Written by Craig Peck A greener, safer way to charge Technical As seen in the Winter 2013 issue of Park Pilot.
Flying clubs without an on-site source of electricity are challenged when it comes to keeping batteries charged. Some pilots drag extra car batteries along while others charge in their automobiles. The truly dedicated use generators to power their chargers. After pondering the possibilities of how to create a safe and effective station to meet the growing demands of our pilots, my solution was a solar-powered system, which I presented to the club last year. It was clear that the club members were excited about this project. I presented the list of materials and estimated cost, and after a unanimous vote to implement the project, it received the green light. Building the 12-volt, centralized solar charging station was not difficult. A 193-ampere-hour, absorbed glass mat (AGM) battery was chosen to power the chargers. The AGM is a specialty battery that typically costs twice as much as premium wet cells. AGMs require a special charge rate, which was addressed by configuring a 30-amp Trace controller. This allows the electrolyte to be suspended in close proximity with the plates’ active materials, enhancing the discharge- and charge-rate efficiency.
Two wiring busses (junction points) are easily accessed, mounted on the clubhouse wall and protected by a clear-plastic cover.
It is important to note that AGM batteries give their best life performance when they are recharged before allowing them to drop below 50-percent discharge rate. Our controller is equipped to take care of this, and because of our choice of solar panels, I doubt that our battery ever gets below 70 percent of its capacity. Initially, we powered the station using a 75-watt solar panel as our charger, but soon realized that the panel could not keep up with the heavy power demand; greater stability and a more robust array of solar panels was needed. Two 235-watt panels were purchased, and they came with a 25-year warranty. The panels were installed on the roof of our field clubhouse, and we were now in a state of fool-proof charging.
Craig Peck’s solar-charging setup uses two 235-watt solar panels mounted on the roof of his model club’s flying site clubhouse.
The sun’s light contains energy, and when light hits an object, the energy typically turns into heat, much like the warmth you feel while sitting in the sun. In a solar panel, the reaction is called photovoltaic. When light hits certain materials, the energy turns into an electrical current that we can harness for power. When exposed to light, the crystals get up and move around, resulting in electricity instead of just jiggling in place and making heat. Typically, solar panels are less than a centimeter thick and made up of a panel of tiny disks of cut crystalline silicon crystals. The thin, wafer-like disks are carefully polished and treated with dopants (materials added to alter an electrical charge in a semiconductor or photovoltaic solar cell), and metal conductors are spread across each disk. The conductors are aligned in a thin, grid-like matrix on the top of the panel, and spread in a thin sheet on the side facing the earth. The crystals are placed between layers of glass, arranged in an aluminum frame. To protect the solar panels after processing, a thin layer of cover glass is bonded to the top and attached to a substrate by an expensive, thermally conductive cement. This keeps the solar panel from becoming overheated; any leftover energy that the solar panel is unable to convert to electricity would otherwise overheat the unit and reduce the efficiency of the solar cells. Elevating the solar panel above ground is imperative. The elevation allows airflow underneath the device to keep it cool. The trace controller is the battery management system. It monitors the voltage of the battery and the current of the loads put on the battery. On a sunny day, when there are multiple chargers in use, the controller will divert all of the energy from the solar panels to satisfy the need of the chargers in use, with the battery bringing up the slack as needed. When the load dissipates, the controller backs down on the current from the solar panels, bringing them to what I will describe as an “idle state.”
Xantrex C30 controller (left) and dual-function circuitbreaker box (right) are on the clubhouse wall above the 193-ampere-hour, gas-matt battery that the solar panels power.
When the battery reaches a specific voltage, it triggers the controller to go into a charge state. The controller charging has three phases: 1) Bulk Phase: The battery is charged at a bulk-voltage setting and maximum-current output from the DC source. When the battery reaches the bulk-voltage setting, the controller activates an absorption stage. 2) Absorbtion Phase: The battery is held at the bulk-voltage setting until an internal timer has accumulated 1 hour. The current gradually declines as the battery capacity is reached. 3) Float Phase: The battery is held at the proper voltage. When the battery voltage drops below the volt setting of a cumulative period of 1 hour, a new charging cycle is initiated.
Four charging stations are available, and each has inputs for two devices. The overhead awning helps shade the work area from direct sunlight.
This all-purpose, solar charging system provides an ample 12-volt power source for battery chargers of nearly every description. Each of the four stations has a weatherproof lid and will accommodate two chargers. The utility bench provides work space, and the area is shaded by an overhang. During peak flying hours, it is not uncommon to have up to six high-capacity batteries charging at the same time. The solar station delivers the bulk of the energy when there is greater demand on the system, and the battery brings up the slack as needed. On cloudy days, the solar panels are not able to create enough energy to be the primary source of electricity. When this occurs, the charged AGM battery becomes the primary power source.
Each charging station is equipped with two sets of banana jacks to accommodate 12V-DC chargers with banana plugs.
Bill of Materials and Approximate Costs
235-watt solar panels, two required: $599 each Xantrex C-30 Trace controller: $90 Circuit-breaker box: $25 193-amp-hour AGM battery: $300 Covered boxes to house input jacks: $6 each Banana jacks, two required per charger: $8 pair Miscellaneous materials for utility bench, panel mounting and roof overhang: $150 Our club is commited to a greener America.
On any given day with sunshine and flying activity, the stations are in constant use by club members. The system is reliable and maintenance-free.
Future plans include a power inverter to run our clubhouse lights, and a 12-volt feed to our lawn tractor to maintain the battery in the off season. The solar charging system has been operating for two flying seasons with zero maintenance costs — and the breakers have never been tripped. There has been nothing but positive remarks for the installation and functionality of the system. -Craig Peck
