maintenance (Campbell, Clark, and Austin 2017). PREPA’s electricity generators were 28 years older than that of the U.S. average, and the outage rates of these generators were 12 times higher than the U.S. average prior to the arrival of Hurricanes Irma and Maria (U.S. Energy Information Administration 2018). Only 15% of transmission lines on the island were built to Category 4 storm criteria (New York Power Authority et al. 2017).

# **4.3 – Resiliency and Building Back Better**

As repairs and rebuilding occur, PREPA has evaluated rebuilding resilience options (and has been the subject of several reports, including New York Power Authority et al. (2017), Rossello (2017), and Bloodgood and Martinez (2018)). Drawing on these and other sources, Table 16 provides asset-level estimates of costs for rebuilding damaged power infrastructure. Recommendations (where given) for rebuilding to a more resilient design standard are also included as are the estimated incremental costs of doing so. More detailed information is provided in Appendix E. Other resilience options are being explored; for example, Siemens Industry, Inc. (2018) presents a vision for mini-grid based systems designed to withstand outages better than an existing island-wide grid.

Results show that the cost of building back better, when compared to baseline estimates, varies greatly in magnitude based on the component. For example, hardening of the transmission grid (lines, poles, circuits) are generally relatively low incremental costs (~10%). Appendix D provides detail on the costs, damages, and baseline and resilient unit cost estimates for upgrading infrastructure design. Results show that there is approximately 3-40% increase in cost to upgrade transmission and distribution infrastructure to withstand Category 3 hurricanes, while there is a 24-70% increase in cost to upgrade to Category 4 hurricanes (130 mph sustained windspeeds). When wood poles (low windspeed design) are compared with tubular steel poles, for example, costs may increase as much as 200% (see Appendix D).

Table 16: Reported damages following 2017 Hurricane season in Puerto Rico. When available, costs represent estimates specific to the Puerto Rico grid (New York Power Authority et al. 2017). Where costs were not available, estimates were used from various sources _(see:_ <u>PG&E 2018; California ISO 2012; Curry and Wilson 2012)</u>

|<br>**Power System Component**|<br>**Transmissio**<br>**Struc**|**n Lines and**<br>**tures**|**Distribution**<br>**Cirit**|**Substations**|
|---|---|---|---|---|
||**115 kV**|**230 kV**|**cus**||
|Number damaged|84 Line<br>Segments, 230<br>Towers/poles|17 Line<br>Segments, 106<br>Towers/Poles|900|252|
|Baseline Unit Repair Cost|1.4/mile|1.6/mile|0.91/mile|$5.5 - $9.5<br>(depending on<br>capacity)|
|Build Back Better Unit<br>Cost|1.5/mile|1.9/mile|2.0/mile|15/substation|
|Incremental Better Unit<br>Cost|0.1/mile|0.3/mile|1.09/mile|277/substation|
|Incremental Better System<br>Cost|41*|13*|357*|4155*|

* _Note_ - not all costs add up exactly; much of the available information did not include cost information or exact miles (unit damages reported in segments or number of poles, while costs are given in miles). Estimates were made from available information. Where missing from Puerto Rico-

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