Strobl Solar Panel Kit for Sailplanes
A new toy finally arrived. A solar panel installation kit from Strobl Solar for my club’s DG-1000S glider “1CH”. More photos of the kit are on flickr.
1CH is the queen of Bay Area Soaring Associates’ (BASA) fleet of gliders. The DG-1000S has two batteries -
- The main battery — a standard 12 Ah 12 volt AGM battery in the luggage area behind the rear seat
- The tail battery — a special DG 14 Ah 12 volt AGM battery that fits inside the tail fin spar
We remove the main battery after each day of flying and charge from an AC charger. We do not remove the tail battery as this requires removing the horizontal tailplane and the associated risk of damaging the tailplane and misconnecting the elevator control on reassembly.
We have relied on a small 5 watt flexible solar panel to trickle charge the tail battery on the ground but that is really insufficient to keep the battery charged. Other schemes with large solar panels or secondary larger batteries to ground charge the tail battery are not practical, especially around airports where we can’t leave equipment out on the ramp for safety reasons.
We’ve needed to find a solution for a while for battery problems with 1CH. Leaving the tail battery undercharged has killed the battery. Being a specialized part this cost us around $500 compared to the $30 to $40 that a standard AGM battery would cost. So spending around $1,500 to $2,000 for a Strobl Solar panel kit and installation does not look too outrageous. Strobl panels are the standard solar panels offered by most glider manufacturers so the decision to use them is pretty obvious.
One reason for really wanting to have two fully charged batteries is that like many responsible glider owners nowadays BASA’s 1CH is equipped with a mode C transponder. The transponder lets air traffic control radar see the glider and reports our altitude. Aircraft equipped with technology like TCAS, can also alert the pilot directly should we get close. The down side of running a transponder is they use a little more power than most other electronics found in gliders (although some high end GPS units and PDAs can come close).
After some shipping problem from Strobl Solar in Germany the installation kit for their 22 watt three panel install for a DG-1000 finally arrived. The shipping took two attempts, problems were apparently caused by Strobl not including the right customs declarations — something that they probably won’t mak a mistake on again. They also sent to first shipment attempt via Deutsche Post which was not trackable in the USA. Hopefully that shipment will turn up back at Strobl. If you purchase a solar panel from them and ship to the USA insist they ship via UPS.
The kit looks very well made and includes three solar panels (depending on the kit, some others come with two panels), various mounting tapes, silicone insulated wiring, a charge controller and panel mount switch to select which of two batteries the panels are charging. The Strobl panels use many small crystalline silicon cells in what looks like a hand assembled plastic laminate that is just flexible enough to curve to the glider fuselage. The crystalline cells let the panels get a much higher efficiency than amorphous silicon flexible panels. The backs of the panel are covered with 3M Very High Bond (VHB) tape. The same material I’ve used to attach a very large UniSolar panel to my glider trailer and that the automotive industry uses for holding panels on trucks etc. This stuff will not come off.
I am curious what sort of charge controller technology Strobl use. For better efficiency I hope it is at least using pulse width modulation and not shunt. The charge controller is sealed with tamper proof connectors and I’m not going to pull it apart. One concern is the label on the regulator says there is are 4 amp input and output fuse inside. What are you supposed to do if a fuse blows?
I’ll post information on the install of these panels which will be done by Williams Soaring in a few weeks. I hope to make some measurements of their performance in real world conditions.
BASA has a second DG-1000S on order and this will likely be configured with factory installed solar panels the same as we’re installing on 1CH.
Hi Darryl, I am interested in knowing the results of the Strobl solar panel on 1CH . My club recently got a used Grob Twin III SL and so far it’s working great but we are having problems with the battery running out when tutoring our members on self launching. All the engine extraction, retractions and short runs are draining it rapidly, yesterday we made 7 extractions and climbs and in the 8′th run the engine only partially got out so we had to land it, my guess is that the main battery has also become weak so I am ordering a new one.
Great blog by the way, but you need to keep posting, I imagine you are to busy for that with your new toy now ;)
Happy soaring.
Sigtryggur Sigtryggsson,
Soaring Club of Akureyri.
Iceland.
Comment by Sigtryggur — June 19, 2007 @ 5:31 am
The club has been very happy with the Strobl solar panel on our DG-1000S. It has worked very well and the tail battery is alwasy fully charged.
The only hassle I can think we’ve found is that we purchased the parts from Jaxida to put a clear panel in the canopy cover so the solar panel will work while the glider is on the ground. There is basically a flexible clear plastic panel that attaches with velcro over a hole cut in the canopy cover. You remove the clear panel and roll it up seperately before removing the canopy cover. We’ve had problem getting club members to remember to do this properly.
If your club’s problem is really near continuious heavy power consumtpiton like repteated extension of the engine then solar chargers may not help, they may just not have enough ability to recharge the battery fast enough.
I’d aslo be looking at battery age/health and battery temperature as possible issues. Just replacing the battery is a sensible approach. If the battery health is hindered by the battery not being kept fully charged then looking at a solar panel on the glider that is mostly used for ground charging may be useful.
At Iceland latitudes solar panel efficiency will be less than we see here in California/Nevada. You should be able to find charts to help guesstimate this.
Cheers
Darryl
Comment by darryl — June 20, 2007 @ 12:20 am
Hello Darryl and all reading, we have found out a new thing about our Twin III SL. We were debugging a problem with the extraction retraction mechanism of the glider and we found out that the extract/retract motor had a steady 12 volt stream after the engine had retracted. We checked the switches that control that operation and they were incorrectly aligned so the motor had a steady drain on the battery at all times the engine electrics were engaged. We did some changes on the micro-switches and after that the sub/retract engine is disengaged after retraction and we have a new light in the cockpit ‘Engine Retracted’ that we did not know about before and it seems the person we bought the glider from did not know about it either. I am looking forward to testing the performance increase of the battery as I hope the fix of the constant drain of the extraction/retraction motor will at least give me a 20-30% increase in power efficience. I wonder about what action to take on the seller of the glider since it was in absolute sub-standard shape when I bought it and the previous owner led me to believe that everything that was wrong with the glider was normal, now I know better and me and my flight mechanics have exchanged a lot of components of it and now we have it in great shape. I absolute love flying the Grob Twin III SL it is now a great ship but we have had to do repairs for about $20.000 to get it in shape after purchasing it for $95.000.
After this experience I and my mechanics know ‘all’ about the maintenance of this glider and that is a good thing so if anyone has any problems then I would love to try to help.
Comment by Sigtryggur — May 22, 2008 @ 5:29 pm