Hi Everyone,

I am planning to begin making a solar powered UAV and have spent some time researching Solar Panels , MPPT’s, Airframes and Autopilots. I think the best way to go is to run the Motor / speed controller directly from the Solar panels / MMPT, but also have a small battery to “back up” the electronics just incase the UAV tips upside down etc.. so it has power to recover.
I have tested the Powerfilm solar panels but don’t think they will be efficient enough for what I want to do. I think I will use the A-300 panels instead.
This is the airframe I am thinking of using.

My question is.. Is anyone else out there trying this, thinking about trying this or done this yet??
I am interested to see some different approaches to the same problems.

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You don't need an MPPT - because you have most of it already.
The ESC is capable of pulling more current or less current - that is the heavy-lifting of an MPPT. You don't want to do this twice because you'll just make more transistors hot and waste energy doing it.

If you have more power, then you should be climbing up to your ceiling, if you have less power, then your esc will slow down automatically; the plane will either level off or descend.

Moving the effective voltage around will, I believe, only waste the heat and weight of the converters, since the esc is probably doing a fairly good job of optimally pumping the available power into the prop, and if not, the better solution may well be to change the prop pitch rather than the voltage.

IF Batteries are in your future, than an MPPT charging strategy might be helpful. The MPPT will only manage the charging current, not the full current.

Generally one should use all solar power to climb until one is close to ceiling, then increase the charging cycle to the point that altitude is stable - until the batteries are full. Only that extra current needs to be handled by the MPPT, so an MPPT much smaller than the solar panel power rating can be used.
Some Spectrolab cells are almost 40% efficient, but their costs are astronomical.
Hi Brandon,

This project is on hold as we are starting to build a UAV for the next Outback UAV challenge!

I have considered mounting the cells inside the wing (close to the covering) and then covering the wing with a clear covering over the areas where the cells are. Hopefully I won’t loose too much light from the covering. The other consideration will be somehow letting some airflow through so the cells don’t get too hot and loose efficiency.

I found some good ideas here.
Where are you getting your cells from as I am having a hard time sourcing them?

After some thought.

For systems with batt and solar,
One could install two ESC's - one to connect the battery to the Motor, and the second to connect the solar cells to the same motor.
This overcomes the need for an MPPT and a DC to DC converter. The solar circuit includes a capacitor.

When the capacitor is charged above the target voltage (peak mppt for current sun conditions), turn on the Solar ESC until the capacitor drops below the target voltage. If you need battery power, you can use batteries during the time the capacitor is charger. You can vary the solar to battery ratio by changing the cycle ratio, But generally, you'll run on one or the other and not both. The total power is controlled by the throttle level to the ESCs. (don't throttle them up together).

To charge the batteries, include a charging transistor and a cheap lion charging circuit. ($5 model) power this circuit when the capacitor is above target voltage AND you're above target altitude.

(probably a very bad idea to power them both up together as even the power up chirp could cause a short.) don't connect the common ground until after power up.

The objective here is to avoid a complex, inefficient and heavy DC chain between your power sources and the motor.
The parallel ESC's offer a single transistor connection between the solar cells and the motor, and alternatively between the batteries and the motor. MPPT tracking can be managed by adjusting the motor power/climb rate and/or charging rate. (I can't think of any benefits of adding extra transistors in a discrete MPPT between the solar cells and motor.)

2 ESC $20
1 Motor $20
1 Lion Charger $5
1 ArduPilot Pro ($?)
1 Power transistor for Charger
1 Capacitor for Solar
1 Current Sensor for Solar Cells
x Solar Cells

MPPT Algorithm includes measuring current and voltage of solar circuit and adjusting the target voltage up and down to find the voltage at which the solar cells are producing peak wattage. In a separate loop, if the solar voltage is above the target, then use the power, if below, then stop using the power. The cell voltage must be higher than the battery to be useful. The second ESC solves the problem of voltage mismatch between the solar circuit and the battery potential.


P.S The nasty problem with parallel ESC is the potential for shorts - to address this place a fuse, and perhaps a inductor between the battery ground and the solar ground as this will minimize the effect of an unpleasant H-bridge short. Better would be a self-resetting fuse.
There sure is allot to consider!

I think I will attempt a solar only UAV first with maybe a low voltage cutout to switch to a very small battery (just for the electronics) so I can still land it if there happened to be a sudden eclipse! :)
A properly designed MPPT is a DC/DC converter with a clever feedback loop Basically, an MPPT uses the ripple from the DC/DC conversion to find the peak power point. There are some off the shelf MPPTs that have adjustable battery (output) voltage. If you use one of these, it takes the guesswork out of the solar cells.

An important thing to remember when using bare cells (not a pre-made panel) is to either make sure they have intrinsic bypass diodes or to put your own in. Basically, it will prevent every cell from being reverse-biased and ruined (in case of physical damage).
Check out University of Michigan SolarBubbles team goal to design, build and test a solar-powered unmanned aerial vehicle capable of 36+ hours of flight with less than a 15 foot wingspan.
Since a DC/DC converter introduces some inefficiency, I proposed using a separate esc to drive the motor (one at a time) one from batt and one from solar. The MPPT algorithm is then applied by the flight logic such that the plane climbs steeper or less steep in order to optimally discharge the solar cells.

In this configuration, the esc /is/ the mppt.
for battery flight, shut down the throttle on the solar, and run up the batt esc. The batt esc can be smaller.
There is no real option for using both simultaneously. (unless you custom design such).

There is also a charging switch between the solar and battery - but this is low current as the charging current is only what is left after the main propulsion current is satisfied.

For inferior lighting conditions, the charging circuit can be used to combine battery and low solar power.
Solar UAV QinetiQ Zephyr breaks world record - 54 hours.

Hi friends

From what I have gathered from the odd picture of them they have to be huge to actually have enough area to power them, they also should fly high and be a wing. The US did a project like this and it was something in the region of 10m across!




I have just started to think about this. My goal is to build a solar powered UAV that can cary a smartphone and Arduino Micro. My initial search of existing designs suggested that most of them were overgrown park flyers. My brother has been working on some UAV software for Android that seems like it has a lot of potential. With what he has already done, we can stream video and telemetry of a cellular data connection. It seems like some really cool things could be done by combining a cellular connection with the ability to stay up for hours at a time (potentially all day).

My main concern is cost and the thing I really need help with is solar cell selection.

thank you very much , i like your Solar UAV, i think Freewing Plane is more better

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