Solar developers have already added storage at solar interconnection locations, but MISO needs to do its part in approving those requests. Once MISO starts calculating solar capacity credit in 2020 fall, the value will be less than the current 50%. There are three reasons why MISO should prioritize hybrid interconnections. First, solar typically does not peak when demand peaks, but with energy storage, it is possible to discharge that solar energy during peak demand hours. Second, solar is resilient with smart inverters design, which enables tighter coordination with the distribution utilities. And the third reason is, solar is part of the resource portfolio for MISO utilities to meet their carbon-free goals.
MISO told FERC in its December 2019 Dispatchable Intermittent Resource (DIR) filing that it intends to start calculating capacity credit for solar later this year. There is currently 464 MW solar interconnected at the transmission level. When the wind reached 8,000-9,000 MW, MISO started calculating capacity credit. MISO Generator Interconnection Queue (GIQ) now has 45,000 MW of solar. Even if we assume 20% of those requests advance to the signed Generator Interconnection Agreement (GIA), it is still significant (9,000 MW). This 9,000 MW solar is the threshold case MISO is making at FERC.
Because interconnected solar is less than 9,000 MW, without running any analysis, MISO currently assigns 50% capacity credit for solar. MISO’s neighbor, Pennsylvania New Jersey Maryland (PJM) Interconnection, found a “composite ELCC” method, which appears as a better option and is relative to individual calculations for wind and solar. PJM’s composite ELCC is 21% for both wind and solar. MISO admits the solar capacity credit calculation process will follow the wind capacity credit process. In 2006, MISO had 1,000 MW of wind. Today, MISO has 22,000 MW of wind, with a forecast of 27,000 MW by 2021. MISO’s wind capacity credit was 12.9% in 2010 for Planning Year 2011.
First reason is fast-tracking hybrid interconnection
The first solution is fast-tracking hybrid interconnection because energy storage at the same solar location increases the capacity value of solar. The historical peak hours at MISO vary over the four hours in the evening, which is typically around 2 pm and 6 pm. This peak duration is the reason behind the four-hour capacity qualification requirement for any capacity resource at MISO. A resource should show that it can deliver when dispatched at its economic output over the four-hour window. However, a solar resource peaks during the 12 noon and 4 pm window. This peak duration is where storage can help, charge when solar peaks, and discharge when MISO peaks.
For this reason, MISO should consider storage at solar interconnection as one interconnection request. Studying storage and a solar application individually does not make sense for solar developers who are at a disadvantage due to the four-hour solar peak window.
Second reason is resiliency
The second reason for MISO to fast-track hybrid interconnection is the resiliency attributes of solar with smart inverters. The ability of a resource to get back online after an event is resiliency for grid purposes. Extreme weather events are forcing both residential and commercial customers to install solar plus storage for resiliency and reliability. Smart inverters can “ride-through” voltage and frequency deviations in a “smart” way, without tripping the solar output for longer durations. To coordinate transmission and distribution connected solar interconnections, MISO worked with distribution utilities and put together a guideline document for implementing IEEE 1547-2018 standard.
Resiliency for MISO’s southern states means recovering from hurricanes and flooding events. For the north region of MISO, resiliency means recovering from polar vortex, snow and ice-storm events. Solar potential also varies by region. The MISO calculated solar capacity credit value is going to change across Commercial Pricing Nodes (CP nodes). Not all MISO states have the same solar potential. According to National Renewable Energy Laboratory (NREL) Global Horizontal Irradiance Map, MISO southern states, Louisiana and Mississippi, have the highest potential measured in kilowatt hour per square meter per day (5.00 to 5.25 kWh/m2/day). So, CP nodes in MISO south will most likely have higher than average capacity credit compared to MISO north (e.g., Minnesota, Iowa states). Hence the resiliency benefit of solar varies by the MISO region.
Third reason is carbon-free goals
The third reason to prioritize hybrid interconnections is that different MISO utilities are spearheading carbon-free goals. Solar is a critical component of these goals. MISO must be technology agnostic in its treatment of wind and solar. The industry understands MISO must run the analysis for calculating solar capacity credit. But at the same time, MISO should recognize the solar industry is at an immediate disadvantage. The solar sector adds more than 20,000 jobs in MISO states. To enable MISO utilities to retain solar as part of their carbon-free resource mix, and MISO states to continue to add jobs, MISO should resolve hybrid interconnections in earnest.
There is a final qualitative reason for MISO to advance solar plus projects. Like wind integration, solar integration also reduces the need for additional assets. By making solar dispatchable, solar provides for more efficient use of existing MISO assets. Nevertheless, these benefits are dependent on the solar location. Which means, MISO operator is making the right decision to have solar dispatchable and solar plus storage should be at the top of that dispatch stack.