With various low-cost and - in some cases - extremely long-range - radio modules available, it's natural to turn to the Arduino when planning a remote sensor project. While you may have sorted communications, though, you're left with one thorny problem: power. If there's nowhere to run a serial cable, there's likely no handy socket - so what can you do to keep your sensors ticking over?
Raj Bhatt over at Embedded Lab has at least one answer: low-cost, two-component solar power. Using a 6W solar panel and an ultra-low-cost 5V buck converter module, Raj has been able to successfully feed power to USB devices in direct sunlight - and at a total project cost of under $8 (around £6 excluding taxes.) While Raj's focus was on charging smartphones for free, the 200mA 5V output he measured is more than enough to run an Arduino and a handful of sensors.
For 24/7 use, though, something more is needed. Raj's build, which includes mounting the buck converter in a neat case on the rear of the solar panel, found most use charging a cheap USB power bank. Connecting an Arduino to the power bank allows the battery to charge in the sun and discharge at night, providing of course that the current drawn by the Arduino isn't more than the current provided by the solar panel. If you're thinking about giving this ultra-simple approach to off-grid electricity a go, one word of warning: some power banks disable their output when charging, so be sure to check that the model you're planning to use keeps its output live even when charging its internal battery.
Yesterday, I built a very simple DIY solar-powered USB charger for my TP-link 10400mAh USB Power Bank. All I needed was a 6V/3.5W solar panel and the TD1410-based 5V buck converter module. I bought both of them on AliExpress for less than $8.