TODAY’S STUDY: How Cities Can Get To 100% New Energy
Resilient Solar and Storage Roadmap
October 2017 (City and County of San Francisco, Department of the Environment)
Resilience to natural disasters is imperative for safe, economically productive cities. In the immediate aftermath of an earthquake, flood, or other disaster, one key element of resilience is continued operation of shelters and critical emergency management facilities. Operation of these facilities depends on reliable emergency power. Traditional emergency power systems use diesel generators with storage tanks, which provide power for only a few days in the absence of the electric or gas grid. However, a recent study has shown that gas and electric networks can require days or weeks to recover from a disaster, leaving facilities with generators at risk of running out of fuel. This has already been experienced in New York City after Hurricane Sandy where a combination of lengthy outages and high flood waters compromised the traditional diesel storage and generator backup infrastructure at hospitals and shelters. With the risk of natural disasters increasing due to climate change, we must turn to more resilient solutions for providing backup power to shelters, medical centers, and emergency operations centers.
From 2015 to 2017, the City and County of San Francisco Solar and Storage for Resilience Project examined the use of microgrids and stand-alone solar electric generation with battery storage to provide resilient post-disaster power to critical facilities. The project evaluated 1,263 potential congregation and shelter sites across the city, 67 of which were identified as shelter sites with power requirements and opportunities to develop resilient infrastructure through solar and storage. Site visits were conducted for 18 of these buildings, spanning all 11 supervisor districts in San Francisco and a range of normal and emergency use types. The project team used observations from these site visits to create representative emergency power profiles for all 67 shelters in San Francisco. Using these profiles, the team found that 8.2 megawatts (MW) of photovoltaic panels and 12.9 MW of battery storage would be required to provide resilient backup power for San Francisco’s shelters following a disaster.
Given the high capital cost of deploying this large resource, the project team investigated various financing options — a public-private partnership was found to be a viable pathway for financing resilient solar and storage. Given the added benefit of energy cost savings in normal operation, a public-private partnership financing model would save the City and County of San Francisco 6% over a traditional design-bid-build approach over a 20-year portfolio lifetime.
This roadmap documents the project’s steps of identifying critical facilities, surveying power requirements, assessing renewable potential, evaluating financing options to develop the solar and storage systems for resiliency, and modeling individual sites for solar and storage installation. This roadmap also examines the challenges critical facilities face in providing resilient power, such as key technical, political, and financing barriers, as well as the opportunities and policy recommendations to further advance resilient solar and storage development in San Francisco. While this report focuses on a detailed study of San Francisco, the methods and outcomes are applicable to any city or town.
Resilience to natural and human-induced disasters is a key imperative for economically productive, safe, and sustainable cities. Planning for resilience requires a view toward both the long-term recovery of a city and the short-term response to ensure that shelters and critical facilities continue operating immediately after a disaster. The importance of short-term resilient planning was emphasized by Hurricanes Katrina and Sandy in 2005 and 2012, respectively, but they are by no means the only examples. According to the U.S. Department of Energy, between 2003 and 2012, 679 widespread power outages occurred due to severe weather, at an annual cost to the American economy of between $18bn and $33bn.1 In a world where the changing climate is creating more frequent and more intense extreme weather events, these outages are likely to become longer and more frequent, placing increasing importance on ensuring that shelters are resilient. Locally, in the Bay Area, outages are likely to become more serious with the region facing the risk of nearly 1 meter (3.25 feet) of sea-level rise and an associated increase in flooding events due to storm surges.2
San Francisco also faces the constant threat of a major earthquake. The San Andreas Fault lies immediately beneath the western portion of the city, and as experienced in 1906 and 1989, earthquakes can devastate the city. As documented in the San Francisco Lifelines Interdependency Study, a magnitude 7.9 earthquake can disrupt infrastructure operations for days, weeks, and even months.3 Other disasters may create disruptions to infrastructure as well. Figure 1 shows that gas and transport infrastructure may require up to one year to recover after a major earthquake. Electricity and telecommunications may experience outages of several days or several weeks, depending on the severity of the event. For shelters, police stations, fire stations, medical centers, food distribution centers, and other critical facilities, even short disruptions in service after a disaster may be intolerable; there is a clear need for local power generation with on-site fuel to sustain critical facilities and shelters following a disaster.
Solar and Storage as an Alternative to Grid and Gas
As shown in Figure 1, the recovery times of energy infrastructure after an event vary widely. Electric infrastructure tends to recover quickly, with 90% restoration of service after only one week, while natural gas can take up to six months due to difficulties in identifying and repairing line breaks. Diesel suffers from the same disruptions as natural gas when used for backup power generation — transport to areas of critical need is limited by pipeline supplies and road conditions.
Conventional wisdom holds that properly maintained diesel generators with code-required fuel storage will sustain the needs of a community after a disaster. However Hurricane Sandy in New York and the Lifelines study have shown that this conventional approach may not be accurate in the face of more powerful floods and disasters. For instance, after Hurricane Sandy, at least one instance was reported of New York aid workers hauling cans of diesel up 12 flights of stairs to keep a generator running at a medical facility; without these heroic efforts, the diesel generator backup infrastructure would have been unable to keep the lights and critical life support equipment running.
Solar and storage systems, on the other hand, do not rely on a combustible fuel that must be transported over long distances from refinery to use. Rather, access to sunlight is common throughout the city, even after an event that causes a utility power outage. On-site battery storage can extend the ability to use solar energy after sunset or during cloudy days. If combined with a diesel generator, solar and storage can ensure that the diesel fuel supply can be preserved for cloudy periods and nights, thereby extending the duration of outage that a facility can sustain.
Solar and storage emergency power systems offer the following additional benefits:
• Safety: Diesel generators require on-site storage of fuel, presenting a health and safety hazard. Solar and storage systems present a significantly safer and less hazardous option by eliminating the need to store liquid fuel. Though there are concerns regarding the safety of lithium-ion batteries, batteries have lower overall risk to human health than diesel fuel storage.
• Reliability: Diesel generators can fail due to periods of non-use and lapses in maintenance and regular operation. Solar and storage systems have greater reliability since the system is operated continuously in normal conditions and not used just in emergency conditions, allowing opportunity for early detection of problems when no critical operation is required.
• Low Maintenance: A solar and storage system requires less system maintenance than diesel generators. Generators require monthly tests under load, regular inspection, regular cleaning, and replacement of filters, oil, and coolant. By contrast, solar arrays and battery storage systems have minimal ongoing maintenance requirements. Solar arrays should be washed once or twice per year depending on dust exposure, and batteries require monthly visual inspection to confirm that they are free from damage or corrosion. Other required voltage and current inspections are performed automatically in normal operation and require no added maintenance.
• Environmental: Through the use of renewable energy rather than fossil-fuel-generated power, solar and storage systems avoid carbon emissions and local air and noise pollution, which are inherent in backup generators. Solar and storage are also used year-round under normal daily operation to reduce grid power consumption and carbon emissions.
• Economical: The ongoing costs of solar and battery storage are low due to minimal maintenance needs. Reduced electricity bills provide an additional financial benefit, which helps offset the higher capital cost of solar and storage compared to diesel generators.
Solar and Storage for Resilience
The City and County of San Francisco (CCSF) Solar and Storage for Resilience Project was designed to provide a strategy for solar electric generation with battery storage to become the primary mechanism for emergency power provided at existing and new critical facilities and shelters. The findings indicate that solar and storage can be the backbone of resilient electrical infrastructure for San Francisco’s critical facilities and shelters, and that solar and storage can be cleaner, more economically productive, and more reliable than conventional backup generators.
This roadmap documents the findings and recommendations of the Solar and Storage for Resilience Project and provides guidance for incorporating solar and storage as resilient power to critical facilities and shelters. The roadmap is the culmination of work to create best practices and examples of solar and storage for disaster-resilient critical facilities. It is hoped that this process and the guidelines documented in this roadmap will be used to continually improve and update San Francisco’s resilience and disaster preparedness, and can also be used by other cities to strengthen their disaster-response strategies. Figure 2 presents the steps taken in the project, which form the outline for the roadmap…