GRID-SCALE SOLAR ENERGY SYSTEMS
Grid-scale (aka large-scale) solar energy projects harness the sun's energy by employing photovoltaic panels or concentrated solar power (CSP) systems.
PV systems are the most common large-scale installations, and they require large tracts of land.
Large-scale PV arrays can consist of hundreds of thousands or millions of solar panels. Given the economics involved, these arrays often incorporate tracking capability to follow the sun's travel during the day. Tracking can increase electrical generation by 20
CSP systems employ massive mirror arrays to reflect and concentrate the sun's energy onto a central receiver to heat a substance like molten salt to extremely high temperatures. The thermal energy collected is used to create copious amounts of steam that propel turbines to generate electricity.
Large-scale solar energy projects are becoming big business. A July 2020 update of the Solar Energy Industries Association database for the U.S. registers nearly 12,000 major ground-based solar projects of one megawatt (MW) size or larger operating, under construction or design. These projects represent over 160 gigawatts (GW) of electrical power capacity, of which 47 GW are in operation.
U.S.-based statistics from late 2019 provide a reliable indicator of how large the solar industry has become in America. Nearly 260,000 solar workers produce tens of billions of dollars in economic value nationally. Solar accounted for approximately 1.5% of American electrical energy in 2018, and the share continues to rise as PV generation is expected to be the fastest-growing sector through 2050. California, the state with the most extensive installed solar energy base, has experienced periods where solar met over 50% of electric energy demand.
LARGE-SCALE BATTERY STORAGE
On-site energy storage often accompanies large-scale solar power installations. Battery banks service the ramped-up demand for power during the morning and evening peaks, level out the price for electricity during high and low demand periods and stabilize the electrical grid to which they are connected, adding to its resiliency.
The cost of battery energy storage continues to drop with advancing technological breakthroughs. Coupling PV generation with cost-effective energy storage is the combination that allows solar power to penetrate beyond about 20% of the overall utility power generation mix. Unquestionably, energy storage represents a significant business growth opportunity for solar companies.
For large-scale solar power installations, battery storage takes on a different look. Two popular battery technologies for distributed solar power systems are the sodium-sulfur molten salt battery and the vanadium redox flow battery.
- Rechargeable sodium-sulfur batteries are manufactured from liquid sodium and sulfur. They are relatively inexpensive to fabricate, offer a high energy density (they can store a lot of energy in a small volume), and are very efficient in their charge and discharge cycle. They operate at elevated temperatures of 300-350 degrees Celsius and are highly corrosive, making them suitable for stationary installations only.
- Rechargeable vanadium redox flow batteries offer several advantages over other grid-scale batteries. One, they can be scaled as large as required to provide the needed energy storage. Two, they are unaffected by long periods of complete discharge. Three, they can be discharged more deeply than other battery types. And four, they can be cycled from charge to discharge many thousands of times without noticeable reduction in capacity, making them an economical choice over their expected life span.
OPERATION AND MAINTENANCE OF GRID-SCALE SOLAR
Large-scale solar power installations for utility and industrial applications depend upon rigorous operation and maintenance (O&M) procedures to maintain system integrity and performance. Neglecting thorough O&M processes can be costly and possibly create significant safety issues for those who work on such plants. Unscheduled downtime seriously affects customers who depend on reliable power generated by the solar power installation.
Owners of large-scale plants employ qualified technicians to undertake a full range of PV maintenance, including periodic visual inspections, verifying system operations, completing required remediation for underperforming or non-functioning equipment and monitoring the system 24/7 year-round.
Operation and maintenance packages commonly include:
- Real-time data collection, review and trending analysis, including key performance indicators
- Ongoing energy production monitoring
- Optimizing the system operation, accounting for financial performance, cash flows, and costs of scheduled and unscheduled maintenance
- Inventory and spare parts management
- Regularly scheduled cleaning of solar cells and panels
- Ongoing maintenance and servicing of thermal components and high-temperature side equipment
- Testing and diagnosing underperforming systems
- Testing and maintenance of circuits, including thermal imaging and tracing of current-voltage curves
- Electrical grounding measurements
- Managing warranties
- Maintaining high levels of personnel and asset safety.
The costs of operating and sustaining large-scale solar installations depend on several factors:
- The location of the plant and its proximity to those providing O&M services, accessibility and restricted hours of operation
- The type of solar arrays used (ground-mounted, pole-mounted and roof-mounted systems) and fixed versus tracking mounts
- The size, type and number of system components
- Environmental factors such as temperature, the amount and types of precipitation, the presence of birds, the levels of air-borne pollution and dust, presence of solar obstructions arising from nearby trees, and the extent of solar radiation received
- The available warranty coverage.