Dear all,

I own a small hill 100m above my summer house with 160° view on 20 km around. It is ideal place to install a LoRaWan gateway. I am on top of a commercial 4G tower (maybe 50 meters higher and 2 km away). I have a direct sight from my summer houses to the top of the hill. The wAP LR8 is working well outside my house and I can connect kilometers away but I would like to boost coverage develop LoRa in this rural area.

What equipment is need for building a solar station to output enough power for a wAP R8 gateway with LoRa and Wifi working 24h/day ? Do you have experience with it ? The other solution would be to dig a trench on 500 meter but 1) I need to cross a road and the road belongs to the state 2) I would cost a lot of money and can be hard to install. So I was thinking about a solar system.

I have difficulties understanding how to size solar system as Specs indicate Max power consumption 7W but we do not know the voltage 9-30V thus I don't know how many amps are needed.

I found this on the wiki : https://wiki.mikrotik.com/wiki/Solar_Power_HOWTO
Do you have experience with a solar system and can you share it?

Kind regards,
FFries

In general: power equals voltage times amperage

Or: amperage equals power (wattage) divided by voltage

If you have influence on solar power design: most electronic gear (Mikrotik included) actually work with pretty low voltages and use DC-DC down converters. And those have slightly lower losses when input and output voltages differ less ... in case of the particular device (wAP LR8) that means running solar power at 12V rather than 24V. OTOH that probably means using double the amount of batteries and increased cost won't be offset by lower power consumption (due to better power economy of powered devices).

Thanks. Some vendors provide kits with a 12v battery, a charger and solar panels. This is ideal for camping. So I am quite confident that I should invest in a 12v solar kit.

The problem is that Mikrotik indicates 7W maximum for the wAP R8 but I don't know the voltage (9v-30v). So I cannot calculate what is needed for three days without sun. I would prefer running 5 days without sun as this is Northern France.

I have a wAP R8 but it is connected on 48v PoE and I have no knowledge of the real consumption in AMPs.

Unless i calculate wrong...
5 days = 120 hours.
7W/h = 840 W
Run at 12V, you need battery storage for 70 Ah.
That's a big battery or otherwise 2 normal , maybe 3, in parallel.

Maybe better for this case to use a battery with higher voltage ?

Specified is input voltage range. So anything inside that range is fine, including 12V. If you use 12V, then device will draw 7W/12V=0.6A (actually slightly less). If you'd power same device using 28V, then current would be 0.25A.

Following an exercise in calculations (take results with lots of grains of salt):

So if you target autonomy of 5 days, then needed battery capacity (12V setup) of 120hx0.6A= 70Ah (I've used exact value for current, not the 0.6A aproximation). It might be possible to get to target autonomy with slightly smaller battery if solar pannel set is decent - even during cloudy periods solar cells produce some small amount of power. Be sure to use "deep discharge" batteries (usual car batteries don't like being deeply discharged) to make them last longer (more deep discharge cycles).

Dimensioning of solar cells is next thing: you want something that will be able to power your gear and charge battery at the same time (because it has to top up what was consumed during previous night). Consider winter time with night duration of, say, 16 hours (depending on latitude, winter nights are longer in more Northern latitudes) and not so sunny during day light. Which means deficit of 9.5Ah or 112Wh.
Decent solar panels have efficiency of around 27% (check the specs of those you're considering) and typical winter cloudy winter day might provide 300W per square meter (if panels are tilted to point directly towards sun ... tilt them for winter, summer has longer days and panel efficiency is not as important). During 8 hours of day light, solar panels have to produce 56Wh (for direct gear power consumption) plus 112Wh (to recharge battery ... actually it will be more because charge/discharge cycle of battery has losses as well), so around 200Wh. Divide it by 8 hours and consider actual solar power (300W/m2 versus theoretical 1000W/m2 which is usually used by panel manufacturers), which gives you needed nominal power of installed solar panels of about 85 Watts. Which should be around 0.35 square meters of solar panels (net effective area).

Now the above calculation only covers night time consumption. Mentioned battery size should be enough to power your gear for 3 days of gray, but recharging to full capacity will be long and painful ... perhaps too long to be rady for next 3 days of gray. So you should consider going for a slightly larger solar panel, something with nominal power of 100W-120W would probably suffice.

Probably it's needless to say that during summer this setup will be pretty overdimensioned, but a decent solar power regulator / battery charger should take care of it.

As @holvoetn mentioned, 70Ah is a pretty big battery. You could go with 24V and then use 35Ah batteries ... since 12V batteries are cheap (due to volume of production) you'd probably end up using two 12V batteries (35Ah each) connected in series (connecting batteries in series means adding voltages). For 12V power setup you could use the same two batteries but connected in parallel (this means added capacities). However, mounting batteries in series, specially when deep discharge is planned, means possible problems (if they don't have exactly the same capacity and they don't age equally well), while having them in parallel means less problems (and as long as they are in decent shape they don't have to be identical).
Using single large battery means easier monitoring of battery state ... batteries in series are easy to monitor as well (it's possible to measure voltage of individual battery, voltage is a pretty good sign of battery state) while it's hard to monitor batteries connected in parallel.

So I'd still go for 12V installation, possibly using single large battery.

Thank you very much.
This is an investment between 300€ to 400€ looking on French sites.

- 2 x Solar panels 100Wc Mono, up 1000Wh per day
- 1 x charging regularor 12/24V 20A
- 1 x battery 100Ah 12V (1200Wh)
PLUG AND PLAY

I will probably build everything in July, thanks.
The spot if very nice, I don't even need a high pole.

Progress reports and pictures when done, please.

To build a solar station for your LoRaWan gateway, you'll need a few components such as a solar panel, a battery, a charge controller, and an inverter. You will also need to determine the power requirements of your wAP R8 gateway. As you mentioned, the maximum power consumption is 7W, but you'll also need to know the operating voltage to determine the amperage needed. Once you have this information, you can size the solar panel and battery accordingly to ensure that the gateway can operate 24/7.

As for my experience with this, I have not personally built a solar-powered LoRaWan gateway, but I do have experience with solar power systems in general. It's important to ensure that your solar panel is capable of producing enough power to recharge the battery during the day and power the gateway at night. A charge controller is necessary to regulate the amount of power going into the battery and prevent overcharging, while an inverter will convert the DC power from the battery to AC power to power the gateway.

PLUG AND PLAY

Don't forget to throw in some fuses. A big battery can cause some impressive firework if there's a short circuit.

And using some pole (a couple of meters high) can be good to keep interested parties away from the gear ... such as cattle, kids or rats.

This handy calculator might help.
https://www.bimblesolar.com/solarcalc

Richard