Grid Intelligent Solar Unleashing the Full Potential of Utility-Scale Solar Generation in Europe

Solar photovoltaic (PV) electricity generation is growing rapidly worldwide. According to SolarPower Europe’s Global Market Outlook 2018 – 2022, more solar PV capacity was installed
globally than any other power generation technology in 2017. Solar alone deployed nearly 100
GW, which is more than fossil fuels and nuclear combined (84 GW), and almost twice as much capacity as wind power (52 GW).1 However, increasing penetration of solar electricity raises challenges for grid operators to balance energy supply and demand in real time.

Current situation: Utility-scale Solar in the European electricity system The European electricity system has proven to be effective and reliable,providing a secure and affordable electricity supply to European consumers. It has also demonstrated agility in supporting the European energy transition, integrating increasing shares of variable and distributed renewables into the system.

EUROPEAN SOLAR PV TOTAL CAPACITY UNTIL 2017 FOR SELECTED COUNTRIES

Why is that? Europe suffers from the misconception that grid-connected utility-scale solar is a trouble maker for the grid, rather than being part of the solution. However, this report shows that incorporating utility-scale solar solutions provides essential services to the European electricity grid. These solutions could save the EU significant money, while advancing the decarbonation process. The debate now is no longer about how to integrate renewables, but how to value them properly on the market to optimize the use of technologies that support the system’s reliability and provide the flexibility needed.

The cost advantage of grid-connected utility-scale Solar
The time is right for an ambitious deployment of utilityscale solar in the European Union. Lowest-cost solar, generated in utility-scale solar PV power plants, is now cheaper than energy produced by new nuclear and fossil fuel power plants .This is not only a European phenomenon. California leads the way when it comes to taking advantage of low-cost solar. In
September 2018, the world’s 5th largest economy, passed a bill targeting 60% renewables by 2030 and 100% carbon neutrality by 2045. Solar is essential to meet these targets. In 2017, 60% of all renewable power capacity in California came from utility scale solar.

SOLAR ELECTRICITY GENERATION COST IN COMPARISON WITH OTHER POWER SOURCES

Despite this limitation, even in Germany, average awarded tariffs in solar tenders have more than halved within 2.5 years and already reached the 0.04 €cents/kWh range (see Fig. 3), with the lowest winning bids even entering the 0.03 €cents/kWh range. Already today, solar is not only cheaper than new fossil fuel and nuclear power generation, but it is often even cheaper than onshore wind. In the second Spanish renewables tender in July 2017, solar won 3.9 GW out of 5 GW; in Germany, solar won 100% in a wind/solar tender in April 2018 as well as in France in November 2018 Of course, high wind countries like the Nordics, as well as high wind sites throughout Europe, provide plenty of useful wind potential that contributes to more
balanced RES generation overall – in fact, solar and wind complement each other very well and are both key to enable very high RES penetration rates.

AVERAGE WINNING BID SOLAR POWER PRICES IN GERMAN TENDERS

FROM SOLAR 1.0 TO 2.0: ENABLING GRID FLEXIBLE SOLAR

In the early days of PV power plant development, large-scale solar systems were designed to take advantage of feed-in tariff remuneration. The objective was to maximize individual system
yield, not harmony with the existing infrastructure. This Grid 1.0, ‘Basic Solar’ phase, works as long as there is low penetration of solar in a region. As soon as the density of solar power systems increases to a certain level, the focus must shift to Grid Flexible Solar plants that contribute flexibility and grid reliability services, such as frequency regulation or ramp control . This chapter will delve into two case studies demonstrating how a utility-scale PV plant with the technical capabilities to provide grid services can help operators meet the flexibility requirements of the grid.

THREE GRID PHASES OF SOLAR POWER PLANT EVOLUTION – BASIC SOLAR, GRID FLEXIBLE
SOLAR, FIRM DISPATCHABLE SOLAR

Essential Reliability Services by Utility-scale Solar PV Power Plants – CAISO 300 MW test
In 2016, the California Independent System Operator (CAISO), First Solar and the National Renewable Energy Laboratory (NREL) conducted a demonstration project on a 300 MW large utility-scale PV power plant in California to test its ability to provide essential ancillary services to the electric grid. The 300 MW plant was designed and constructed by First Solar.

Value of Dispatching Solar Power Plants – The TECO study
Many operational challenges can be addressed by making utility-scale solar “dispatchable” i.e., enable it to provide flexibility for grid operations. For example, some ramping demands on conventional generation resources can be reduced if solar plants can control ramp rates during both morning and evening hours, thereby providing the means to flexibly operate the grid even in the presence of a high penetration of solar. In the previous section, we demonstrated that PV plants have the technical capabilities to provide grid services such as spinning reserves, load following, voltage support, ramping, frequency response, variability smoothing, frequency regulation, and power quality. By leveraging all these operational capabilities, utility-scale solar resources can become an important tool to help operators meet flexibility needs of the grid.

CONFIDENCE IN SOLAR FORECASTS AHEAD OF REAL TIME AND RESULTING FORECAST ERROR
RESERVE LEVELS ON AN EXAMPLE PARTLY CLOUDY DAY, NORMALIZED TO SOLAR POWER PLANT CAPACITY

limited to the lower bound of forecasted solar production potential (the distance between zero and the Production Lower Bound line . In other words, dispatchable solar can be used to provide the downward regulation service that system operators have sourced from conventional generators for 100 years. In contrast to the non-dispatchable case, even at 28% annual solar production potential, dispatchable solar has a significant positive marginal energy value. Provision of balancing services from solar plants allows thermal generators to operate more efficiently by reducing the need for cycling and load following services, resulting in less fuel consumption and emissions. This also avoids commitment of inefficient thermal generation, reducing curtailment of solar during times of over-generation. These savings can be substantial, particularly for systems in which these services would otherwise be provided by relatively expensive or inflexible thermal generators.

SYSTEM DISPATCH AT HIGHER SOLAR DEPLOYMENT LEVELS FOR AN EXAMPLE SPRING DAY

SOLAR 3.0: A SWISS ARMY KNIFE FOR THE ENERGY SECTOR

Solar 3.0 is the combination of solar with stationary batteries. In this form, the system works like a Swiss army knife for the energy sector, as the same hardware can take on a variety of different applications with a number of benefits. In Europe, the central application of storage systems are grid services. On the one hand, it is possible to aggregate rooftop solar and small storage systems to offer such services. However, the much bigger impact will come from combining lower cost large utility scale solar plants with large storage systems. Off-grid applications have also proven especially beneficial in ecological and financial terms, but that’s not relevant for the bulk of European energy demand.

A 10 MW SOLAR + 1 MWH BATTERY PLANT IN CATANIA, SICILY WAS INSTALLED TO ASSESS
INTEGRATION OF RES AND BESS, AND VERIFY THE BESS BENEFITS REGARDING INCREASED RES AND
PROVISION OF SERVICES FOR THE GRID

UK. It does not benefit from any solar incentive scheme, such as Contracts for Difference or Renewables Obligation, which have been reduced and withdrawn. The revenue streams are guaranteed by the battery system that allows the project to be profitable.The Clayhill plant is used for periods of peak demand during winter. In addition, it can be used to provide ancillary services to the British TSO National Grid – the sale of these services is a source of extra revenues for the solar farm. Anesco plans to bid generated power into National Grid’s “T-4” capacity market and its enhanced and fast frequency response markets. The batteries pre-qualified to bid for capacity market tenders in 2017.

POLICY RECOMMENDATIONS FOR SOLAR 3.0

CONCLUSIONS

Several studies and operating examples across the world show that dispatchable utility-scale solar is already possible today. PV power plants, which are following an advance layout and design, and are equipped with intelligent plant controls, modern power electronics (inverters) and advance communication capabilities, are not less advanced than any conventional power generation assets when it comes to grid stabilization and ancillary services. On the contrary, PV power plants are economically more efficient, they offer frequency stabilization even faster than conventional generation, and provide intelligent grid services while they prevent the
carbon emissions from running spinning reserves.

A 10 MW SOLAR + 1 MWH BATTERY PLANT IN CATANIA, SICILY WAS INSTALLED TO ASSESS
INTEGRATION OF RES AND BESS, AND VERIFY THE BESS BENEFITS REGARDING INCREASED RES AND
PROVISION OF SERVICES FOR THE GRID

ESSENTIAL RELIABILITY SERVICES BY UTILITY-SCALE SOLAR PV POWER PLANTS

In 2016 the California Independent System Operator (CAISO), First Solar, and the National Renewable Energy Laboratory (NREL) conducted a demonstration project on a 300 MW large utility-scale photovoltaic (PV) power plant in California to test its ability to provide essential
ancillary services to the electric grid. The 300 MW plant was designed and constructed by First Solar. A key component of this PV power plant is the plant-level controller (PPC) developed by First Solar. It is designed to regulate real and reactive power output from the PV power plant so that it behaves as a single large generator.

AGC Participation Test
The purpose of the Automatic Generation Control (AGC) tests is to show the power plant capability to respond to new active power points set that is typically provided by transmission operators in order to support grid frequency. When in AGC mode, the PPC initially set the
plant to operate at a power level that was 30 MW lower than the estimated available peak power to have headroom for following the up-regulation AGC signal.

REGULATION ACCURACY BY PV PLANT IS ABOUT 24-30% POINTS BETTER THAN FAST GAS TURBINES

Voltage Control Tests Grid voltage is normally regulated by generator operators, which are typically provided with voltage schedules by transmission operators.14 The growing level of penetration of variable wind and solar generation has led to the need for them to contribute to power system voltage and reactive regulation because in the past, the bulk system voltage regulation was provided almost exclusively by synchronous generators. In its proposed reactive power capability characteristics for asynchronous generation, CAISO defined the requirements for dynamic and continuous reactive power performance by such resources.15 The primary objective of the reactive power test was to demonstrate the capability of the PV plant to operate in voltage regulation mode within the power factor range of 0.95 leading/lagging.

COMPARISON OF REACTIVE POWER CAPABILITY
FOR SYNCHRONOUS GENERATOR AND PV INVERTER OF
SAME MVA AND MW RATINGS

Conventional synchronous generators have reactive power capability that is typically described as the “D curve”, as shown The reactive power capability of conventional power plants is limited by many factors including their maximum and minimum load capability, thermal limitations due to rotor and stator current carrying capacities, and stability limits. The ability to
provide reactive power at zero load is usually not possible with many large plant designs. The reactive power capability of a PV inverter is determined by its current limit only. With proper MW and MVA ratings, the inverter should be able to operate at full current with reactive power
capability similar to the yellow area shown.

Source:SOLAR POWER EUROPE

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