The development of utility-scale solar power technology is gaining momentum as component suppliers are improving the capacity, efficiency and reliability of their products.
But work still needs to be done to get system elements to work together efficiently and to solve issues relating to building large-scale solar power plants and connecting them to the grid.
The U.S. government has taken note of these challenges and, in 2008, the $24 million Solar Energy Grid Integration System (SEGIS) project was commissioned by the U.S. Department of Energy as part of the government’s Solar America Initiative (SAI).
Now in its second phase, five SEGIS teams across the country are working on various aspects of the project. PV Powered, Inc. leads a team of industry experts that is developing an integrated solution with the functionality essential to improve productive grid connectivity.
A byproduct of the program is fostering constructive relationships between utilities and technology providers, which will help improve the economics of solar power.
One of the technical problems being addressed relates to making and breaking connections to the grid. There are safety-related rules that govern when solar inverters need to disconnect from the grid, but there are times when you want to keep the inverter connected (e.g., during brownouts), even when the normal indicators would cause the solar power plant to disconnect.
The command and control interface between the utility and the solar power source needs to enable the power to stay on during brownouts (to assist the grid in supplying power), while still causing the inverters to disconnect when necessary for safety reasons (such as during an un-intentional island situation).
Following research into this problem, the PV Powered SEGIS team will demonstrate a new method for detecting power outages by taking multiple phase voltage measurements at different locations in a power system using the same absolute time base.
By correlating measurements from different locations, the inverter can differentiate between blackout and brownout conditions on the grid. This enabling technology will serve to lower the barriers to high grid penetration of PV.
Another class of issues that require engineering support from technology providers is extending the useful life of solar power system components to 25 years and longer. This may not sound like a big challenge until you think about the harsh environments that are present out-of-doors.
Exactly the environments (lots of sun) that can make solar power generation most economical can also be the hardest environments on electronic subsystems. To improve system reliability, a complex time-dependent modeling approach is being used to accurately predict component stresses and associated wear-out mechanisms experienced due to natural daily cycles.
Because temperature cycling contributes to device wear-out, simple linear failure rate calculations are not sufficiently accurate. Once wear-out and failure mechanisms are isolated, component engineering can be directed at solving the problems.
Maximizing the uptime and performance of utility-scale solar installations requires the monitoring of individual system components, not just the AC output of the entire system.
For example, by adding a “smart combiner” device between the arrays and the inverter, current monitoring for individual strings or groups of strings is possible. And by developing a dynamic test protocol that quantifies the efficiency of new inverter MPPT (maximum power point tracking) algorithms that adjust the voltage/current ratio delivered by a solar array to maximize power as the output from the array changes, the total energy harvest of inverters can be optimized.
All of this contributes to a tightly integrated balance of system architecture that is being developed through the SEGIS program to enable better system management and increase overall energy production at an acceptable cost.
With the successes being made by the SEGIS team comes the realization that the old “proprietary” ways of designing and implementing utility technologies are giving way to cooperative developments. Making the transition to using technologies from the outside may be difficult for some utilities who have been accustomed to developing their own power generation systems.
In some cases, utility cultures may need to change. The utilities that understand the need for collaboration to achieve an open, interoperable power grid first are the ones who will capitalize soonest on the technologies developed under the SEGIS program.