Brittle Power- PARTS 1-3 (+Notes) - Natural Capitalism Solutions

Chapter Thirteen: Designing for Resilience 199ly to be well placed to capture it. In particular, dispersing wind machines overa large enough area (typically a few hundred miles long) increases the averageoutput of an array of wind machines: 68 although they may not all be exposedto high winds at the same time, neither are they likely to be simultaneouslybecalmed. Thus the risk of total failure (zero output) is greatly reduced.Dispersion does not necessarily imply that each unit is small; only that whateverthe size of the units, they are not near each other and hence not prone tothe failures that can simultaneously affect units at one site. On the other hand,it is also true that a system containing many dispersed modules will be less vulnerableas a whole if each module is relatively small. Since not only modulesbut also nodes and links are potential sources of failure, the tradeoffs betweendifferent kinds of vulnerability can become quite complex. For example, electricitygenerated by many small sources is more reliable (Appendix One) thanequivalent generation by a single, large, equally reliable source.But whether this advantage helps the final user(s) of the electricity dependsalso on the structure of the grid. If there is a single user, the single source couldbe sited at the point of use, eliminating the risk of transmission failure. A singleuser linked to many small dispersed sources via a single master transmissionline could lose them all if that line failed. A separate line radiating individuallyfrom each dispersed source to the user would be far more resilient (and expensive).In a more common situation—many dispersed users—the position wouldbe just the inverse of that of the single user. Dispersed users are most vulnerableto transmission failures if their supply arrives via branches from a trunk linefed by a single source (which would also make the users vulnerable to generatorfailure). A more richly interconnect grid fed by many dispersed sourceswould be far more resilient—and somewhat more expensive, though far less sothan individually radiating lines from a single source to each user.Dispersion is possible in other senses than different places on a map. Forexample, dual diagonal brakelines help to protect cars from brake failurecaused by rupture of the brake lines on either side. (The functional redundancyof disc and drum brakes also helps to protect against common-mode failures—e.g.,from wet brakes or from wearing out all at the same time.) The lackof spatial separation caused the 1974 crash of a DC-10 airliner near Paris whensupposedly independent hydraulic lines were cut by the collapse of the cabinfloor after an unlatched cargo door sprang open and depressurized the hold.The lines were numerically redundant and could thus cope with ordinaryleaks; but being neither dispersed nor backed up by other, functionally diversesystems located somewhere else, they could not resist the collapsing floor.Hierarchical embeddingA fourth strategy for isolating the effects of failed