A new report from New York’s electric grid operator highlights the uncertainty around the state’s plan to power most of the economy using wind turbines and solar panels.

The New York Independent System Operator (NYISO) issued its annual System and Resource Outlook, which among other things projects how much will be needed by the grid over the next two decades.

The Outlook includes “twelve by twenty-fours,” tables that show how much electricity (as a percentage of the maximum possible) will be generated by wind and solar in a typical hour and how that varies in each month of the year. For instance, utility-grade solar panels typically begin generating electricity at 5 AM in June but not until 8 AM in January, and total output around noon in July is double what’s expected at the same time of day in January.

What’s remarkable is the extent to which the data show how much electricity generation from the same wind or solar resource mix would have varied each year, and therefore on individual days, over 22 years.

For instance, the maximum solar generation output in 2016 was 12 percent more than it was in 2003. For planned offshore wind turbines, the potential output variance was even higher, with 2010 generation coming in 16 percent higher than 2012. These variances must be accounted for in resource adequacy planning.  

To keep the lights on, the grid needs enough generation (and backup storage) to meet demand when generation is at its lowest. Resources have to be built for that period.

In other periods when solar or wind generation is projected to be consistently higher than expected load the excess can only be put into energy storage to a point.  When the energy cannot be used for storage the economics around renewables gets more complicated and unacknowledged costs are expected. 

The report includes the most detailed projection yet on how New York would fare amid “lulls,” multi-day periods during which offshore wind turbines—on which New York City and Long Island would be especially reliant—are barely turning.

The analysis found one hypothetical lull in which output from land-based wind turbines across New York would have lingered below 10 percent for 83 hours, and over a dozen events in which output would have remained below 10 percent for at least 24 hours. Similar lulls are found for offshore wind turbines. Most concerning: a 36-hour period when the output from all the land-based wind, offshore wind and solar across the state would have been less than 10 percent. Addressing this will require an enormous amount of energy storage backup. 

NYISO’s 22-year projection is a good start, but officials should look at how circumstances would have played out on a longer time period and over a larger area than New York to better understand the potential risks for the grid. 

These projections render models produced by state climate officials (NYSERDA’s “Integration Analysis”) obsolete, and show that state models have likely been too optimistic about how much electricity the state’s existing and planned wind and solar projects would generate. 

For a more detailed exploration, visit Pragmatic Environmentalist of New York. The opinions expressed in this article do not reflect the position of any of Roger’s previous employers or any other organization he has been associated with. These comments are his alone.