Intelligent PV Integration into the Local Grid - January 23, 2012
Electricity grids are increasingly supported by decentralized energy sources like photovoltaic (PV) systems. To date, PV systems have played a passive role in grid control and injected unregulated real power into the distribution network. As penetration levels of renewables increase, intelligent solutions are required to ensure grid stability.
Forecasting of PV electricity feed-in turns the generated PV into a foreseeable power source, grid management features of inverters make PV controllable and easier to distribute and home energy management systems can increase the amount of self-consumption and therefore reduce stress on the grid.
PV development in Germany
In Germany, more than 20 GW of PV systems are connected to the grid today. This has already had a significant impact on grid operations. On days with high insulation, the peak system demand can be largely reduced which, in turn, reduces market prices. Within the last few years these changes due to the increased amount of PV have gained attention. The results are new grid codes which assign PV an important role for grid stabilization. One major development is the advent of inverters equipped with the ability to provide precise PV generation forecasts, which allows system operators to optimize the operation of conventional power plants. Additionally, operators now have the ability to react to this information and regulate inverters by setting maximum power injecting limits through power curtailment features. In line with these modifications, incentives were put in place in 2009 to increase local consumption of PV power to reduce grid stresses and losses.
PV generation as a foreseeable power source
The Sunny Portal is a free, web-based service which SMA provides to its customers for visualisation and monitoring purposes. 30,000 systems in Germany (70,000 globally) are currently sending their generation data to the Sunny Portal. They represent 2.6 GW or around 15 % of the total installed PV capacity in Germany. From such a sample the grid operator can infer the total PV output connected to the grid. Combined with meteorological data, this information can be used to generate regional forecasts of the expected PV energy in the following days. Hence, the whole power generation portfolio can be planned and operated more efficiently.
Inverters with grid management features for better distribution and control
The ability to control PV systems and, if necessary, to adjust the electricity feed-in is an important and logical addition to forecasting. With the publication of the German low and medium voltage grid codes these significant changes for the PV industry have been defined. Depending on the size of the system, inverters are required to provide reactive power, to steadily reduce active power in case of over-frequency and to avoid load imbalance. As a result the independent feed-in operation of PV plants is restricted and even smaller residential plants have to be controlled by the grid operator.
Reducing stress on the grid by consuming PV energy locally
Home energy management systems (HEMS) such as the SMA Sunny Home Manager can increase the share of PV energy being consumed at the distribution customer‘s site. Thus decentralized consumption is increased and stresses and losses in the grid are reduced. Self consumption is motivated by governmental incentives like in Germany or by feed-in tariffs being lower than the electricity purchase price. Considering the PV forecast, HEMS can shift loads to times of high PV generation. They have the ability to control appliances for load shift purposes via radio-controlled sockets and to store generated PV energy in a battery system, if present.
Solutions for today and tomorrow
The addition of a large number of small, distributed power sources within an electric power network presents huge opportunities and challenges for system operators. New interconnection requirements and financial benefits demand more operability from PV systems, including communications protocols, voltage controls, and integrated energy management systems. Through innovative design and functional enhancements, the next generation of integration methodologies for grid interactive products can guarantee a stable, safe and efficient grid operation. Today, SMA offers powerful tools to achieve better grid operations and interaction with PV systems.
