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Solar Powered Flight.

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Patrick

Mon Jun 04 2018, 05:46AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im looking to give my friend Daniel Riley some advice on solar powered long duration flight.

His video can be seen here :

And his patreon page :

The question is how to handle the impedance change from battery to solar cell. Theyre needs to be a SMPS to match the two sources right ? He is just connects the solar cells and battery cells in parallel and tries to match the voltage.

Im thinking two buck/boost converters one for each source.

Any other ideas ? Is it that simple ?
I was thinking of two of these :

Ideally you'd only use the battery for short bursts for energy intensive maneuvering like take off and turning , then you'd switch over to running on the solar cells and charging the battery till dark.

so you'd have three sources of energy for flight. Battery, electric solar, thermal updraft (solar too). modulating the three would in principle allow one to fly 24+ hours i suspect.

Carbon_Rod

Mon Jun 04 2018, 09:37AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

When solar cells exceed their rated current the output rolls off to 0v.

CN3791 is a 4A MPPT LiIon charger (must be tuned for specific cells)

LT3652 is a 2A Battery Charger for Solar Power (does step-down charging of LiPol)

There are 30A 24vDC MPPT solar charge managers for LiIon, but not sure abut LiPol.
Also, solar cells must have high current Schottky protection/bypass diodes to prevent abnormal discharging/fires.

IIRC, 3 cell LiPol usually allow the maximum weight+KV efficiency for fixed wing RC craft, and should also make finding charge managers in the 12v class easier. Notably the C rating of larger/better cells allows handling surges in power demand, and with better energy density.

Plasma

Mon Jun 04 2018, 01:57PM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

Hi I think a solar panel, battery powered and smps are power sources, you still have to adjust the load to half open circuit voltage of the source, change the load from just the motor to have a second load storage, preferably a couple hours storage, and design the motor to draw half ocv at 80%light,when it's really sun dividet to the second load.
What the internal resistance of the battery, you might need multiple batteries each one gets combined with the other in stages at higher power source energy

Patrick

Mon Jun 04 2018, 06:15PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

He theoretically has demonstrated full prop power with no battery contribution. So I wonder if an arduino could select solar cells to charge the battery as needed then reconnect them to the stack via transistors.

Dr. Slack

Tue Jun 05 2018, 09:36AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Pure buck or pure boost converters should be slightly more efficient than buck-boost. It would be sensible to plan the voltages so these can be used, say low voltage solar array, high voltage battery, low voltage motor (whose ESC is basically a buck converter anyway). You want to extract every last watt from the panels, so MPPT is a must.

He has two means of energy storage, batteries, and height. When there's an excess of solar insolation, does he have a good feel for which is the more efficient place to store the energy. Knowledge of wind speeds and directions may help. Obviously both mechanisms have a maximum 'capacity'. This is a storage mechanism unavailable to land vehicles, so there might not be too much discussion of it in the literature. What flight rules does the flight have to comply with for height? Obviously if there's a low ceiling for safety mixing with other air traffic, then the height capacity is minimal and the manipulation of height is pretty moot.

Similarly, when there's not enough solar, is it more efficient to lose height gliding with all power off, maintain height with an appropriate amount of battery use, or some other strategy? I don't know, I'm just asking the question.

Patrick

Tue Jun 05 2018, 06:24PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I have FAA permission in 20 mile diameter several times a year upto 500k+ feet.

Yes we plan to go up, and thermals ar powerful, they interfere with experiments and calculations. We do plan to day time fly to 50 or 70k then wisely trade down to 2k feet by dawn. Then you can repeat. Way cheaper than closed loop hydrogen fuel cell stuff on helios like designs.

We also plan to fly over international waters off California to avoid legal issues. I been told by some aviation experts with 50+ years training air traffic controllers that this is the better idea.

Patrick

Mon Jul 02 2018, 03:48AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

will this circuit do some of the solar/battery "mixing" that we need done ?

3S-PCB-BMS-Protection-Board-25A-11-1V-li-ion- Lithium-Battery-Protection-PCB

Or is this better ?
https://www.ebay.com/itm/2A-solar-LT3652-lithium-battery-charger-with-MPPT-and-protection/332187875920?hash=item4d57f0ba50:g:eGwAAOSwmCVY9w3e

2Spoons

Mon Jul 02 2018, 09:54PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Er - those two boards do completely different things, so its not clear what you are trying to achieve.

klugesmith

Tue Jul 03 2018, 12:12AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

We might learn something from history, specifically the first year (1987) of World Solar Challenge (solar cars crossing Australia).

One key player on the winning team was a college buddy of mine. Here's what I remember hearing about the electric power architecture. It had to handle hills and winds, and clear or cloudy skies, with batteries that were primitive by modern Li-ion standards.

Many details below are just like Dr Slack advised:

The motor speed control is essentially a SMPS standing between the battery bus and the traction motor.

Battery bus voltage is simply the response of the physical battery to the net power (charge or discharge) at
that moment. Battery current may be limited according to the battery charge/discharge protocol.

Another variable ratio SMPS stands between battery and PV panel. Its ratio automatically changes to keep the PV operating at its maximum power point (which depends on illumination and temperature). Actually, the PV is divided into sections with independent SMPS ratios, because aerodynamics dictates cells facing in different directions.

The only reason for a PV operating point that isn't Max Power, is when the battery is full and it would be unsafe to drive any faster.

Back to 2018: I see no benefit from using a buck/boost converter. The battery, PV cell, and motor configuration can be chosen so each converter is always boost or always buck.

Patrick

Tue Jul 03 2018, 04:48AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

klugesmith wrote ...

Back to 2018: I see no benefit from using a buck/boost converter. The battery, PV cell, and motor configuration can be chosen so each converter is always boost or always buck.

Boost is what im beginning to test. so far it looks tiny and efficient.

2Spoons wrote ...

Er - those two boards do completely different things, so its not clear what you are trying to achieve.

Yes they are different but i dont know which to use.

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