Abstract
The high variability of solar irradiance, originated by moving clouds, causes fluctuations in Photovoltaic (PV) power generation, and can negatively impact the grid stability. For this reason, grid codes have incorporated ramp-rate limitations for the injected PV power. Energy Storage Systems (ESS) coordinated by ramp-rate (RR) control algorithms are often applied for mitigating these power fluctuations to the grid. These algorithms generate a power reference to the ESS that opposes the PV fluctuations, reducing them to an acceptable value. Despite their common use, few performance comparisons between the different methods have been presented, especially from a battery status perspective. This is highly important, as different smoothing methods may require the battery to operate at different regimes (i.e., number of cycles and cycles deepness), which directly relates to the battery lifetime performance. This paper intends to fill this gap by analyzing the different methods under the same irradiance profile, and evaluating their capability to limit the RR and maintain the battery State of Charge (SOC) at the end of the day. Moreover, an analysis into the ESS capacity requirements for each of the methods is quantified. Finally, an analysis of the battery cycles and its deepness is performed based on the well-established rainflow cycle counting method.
Highlights
It is estimated that PV energy has surpassed the 400 GWp worldwide capacity at the end of 2017 [1].This represents less than two percent of the worldwide electricity demand, but when compared to the ambition of China alone, of 1300 GW of solar capacity by the year of 2055 [2], illustrates what is yet to come for PV energy systems
For a window length greater or equal to 10-minutes, the algorithm proves sufficient in maintaining the RR below 10%/minute of the rated power
This work presents an in-depth analysis of the most common methods for PV power smoothing with battery energy storage systems (BESS)
Summary
It is estimated that PV energy has surpassed the 400 GWp worldwide capacity at the end of 2017 [1].This represents less than two percent of the worldwide electricity demand, but when compared to the ambition of China alone, of 1300 GW of solar capacity by the year of 2055 [2], illustrates what is yet to come for PV energy systems. The increased penetration of solar energy brings new challenges for grid operators, one of which concerns the short-term variability of solar irradiance [3]. This causes high variations in the injected power that can cause serious grid stability issues. To mitigate this problem, power ramp-rate limitation measures have been included in the electrical grid codes of many countries [4]. Power ramp-rate limitation measures have been included in the electrical grid codes of many countries [4] These RR limitations are defined on a second or minute time frame or even in both. For Germany [6] and Puerto
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