Explore the Sculpture

What components make up the sculpture?

The sculpture itself consists of twelve aluminium shafts, each having several lamps and solar panels affixed to its faces. Inside each shaft is an electronics drawer containing a battery for storing solar energy, a commercial charge controller, and custom electronics that are the “brains” of the shaft.

In addition to the shafts and their contents, the sculpture is supported by a host computer located on-site in the EMS facility, and a remote database and web server.

How your patterns get to the sculpture

Visitors to the sculpture’s website compose patterns via the Create applet, which sends pattern parameters to a back-end database. A tiny host computer (really! it’s smaller than a box of Kleenex!) running in the EMS building at 100 Maple Grove Road retrieves the pattern list every evening from the database. To begin the show, patterns are communicated over wireless modems between the host computer in the EMS building and an antenna inside the nearest shaft. From there, they are distributed to each of the shafts over a communication cable. The host computer knows when to begin the show each night based on a calculation of sunset time for the date and locale.

Illumination is provided by high-efficiency LEDs

Each shaft has nine lamps on each face, organized in three groups of three. Each lamp pulses in sync with the corresponding lamp on the other three faces, forming a “pixel” that appears to have its light source inside the shaft. In reality, each of the four lamps in a pixel is a triangular sandblasted glass prism, with a group of three high-efficiency white LEDs at either end. The surface treatment of the glass prisms help to diffuse the LED light evenly.

Each pixel is fed by a constant-current (60mA) circuit and is made up of eight series bundles of three LEDs in parallel. A DC-DC converter inside the shafts boosts the 12V battery supply to 30V to drive the LEDs, and brightness is controlled using pulse-width modulation (PWM) to pulse the LEDs on and off faster than the eye can see.

Solar cells

Each shaft has a single solar array, made up of 24 series-connected A-300 solar cells from SunPower. At the time of construction, the A-300 cells were some of the most efficient monocrystalline silicon cells available on the commercial market (>21% efficiency). Each 5”x5” cell produces 3.1W, at peak operation, so in bright sunlight, the sculpture is generating 890 Watts of power. That is enough to power a small vacuum cleaner.

Physically, the 24 cells are laminated into six 1x4 sub-arrays (encapsulation by Alain Chuzel at SunCat Solar), which are then incorporated in pairs into the three 1x8 panels seen on the shafts. The panel frames are made from bent aluminum, with an aluminum backing for cooling, and are gasketed to prevent moisture from accumulating along the edges of the laminate.

Batteries and charge controller

The 12V, 7.2Ah sealed lead-acid (SLA) batteries used in Solar Collector are of the “absorbed glass mat” (AGM) type. Unlike traditional “gel-cels”, AGM batteries can tolerate freeze/thaw cycles without cracking or internal damage. The battery dimensions are 70 x 90 x 101 mm. The capacity calculations were done based on achieving a show of minimum acceptable length during the lowest average insolation conditions while maintaining battery voltage above 11.5V to increase lifetime. Safety factors were included to increase error margin and account for temperature derating and efficiencies of the charge controller and high-voltage DC-DC converter used to drive the LEDs.

The Morningstar Sunguard 4 charge controller monitors the charge state of the battery and regulates power from the solar array to ensure optimal battery conditioning. In order to increase the battery lifetime, the charge controller disconnects the lamp load when battery voltage drops to 11.5V.

Microcontrollers control the pulsing of the lights

A small computer circuit, based on Microchip’s PIC 16F877A microcontroller, is responsible for controlling the intensity of each pixel using a pulse-width modulated (PWM) control signal. The microcontroller also monitors battery voltage and current, solar panel voltage, and internal shaft temperature. This sensor data is communicated wirelessly back to the host computer in the EMS building which in turns records it in the back-end database. In this way, battery condition can be monitored and show timing can be calculated on a given day.

Robustness and graceful degradation

The entire design is conceived for graceful degradation, should different components of the system fail at any time. For example, each evening at the end of the performance, each shaft stores show data in local memory on the shaft controller board. If for any reason the host computer should fail to transmit show data the next day, the shafts will independently begin a show based on their stored data. They know when to begin the show independently of the host computer by monitoring the output voltage from the solar panels and using the sensor output as a dusk sensor.