The German experience with integrating photovoltaic systems into the low-voltage grids

Abstract

a b s t r a c tThe integration of rooftop photovoltaic systems in the low-voltage distribution grids has become a major international trend, helped by the sinking prices for photovoltaics. One of the key questions revolves around the technical challenges brought about by the grid integration of these decentralized systems. This paper therefore analyzes the substantial practical experiences of ten representative German distribution system operators, who play a leading role in this field. Our findings show that grid expansion measures are primarily undertaken to ensure compliance with the permissible limits for voltage and current. Grid optimization measures represent the most economical initial step and include, for instance, changes in grid structure and wide-area control. Once their potential is maximized, classic grid expansion measures such as laying parallel cables are implemented. In individual cases, the low-voltage grid is reinforced by so-called intelligent operating equipment such as voltage regulators or voltage-regulated local distribution transformers. Moreover, improved grid planning measures lead to a better use of the available low-voltage grid capacity. The practical solutions successfully implemented by German distribution system operators should also prove relevant for other countries that are currently planning the deployment of decentralized renewable energies.

Forecasting in Blockchain-Based Local Energy Markets

“…The present research had the objectives: (1) to evaluate the prediction accuracy achievable for household energy consumption with state-of-the-art forecasting techniques; (2) to assess the effect of prediction errors on an LEM that uses a closed double auction with discrete time intervals as market mechanism; and (3) to infer implications based on the results for the future design of blockchain-based LEMs.…”

“…The "Energiewende", or energy transition, is a radical transformation of Germany's energy sector towards carbon free energy production. This energy revolution led in recent years to widespread installation of renewable energy generators [1,2]. In 2017, more than 1.6 million photovoltaic micro-generation units were already installed in Germany [3].…”

Accurate Assessment of Decoupled OLTC Transformers to Optimize the Operation of Low-Voltage Networks

“…Advanced volt/var control solutions specifically adapted to active distribution systems propose the use of new control sources: utility and customer-owned distributed power electronics (mainly those linked to DG), energy storage systems, power curtailment of DG generation and/or load, etc. All these novel control tools are well developed in the literature but not so much in practice [18,19]. For LV levels, in practice, most utilities with a European-style network design use only the secondary distribution transformers equipped with off-load tap changers to control voltages.…”

“…Once again, the use of both the traditional and novel MV volt/var control solutions mentioned above has been intensively proposed in the most current literature, but it is not applied in practice [20][21][22][23][24][25][26][27][28][29][30][31]. The use of OLTC transformers in secondary distribution substations is currently the closest to realizing an LV reality [19,[32][33][34][35]. This paper focuses on this last point: the use of OLTC MV/LV transformers (OLTCST) to control voltage in LV networks.…”

“…Depending on the technology, two different methods of operating an OLTCST are possible: (1) a synchronized tap change among the three phases or (2) decoupled control [32]. Most previous works have dealt with uniform and common tap positions for all three phases of the MV/LV-controlled transformer (3P-OLTCST) [19][20][21]28,30,31,[33][34][35], but increasingly, more tap position settings among transformer phases are being proposed (1P-OLTCST) [24,25,29,32,36]. Decoupled control is obviously a great deal more attractive for LV networks because of their unbalanced nature.…”