Building a Solar-Powered Repeater

Here's the parts list that Austin Mesh came up with as their preferred way to build a solar powered repeater.
This design doesn’t require any soldering or complicated connectors. It also doesn’t require any battery management chips (which often have long shipping lead times and can be hard to get).
For this design the solar panel is connected directly to the battery pack via USB. Then the battery pack is connected to the board via USB.
The Voltaic Systems V25 battery is nice because it is optimized to charge from a solar panel and it is set standard to an “always on” mode which means the battery bank does not shut off after a set amount of time like other battery packs – this is useful as the RAK chip uses very little power and can trick other battery packs into shutting off.
The other really nice thing about the Voltaic pack is than when it drains down completely it shuts down, but then once the solar panel has sufficiently charged it back up it will automatically turn itself back on again. Right now they're testing the V25 battery which has 6,400 mAh, but if we were going to install a node in a very hard-to-reach place we’d probably use the larger V75 19,200 mAh battery.
The RAK radio uses between 100 and 1000 mAh per day, with about 400 mAh per day being average so theoretically the Voltaic V25 could keep the radio working for 16 days without any solar power and the V75 could keep the radio running for 48 days without solar.

Comparing it to APRS on Ham Radio

For people who are familiar with using the Automatic Packet Reporting System (APRS) on ham radio, Meshtastic is similar in a few ways:

Digipeaters: APRS radios can be set up as clients, which receive all messages and only transmit the users messages, or APRS radios can be set up as digipeaters, which repeat all the messages they hear. Meshtastic radios by default all act as repeaters – just like APRS digipeaters.

iGates: MQTT Gateways are like APRS iGates – they repeat all local traffic over the internet to other MQTT Gateways around the world.

ANSRVR: APRS users can subscribe to groups using the ANSRVR service. This allows for group chats like the popular #APRSThursday net. Meshtastic has “Secondary Channels” that can be subscribe to, allowing users to send messages to everyone on the channel.

Burst Communication: APRS uses the AX.25 protocol which sends messages using data bursts between 0.3 and 0.5 seconds long. Meshtastic uses the LoRa protocol which sends messages in data bursts between 0.5 and 10 seconds long.

But Meshtastic is also different than APRS in a few ways:

Primary Channel: APRS doesn’t have a way to broadcast a message to everyone on the network. Messages sent to Meshtastic's Primary Channel go to everyone.

Encryption: APRS is unencrypted because it is illegal to use encryption over ham radio. Meshtastic is encrypted for communications on private group channels and for direct messages between users, because it runs on the 900 MHz ISM band, which does not have restrictions on encryption.

License: APRS requires the user to have a ham radio license. Meshtastic does not require any license and is open for anyone to use.

Equipment Cost: APRS capable handheld ham radios cost upwards of $400. Meshtastic radios cost less than $100.

Email and SMS: APRS has services which allow users to send emails and SMS text messages to people who aren’t ham radio users. Meshtastic does not have this feature but it could be added in the future.

Simplicity: APRS is quite a bit more difficult to use than Meshtastic. APRS does not have any standardized user interface – there are dozens of software packages available. Meshtastic has a standardized iPhone and Android app which is easy to understand for new users.