One of the main topics at the EM-Power Conference was the grid integration of large solar power plants in combination with battery storage systems. We spoke to Jaideep Sandhu, CTO at ENGIE, about the joint potential of PV and BESS (battery energy storage systems).
What are the challenges for power systems with significant PV and wind generation?
Predictability and forecasting accuracy have improved, particularly for PV and wind power generation coupled with BESS. Despite that, there is a reluctance to consider this kind of set-up to be dispatchable. We’re also seeing a reduction in inertia as the share of conventional generation drops and that of non-synchronous variable energy and electronically-coupled generation resources, such as wind and solar PV, increases. The provision of ramp-rate control for both wind and solar PV, for example using energy storage devices, is also very difficult.
How can PV and BESS provide grid stability and resilience?
Solar PV together with BESS helps address these challenges and can provide resilience and grid stability just as conventional generation does. Obviously, for cost effective solutions providing the necessary grid stability and resilience, the time range is more limited as compared to conventional fossil fuel fired generation.
Solar PV with BESS provides synthetic inertia to replace the inertia provided by spinning generators. In addition, rapid response times of Solar PV and BESS to changes in system frequency reduce the need for inertia. The BESS is quite flexible and can be set up with droop control as required. The PV system coupled with BESS also provides clarity for load planning, enables ramp-rate control, provides reactive compensation at night even when the PV plant is not generating power, and allows for time shifting of generation, peaking power, black-start capability, islanding operation, ride-through capability and damping and management of system oscillations.
What are the typical configurations for coupling PV and BESS? And, what are the main differences between AC and DC coupled systems?
There are two typical configurations to couple the BESS with the PV. The first is AC coupling in which both the PV and BESS have separate inverters and are coupled on the AC side usually at the substation. The second configuration is DC coupling in which the BESS is coupled to the PV on the DC side with DC-DC couplers and then to the grid via a common inverter. In the case of a large plant with multiple inverters/inverter stations, the BESS is distributed and typically located near each of these inverters/inverter stations.
Each of the two configurations have their pros and cons. In general an AC coupled system offers more flexibility, may not be co-located, has less common equipment for common failure and has more suppliers. On the other hand, an AC coupled system does not provide any reduction in clipping losses and can have potentially higher Capex. On the other hand DC coupled systems are only feasible with co-location, help to reduce clipping losses, have somewhat higher efficiency and lower Capex.
How widespread is the use of PV and BESS in Europe today?
Up until recently, most BESS in Europe were deployed as stand-alone systems, usually for shorter storage periods and to supply ancillary services to the grid. However, this has been changing. A number of new PV developments coupled with BESS or capable of future integration of BESS have been put forward. Secondly, storage times have become longer, i.e. from around one hour to two hours or even longer. This is meant to enable time shifting of generation, arbitrage, firm dispatch and offering capacity.
Appropriate market mechanisms that better remunerate such services could be an accelerator for PV with BESS. Furthermore, the much needed adaptations to regulations would facilitate such acceleration.
What expected developments will enhance grid support in the future?
We can expect several new developments on both the generation and transmission side, which will enable better forecasting, control, line loading, balancing and acceleration in growth.
One such development concerns improved weather forecasts, in turn leading to better production forecasts. Work is also ongoing on the development and implementation of dynamic models that facilitate better control and quality of planning. In addition, transmission barriers are being reduced, leading to faster and higher deployment of new capacity. Another interesting development are larger balancing areas that mean that inter-connectivity can be better leveraged. We’re also seeing improvements with demand side flexibility, management and operational flexibility. And a range of grid enhancement technologies are also underway, such as dynamic line rating to more accurately determine line capacity based on calculating thermal limits and Power Flow Controllers that help balancing.
Are there any other exciting trends or developments in terms of grid stability?
Significant deployment in energy storage is an important trend that is already being witnessed and this is expected to accelerate. New battery chemistries that are developed around stationary storage applications are expected to lead to the expected reductions in costs, have lower degradation and longer cycle life.
Data and the speed of capturing and receiving the same is key to superior management of grid stability. The development and evolution of Smart grids at scale with installation of sensors, measurement devices and communication systems to enable dynamic balancing and management of the grid is also anticipated in the coming years. (SP)
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