Home of Professional Cinematography since 1996

Power Source In Remote Location

Published : 29th August 2003


I am trying to spec an HD equipment list for an extended trip by pack horse. I was wanting to carry the least amount of weight possible.

Has anyone had experience with solar charging?

How does it compare, amp hours to package weight, when compared to disposable sources?

Any good resource companies?

Thanks,
Bert Guthrie
DP Dallas



Bert Guthrie writes :

>I am trying to spec an HD equipment list for an extended trip by pack >horse.


Real Goods ( www.realgoods.com ) can probably steer you in the right direction. Make sure you tell them that your batteries are exotic professional ones, not consumer-type thingies.

The best solar panels for your purpose are the ultra-lightweight ones made by Solarex. They're made on a thin aluminium substrate with a plastic (not glass) coating. Top of the line is a 30-watt unit (~2.5 amps at 12 volts nominal) that weighs a couple of pounds at most. The trick is controlling the panel's output to safely charge the batteries without getting into a lot of heavy voltage conversion and reconversion hardware.

If the batteries are ni-cads or gel-cells, you can probably get by with a small, off-the-shelf charge controller. NiMH and Li-Ion batteries are much more finicky, and more easily damaged by imprecise charging.

If you have an automobile cig-lighter-powered charger (which, of course, will provide you with the proper battery contacts), you MAY be able to use it directly with the solar panel, but this MUST be tested. Connect the panel, the charger and the battery before exposing the panel to the sun -- the open-circuit voltage of a 12-volt solar panel can be close to 20 volts in full sun, which conceivably could fry the controlling semiconductors in a charger accustomed to receiving no more than about 14 volts max from a car battery.

If the batteries are 12 volts nominal, use one 12V panel or several in parallel. If 24 volts, use two in series, with a 24V charge controller.

Figure 5 hours of full output per cloudless day (30 watts x 5 hrs = 150 watt-hrs. That's WATT-hours, not amp-hours) per panel, if you can only set the panels at a fixed angle. If you can keep turning them to stay BROADSIDE to the sun, you can do better than that.

Any dirt, dust, oiseau-poopoo or any shading whatsoever will radically diminish your panels' power output.

Why not print out this email and read it to the folks at Real Goods, and see what they say.

Good luck, and keep us posted!

Dan Drasin
Producer/DP/Solargeek
Marin County, CA



A friend of mine is an electrical engineer and was consultant to a group of doco makers shooting a show on Cycling across Mongolia. They shot on a VX1000 (Yuk) but required charging facilities. In the case of this camera they were able to go the cigarette lighter off solar panels due to the charging product being available....the solution though was something I hadn't seen....a solar panel that rolled up like a plan.

On quizzing my friend on how to solve the same problem for professional chargers, he said that the input voltage for most chargers is reduced through a transformer anyway. All you need do is to bypass the transformer on a professional charger and find out the input voltage to the actual charge regulation board and make sure your solar panel through its own regulator outputs the required input voltage.

Nick Paton
Film & Digital Cinematography
www.npdop.com



Bert:

I just did a three week job in Africa with a Varicam. On a previous trip with an Aaton and a DAT machine, we used a large solar power system. It was cumbersome, required a large truck battery, and did not produce enough power, especially for the DAT batteries. This time I took a Yamaha inverter generator, about the size of a small cooler and only 27 lbs. This generator acts like a car alternator, only running as hard as the load dictates. As my quad charger only draws 135 watts, the generator would run ten hours on 1/2 gal. of gas. Reliable and easy.

RE: previous concerns about X-rays -- out of curiosity I left a test tape in the camera to see the effect of x-ray checks. After 4 trips through the box, 3 overseas, I saw no artefacts on the DVCPROHD tape.

Rod Paul



>Has anyone had experience with solar charging

We have always had good luck with the disposable Lithium "Expedition Batteries" built by Stuart Cody at Automated Media in Boston :

http://www.automatedmedia.com/products.html

On many expedition films over the years (16mm, HD, M-II etc.) I have found that the cost of shipping, transporting, and using gas generators ends up being greater than the cost of shooting the whole show on a combination of as many rechargeable bricks (Hytrons are great) as you can muster, then switching to the disposable Lithium’s until you get back to some kind of AC again.

It often seems to be the case that a lot of shooting will take place as the story works through towns or venues with AC, then when the jumping-off point occurs, fewer amp-hours are needed than one might expect.

If you are constantly on the move, either on horseback or on foot, or it is cloudy, solar can be very problematic and if it were your only option, you could be in big trouble. If you'll be at a base camp in reliably clear weather, then use the panels, but have some lithium throw-aways just in case!

The Stuart Cody site also has solar info. He is available by phone and has a wealth of experience powering remote expeditions around the globe.

PS: I shot the Death Valley doc for Discovery that was referred to (CR was my very talented and brilliant engineer) and we worked out of hotels with chargers, and also used a generator, although CR had rigged a very useable solar array on the roof of the truck. This was earlier in the HD era, with two-piece camera/recorder, using a lot more power.

Peter Pilafian
Wilson, Wyoming
www.hpix.com



>I am trying to spec an HD equipment list for an extended trip by pack >horse.


Hallo Bert :

I recently did an extended trip on foot in the Namib desert (Southern Africa) and my load was +/- 40kg. Lithium Ion chargers don't do well when connected straight to solar panels or generators. They don't enjoy any power surge. The other problem is that you need such a long charge period with lithium ion batteries. Siemens produce a 20 watt solar panel 32 cm x 50 cm (9.6 x 15.1 inch) that's small enough to carry around on horse back. I've put two solar panels in a collapsible butterfly manner together to transport and protect the solar surface to give me 40 watts which will give you a charge of about 3.3 amps per hour which will charge three 12v - 7ah batteries per day - with 7 hrs of full sunlight Your solar dealer will supply you with a small regulator box. I used a 5 ah regulator to prevent me from cooking the battery.

I bought six 7 a/h Led acid batteries to be able to alternate a set of three batteries every day, each battery ways about 1.6 kg (+/- 3 pounds) I know its heavy but at least they handle the external temperatures well. You should be able to get them at your local security shop and they are really cheap. I've used this system since March 2002 and have yet to run out of battery power, if you want to take lights with try some of the various 12v florescent outdoor/camping lights, you will save a lot of battery power - just do a Kelvin test on the lights. The average is about 4300K. Do yourselves a favour and don't take a generator, it will kill the ambience with noise and air pollution never mind the other unhappy campers.

Please excuse my English its not my first language
Good luck
Jacques Nortier - Environmental cameraman