7.6 Future plans of action and expected changes to manage increased penetration

In Austria, there is a business case for increased PV penetration to resolve grid bottlenecks [49]. Grid re-enforcement is not seen as the most cost-effective option, with PV estimated as providing a 50% increase in capacity for 10% of the cost.

The Danish government plans to implement smart grids as part of their energy strategy [50] and Germany expects the following to be required to allow for greater penetration [51]:

  • demand to react to non-controllable generation - energy management between generation, storage and loads
  • renewable energy generation, loads and storage to provide ancillary services
  • active control of distribution grids.

Future work to be done by PEPCO [58] includes:

  • Impact studies:
    • High voltage at low load
    • Power flow reversal
    • Impact on under load tap changer at substation transformer with and without dynamic Var compensating inverter
  • Var Control for mitigating voltage fluctuations:
    • Non-dynamic for smaller systems
      • 0.99 pf when PV at 0-50% output
      • 0.98 pf when PV at 50-75% output
      • 0.97 pf when PV at 75-100% output
    • Dynamic Var control for larger systems
      • Set voltage and frequency ride through parameters
      • Control voltage at POI
      • Requires Droop and time delay setting to mitigate interference with existing automatic line equipment

HELCO believes they need the following to help mitigate issues they have been experiencing and to ensure grid stability [52]:

  • remote monitoring and control (SCADA)
  • forecasting
  • more knowledge on intra-hour variability
  • better prediction of net load
  • provide monitoring and curtailment capabilities on the RE additions > 250 kW
    • to be managed by system operator
    • may not be feasible for small installations
  • storage (centralised and distributed). May be technically feasible but not economic
  • changes to the interconnection rules
    • under-frequency and under-voltage ride through capability required
    • provide for adjustable voltage and frequency trip settings to avoid nuisance tripping and coordinate with the under-frequency load shedding scheme.

Studies/work planned by HELCO include:

  • generation mix - best mix to provide system stability through faults and contingencies
  • modifications to system protection (under-voltage and under-frequency) needed and associated requirements of PV (ride-through)
  • inquiry into required operational changes (modification of reserves)
  • collection of real time stability data using synchronized phasor measurements (synchrophasors - provide real-time measurement of electrical quantities from across a power system)
    • detect stability issues in real time
    • validate stability models tom improve simulation of dynamic response
  • investigate low cost communication and control of DG.

For a high percentage of RES, it is predicted that large amounts of curtailment and flexible backup capacity will be required [54]. Figure 79 shows how curtailment could be reduced through the implementation of flexibility technologies. A reduction from 17% to 5% curtailment is projected with the deployment of Demand Side Management (DSM), Electric Vehicles for energy storage (EV), increased interconnectivity and general storage.

Figure 79 Reduction in curtailment through flexibility technologies [60]

To manage the challenges presented from the integration of RES, Spain [55] is planning the following:

  • power system studies into wind farm requirements
  • wind and solar forecasting tools
  • monitoring and controllability
  • network developments/enhancements.

Spain is planning to improve observability and control to counteract RES variability [55]. Observation will consist of:

  • real time measurements (12 sec cycles) to assist in production forecasting and for avoiding demand forecasting errors. This will lead to more accurate evaluation of reserves and efficient dispatch
  • increased observability decreases uncertainty and therefore increases system security.

Increased controllability of RES is also planned. RED Electrica de Espana has developed CECRE, a control centre devoted to RES generation, especially wind. All RES is to be linked into this integrated control structure which provides supervision and control instructions. Dynamic voltage support is also to be managed through CECRE.

In the long term, Spain is looking into:

  • RES providing frequency support
  • increased international exchange (power exchange with neighbouring countries) capacity
  • storage through hydro-pump units and very fast thermal plants
  • demand side management.

Portugal [56] has stated that the actions required to facilitate high penetration of renewable include:

  • greater cooperation between TSOs and DSOs
  • the implementation of new issues in planning, construction and operation
  • revision of codes and rules at an early stage of the process
  • specification of new technical requirements for stability, security and operation of electrical grids.

The United States [62] has been working on a wide range of approaches to address high penetration issues through:

  • development of advanced inverter technologies
  • updating power system simulation and planning practices
  • updating interconnection standards and codes
  • documenting successful case studies on high penetration PV projects.

China [57] is researching the following for two systems, one of which is a 10 MW plant already constructed and another a 2 MW system currently under construction:

  • modelling of grid connected PV (GCPV)
  • power system analysis including PV
  • development of algorithms to determine install capacity limit of PV
  • testing of inverter types: Scheduled, dual-mode, self-synchronising
  • testing of DC-DC 100kW battery charger
  • automatic monitoring and control of PV.

China is also starting a new research project titled Key technologies of co-ordination between high penetration and multi PCCs (points of common coupling) PV System and distributed grid. Research will include:

  • simulation of high penetration PV system in distributed grid
  • PCCs layout and optimization of high penetration PV system
  • energy storage system integration and bi-directional converter
  • power quality control of regional high penetration PV systems
  • new technology for island detecting and anti-islanding
  • new relay of distributed grid suitable for PV characteristics
  • monitoring and controlling system of regional PV systems
  • energy management technology of regional PV systems.

One of the conclusions made by the Task 14 working group at the recent meeting in Lisbon, Portugal, was that more sophisticated analysis tools are needed to analyse system balancing requirement and capability, including future technologies such as demand activation and EV charging control, to counteract the intermittent nature of generation from RES.

Discussions at the IEA Task 14 workshops indicate that there has been substantial worldwide growth in intermittent generation from renewable resources, mainly PV and wind. Countries involved in Task 14, including Germany, Denmark, Spain, Japan and China, are currently experiencing a significantly high rate of increase in PV installations, both small- and large-scale systems, and expect to see an increase of their intermittent generation capacity by a few hundred percent by 2020. The Task 14 representatives acknowledged one of the main challenges they expect to face with increased PV penetration is issues associated with the variability and predictability of solar systems.