Design considerations for a solarturtle

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

The SolarTurtle is a Spazashop style micro-utility unit designed for rural electrification in less-privileged communities of Sub-Saharan Africa. A standard 6m shipping container is converted into a theft resistant solar battery charging station business from which community members can buy a rechargeable battery pack. These battery packs are charged via solar power then carried home to where it can provide a versatile source of electricity. At night the solar panels fold away for security purposes, this is made possible by employing a unique ‘book-style’ mounting structure. During the design process several design challenges had to be overcome in order for the SolarTurtle to survive South Africa’s harsh realities. Firstly, solar panels are often the target of theft and vandalism, therefore security measures must be in place. Secondly, maintenance in rural settings is difficult at best. The design must be robust enough to last as long as the solar PV panels. Thirdly if something should go wrong the broken components must be easy to replace, with minimal skills required. Hence a simple design is required without compromising the efficiency of the design. Lastly, the economic factor is of vital consideration. If the SolarTurtle is not economically viable the project will be unsuccessful. The previously mentioned challenges are only a portion of the design challenges that had to be met during the design process. With a host of conflicting requirements a prototype SolarTurtle came to light. The prototype 3.6kW PV system powers a fleet of 300 battery packs and can serve households or businesses with basic electricity all year around. This paper will explore the journey taken to overcome some of the difficult design challenges faced in order to ultimately deliver a fully functional SolarTurtle prototype destined for the rural Eastern Cape of South Africa. The SolarTurtle is a micro-utility that sells electricity to rural communities. It is a solar battery charging station (SBCS) fitted into a 6m shipping container and a solar panel security system. This women empowerment franchise business uses solar PV to recharge any battery off-grid communities might have - phones, tablets, car batteries, penlight batteries and bottled battery packs1. This enables woman entrepreneurs to sell electricity in any quantity require by turning all rechargeable batteries into solar power distribution devices. This enables the micro-utility to wirelessly reach numerous customers without relying on a grid connection. The challenge is to design the SolarTurtle in such a way that it is practical and affordable from an African perspective. The design of the SolarTurtle has to consider many aspects. Some are considered more important than others, though none can be disregarded. To find an optimal balance between simplicity, security, robustness, scalability and numerous other considerations while keeping the final product affordable is the ultimate challenge. To do this a scoring matrix was devised against which several designs were rated. This rating process lead to the final design discussed in this paper. However, true to the iterative design methodology the new SolarTurtle design had to improve on the previous design as presented at SASEC 2014 [1]. For this we have to understand its shortcomings. In the original SolarTurtle concept it was the responsibility of the turtlepreneur2 to carry the solar panels from the container each morning and deploy them in the sun. In the evenings she had to reverse this process in order to lock the panels away in the container. This provided a cost effective solution for providing optimal security while still allowing the container to be transportable. However, there is a serious social risk. Deploying the panels in this way could lead to complacency, as it would require great dedication to deploy all the panels before the sun comes up and secure them after the sun goes down. First there is a risk of damaging the panels. Manhandling panels in and out of the container would surely lead to a breakage before the typical 20 year guarantee of the panel expires. Secondly the security advantage is only valid if the panels are packed away. However, the prototype is set to use around 4kW worth of PV capacity. This means either multiple panels, or larger and heavier panels are required. This risk of the panels eventually just staying outside for convenience sake is too great. For these reasons an alternative solution was required. This led to the ‘book-style’ solar panel security system, which allows the panels to be packed away quickly and with minimal risk of manhandling. The ‘book-style’ solar panel mounting concept is easy to use and fast to deploy. In the morning the turtlepreneur opens the gates attached to the north facing side of the container. Once the gates are open the panels hanging from the gate and the container is propped up with struts so that an optimal sun inclination angle is achieved. At night the panels fold down again by removing the struts and the gates close onto the container, sandwiching all the panels for safety. The gate locks securely on the inside of the container. Research shows this design is unique and offers the extra security needed without overburdening the turtlepreneurs. This paper will explore the book-style design as well as various other possible designs considered for mounting the solar panels and how they were judged. Furthermore the interior design of the SolarTurtle will also be explored with special attention on security and safety. Finally the future of the SolarTurtle will be discussed. What other challenges are there still to overcome and how will these problems be tackled to deliver a fully functional micro-utility in a container.