The solar industry has much to be proud of. Great strides have been made in lowering the costs and raising the generation capacity of solar power plants. When it comes to actually delivering that power (kW, not energy or kWh) onto the grid, however, the PV industry still faces challenges in providing consistent, dispatchable power throughout the day.
Due to the sun’s movement throughout the day and year, the sun is almost always at a suboptimal angle to fixed-tilt solar arrays. PV systems with fixed-tilt racking frequently only deliver a portion of their nominal capacity during lower light times, during winter months, and at higher latitudes (eg. >30o). This efficiency problem is amplified by the fact that modules on fixed-tilt racking systems reach their operational peak efficiency at midday and produce very little power in the morning and evening, when the grid demand is greatest.
As solar’s presence on the grid expands, it must provide a more consistent power output throughout the day, or a more “square” power curve. Currently, most systems offer a fixed-tilt power curve that provides much less production at the beginning and end of the day. To address this issue, some developers, installers, and utilities have begun to implement solar installations that automatically tilt east to west to track the sun across the sky, also known as single-axis tracking, which reduces the amount of time the sun spends at suboptimal angles to the modules.
Single-axis tracking amplifies the power generated in the morning and evenings, when residential and commercial power demands are greatest. Adding a second, or dual-axis to the racking system so that the PV panels can track the sun as it rises and falls on the horizon and as the seasons change, further increases energy generation and creates an even higher, more consistent, “square” power curve throughout each day of the year. Simply put, dual-axis tracking provides more and better power.
The square power curve is a better match for utility grid load demand, and this shows up in the higher Time-of-Day (TOD) and Capacity Value rates that utilities ascribe to power when they need it and “how” they need it. The capacity value of solar – the percent of power plant nameplate capacity that is able to meet and reduce the demand load – is one issue in particular that is not well established. In future blog posts, we will further explore Time-of-Delivery and Capacity Value.
While energy storage (such as with batteries) is the only way to “firm” the daily (and nightly) variations in solar power plant output such that the power profile is 100% of capacity all day (and night, potentially), we can improve or “square” the power curve and increase the value of the power by using an optimized dual-axis tracking system. As opposed to storage, which adds cost, an optimized dual-axis tracking system with the same Levelized Cost of Energy (LCOE) or energy-only-Power Purchase Agreement (PPA) as a fixed-tilt array is delivering better quality power – for free.
Understanding the benefits of the “square” power generation curve that dual-axis solar arrays provide is essential to those who see solar effectively competing with conventional energy sources. As Huey Lewis and The News put it back in 1986, it’s Hip To Be Square!
