Home‎ > ‎Projects‎ > ‎

Solar Golf Cart

The Chinquapin Engineering class has modified a golf cart so that a solar panel charges the batteries.
 







 


Our Cart

 
 
The golf cart, a 1993 EZ-GO, has been donated by Golf Cars of Houston.  Special thanks to Sonny T. at Golf Cars of Houston.  Here's Robert and Elber checking the batteries. 
 
 



 
 
 


Solar Panel

We already have a Suntech 175W panel (links tp PDF).  The panel was donated by Alternative Power Solutions (APS).  Special thanks to Christian L. at APS.  The critical panel specs are as follows:
  • Open-circuit voltage = 44.2V
  • Current @ maximum power point =5A
 

Mounting

 
The panel is a little longer than the length of the roof, so we've attached the panel to the roof mounting locations with 1/8" x 1" aluminum bar stock and #10 stainless steel hardware on the panel corners and 1/4" stainless steel hardware at the roof mounting locations.  Stop nuts are required to keep the bolts from working themselves loose.  (We tried hex nuts and lock washers, but they worked themselves loose.)  Some weather stripping on the bottom of the panel's frame a piece of rubber inner tube sandwiched under the panel's junction box help reduce vibration noise.
   
 


Connection Schemes


We have two connection schemes: a diode and a charge controller scheme.  Here is the diode connection scheme we're trying first.  This has the advantage of low cost, but it is not as efficient at pulling energy out of the solar panel.  The dashed circuitry is needed to provide the meter with some power at night; otherwise, the meter loses all data from the day.
With this simple diode circuitry on an average day, 572Wh of energy was generated.  This possibly could have been as much as 50% more, but the batteries did not need very much charging.  The maximum power observed was about 130W.


Here's the charge controller scheme that is more expensive but is more energy efficient:

With the charge controller we should be able to maximize the energy produced by the panel.  We have a charge controller from Helios Solar Power: model HSC C48.  A little poking around reveals the unit is a Genasun Model GVB36-8.  The unit was purchased through SunCoast Solar, which is a reseller.  Here's SunCoast's page on the controller: 36V Boost MPPT Controller.  Cost was $250, purchase date 2/27/10, warranty is 2 years.  Thanks to Arthur S. at SunCoast for his help (and discount).  Note: the unit contains a 10A automotive-style fuse inside.  We have mounted the controller under the seat in the battery compartment, as shown here.


Upon first connection we saw 150W being generated into batteries at about half-charge.  This is 20W (about 15%) more than with the diodes.  We later saw >180W in intense sun, which is curious, since the panel is rated at 175W.  We suspect the way the charge controller draws current (in pulses) is confusing the power meter. (The meter probably does not calculate a true RMS value.)




Wiring and Connectors

14-3 SOOJ cord is routed around frame with cable/zip ties.  14 gauge wire is borderline for minimizing voltage drops, but we wanted to keep the cabling as low-profile as possible.  Plus, the charge controller will compensate for some cabling losses.  We have used wire nuts to connect the solar panel and power meter, since we want to be able to remove the panel should the need arise.  Battery connections are made with ring terminals.  Battery terminals are 5/16".

We also have a new connector to mate to a electric charger.  We'd like to make as little use of this as possible.

ToDo:
  • Install charging connector

Gauges

Here's the power meter we've got to help us characterize the solar panel's performance: WU100.  There is a problem with this meter in that it loses all data every night, i.e., when the solar power goes away.  We're have a fix in that we feedback some battery power to keep it running at night. (This is the dashed circuitry in the schematic diagrams above.)  It was decided the best location for this meter is the under-side of the roof, and we have installed it there.  It would be nice to install an enclosure to clean up the cabling, but we're about out of time and funds.  (The green wire is now used to feedback power to the meter.)
                    
 


Seat Repair

The seat needs some repair. The plastic flange in the back was falling off and cracked, so we stapled (via staple gun) it back in place, and that repair is done. There are also two hinges on the front of the seat that need repair. One hinge was completely missing, and the other was falling out. The wood is suffering some rot, but it looks possible to repair. We've used some wood hardener and have pounded some flat iron braces into the proper shape. Here's what they look like.  Hey, it works.






Conclusions

We have shown that it is possible to add an off-the-shelf solar panel to a golf cart.  There are significant mechanical and electrical considerations, and the mounting and wiring will differ for different cart and solar panel models.  Here are our recommendations and conclusions, based on our project experiences:

  • Good candidate carts have a relatively flat roof.  Our panel is longer than the roof, and it is recommended to select a panel that does not extend beyond the roof more than a few inches or fits completely on the roof.
  • Panel vibration must be addressed
  • There must be access to the underside of the panel for wiring
  • SOOJ cord is a good choice for wiring, since it is weather-resistant and flexible
  • The lowest cost version has no charge controller and no power meter.  The only added electrical component is a series diode to prevent the batteries from discharging through the solar panel at night
  • With normal daily usage, a solar panel cannot eliminate the need for a proper golf cart charger, but it can reduce electricity charging costs and extend battery life
Comments