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Industrial Design of a Home Solar Energy System
February 2018 Bianchini
The MIT Development Lab (D-Lab) connects student teams with international community partners who work on projects to better developing communities. Through a D-Lab class, I partnered with Voya Sol, a company that develops home solar energy systems for rural Zimbabweans to build their own micro grids. I and my team focused on the industrial design of the appliance, including the user interface and features that would define how the appliance lives in the home.
Overall architecture and motivation
The elementary Voya Sol solution to the electricity shortage in rural Zimbabwe begins with a box, to which users can hook up solar panels to capture energy from the sun, plug in devices to make use of that energy, and connect an external battery to keep an overflow reserve. While the solar panels, user devices, and external batteries would be made from a third party vendor, Voya Sol is designing the box itself. The user interface is where my team and I came in. We addressed the following question:
- How might we design the Voya Sol box such that it is very intuitive for someone who cannot read to connect and scale the system?
The MIT D-Lab works with developing communities in order to help drive sustainable human development, which should not be confused with sustainable environmental development. The following figure can help clarify this distinction. Ben Linder of Olin College first introduced me to this material in a guest lecture.
Human Development Index versus Ecological Footprints by country. [Source]
The x-axis plots human development index (HDI), for which above a 0.8 is considered to be high human development. This index takes into account basic health like mortality and morbidity, education like literacy and rates of school completion, and economics like income relative to purchasing power. The y-axis plots ecological footprint per capita, under which ~1.8 global hectares would yield equal environmental allocation for every person.
This means that for a country to provide a good quality of life as well as be environmentally sustainable, it must fall in the blue region at the bottom right corner of the graph. The only dot in that region (in 2003) was Cuba. Countries that are above the ecological footprint maximum but above the HDI minimum, like the US, need to put efforts towards environmental development: maintaining a high HDI while lowering economic impact. Countries that are behind the human development index minimum typically are already under the maximum ecological footprint, so they need to put efforts towards sustainable human development: maintaining a low ecological footprint while raising their HDI. This sustainable human development is where the MIT D-Lab aims to assist communities in developing nations. This distinction is deeply engrained into the D-Lab projects and is why I performed a life cycle analysis for my developed product.
The specifications which we used to define the box's scale, proportions, and functionality were given to us from Voya Sol themselves.
|solar panel ports||quantity||4||solar panel|
|solar panel ports type||type||MC4||solar panel|
|solar panel ports maximum voltage||volts||18||solar panel|
|solar panel ports maximum current||amps||0.56||solar panel|
|solar panel power||watts||10||solar panel|
|external battery type||type||lead acid||battery|
|external battery ports||quantity||1||battery|
|external battery ports maximum voltage||volts||12||battery|
|external battery ports maximum current||amps||7||battery|
|output ports type||type||USB||devices|
|output ports voltage||volts||5||devices|
|output ports maximum current||amps||1||devices|
|able to be stacked||binary yes/no||yes||box|
|connections impossible to do backwards||binary yes/no||yes||safety|
|maximum operating temperature||Celsius||50||safety|
|able to be understood by an illiterate user||binary yes/no||yes||usability|
Table 1: Specifications that defined the industrial design of the Voya Sol box.
The most challenging part of the design would be that illiterate users would be interacting with it. Another driving factor for the design was the style of house typical in the rural villages. It is common for these to be single rooms for the entire household, as well as mud floors with common flooding outside and inside during the wet season. Additionally, the boxes should ideally be able to be repaired locally. And lastly, families who were to own systems like this would want it to be a beautiful object in their house since it would be a status symbol. These additional factors drove the design further:
- I took to using symbols that are common on cell phone interfaces used in the region, in order to draw upon already associated visual cues to give illiterate users a sense of how their box works and is performing.
- Any lights on the box to indicate the box's status might become bothersome at night if people are trying to sleep in the same room. Thus I developed a folding panel that would obscure the lights when in the closed configuration.
- To avoid electrical components from interacting with flood waters, I incorporated a dual-design for both sitting on its own feet on the floor or shelf, as well as a built-in wall mount if possible.
- I limited the visual indicators to be just colored LEDs, inspired by the need for the box to be repaired locally. Other possible solutions included a screen, though we determined that the availability of LEDs was much more reliable in these remote villages than would any kind of screen.
- The box had to be visually appealing in addition to functional. Colors are important, as wildly colorful and patterned textiles in Zimbabwe are commonplace and highly regarded.
I drew the original design, from which our final proposal was derived. I incorporated feet as well as a hanging mount, bright color-coded bands, lights on the front face with connectors on the sides, and icons to give users indications of how the box is working.
To improve the design above, I devised a front panel that could swing closed to keep the icons hidden or swing open to reveal the front and/or form a shelf to hold charging objects.
I built the prototype by laser cutting and engraving acrylic panels, attaching them with hot glue (meant to be temporary if the boxes had to be transported to Zimbabwe for testing), and applying color by using marker on engraved surfaces. I incorporated puzzle-piece-like tabs for the pieces to fit together properly. While this would not be the manufacturing method for large scale manufacturing, this was a quick, high-fidelity prototyping method that gave me results incredibly similar to my initial drawing on paper.
Two of the laser cut panels, before coloring in most of them. I engraved all of the graphics that would keep some color so that I could use marker to color it in. The rough, engraved surface traps the ink while the excess ink on the smooth acrylic wipes right off. This was a quick, effective prototyping method.