Renewable Productivity - ORIGINAL CONTENT

The wind and solar generation systems installed in the US have been installed in the most favorable locations available, for obvious reasons. However, as wind and solar generation are expanded toward a renewable plus storage generation infrastructure and electric demand increases as the result of electrification of transportation, residential, commercial and industrial appliances and equipment, wind and solar installations will have to be extended into less favorable locations.

US EIA Electric Power Monthly reports the annual average capacity factor of US wind installations as 35.3%, with capacity factors ranging from 28.2% - 41.1% seasonally. The annual average solar photovoltaic capacity factor is reported as 24.2%, with capacity factors ranging from 14.9% – 33.3% seasonally. These capacity factors would be expected to decrease somewhat as installations expanded into less favorable locations. However, capacity factors for offshore wind installations are expected to be somewhat higher than for onshore wind, in the range from 40-50%.

Solar installations in the northern tier of the US would be expected to have lower capacity factors during the Winter as the result of the lower sun angle and snow accumulations on the collector surfaces. Wind turbines operating in colder climates would require heating of the blades to avoid snow and ice accumulations, which would impose parasitic power consumption on the turbine generating capacity.

However, the greatest expected impact on renewable generation capacity factors would likely be the need to overbuild generation to have excess capacity available to recharge storage when storage replaces fossil generation as grid support when renewable generation fluctuates and during periods of low/no wind and solar availability. Significant renewable generation capacity would be in surplus during periods of good wind and solar availability when storage is fully charged.

The analysis of the need for storage is somewhat simpler for solar than for wind. On a clear day, solar collectors might generate at rated capacity for as long as 8 hours. However, they will predictably generate no electricity for the remaining 16 hours of the day. Therefore, any loads they serve would have to be served from surplus wind availability or from storage. Some solar generators are installing 4-hour storage to serve the daily peak in the late afternoon, after the solar system stops generating. However, that storage capacity must be recharged from excess capacity during the 8-hour solar generating day.

Wind generation is less predictable throughout the day and its fluctuations and interruptions must be met from storage, which must also be recharged from excess capacity during the day.

The increased investment resulting from generation overbuilding and the requirement to provide short and intermediate duration storage to smooth fluctuations in renewable generation output and long-duration storage to support the grid during periods of low/no wind and solar availability will also substantially increase the cost of the renewable plus storage grid. However, these additional costs are unavoidable if the grid is to be stable and reliable and not subject to catastrophic failure. Renewable generation developers have been able to ignore these issues in the mixed renewable and fossil grid, but will be unable to do so going forward.