NITECORE FSP30 Solar Panel Controller Teardown

The NITECORE FSP30 is a foldable solar panel with two USB–A outputs and one USB–C output. The manufacturer specifies a total power output of up to 30 W, but numerous measurements suggest that the real output is lower. This made me curious about why this happens and whether it can be fixed.

Controller design

Inside the FSP30 there is a small PCB with several DC/DC converters. The solar sections feed an input voltage, Vin, into the board. The controller converts this voltage into standard USB voltages: 5 V for USB–A and 5/9 V for USB–C. All outputs draw power from the same source – the solar sections of the panel.

After opening the regulator block, it became clear that the FSP30 contains an ordinary USB converter board rather than a specialized solar charge controller. There are no signs of an MPPT stage or separate logic that keeps the solar sections operating at their maximum power point. This explains why the panel can be rated as 30 W while the actual power available at the USB outputs is lower.

There are more suitable circuit solutions for solar panels: DC/DC converters with MPPT, or at least input-voltage regulation such as VINDPM. Their task is to monitor the panel input. When a phone or power bank tries to draw too much current, this type of controller reduces the load and prevents the solar sections from collapsing in voltage. Judging by the board, the FSP30 uses simpler logic: the controllers mainly regulate the USB outputs, while the panel input behaves according to the current sunlight and load conditions.

The USB–C channel is handled by a chip marked PL6520, located next to a 470 inductor. Judging by its placement and surrounding components, it resembles an IP6520-class controller. This stage is responsible for USB–C, detects the connection through the CC lines, and enables fast-charging modes. It can output 5 V or 9 V, while being powered from the higher voltage of the solar sections. This is a buck converter. When the input voltage drops, the USB–C channel reduces power, exits the fast-charging mode, or restarts.

The USB–A section is built around a separate 5 V channel. The board has a 5436A stage with a 220 inductor, which likely generates 5 V power for both USB–A ports. Near the left USB–A port there is a small 2513 chip. It does not carry power; it works with the D+ and D− data lines. Its role is to signal to a phone or power bank that the port is a charging port and can supply increased current.

The presence of three inductors is also interesting: two marked 470 and one marked 220. Because of this, a circuit with two independent power channels for the two USB–A ports looks less likely. A more logical version is this: one 5436A stage with a 470 inductor first generates an intermediate bus of about 12 V – there is even an unpopulated connector footprint on the board – and from this bus the PL6520 USB–C controller and the shared 5 V USB–A channel are powered.

In terms of efficiency, this architecture does not look ideal. If energy passes through two conversion stages, the losses of each stage add up. For example, with 90% efficiency in the first stage and 94% efficiency in the second stage, the total efficiency is about 85%.

The likely functional diagram is as follows: the solar sections feed a common input bus; the first 5436A converter with a 470 inductor generates an intermediate 12 V rail; this rail powers the USB–C channel based on the PL6520 and the 5 V USB–A channel based on the 5436A with a 220 inductor; the 2513 chip handles the USB–A signal lines. When a load is connected to USB–A, part of the total available power goes into that channel, so the available USB–C power may decrease.

This leads to the conclusion that the 30 W rating most likely refers to the solar panel as an energy source under good laboratory conditions, rather than to the entire system as a finished USB charger. Let’s check this hypothesis.

Estimating maximum power from the panels

The power of a solar panel can be roughly estimated from its area. One FSP30 section measures approximately 27 × 15.5 cm. Converted to meters, this is 0.27 × 0.155 m. That gives about 0.042 m² per section.

The panel has four sections. Therefore, the total area is approximately 0.167 m². This is the area of the visible outer rectangles. The active area of the solar cells is usually slightly smaller.

For a simple estimate, bright direct sunlight is taken as 1000 W per square meter. This is the laboratory reference value normally used when comparing solar panels. Under these conditions, the four sections of the FSP30 receive approximately:

0.167 m² × 1000 W/m² = 167 W of solar energy.

A solar panel does not convert all of this light into electricity. The manufacturer specifies a cell efficiency of 24%. This means that roughly one quarter of the incoming energy is converted into electrical power. The calculation is:

167 W × 0.24 ≈ 40 W.

These 40 W are an upper estimate based on geometry and cell efficiency. In reality, part of the area is inactive, the cells heat up, the angle to the sun is rarely ideal, some light is lost in the surface layer, and then the energy passes through the USB controller. Therefore, the 30 W rating looks plausible as the maximum output of the solar part of the panel under good conditions.

Electronics efficiency and real USB output power

After that, the electronics come into play. The IP6520 datasheet for this class of chips specifies efficiency up to 93.8%. This is a good figure, but it is obtained under laboratory conditions. In a real solar panel, outdoors, in a heated pocket, and with a fluctuating input voltage, it is more reasonable to assume that some energy will be lost as heat.

If USB–C delivers 18 W to a power bank, the board itself must receive a little more – roughly 19–20 W.

The USB–A section behaves similarly. According to the specifications, the two USB–A ports together provide 5 V at 3.1 A, which is about 15.5 W. But these 15.5 W also come with conversion losses; the efficiency of this stage is lower, around 85–90%, depending on the current passing through it.

In terms of efficiency, the intermediate-voltage architecture is not particularly good: each conversion stage adds its own losses. For example, if the first stage has an efficiency of about 90% and the second stage about 94%, the total efficiency is already around 85%.

The practical conclusion is that the most efficient operating mode is USB–C PD at 9 V 2 A, or about 18 W in good sunlight. In this mode, the panel works closer to its real limit.

USB–A should be treated as a backup or auxiliary output. It can charge a flashlight, watch, navigator, or phone when charging speed is not critical. But if the goal is to collect the maximum amount of energy during a short stop, it is better not to split the panel between several devices. One power bank connected through USB–C usually charges more stably. It makes sense to charge it to about 80% using fast charging, and then, when the remaining batteries need topping up, connect several devices. This approach can increase the total harvested energy, because toward the end of battery charging the current drops and charging becomes limited more by time than by available power.

Charging time can be estimated as follows. A 10,000 mAh power bank stores roughly 37 Wh of energy. If the panel outputs about 18 W over USB–C, and the power bank loses part of that energy in its own charging electronics, about 15 W will actually reach the internal battery. Ideally, this gives about 2.5 hours. On a hike, a more realistic figure is 3–4 hours of good sunlight.

For a 20,000 mAh power bank, the stored energy is about 74 Wh. With the same useful charging power of about 15 W, the minimum is around 5 hours, while in real conditions it is better to expect 6–8 hours of good sunlight.

In practice, the angle to the sun and the absence of shade often matter more than the difference between 90% and 94% efficiency. The panel produces maximum power when it faces the sun almost directly. If it lies flat, hangs from a backpack, or is partly shaded, the power drops faster than expected. A shadow from a branch, strap, tent guyline, or even a cable can disrupt charging more severely than controller losses.

Photos of the opened panel

Moisture protection is almost absent. The only protection is the impregnated fabric of the pocket that holds the controller.