Solar Input Range

The single most important match. A board built for a 6V cell will choke on an 18V panel — and vice versa. Wide-input managers (6–24V) are flexible; bare CN3791 boards come tuned per panel voltage. Buy the version that fits your panel.

MPPT vs Linear

MPPT charging keeps the panel at its most productive voltage, harvesting far more energy in weak light than a linear (TP4056-style) charger that just clamps to the battery voltage. For anything beyond a small 5V cell, MPPT is worth it.

Output Rails

Do you want raw battery voltage to a regulator you already have, a clean 3.3V for a bare ESP, a 5V/USB rail, or both? Power managers with a built-in DC-DC save you a board; bare chargers hand you raw cell voltage to regulate yourself.

Battery Protection

Over-charge, over-discharge, over-current and reverse-polarity protection keep an unattended outdoor node safe for years. Managers usually bundle it in; some bare charger boards leave over-discharge to a separate BMS — check before you deploy.

Charge Current & Cells

Most of these charge a single 3.7V Li-ion/LiPo (1S) cell at 0.9–2A; a couple target LiFePO4 or tiny harvested loads. Bigger current fills a bigger battery faster, but only if your panel can supply it. Confirm the cell chemistry and count before wiring.

The Solar Energy Manager A is essentially a solar-fed power bank for your projects: a wide 5–24V solar input, MPPT charging into 18650 cells, and dual USB outputs at 5V/3.1A plus a Type-C fast-charge port. That makes it great when you want to power more than one thing — say an ESP32 gateway and a USB camera — or want a friendly USB rail instead of solder pads. It’s a consumer-flavoured board rather than a maker breakout, so documentation is thinner, but the raw capability per dollar is excellent.

The original Waveshare Solar Power Management Module is the value pick in the range: the same friendly 6–24V panel input and onboard MPPT as its bigger sibling, but with a 5V/1A output sized for typical microcontroller nodes rather than a Pi. It charges a 3.7V Li battery from solar or USB, wraps in over-charge, over-discharge, reverse and over-current protection, and is a proven choice for mini weather stations, solar monitors and low-power IoT. If your load is an ESP32 or ESP8266 and you want wide panel flexibility on a budget, this is the one.

The HiLetgo CN3791 is the classic bare-bones MPPT charger for a single 3.7V LiPo cell. There’s no 5V rail or fuss — you feed it a 12V-class solar panel on the JST connector, wire a cell to the other, and the CN3791 tracks the panel’s maximum power point while charging at up to ~2A. It’s the enthusiast’s building block: cheap, effective, and perfect when you already have your own 3.3V/5V regulator and just need efficient solar charging into the battery. Just remember it’s a charger, not a full manager — pair it with a battery that has its own protection.

The Waveshare “Recharged” module covers a gap the others don’t: it offers a jumper-selectable 3.3V/1A output as well as 5V/1A, so you can feed a bare ESP32, nRF52 or STM32 sensor at its native voltage without a second regulator wasting energy. Same wide 6–24V solar input and MPPT as the family, with USB backup charging. For ultra-low-power 3.3V sensor nodes where every milliamp of overhead matters, that dual rail is a genuinely useful trick.

The Taidacent CN3791 is the same proven MPPT charger tuned for the small 6V panels most hobby solar nodes actually use. If your build has a 5–6V garden-light-style panel rather than a chunky 12V one, this is the correct variant — the fixed MPPT voltage is matched to that panel so you get efficient single-cell LiPo charging at up to ~2A. It’s a bare charger like the HiLetgo, so plan for your own regulation and battery protection, but for compact 6V setups it’s the natural fit.

The TP4056 is the cheapest way to charge a single Li cell, and a 3-pack costs less than a coffee. With a small 5V/6V panel on the input it will happily top up an 18650 for a light-duty sensor, and the protected version adds over-charge, over-discharge and over-current safety via its DW01 chip. Be honest about what it is, though: it’s a linear charger with no MPPT, so it wastes energy from anything bigger than a small 5V panel and won’t harvest well in weak light. For a bright-location, low-power node on a shoestring, it’s unbeatable value; for serious harvesting, step up to an MPPT board above.

Most boards here charge Li-ion/LiPo, but if you want the long cycle life and rugged temperature tolerance of LiFePO4 for a deploy-once outdoor node, you need a charger tuned to its ~3.6V charge voltage. This CN3801-class MPPT module takes a wide 4.5–28V panel and charges a single 3.2V LiFePO4 cell with maximum power point tracking, at a current you set with a resistor. LiFePO4 shrugs off heat and thousands of charge cycles far better than LiPo — exactly what you want on a rooftop for years — just make sure your regulator is happy with the ~3.2–3.6V cell voltage.

When there isn’t much light at all — an indoor sensor, a shaded corner, a tiny cell — a normal charger won’t even start. The TI BQ25570 is a nano-power energy harvester built for exactly this: it cold-starts from as little as ~330mV and keeps harvesting down to ~100mV, with adaptive MPPT sipping microwatts to milliwatts from a small PV cell into a battery or supercap. It’s the specialist choice for battery-light or battery-free IoT — door/window sensors, beacons and ultra-low-power nodes running on indoor light. It won’t fast-charge anything and expects a genuinely low-power design, but nothing else here harvests in such dim conditions.

Running a Raspberry Pi off-grid?

Get the Waveshare Power Manager (D) — 6–24V input and a stiff 5V/3A output that a Pi or Jetson can actually live on.

Building an ESP32 sensor node?

The DFRobot Power Manager 5V gives you MPPT, a clean 5V/1A rail and great docs in a compact board.

Powering a bare 3.3V MCU?

The Waveshare Recharged module’s selectable 3.3V rail skips a regulator and saves precious energy.

Rolling your own power stage?

A bare CN3791 (12V) or Taidacent CN3791 (6V) gives efficient MPPT charging you pair with your own regulator.

Need to power two devices?

The Solar Energy Manager A offers dual USB 5V/3.1A plus Type-C — a solar power bank for your build.

On a tight budget in bright sun?

A protected TP4056 3-pack with a small 5V panel is the cheapest way to keep a low-power node topped up.

Deploying outdoors for years?

A LiFePO4 MPPT charger handles heat and thousands of cycles far better than LiPo for set-and-forget nodes.

Only have indoor or dim light?

The BQ25570 harvester cold-starts at millivolts and sips power a normal solar charger can’t touch.

Do I really need MPPT, or is a plain TP4056 enough?

It depends on your panel and location. A TP4056 is a linear charger: it drags the panel down to roughly battery voltage, so any extra voltage the panel could deliver is lost as heat. With a small 5V panel in bright sun that’s fine. But with a 6V, 12V or larger panel — or in cloudy, low-angle light — an MPPT board keeps the panel at its most productive point and can harvest substantially more energy per day. For a node that must survive marginal weeks, MPPT is worth the few extra dollars.

How big a solar panel do I need for an ESP32 node?

Work from daily energy, not peak watts. Estimate your node’s average draw (a deep-sleeping ESP32 waking to send data might average a few mA; an always-on ESP32-CAM far more), multiply by 24 hours for daily mAh, then size a panel that can replace that in about 3–4 hours of usable sun with margin for cloudy days. As a rough starting point, a 5–6V/1–2W panel and a 2000–3500mAh 18650 keep a well-behaved sleeping sensor running indefinitely; camera or always-on nodes want a bigger panel and battery.

Can these modules power my board and charge the battery at the same time?

The power managers (Waveshare, DFRobot, Solar Energy Manager) are designed for exactly that — they charge the cell and run their regulated output simultaneously, drawing from solar first and the battery when the sun dips. Bare chargers like the CN3791, LiFePO4 board and TP4056 only handle the charging side; you tap the battery through your own regulator for the load. If you want true seamless “run while charging” behaviour without designing it yourself, choose a manager, not a bare charger.

Should I use LiPo or LiFePO4 for a solar IoT node?

LiPo/Li-ion packs more energy in a smaller, lighter cell and is fine for most builds, but it ages faster and dislikes heat — a real issue in a sun-baked enclosure. LiFePO4 stores a bit less energy per gram and sits at a lower ~3.2V, but it tolerates high temperatures, survives thousands of cycles, and is far safer against thermal runaway. For a node you want to install once and forget for years outdoors, LiFePO4 with a matched charger (like pick #9) is often the smarter long-term choice; just confirm your regulator accepts the lower cell voltage.

Why does the solar input voltage of the module matter so much?

Because a fixed-MPPT board is tuned to hold the panel at one voltage. Feed a 6V-tuned CN3791 from a 5V panel and it can barely start; feed it an 18V panel and you risk exceeding the input rating and damaging the board. This is why CN3791 boards are sold in 6V/9V/12V variants — buy the one that matches your panel’s rated voltage. Wide-input managers (6–24V) and the LiFePO4 board (4.5–28V) sidestep this by accepting a range, which is part of why they’re more beginner-friendly.

Do these boards include battery protection, or do I need a separate BMS?

The full power managers bundle over-charge, over-discharge, reverse and over-current protection, so a bare cell is safe. The protected TP4056 version adds a DW01 protection stage too. Bare CN3791 and LiFePO4 charger boards, however, generally handle only the charging side — for an unattended outdoor deployment you should use a protected battery or add a small BMS so a deep discharge can’t kill the cell. Always confirm what a specific listing includes before trusting it outdoors.