Solar Charge Controller Improves Efficiency of Solar Panels

The simplest and easiest way to charge a battery with a solar panel is to connect the panel directly to the battery. Assuming the panel has a diode to prevent energy from flowing through it from the battery when there’s no sunlight. This is fairly common but not very efficient. [Debasish Dutta] has built a charge controller that addresses the inefficiencies of such a system though, and was able to implement maximum power point tracking using an Arduino.

Maximum power point tracking (MPPT) is a method that uses PWM and a special DC-DC converter to match the impedance of the solar panel to the battery. This means that more energy can be harvested from the panel than would otherwise be available. The circuit is placed in between the panel and the battery and regulates the output voltage of the panel so it matches the voltage on the battery more closely. [Debasish] reports that an efficiency gain of 30-40% can be made with this particular design.

This device has a few bells and whistles as well, including the ability to log data over WiFi, an LCD display to report the status of the panel, battery, and controller, and can charge USB devices. This would be a great addition to any solar installation, especially if you’ve built one into your truck.

This is [Debasish]’s second entry to The Hackaday Prize. We covered his first one a few days ago. That means only one thing: start a project and start documenting it on

A Swamp Cooler for Burning Man


For those who don’t know, Burning Man is a week-long festival in the middle of the Black Rock Desert in Nevada. The event attracts a wide range of creative people from all over the world.

This year, [Jake] is going to bring his homemade evaporative ‘swamp cooler’ to help battle the heat. His design uses a medium-sized shipping container with two large holes cut out of it and two 200mm PC cooling fans embedded into the plastic. The fans blow air from the outside into the bin. Humidifier filters sourced from a local dump are inserted into the middle of the container. The filters acts as an absorbent material to hold melt-water being pumped in from another cooler chest above.

A 30 watt solar panel provides enough power to keep the swamp cooler going while giving enough juice to energize decorative LED interior lights along with some backup batteries for phones and cameras. [Jake]’s system contains a re-purposed A/C computer load center for the solar system. He plans to take temperature and humidity readings at the Burn, bringing back the data from the desert to share with the world.

[Jake] does warn about mold with this system though, but one of the advantages with the filters he chose is that they are pretreated with biocidal compounds. This should help to reduce the chance of mold growth. High humidity conditions are also a disadvantage with this type of cooler, but this is a non-issue in the extremely dry desert of The Playa.

If you plan to go to Burning Man, tell about your energy/cooling preparations. Will you be bringing a system similar to this? If so, let us know.

A table saw to cut solar panels


Steampunker extraordinaire [Jake von Slatt] loves the idea of solar-powered garden lights soaking up the sun’s rays during the day and powering a LED in the evening. Commercially available solar lanterns, as [Jake], you, me, and everyone else on the planet have discovered, are universally terrible and either don’t have solar panels large enough to charge a battery, or only last a year or so. [Jake]’s solution was to make his own solar lanterns and in the process he came up with a great way of cutting his own solar panels.

[Jake] turned to ebay to source 100 3″ x 6″ solar panels for about $30. These are broken panels, factory rejects, but still are able to produce the 0.5 Volts they should. Since these are rather large panels for a solar lantern, [Jake] needed a way to cut these panels into manageable sizes.

To cut the panels, [Jake] made a box to fit a Dremel with a right angle attachment and a port for a vacuum cleaner. There’s a sled for the panels with markings at 40, 80, 75, and 150 mm so the panels can be quickly cut to size with a diamond cutting wheel.

After the boards are cut, [Jake] checks them out with a multimeter to be sure they’re producing the half volt they should. After that, it’s a simple matter of soldering them together and adding them to his solar lanterns.

Driving your home appliances with hybrid power

This system of hybridizing your home’s electric appliances is an interesting take on solar energy. It focuses on seamlessly switching appliances from the grid to stored solar energy as frequently as possible. There’s a promo video after the break that explains the setup, but here’s the gist of it.

Follow along on the pictograph above. We start on the left with solar panel. This feeds to a charger that tops off a 12V battery. When that battery is full, the charger feeds to the inverter which converts the 12V DC to 110V AC power. This is fed to a pass-through which is in between the appliance (in this a case a lamp) and the wall outlet. The pass-through will switch between mains power coming from the outlet, and the 110 coming from the inverter. The homeowner won’t know, or care, which power source is being used. But sunny months should result in lower energy bills. The real question is how long it takes to cover the cost of the system in saved electricity.

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Using solar cells to track the sun for your solar cells (dawg)

This solar panel tracks the sun using solar cells. It’s a pretty interesting technique, and can be done on the cheap.

The rectangular panels are doing the actual energy harvesting. The circular modules seen below are solar cells from some landscaping lights. They’re being used as sensors to help judge if the device is aimed directly at the sun. We’ve already seen this type of thing done with a quartet of light dependent resistors. In this case, if the negative leads for both landscaping lights are connected, a voltage may be read from the positive lead of each panel. If you measure that voltage, and use a rotating stand to adjust the position until the readings balance, you can be assured that your array is getting the optimal amount of sunlight.

[Gtoal] had been trying to drive motors directly from the output lines of these panels without success. We’re sure there’s a simple analog comparator circuit which would facilitate this. Grabbing a small microcontroller is another option (and some chips have an analog comparator built in).

Heliowatcher positions solar panels for highest efficiency

[Jason Wright] and [Jeremy Blum] are showing off the project they developed for their Designing with Microcontrollers course at Cornell University. They call it the Heliowatcher, and if you know your Greek mythology we’d be you figured out this watches the movement of the sun and adjust a solar panel to follow it.

Their design is simple and effective. The base is mounted like a Lazy Susan, able to pivot on the horizontal plane. The bottom edge of the solar panel is mounted with two door hinges, with a motorized screw jack used to raise and lower it. The system uses a GPS to provide geographical position, day, and time feedback. This is used in conjunction with an array of four LEDs to determine the best position of the panel. Those LEDs are acting as light sensors; when the top and the bottom detect similar levels, the panel is at its most efficient orientation. The left and right LED sensors work the same way.

Now if we can just work out a self-cleaning system to keep the panels free of the dirty film that builds up over time we’d be set!

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Solar charging a Buddha Machine

While having ambient music playing in the background can lead to a more relaxed state of mind, we can’t imagine the annoyance of having to replace the batteries constantly. Thankfully, [Phil] added solar charging to his Buddha Machine so he won’t have to worry about batteries anymore.

If you’re not familiar, the Buddha Machine is a small plastic box that loops nine tracks of ambient music inspired the Buddhist temples of south-east Asia. There’s not much to these little boxes; they’re just a plastic box with a speaker, on/off knob and an EEPROM loaded up with samples of music.

A year or so ago, the people behind the Buddha Machine posted a prototype of a solar-powered meditative noise box that was unfortunately never made. Thankfully, [Phil Stearns] stepped in posted a guide on how to convert a AA-powered Buddha Machine to solar power.

The modification is incredibly simple: after replacing the disposable AA batteries with NiMH rechargeable, two wires are swapped connecting the battery compartment with the main PCB and the box is sealed up again. Now, whenever one of [Phil]’s solar panels is connected to the power jack the batteries begin charging. [Phil] says he can get two days worth of runtime with a full 8-hour charge, so he shouldn’t need any batteries for his Buddha Machine anytime soon.