're eager to get online go lithium. Little extra upfront for far less mickying about.

The Continental Op · 14-11-2020 1:53pm

ED E wrote: »

If they're eager to get online go lithium. Little extra upfront for far less mickying about.

Figures I'm looking at make Lithium 4 times more expensive at around 400 quid for 12V 100Amp, but not an impossible price in the overall scheme of things.

There are two people with very senior jobs working from home and using a Satellite connection. It works if they don't use the internet for anything other than business.

ED E · 14-11-2020 1:59pm

New off the shelf it's twice. 100ah lead is really 50ah. 40ah if you want it to last. 50Ah liion can easily be drawn down 90% without issue especially as charge/discharge rates will be low.

Recycle surplus scooter packs etc and you can get decent pricing too.

The Continental Op · 14-11-2020 2:24pm

At the moment I'm still trying to get some idea of the actual power required. The link I was testing has gone down probably a bit of wet somewhere after all this rain and I can't get to the other end of it for a while to fix it.

What I've set up as a test is a 500VA desktop APC UPS and I've tapped directly off from the 12V battery (yes I've also used a fuse) and I'm using that to power the nanostation at my end. When the link is running again I'll set up some downloads and see how long it takes the battery to get down to 50% and see if I can gain meaningful data. Battery is the usual 12V 7amp sealed battery so the test may not take that long. I can monitor the UPS from a PC (UPS unplugged and only powering the Nanostation not the PC).

The Continental Op · 14-11-2020 3:16pm

Quick question on panels can I use a 24V (so called) panel to charge a 12V battery with a 12V controller?

Is there any advantage to getting say 2 150W 12V panels for 12V battery charging over a single 300W 24V panel?

I'd go with the 2 12V panels in series but is that the way is works?

unkel · 14-11-2020 6:37pm

The Continental Op wrote: »

Figures I'm looking at make Lithium 4 times more expensive at around 400 quid for 12V 100Amp, but not an impossible price in the overall scheme of things.

Link to that battery?

Solar powered WiFi link?

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