Renewable Energy Integration

CAISO’s 20-year Transmission Outlook for California

The California Independent System Operator (CAISO) is the largest ISO of about 38 balancing authorities in the western interconnection, handling over two-thirds of the electric load in the West. In collaboration with the California Pu­blic Utilities Commission (CPUC) and the California Energy Commission (CEC), CAISO recently published its first-ever draft 20-Year Transmission Outlook, with a focus on providing a longer-term view of the transmission facilities needed to reliably meet the state’s clean energy goals.

California’s 100 Percent Clean Energy Act of 2018 or Senate Bill 100 (SB 100) calls for a switch over to carbon-free electricity by 2045, in addition to accelerating the in­tegration of new renewable electricity reso­ur­ces into the grid. It also aims to en­sure that at least 60 per cent of Cali­fornia’s electricity is renewable by 2030. CAISO’s draft de­velops a long-range blue­print of the in­ter­connected high voltage wires required to meet these goals. It was conducted in pa­rallel with CAISO’s customary annual 10-year transmission planning process (TPP).

The draft outlook was open to stakeholder feedback until February 22, 2022, and will be finalised in March 2022 in parallel with CAISO’s 2022-23 transmission plan. It envisages an investment of $30.5 billion in transmission, with over 65 per cent ($19.76 billion) being allocated to the integration of offshore wind as well as out-of-state wind. The remaining will be invested in upgrading the existing transmission infrastructure in CAISO’s footprint.

CAISO’s current footprint

CAISO manages the flow of electricity ac­ross the high voltage, long distance power lines for the grid, serving 80 per cent of California and a small part of Ne­vada. As the only independent grid operator in western US, it provides equal acc­ess to roughly 26,000 circuit miles (41,843 km) of transmission lines, and co­ordi­na­tes competing and diverse energy resour­ces into the grid. The transmission network under its jurisdiction ope­rates acro­ss several voltages, including 70 kV, 115 kV, 230 kV and 500 kV. Three in­ves­tor-ow­ned utilities (IOUs) fall under CAISO’s ju­ris­­diction – Pacific Gas & Elec­tric, So­ut­he­rn California Edison (SCE) and San Diego Gas and Electric.

Key drivers for long-term planning

CAISO has witnessed an increase in the demand for new transmission, particularly over the last couple of years. For instance, while the 2020-21 transmission plan was based on a 10-year projection of adding 1 GW annually, the 2021-22 plan is based on a projection of adding 2.7 GW per year, and the current drafts being proposed for the 2022-23 plan call for additions of over 4 GW per year. The accelerating resource re­quirements over the next 10 years are be­ing driven by several circumstances, including the need to decarbonise the el­ec­tricity grid, the expected electrification of transportation and other carbon-emitting industries driving up electricity demand fo­re­casts, issues related to reduced acc­ess to imports as neighbouring systems also decarbonise, higher-than-anticipated im­pact of shifts in peak loads due to in­crea­s­ed solar penetration, and the need to maintain system reliability in light of retiring gas-fired generation and the Diablo Ca­nyon nuclear power plant.

In addition to solar power and battery storage, other resources including geothermal, offshore wind and out-of-state wind re­so­urces are expected to play a greater role and create unique challenges in planning and interconnection processes in the fu­tu­re. Addressing these challenges will re­qui­re adaptations and enhancements to existing processes and efforts. Currently, 605 projects aggregating 236,225 MW are in CAISO’s interconnection pipeline. This level of hypercompetition hinders the integration of resources that must be added to the grid, and thus imposes gr­eater pressure on resources of the ISO and transmission owners. In this context, the draft 20-Year Tran­s­mission Outlook essentially pro­vides a lo­ng-term conceptual plan for the transmission grid, matched with the state agency inputs on integrated load fo­r­ecasting and resource planning, to meet resource and electric load needs.

Key assumptions and transmission needs

The draft 20-Year Transmission Outlook provides a baseline architecture for future planning activities. It includes high-level technical studies to test the feasibility of alternatives, focusing on the bulk transmission system.

The report uses a Starting Point scenario based on the 2021 SB 100 Joint Agency Report (2021 SB 100 Report) published joi­ntly by the CEC, CPUC and the California Air Resources Board (CARB) in line with the SB 100 mandate. CAISO coordinated with the joint agencies on the steps to plan for the SB 100-driven resource build that has been used as input for the outlook. This included workshops on potential transmission projects and resource mapping.

This Starting Point scenario includes di­verse resources known to require transmission development, such as offshore wind energy, out-of-state resources and geo­thermal energy. It also takes into ac­count gas power plant retirements that may re­quire transmission development to reduce local area constraints. The scena­rio is ba­sed on the 2040 SB 100 Core scenario and was created by increasing the expected na­tural gas power plant retirements to 15,000 MW. Additionally, to generally offset the additional assumed natural gas power plant retirements, geothermal, offshore wind, out-of-state wind and battery energy storage system capacities were added to levels that are generally reflective of other 2021 SB 100 Report scenarios.

On the demand side, CAISO started with the SB 100 Core state-wide high electrification load projection, in which the 2040 peak load is 82,364 MW. This represents a 28.5 per cent increase from CEC’s Inte­grated Energy Policy Report 2020 load forecast of 64,076 MW in 2031. The load to be served by the system was ag­ain lowered by the forecast of behind-the-meter resources.

The resulting transmission plan calls for si­gnificant 500 kV AC and high voltage direct current (HVDC) development to access offshore wind and out-of-state wind, and expand the existing CAISO footprint.

Figure 1 represents the transmission de­ve­lopment required to integrate the re­sources of the SB100 Starting Point scenario and the high electrification load projection by 2040.

Offshore wind

According to the outlook, 10 GW of offshore wind will be developed in California, including 6,000 MW in the Diablo Canyon and Morro Bay call areas on the central coast and 4,000 MW in the Humboldt call areas on the north coast. The offshore wind resources on the north coast will re­quire significant 500 kV HVDC facilities to interconnect to CAISO’s existing 500 kV system. CAISO has identified the need for two 500 kV AC lines connecting to the 500 kV Fern Road substation and an HVDC line to the 500/230 kV Collinsville substation. Another alternative considered in CAISO’s 2021-22 transmission plan is an HVDC-voltage source converter (VSC) deep sea cable to a new Bay Hub station lo­cated in the Greater Bay area. The central coast offshore wind capacity will be in­terconnected to the existing 500 kV Diablo substation and the new 500 kV Morro Bay substation looping in the existing 500 kV Diablo-Gates line.

Out-of-state wind

To interconnect out-of-state wind to the CAISO grid, it has identified new transmission projects to link 9,900 MW of capacity from Wyoming (4,685 MW) and New Mexico (5,215 MW). Further, another 2,100 MW from the northwest (1,500 MW) and Baja California (600 MW) will be connected to the existing transmission. The id­entified transmission projects include Southwest Intertie Project-North, Cross-Tie, Robinson-Eldorado, TransWest Express, and additional transmission for more wind resourc­es from Wyoming/Idaho and the New Mexico area.

Upgrades to existing lines

CAISO has planned upgrades for 14 existing transmission projects in its footprint at an investment of $10.74 billion. The ma­jority of these lines are at 500 kV, and they account for a total line length of 1,558 km. The key upgrade projects are the El­do­rado-Lugo line, the Colorado River-Devers line, the Second Los Banos-Tracy line, the Manning-Moss Landing line, the Dia­blo-North HVDC project, the Diablo-South HVDC project and the 500/230 kV Round Mountain and Lugo transformers. The key developers include SCE, DCR Trans­mission LLC and the Duke-American Trans­mission Company.

Investment requirements

The cost estimate for transmission development to integrate the resources in the SB 100 Starting Point scenario has been identified at $30.5 billion.

The way forward

In a bid to explore the longer-term grid re­quirements and options to achieve the state’s 2045 objectives, CAISO’s draft 20-Year Transmission Outlook has identified the system needs by mapping resources aggregating 120.8 GW to the appropriate regions, as well as the transmission additions necessary to add those resources to the grid. It has subsequently examined the need to deliver those resources over the bulk transmission system.

CAISO’s outlook is intended to help sco­pe the challenges faced by the ISO, help the state to further refine resource planning, and provide a longer-term context for decisions made in the 10-year TPP. Es­sentially, it provides a long-term conceptual plan of the transmission grid for 20 years, and forms the basis for further dialogue. After finalising this draft in March 2022, CAISO intends to continue discussions on the findings in ongoing SB 100 processes, collect inputs on issues and parameters that could be considered and refined in future outlook development cycles, and provide an update on the 20-year outlook activities and communicate intentions, by the end of 2022.

California has exciting times ahead as it aligns its transmission planning and deve­lopment to meet the requirements posed by the state’s ambitious climate and energy goals.



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