A Rough Guide to Solar Powered Meshtastic Routers & Repeaters

So you want to build and deploy a solar and bat­tery pow­ered Mesh­tas­tic router or repeater to help grow your local net­work’s cov­er­age? Let’s jump in!

I know, I know, you just want to throw your new node in some tiny box with a solar pan­el the size of your palm glued on the cov­er, slap the whole thing on a tele­phone pole some­where and then snap shots for the ‘gram to show how easy it is to build a repeater network. 

That’s fun and it looks cool, but most of those aren’t actu­al­ly large enough to sup­port long term reli­able pow­er pro­duc­tion and stor­age. If you want a deep dive into real geek­ery, they exist, but it won’t be as easy as this guide to make. 

If you’re will­ing to learn a lit­tle bit and accept the fun­da­men­tal laws of physics, you can eas­i­ly build one about the size of a toast­er oven that requires no sol­der­ing for just over $100. You could tweak on this design and prob­a­bly get slight­ly small­er and maybe cheap­er at the cost of being far more care­ful and clever. If you want to dive into the details, check out Kei­th­Mon’s work here.

This guide is some­thing any­one can fol­low with­out being a RISD grad, and yes, the buy-list is at the bot­tom if you’re impatient.

Let’s start with an over­all con­cept, then we’ll dive into the details. At a high lev­el, your Mesh­tas­tic node needs pow­er in order to oper­ate. That pow­er is mea­sured in volts and amps. Think of this as water flow­ing through a pipe; volts is the water pres­sure, amps is the amount of water.

When you mul­ti­ply volts x amps, you get watts, which gives you the ener­gy flow­ing through the lines.

For any pow­ered device you use that isn’t con­nect­ed to grid pow­er, there’s a 5 part sys­tem you need to implement.

• Cap­ture the pow­er (solar panel)
• Store the pow­er (bat­ter­ies)
• Man­age pow­er (charge con­troller AND a bat­tery man­age­ment system)
• Use the pow­er (for the actu­al device)
• Pro­tect the com­po­nents (enclo­sure, which you could also just call a fuck­ing box)

The whole thing is a lot of fun to put togeth­er, but before you do any­thing, we’re going to start with find­ing out the first crit­i­cal ele­ment: How much pow­er do you need?

What­ev­er else you do, start by KNOWING YOUR POWER REQUIREMENTS! If you get those wrong, you’re wast­ing time, ener­gy, and mon­ey. It’s also pret­ty easy to get right.

You can mea­sure pow­er with a fan­cy pow­er sup­ply, like this:

That Mesh­tas­tic device, by the way, is a Lily­Go T‑beam v1.2 run­ning as a Router (NOT as a client).

You can also mea­sure pow­er using a small­er and cheap­er USB device, like this:

That is mea­sur­ing a Lily­Go T‑echo run­ning as a Client.

How­ev­er you mea­sure it, you MUST mea­sure if you want to build a good, reli­able system.

Let’s take a look at the two exam­ples I gave, then we’ll walk through build­ing a system.

We’re com­par­ing two dif­fer­ent chips (NRF to ESP) as well as two dif­fer­ent modes (Client and Router). Before you start howl­ing about how I should have done this or that, this is just a demon­stra­tion, relax. The T‑echo will prob­a­bly draw less, this mea­sure­ment was tak­en towards the end of a charg­ing ses­sion. The point here is not what uses more or less pow­er but to make sure you mea­sure YOUR pow­er draw.

System Goals

Let’s lay out my goals for a sys­tem. They may be dif­fer­ent than yours, but if you know what mine are, you can adjust for yours.

First, I don’t mind spend­ing a lit­tle extra mon­ey to get good enough qual­i­ty so that once I build it, it’s unlike­ly to fail for a few years in the field. 

Sec­ond, it should be pret­ty easy to put togeth­er. I’m not an EE, I don’t play one on the inter­net, and fid­dle-fuck­ing with the ben­th­ic depths of elec­tro­mag­net­ic the­o­ry to squeeze every pos­si­ble fem­to-ohm opti­miza­tion out of the sys­tem is not inter­est­ing to me. 

Final­ly, and relat­ed to the first thing, the sys­tem should reli­ably work.

So, giv­en the two exam­ples we have above, what’s the first step? If I want­ed the cheap­est and small­est pos­si­ble sys­tem, I’d build some­thing for the T‑echo. How­ev­er, those aren’t in stock right now. The T‑beams are in stock, they’re cheap, and the pow­er draw dif­fer­ence isn’t enough to make a huge dif­fer­ence in components. 

So, for this arti­cle, we’ll focus on build­ing a sys­tem for the T‑echo v1.2 run­ning as a Router, with a .047 amp draw at 5 volts.

From here, we just run some basic math to find out how much ener­gy we need to cap­ture and store. 

Location

Start with where you’ll put your Mesh­tas­tic repeater or router. I live in San Diego, which is one of the sun­nier places in the US.

I’ll make the assump­tion that I’ll nev­er have to store more than 3 days of ener­gy (solar pow­er from the sun) and that I’ll need to be able to ful­ly recharge my sys­tem on a short win­ter day.

The absolute eas­i­est way to fig­ure out what sys­tem you need is to use (wait for it) Chat­G­PT. You can even use this prompt:

Hey, I live in [town] in [country].  I'm building a power system for a Meshtastic device which I've measured drawing [volts] and [amps].  What size battery and solar panel will I need in order to have enough energy to stay powered through our average winter storm and be able to recharge quickly after the storm passes and I'm getting full solar power again?

It should return some­thing like this:

For your Meshtastic device to stay powered through an average winter storm in San Diego and recharge quickly afterward, you should consider using a battery with at least 20 watt-hours of capacity and a solar panel of around 5 watts. This setup should provide enough energy resilience and recovery capability for the conditions you described.

Next let’s con­vert watt-hours to amp hours, which is how many bat­ter­ies are mar­ket­ed. It’s not hard; you divide watt hours by the bat­tery voltage. 

Batteries & Voltage

Now you’re faced with a deci­sion: What type of bat­tery and bat­tery volt­age should you use for Mesh­tas­tic? Most of the Mesh­tas­tic devices are 5 volt devices (run­ning off a USB con­nec­tor). I’d sug­gest build­ing a sys­tem that’s as close as pos­si­ble to that volt­age, which gives us a 6 volt system. 

You might be tempt­ed to use 18650 Li-ion bat­ter­ies at this point because they’re easy to install and replace, but for me they’re not the best choice for a few reasons. 

First, we’re look­ing for some­thing that can take hun­dreds (if not thou­sands) of charge cycles. This unit will be out in the field, with no main­te­nance, for years, charg­ing and dis­charg­ing every day, with occa­sion­al deep dis­charges. Li-ions are pret­ty good, but LiFePO4 have about 4x the charge cycles of a Li-ion, and are usu­al­ly rat­ed to last around 5,000 cycles or about 10 years.

Sec­ond, wild­fires in San Diego are a high haz­ard, so any­thing I can do to decrease that, espe­cial­ly for nodes I might deploy out in the back­coun­try, needs to be as non-flam­ma­ble as pos­si­ble; LiFePO4 are about as good as you’ll rea­son­ably get for an off the shelf bat­tery. I’ve bought from Bioen­no a bunch, I like them and their cus­tomer ser­vice. You can prob­a­bly find cheap­er places online if you want to hunt around.

Solar

With a 6 volt LiFePO5 bat­tery select­ed, it makes the pan­el selec­tion eas­i­er: Get a 6 volt 5 watt pan­el. I know, I know, you want­ed a dis­ser­ta­tion on how and why and where to find a 18.97% effi­cien­cy pan­el. Just get a 5 watt 6 volt pan­el. If you want to dive into it with GPT, go for it.

Charge Controller

Now that you have a bat­tery and a solar pan­el, you’ll need a charge con­troller. This is the thing that takes the input from the solar pan­el, charges the bat­tery, then out­puts pow­er to your Mesh­tas­tic device. You can build one cheap­er (and you can cer­tain­ly spend more mon­ey) but the Ren­ogy Wan­der­er is a great lit­tle unit that I’ve used a bunch.

The Box (Enclosure)

You’ll need a box to put all this in to pro­tect it from the weath­er. While you and I might just call it a box, it’s var­i­ous­ly called a junc­tion box or enclo­sure in more pro­fes­sion­al cir­cles. I’d pick one up from Ama­zon (link above) rather than 3D print­ing one. You won’t save that much (if any) mon­ey 3D print­ing, and pre-built enclo­sures are usu­al­ly water resis­tant and the door is easy to open/close and latch. 

Buy List

Here’s a list of what to buy:

Some of those are affil­i­ate links, some are not. If you buy using an affil­i­ate link you’re sup­port­ing the writ­ing I do here. There’s no extra cost to you if you do that, and thanks!

Fancy Wiring Diagram, Ikea Level: Easy

Here’s how the set­up looks as a diagram:

Solar Panel Mount (3D print)

Final­ly, you’ll need a way to mount the solar pan­el. This is where a 3D print­er might come in handy using ASA to print a lit­tle mount for it. I know, I know, some of you will want to use PETG or PLA. Resist the temp­ta­tion to go easy ‘n cheap on this one. If you’re in San Diego and read­ing this (and I have ASA on hand, which I usu­al­ly do), I’m hap­py to print one up for ya.

So that’s it! It may not be the “slap ‘n for­get” thing you want­ed, but if you want a great option for get­ting a Mesh­tas­tic repeater off grid and rockin’ for a long time, this is how I’d do it.

Crush!