Solar Powered AC Voltage--No Battery

Battery free solar (think long term reliability) using a four dollar charge controller.

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For daytime AC power (and a small bit of night time emergency power) I use super capacitors (three 3000 farad units). They will keep things stable when a cloud passes and they last a long time. I have a bank of super capacitors (connected to a light and hand crank generator) that have been in service for more than 13 years with no noticeable degradation.

To prevent over voltage on the capacitors, I use a small relay module (regulated with a zener diode/resistor pair). To prevent stress on my dc to dc upconverter (provides 12 volts to the inverter), I use another relay module zener combination to halt the up conversion when the capacitors fall to about 5 volts.

When voltage on the capacitor bank reaches about 7.4 volts, the normally closed contact on R1 opens and disconnects the solar panel. It closes when the voltage drops below 7.0 volts to reconnect the solar panel. The normally open contact R2 closes at 5.4 volts and opens at 5.0 volts (open stops output from the capacitor).

The voltage regulating components (cost about four dollars) are here.

The overall shematic is here:

I have used this human powered light for more than 13 years. If you are in the "back of beyond," the super capacitors provide more longevity than batteries.

The quickly pieced together assembly (using parts I had on hand) is shown below.


Long term reliability

Simple charge control

Stabilize power (protects against a few minutes of cloud)

A few watts of night power (think emergency light for an hour or so)


Bulky and costly compared to battery

f3d - 98.73 kB - 04/05/2022 at 18:31


Standard Tesselated Geometry - 38.17 kB - 04/05/2022 at 18:31


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  • Two Week Analysis

    Mike Rigsby04/29/2022 at 17:08 0 comments

    System losses (inverter) are greater than I anticipated--probably the inverter's cooling fan.

    The very low cost inverter I selected (see components) consumes more energy than my 15 watt panel provides. This means that any attached AC load will drain the capacitors down regardless of the amount of solar energy received. 

    I would suggest using a larger solar panel (I just happened to have the panel and inverter used for this assembly) or an inverter that uses less energy in standby mode.

  • Practical Device

    Mike Rigsby04/11/2022 at 19:46 0 comments

    The "proof of concept" prototype works, but the inverter (unloaded) draws more energy than the 15 watt solar panel can provide. Add a 6 watt load and the capacitor voltage drops to 5 volts within 20 minutes or so.


    I would like to attempt powering a small freezer or refrigerator. By adding two more 3000 farad capacitors (5 total), I can eliminate the dc to dc up converter--let the inverter do all the work. The over/under voltage relays will need to be modified. Two hundred watts of solar panels should provide the power for the refrigerator (80 watts or so) for at least five hours on a sunny day.

    A freezer (unopened and loaded) will easily keep items frozen for 19 unpowered hours. A refrigerator is supposedly only good for about 4 hours. Can a small refrigerator/freezer (with a chunk of ice filling the freezer area) maintain a decent temperature for 19 hours? I don't know--will have to experiment and measure to see. 

    The concept here is to provide reliable ac power for five hours per day and depend on thermal storage to keep the items inside cool. To continue operation for multiple cloudy days, more solar panels (600 to 800 watts total) would probably be needed (solar panels do produce on cloudy, dreary days--just a reduced amount).

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  • 1
    Building the prototype

    Start by examining the component list and schematic.

    I attached the capacitors to my "test board" using velcro.

    Complete the wiring, using screws or velcro.

    The total assembly looks like this.

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Enjoy this project?



Mike Rigsby wrote 04/12/2022 at 16:54 point

They can be found at

Or Digi-Key:

  Are you sure? yes | no

Ajalchatta wrote 04/12/2022 at 01:52 point

do you know where I can get these super capacitors?

  Are you sure? yes | no

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