Led by Governor Andrew Cuomo, New York’s solar ambitions are a key component in his agenda for to ensure “vital progress on the climate” is continued. This is a post on one aspect of the NY-Sun program. I am a retired meteorologist who worked in the electric generation sector for over 35 years and I know that New York is not a particularly sunny place in the winter so I wanted to check out potential issues with solar variability during the peak summer and winter loads. The opinions expressed in this post reflect my personal opinion.
NY-Sun is supposed to make solar affordable for all New Yorkers. According to the NY Sun section in the NYS website Leading on Climate Change and Protecting our Environment:
- NY-Sun is developing a sustainable, self-sufficient solar industry in the State by incentivizing New Yorkers, businesses, and communities to invest in solar energy.
- The Governor’s $1 billion NY-Sun program has grown solar power in New York State by nearly 800% since 2011, and has reduced greenhouse gas emissions by nearly 25%.
- The program aims to add more than 3 gigawatts of installed solar capacity in the State by 2023, enough solar energy to power 400,000 homes.
(Proof reading this before publication I was struck by these claims so I posted on them at my companion site.)
In order to evaluate the effect of solar variability on the transmission grid I needed an example facility. New York State’s permitting process for power plants of 25 megawatts or higher has extensive requirements for public involvement. Invenergy Solar Project Development LLC has started the permitting process for construction of Horseshoe Solar Farm which I will use as my example. According to the Horseshoe Solar Farm – Public Involvemen Program it will be a 180 MW Solar Electric Generating Facility Located in the Town of Caledonia, Livingston County, New York. Eventually I will address this particular project in detail later but this post only looks at potential performance during peak periods.
It is interesting to note that the New York Independent System Operator had this to say about solar photo voltaic (PV) facilities in their 2018 Load & Capacity Data report:
The actual impact of solar PV varies considerably by hour of day. The hour of the actual NYCA peak varies yearly. The forecast of solar PV-related reductions in summer peak reported in Table I-9 assumes that the NYCA peak occurs from 4 p.m. to 5 p.m. EDT in late July. The forecast of solar PV-related reductions in winter peak is zero because the sun sets before the assumed peak hour of 6 p.m. EST.
Because reliability planning necessarily focuses on peak periods I decided to look at the loads on the 2017 peak summer day (July 19, 2017) and the 2017-2018 peak winter day (January 5, 2018). The load data are available from the NYISO on hourly or 5-minute intervals. I decided to estimate the capacity from this facility during these peak periods (one week before and one week after the peak day) using the hourly data. I also wondered about the short term variations so I used the five minute data for the 72 hours around each peak day.
In order to estimate the solar generation output from this facility I used solar radiation data from two nearby NYS Mesonet meteorological systems (Rush and York). The NYS mesonet is a network of 126 weather observing sites across New York State. The official website of the Mesonet includes a tab for live data that brings up station information for the 125 operating individual sites. You can change the station by clicking on any dot on the state map. Data available include wind direction and speed, temperature at two levels, relative humidity, precipitation, pressure, solar radiation, snow depth, and camera images. I got archived solar insolation data on an hourly and 5-minute interval for two nearby sites that I used to estimate solar generation.
I calculated the electrical generation output from the 180 MW Horseshoe Solar Farm based on my internet research. I think it is a pretty good estimate but if someone reading this could confirm that or tell me what I am doing wrong I would appreciate it. The mesonet stations provide solar insolation measured in watts per meter squared. I assumed that the 180 MW of solar cells produced 180 MW when the solar insolation equals 800 watts per square meter (the PVUSA test condition) and I did not account for any other factors such as the cell temperature or any losses. So my naïve formula was simply the observed input solar insolation times 180 divided by 800.
The first question to address is how much power can we expect from a 180 MW facility in upstate New York during the peak periods? Frankly, I would expect this location to be pretty good relative to other central to western New York sites. Locations closer to Syracuse would be worse and locations due east of Lake Erie or Lake Ontario would be much worse because of lake-effect clouds. The Estimated Solar Generation from Horseshoe Solar Farm table lists the results. In the summer the results are pretty good. According to my methodology peak output could be over 200 MW when insolation is highest and the capacity factor over the entire 15-day peak period is over 23%. However, in the winter the solar generation output would be abysmal. The peak generation hour was only 103 MW and the capacity factor of the 15-day peak period would be no more than 7%.
The second question is what about the shorter term variability in solar generation output. The Genesee Load and Horseshoe Solar figure lists 5-minute load (MW) data for the Genesee Control Area Total Load (pink circles), estimated Horseshoe solar potential output using the Rush NYS Mesonet station solar radiation data (blue box) and the estimated Horseshoe solar potential output using the York NYS Mesonet station solar radiation data (red cross).
There are several issues. Note that the scales are different so for starters this solar farm makes little difference to the energy needs of the Genesee NYISO control area load. As noted by NYISO the solar potential energy diurnal cycle does not match the load peak well because actual load peaks after solar generation peaks. The estimates of solar generation from both sites shows quite a bit of variation during the day. For example, the peak insolation at 12:55 EDT is 1,046 watts per square meter but ten minutes later it is down to 491. I estimate that will translate into a swing of over 100 MW that some facility somewhere has to cover. Also note that there are numerous periods when the estimated solar generation using Rush data differ from estimates using York data. This suggests that it was a partly cloudy day with significant variations in solar insolation. Because these are 5-minute averages the instantaneous variations are likely larger.
As I suspected these data show that the proposed NY-Sun solar buildout in Upstate New York will not end well. With respect to the abysmal capacity factor of the winter peak keep in mind that Cuomo’s Reforming the Energy Vision includes plans to convert residential home heating to electrical heating and there are activists that not only want to do that on an accelerated schedule but also are insisting that all the electrical power be produced by wind and solar energy only. Theoretically, battery storage could provide all the renewable power. However, only the energy innumerate or energy naïve could possibly think that solar energy coupled with battery storage could provide enough energy to heat all upstate residences during winter peak periods without massive overbuilding of both solar farms and battery storage simply because solar potential in the winter is so poor.
The summer short-term period data illustrate the fallacy that solar is cost-equivalent to coal or gas or whatever the claim is today. Fossil-fired facilities provide near constant energy but these data show that solar has huge variations. When considered alone, if this facility or any other solar facility gets built someone else on the grid has to provide support so that power sent to the grid is near constant. Battery energy storage can provide that service and frankly given the degree of intermittency on a day like the peak summer day would be the only solution that might work. However, any battery solution at least doubles the cost of solar. Not surprisingly it is even worse. If you dedicate a battery array to providing smooth power you cannot use the battery array for storage. The State really needs to explain how they propose to incorporate 3 gigawatts of solar.
On the other hand, if battery storage is a requirement for a solar facility these impacts are addressed. That way their wildly fluctuating output does not impact the grid and the units can be dispatched to match the observed load. Of course if that is required the price of solar at least doubles so it is unlikely that prudent and politically inconvenient approach will be adopted.