Objective 1
Increase the robustness of the power system towards abrupt frequency changes by introducing virtual inertia and damping in DRES, thereby adopting characteristics similar to SGs
Fast Storage Systems (FSS) will be placed and controlled at the DC bus of each converter-interfaced DRES enabling the provision of adaptable and controllable inertia independent of the DRES operating status. This will enable the real-time values of inertia to be adjustable according to optimization criteria set after a bilateral communication and agreement between the TSO and the DSO. As the increased penetration of DRES displaces conventional SGs, the value of individual and aggregated inertia will be determined so as to retain at least the same equivalent power system inertia. At the same time, the DSOs should ensure that the proper operation of the distribution systems is maintained (avoidance of overvoltages, line congestions, protection system malfunctions, etc.), when the DRES provide high power during the inertial response. In general, the provision of adjustable inertia can be regarded as a new AS offered to TSOs, allowing them to replace the conventional spinning and non-spinning reserves. The ambition of EASY-RES is to demonstrate that the average overall system inertia will be increased by at least 1.5% for every 10% increase in DRES penetration.
Objective 2
Contribute to the stability of the grid by providing frequency-dependent active power.
Similarly to the conventional SGs, the DRES and Battery Energy Storage Systems (BESS) will be equipped with an active power-frequency (P-f), droop curve with adjustable (by the DSO) slope in order to manage the order of the various DRES participation in the primary frequency response (PFR), along with the respective speed and degree (i.e. determine the headroom) of participation. The DSO will be able to provide to the TSO or to a Balancing Service Provider (BSP), almost in real time, a range of frequency-dependent active power amounts along with their associated cost. By acquiring (through a distributed ICT infrastructure) this information from each DSO, the TSO will be able to estimate and plan the available primary frequency reserves and their cost from each distribution system in almost real time. The ambition of EASY-RES is to show that for every 3 MW of DRES entering the system, more than 2.5 MW of conventional reserves will be decommitted. The rest 0.5 MW or less will appear as reduction of the power output of conventional base-load units.
Objective 3
Increase the DRES penetration levels at both LV and medium voltage (MV) level, while avoiding investments for grid reinforcement.
Overvoltage is one of the main obstacles in the penetration of DRES in both LV and MV grids. Towards this objective, the reactive power capabilities of the DRES and LV μGs will be fully exploited, along with the physical limits of the existing grid infrastructure and the voltage limits imposed by the EN 50160 Standard.
Objective 4
Make the RES more grid-friendly by i) reducing the short-term electric power fluctuations at both DRES and HV/MV substation level and ii) introducing active harmonics filtering to each DRES converter.
To accomplish the first part of the objective within the context of EASY-RES, each DRES will be combined with a FSS, which will react to high and medium power-ramps (ΔP/Δt). Furthermore, BESS centrally placed at the HV/MV substation and at the connection point of LV μG to the MV grid will absorb the low ΔP/Δt. Therefore, by reducing the power volatility, the required SG spinning reserves will be decreased. The second part of the objective will be addressed by making the converter-interfaced DRES act also as distributed active harmonic filters, based on local voltage measurements. This functionality will maintain the voltage harmonic pollution in the distribution grids within the limits specified by the EN 50160 standard, despite the increasing DRES penetration.
Objective 5
Preserve the long-term grid security even under very large DRES penetration, by reducing reserve requirements after fault recovery.
Preserve the long-term grid security even under very large DRES penetration, by reducing reserve requirements after fault recovery. This will be accomplished by introducing fault-ride-through (FRT) capability and coordinated contribution to fault current for each DRES type, in a way similar to the conventional SGs. Each DRES will contribute to fault currents according to its rated power and relative location to the fault. The aim is to preserve the current level of fault clearing coordination with the existing protection means even under increasing DRES penetration.
Objective 6
Develop viable business models for all the stakeholders by (i) proposing new metrics for the quantification of the various AS and (ii) evaluating the economic cost and benefit of all the developed AS.
An extensive parametric evaluation of each solution will be addressed by performing cost-benefit analysis to counterweight deferral of investments for grid reinforcement and reduction of SG spinning reserves as function of the penetration level and mixture of DRES. Metrics will be developed for the quantification of each of the developed AS, so that they can be traded in the AS market. New business models will be developed for various stakeholders such as DSOs, BSPs, Balancing Responsible Parties (BRPs), TSOs, independent electricity producers by DRES/BESS, etc. Additionally, EASY-RES will suggest reforms in the current AS market regulatory framework and modifications in the existing grid-codes to enable distribution grids to offer the aforementioned AS. It will be shown that the incremental (with respect to the current situation) implementation cost for offering all the aforementioned AS will be less than 10% for DRES with rated power <100kVA and less than 7% for DRES with larger rated power.