Heliosphere Documentation

Background:

Solar Cell Testing: Class AAA Solar Simulator

• Class AAA is a global standard for solar simulators. The three A’s are based on three specific criterias: 

  • Spectral match: The deviation from the ideal percentage is within 0.75 to 1.25 times. 

  • Beam uniformity: Typically less than or equal to 2%. 

  • Beam divergence: Typically less than or equal to ±4°. 

  • Output power: Typically 100 mW/cm2 (1 Sun) ±20% adjustable

• Standards:

  • Air mass 1.5 spectrum (AM1.5G) for terrestrial cells and Air Mass 0 (AM0) for space cells.

  • Intensity of 100 mW/cm2 (1 kW/m2, also known as one-sun of illumination)

  • Cell temperature of 25 °C (~300K)

  • Four point probe to remove the effect of probe/cell contact resistance

Design Choices:

• Light Source Choices: LEDs

  • LEDs are a cheaper, more long-lasting, easier to control (wavelength, dimming) option compared to other options (Xenon Arc lamps, metal halide lamps). However, they need constant cooling. High power LEDs are preferred. 

  • LEDs selection:

    • LED Selection 1 → CONS are kinda crazy so probably will not be used.

      • PROS: wavelength choice based on research paper, which is validated through simulated uniform irradiance diagrams.

      • CONS: long lead times (most 8 wks, one 22 wks); can’t find some of the wavelengths they listed. 

    • LED Selection 2 → high power grow LEDs SMD

      • 70400 lx as compared to 120000 lx (1000 W/m^2) if the max luminous flux and the area of a single solar cell (125 mm x 125mm) is used.

      • Wavelengths 380-840 nm

      • 1500 mA (1400-1700)

      • DC 30V-34V

      • 1000-1100 LM

      • 50,000 hrs life span

      • Working temp should be less than 60C (140F) with a heat sink system

      • 50W (but reviews say not exactly, one said not a real multicolor diode, but i think this is very similar to the LED we used in the previous iteration)

      • $10

    • LED Selection 3 → high power grow LEDs SMD [SELECTED]

      • 100W

      • 380-840 nm

      • 30-34V

      • 2800-3500 mA

      • 2000-2100 LM → 128,000-134,400 lx (compare to 120,000 lx aka 1000 W/m^2)

      • 120-140 degrees light emitting angle

      • 50,000 hrs life span

      • Working temp should be less than 60C (140F) with a heat sink system

      • $18

• Optics (Lens) Choices:

  • Option 1: research paper-based

    • Aplanatic lenses (for no spherical aberration, aka loss of definition in the image arising from the surface geometry of a spherical mirror/lens),, plano-convex lens, field lens → difficult to acquire

      • Originally thought to take apart the incandescent light bulbs to keep the sphere to get the hyper-hemispherical aplanatic lens. Nevermind, this won’t work because it won’t have the same refraction properties. 

  • Option 2: Plano-convex Lenses

    • Design: These lenses have one flat side (plano) and one outward-curving side (convex).

    • Function: They focus light to a point or collimate it, much like a magnifying glass.

    • Advantages: Simple design with excellent image quality.

    • Drawbacks: Thicker and heavier for large-diameter lenses, which can result in more material cost and light loss due to absorption or scattering in thick lenses.

  • Option 3: Fresnel Lenses

    • Design: Composed of a series of concentric ridges or rings, each of which acts as an individual segment of a plano-convex lens.

    • Function: Like plano-convex lenses, they focus or collimate light, but their segmented design allows them to be much thinner and lighter.

    • Advantages: Ideal for large-diameter lenses that need to remain lightweight (e.g., lighthouses, solar concentrators, or theater lights).

    • Drawbacks: Slightly lower optical quality, with some light scattering due to the stepped surface.

• PCB Design:

  • Using PWM to current drivers to simulate different weather conditions:

Open

• Constant Current LED Driver