ANALYSISMANUFACTURING COST
Figure 2: Using a modular block model allows early estimates to be refined by expanding to an appropriate level of detail as required. Top level estimates can be replaced with calculations based on detailed estimates, which can themselves be replaced with mathematical calculations, test data and proposed decisions
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Cost analysis finds the right balance A lot of recent focus has been put on reducing cell costs and increasing their efficiency but this is only part of the story. The costs are system wide, so logically the cost reduction should also be system wide. The entire system is a value chain, without which the cell would hold little value, and cost reduction and efficiency gains are not just limited to the cell. UK solar technology company Circadian Solar is championing a system-wide approach, often stating how much ‘holistic design’ is enabling them to leverage their efficient multi- junction cell technology.
To allocate development effort appropriately, cost and efficiency losses for the whole system need to be identified, mapped and prioritised to enable development focus on the areas of greatest potential gain. Identifying key sources of costs and losses can also highlight easy wins, where a simple change can significantly boost performance.
A block model of the system is a very powerful way of processing this information simply, where top level effects of any proposed changes can be seen quickly, aiding design decisions throughout the development. The modular nature of the block model allows the system to be sketched out with top level estimates during the early design, and detail to be added later. As the block model shows the relevant interactions of any changes, not only can the effects be visualised in percentage terms without the need for overly accurate first estimates,
but also it is immediately clear which factors have significant sway on the outcome. Several important factors impacting on the cost–benefit analysis are addressed below, with focus on their implications for design and where to assign development effort. These are drawn from and discussed in the context of the recent work 42 Technology completed for Circadian Solar but the points raised are general and are intended to be broadly applicable to solar, rather than being specific to this CPV system.
Spacing collector arrays
Models also allow computation of complicated interactions that are difficult to estimate, while allowing easy changes to other variables. For example, the effect of collector array spacing on the output yield in a CPV farm is a complex function of the solar geometry at the latitude of the site and the layout of the arrays.
To assess the effect, the proportion of collectors that are in shadow must be averaged across all times of day and over the year. Once we have a figure for the proportion of collector area in shadow averaged over the year we can simply treat that area as ‘waste’. This allows us to optimise the spacing using the modular model approach. The cost per unit area of collector is defined elsewhere in the model, so we can associate a cost to the wasted collector area in dense packing densities.
Similarly, we can input land costs per unit area giving a cost function for sparse packing densities
www.solar-pv-management.com Issue VI 2011
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