Very rapid growth in intermittent renewables, especially in California and Texas, is creating challenges and opportunities for the natural gas industry. Executives of the power and gas pipeline industries met in a session February 1, 2018, at the Gas/Electric Partnership Conference to discuss the need and challenges for integration of renewables and gas. This paper is based on these discussions. Participants are listed in Table 1.
The need for the rapid backup of solar power is seen most dramatically in California, where very rapid ramping up of flexible generators, often gas-fired, is needed when the sun recedes. Wind is significant in California and a band of US states east of the Rockies, especially Iowa, Kansas, Oklahoma, and Texas, and backup is required for wind changes, which are often not well predicted. Wind and solar energy also do not provide much voltage support, but fast-start resources, which are often gas-fired, may be able to address these challenges. Batteries and energy storage technologies are entering the market to fill this need and compete with gas.
Power grid reliability is a primary concern for transmission systems. Generation and load must be balanced in real time, and essential reliability services must be provided to keep the transmission grid operating in a stable fashion during disturbances and to minimize curtailments.
The California Independent System Operator, CAISO, has an installed capacity of 71,470 MW, serving 30 million people who comprise 80% of the state population, based on the beginning of the 2018-year data. Twenty nine percent of this capacity is renewables and 53.5% is natural gas. Solar is 48% of the renewables and wind is 30%. In addition, there is an estimated 5000 MW rooftop solar, which is not included in grid demand numbers, but power from the transmission system is called for when solar is interrupted or ceases to operate. A state mandate referred to as a Renewables Portfolio Standard (PRS) requires 400 MW of additional renewables by 2020 and 10,000 to 15,000 MW more by 2030. The California situation illustrates what is happening in other regions and this state shows the most dramatic trends.
The solar peak and electric demand peak, which occur in the evening do not generally match. Other systems’ resources, primarily gas, need to ramp up or down very quickly. Net load and gas ramp profiles for CAISO are shown below for a typical spring day, showing a ramp of 13 GW of intermittent power supply, mainly gas, over three hours.
Also, solar currently does not provide much voltage support, and gas or other power sources are required to maintain transmission system stability. Solar interruptions can be very large, for example, in a major forest fire, inverters tend to act in concert because they are optimized to protect panels. Curtailments are becoming a problem and they are forecasted to worsen. In 2017, approximately 2.6% of potential solar production was curtailed. Spring curtailments ran as high as 175 MW (about 8.8% of energy demand in a n hour). Current curtailment is manageable, but as the generation portfolio approaches 50% renewables, curtailments will occur year-round and become much larger unless a suite of strategies to contain curtailment are pursued, according to CAISO management.
The renewables portfolio standards are projected to lead to 27 GW of solar and 6 GW of wind capacity by 2030 in the Western Electricity Coordinating Council (WECC) region, which represents most of North America from the Rockies westward. This will require approximately 24 GW of flexible gas-fired or equivalent generation capacity to act as buffer, thereby increasing volatility in power burn, according to Christopher Miscek, Haddington Ventures. Percentage of daily intermittent resources in the CAISO generation portfolio has increase from 5 to 35% in the past seven years. Ten GW of coal generation capacity is planned for retirements in WECC by 2030 also, creating room for more intermittent renewable and gas capacity.
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