Electronic – Pitfalls in charging a supercapacitor from a small solar panel


I'm designing a circuit which occasionally requires small amounts of power (it's switched off most of the time). I want to use small solar panels to charge a supercapacitor, and the cap then serves as an energy reservoir in the absence of full sunlight.

I have already set up a basic circuit with a EDLC supercap (VINAtech, 100F, 3V), a small solar panel (3V, 270mA) and a 1N4001 diode. It seems to work fine, the supercap voltage appears to stabilise at around 2.85V with the panel pointed at the sun, full sunshine and the panels clean. Such ideal conditions will be rare though, the panel may be shaded most of the time. I know that an MPPT charger would be more efficient but I want this to stay as cheap and simple as possible.


simulate this circuit – Schematic created using CircuitLab

In this schematic, V1 is the solar panel, C1 is the SuperCap and U1 is a generic boost converter based on a CE8301A50T. I'm not sure about the final circuit yet, but there will certainly be a microcontroller (Atmega16A) and an HD44780-based LCD with LED backlight. SW1 will only be closed for a few minutes at a time (no more than 15 minutes), very few times a day (probably not at all for several days in a row).

Datasheets: Boost converter IC: https://www.mpja.com/download/ce830.pdf SuperCap: https://www.vina.co.kr/winko/data/product/SS_EDLC_VEC_3R0_107_QG.pdf Sorry, there is no datasheet for the solar panel.

I just want to know if there might be any pitfalls I might have missed. The circuit will operate outdoors, i.e. it will have to survive temperatures of -25°C (-13F) with no problems. Unfortunately, manufacturers don't seem to test the behaviour of their supercaps at low temperatures (as far as leakage current or change in capacitance goes) so I'm not sure if there might be issues. I don't think temperatures will rise above 50°C (122F) in the summer.

Any thoughts?


Best Answer

Any thoughts?

The devil will be in the detail and you have provided little.

  • Start with defining your load and the current consumption profile. You also need to state how low the capacitor voltage can drop before your load fails on under-voltage.

  • define peak currents in terms of amps and duration - i.e. the full load profile.

  • Data sheets for everything is needed. Leakage currents for the supercap WILL be an important consideration.

  • Anything that doesn't support your temperature range is going to make decisions on the circuits ability to fulfill your needs extremely dubious.

  • Make no assumptions that something "should" work - prove it by due diligence.

and a 1N4001 diode

I'm unsure about this - I think you need to show your proposed circuit.

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