naviguesser

Need some discussion/recommendations on intalling photovoltaic (solar) cells on an electric Telemater. I am working with 4th year mechanical engineering students at University of California Merced. Phase 1 of their Capstone Project (senior year project) is to build and fly an electric powered aircraft to determine the "average" flight time on the 4500ma battery flying at minimum airspeed. In phase 2 they are to design and install a photovoltaic system coupled to the electric motor battery. Phase 3 is to fly the aircraft to determine the anticipated "increase" in flight time relative to the phase 1 flight.
I am not an engineer, rather the test pilot and advisor on the construction and subsequent modification of the aircraft. The students have completed phase 1 and are now working on phase 2. We are looking for information on how to connect the cells to the a/c battery: what interface in needed between the cells and battery, where to buy the hardware, and any other information/recommendations you might have to complete phase 2 of this project. For what it's worth this is a "time sensitive" project so any quick response would be appreciated.

ChuckW

I am by no means even close to being an expert on this. One thing I would say though is that the photovoltaic cells need to be lightweight and hopefully flexible so they will conform to the airfoil and other parts of the plane.

Their output voltage will also have to match the battery. If it is higher, some sort of regulator may be necessary.

Assuming that the photovoltaic cells just output a DC current then I imagine just putting the solar cells in parallel with the batteries would be sufficient? That's what you would do if you were using two batteries and wanted to keep the same voltage but increase capacity.

Looks like you are more experienced than I am and I'm sure you'll have plenty of help from people in one of the local clubs up there but I'm only about 50-60 minutes away if you need a hand with anything. Just PM me or feel free to drive by the field (www.frcm.org)

There's been a group from CSU-Fresno at our field recently working on some sort of GPS/UAV/who-knows-what project. Not sure if they've finished or not, haven't seen them in a couple weeks.

KW_Counter

Naviguesser,
I saw on the Science channel there is a new type of photvoltaic material out that is flexible and cost about 1/4 to make than the older cells. I have no idea where to but them but I'm sure Google does.
I hope your battery is d/c and not a/c as you stated in your question.
The other thing I'm not sure of is if the battery and solar cells need to be isolated.
This may be necessary if the two are drastically different in voltage or capacity.
I'd make friends with some electrical engineering students for this phase of the project.
Good luck and keep us posted on the project.
KW_Counter

huck1199

Seems like the 4th yr engineering students should be able to figure out how to do this. Isn't the object of the project for them to investigate and experiment with solutions until they achieve a workable system or show that it is not feasable?

TFF

You will need some diodes to keep the current flow from going backwards to the solar cells from the battery. Check out what the off grid home people are doing. Lots on the internet.

Dsegal

Go to http://www.ezonemag.com/ and click on Discussion and then do a search for "solar power". Sounds very expensive to go this route.

hayashiox

[link]http://www.rcgroups.com/forums/showthread.php?t=815270[/link]

[link]http://www.rcgroups.com/forums/showthread.php?t=291266[/link]

[link]http://www.rcgroups.com/forums/showthread.php?t=155881&highlight=solar+panels[/link]

longdan

A couple of diodes in the wires that connect the cells to the battery will stop the battery discharging if the solar panel voltage drops too low.
A regulator will be needed to keep the charging voltage within the limits that the battery can stand.
You can buy simple DIY kits for these from radio shack, but they are intendec for use with 12V lead-acid batteries. Not sure how they would go with LiPos or NiMH or whatever you are using.
I guess the ultimate end to this experiment would be a plane that could fly as long as the sun was shining. Take off at dawn and land at dusk.

Jetdesign

My Feedback: (8)

It's amazing how little most engineering students actually know. They seem to be good at math, copying homework, and cheating on exams [:@]. Try actually talking to them about building something and you will either laugh or cry at how ridiculous they sound. Of course there is the minority exception of talented and skillful engineers, but they are few and far between.

I think the first thing that has to happen is to determine the output of the photovoltaic unit and how it's configured. Maybe there are some that are configured to give a constant output of 12 volts? Maybe it will be as simple as running an 11.1volt lipo regulated to 11.x volts and plugging the photovoltaic into the receiver essentially in parallel with the battery.

Photovoltaic systems on a house don't drain energy from the grid when they're not generating power, so maybe they are already configured with diodes?

Unfortunately I'm a transfer -> junior, so I have yet to take my EE courses and can't help with the finer details.

longdan

The output of a given photovoltaic cell depends on how much light it is getting. More light = more volts. This is why a regulator is needed. On house systems, they always use a regulator which is a little black box that all the connections go to. These can be fairly basic or very sophisticated, but their main function is to provide a constant voltage to the batteries from the panel, and they house the diodes to prevent the batteries discharging back through the panel.

I have actually seen (in a shop) a r/c powered glider that was supposed to run almost indefinitely on solar panels. It had a small battery, but the majority of the power came from panels that covered the upper surface of the wing panels. This was for sale in a model shop in Hong Kong. Not sure if at actually worked or not, but it caught my eye at the time.

beau0090_99

I second the idea of befriending some EE students. As an ME, there would have been no way of me figuring this stuff out when I graduated 8 years ago.

Here is an idea for you... The mean voltage of these cells put into series, should be above that of the battery pack you are using. I would recommend using some sort of bus capacitors to store the energy obtained from the PV cells as it will fluctuate greatly by which way the plane is pointing and as far as cloud conditions go. I would regulate the voltage from this sub-system down to the voltage of the battery and try to isolate each sub-system (battery and PV cell) from each other by way of a diode bridge. This is more EE than most ME's would ever care to get into, but chances are most of them will pick this stuff up once they are out in the workforce a while. Engineering school is about learning to problem solve, real world is where you pick up your real knowledge.
Good luck,
Curtis

ChuckW

I have occasion to deal with some engineers. Most are great people, very talented and I have a lot of respect for them. A few however make me wonder how they stay employed. They can spend an hour explaining why something "can't work" although you've made it work yourself in the field or seen it work somewhere else. They seem to come up with the most complicated, convoluted solutions possible to even the simplest of problems. The problem is that they've never spent any time outside of a textbook or behind a computer. They have no real-world experience with how things actually work and behave and they have no idea what the rest of the world is doing.

I don't think it is an "engineer thing" necessarily but more of a people in general thing. I see it in other fields too. Give someone a title and they think they are automatically qualified. It takes all types I guess,.

Jetdesign

My Feedback: (8)

http://scientificsonline.com/product.aQ_pn_E_3026810
http://scientificsonline.com/product.aQ_pn_E_3052286

Here are a couple of links to a thin, flexible (ideal) photovoltaic cell system. These units are designated at specific voltages based on the model, and it explains that they are designed specifically for recharging batteries as well as for other sources. There is a 12 volt unit, and it also says units may be wired in series or parallel.

This is why it is important to know the specifications of the unit. It does not give information about regulators or diodes. It is possible, judging from the listed specifications, that they are already included in the system, or some other system may be used to eliminate the need. You can check out Powerfilm's website. They talk about "proprietary circuitry" meaning it is really not safe to make any assumptions about installation until you understand how this thing works.

To me it sounds like you can regulate the battery to a voltage lower than the operating voltage of the solar cells and just wire the solar panel in parallel for power and charging.

Jetdesign

My Feedback: (8)

Check out tech-aero.net for regulators. You can email or call Ed and I am thinking he might make whatever you want, custom. He was an electrical engineer.