// Optimisation of energy systems

A successful transition to renewable sources of energy will involve a high proportion of electricity from sun and wind energy, as increasingly used in the heating, refrigeration and mobility sectors. There will also be a mixture of short-term storage (batteries, heat accumulators), long-term storage (power-to-gas) and demand-side management (operation of air conditioners, production lines, etc. depending on the availability of electric power).

The perfect energy system will include the correct design and optimum operation of the installations and their components. Having developed the tools and gained an understanding of the commercial and technical framework requirements, the ZSW is thinking through scenarios, pathways and solutions at various levels. This is happening with reference to the specifications in any given case, such as the desired degree of penetration with renewable sources of energy at national or regional level, the interaction on the energy market for any given district, or the desired degree of self-sufficiency for any given household.

Modern tools are used for the optimisation processes, depending on the task at hand, and the input parameters are the weather conditions over several years, performance data and statistical evaluations of consumption profiles, energy market data and metadata relating to the systems and storage facilities used. The output then provides examples of the optimum way to supply a region with electricity or a district with electricity and heat, or the optimum type of storage facility depending on the local energy market.

Sector coupling

// Sector coupling

Photovoltaic and wind power are the drivers of the new energy world. Looking at the system as a whole enables us to provide all useful energy both at the right place and at the right time in a cost-efficient way. The interfaces between the systems which up to now have been acting mostly separately of each other are energy converters, heat pumps, combined heat and power plants, fuel cells or infrastructures like charging poles, heat grids and heat reservoirs.

This coupling of sectors can be realized in various degrees of granularity, from the large plant for the production of renewable fuels from electricity by power-to-gas technology (also known as efuels) through combined heat an power in the district and intermediate storage of solar power for e-mobility in the private household.

For a detailed discussion, please see our focus report "Energy considered as a system".

Coupling of energy sources with demand in the electricity, heat and fuel sectors
Coupling of energy sources with demand in the electricity, heat and fuel sectors
Energy supply in the district

// Energy supply in the district

The demand for energy and the supply of urban and industrial districts have to be kept in mind when planning a neighborhood or district. This is the only way to achieve efficiency in supplying the necessary energy mix for subsequent use. The key players, from the local authorities and envisaged users right through to the utility companies and planners, need to sit round the table early on in order to discuss objectives and strategies and think through how they will be put into practice. This is an appropriate way to establish the power supply structure at an early stage.

In various projects on the federal state, federal and european levels, ZSW has gained a great deal of experience. The ZSW helps to analyse the potential, produce plans and optimise the operation of the plants. The expected or measured annual usage cycles are linked to a selected set of installations and the supply is optimised according to the relevant variables and specifications. The outcome of this process is a variety of options for the design and operation of the systems and installations. The general situation in the energy market is of course taken into account in the process.

In a meta study, various approaches for realising smart neighborhoods or districts have been analysed. Our experts delivered contributions to concrete issues such as decentralized combined heat and power, the orchestration of various different plants in an industrial district aiming at an optimized collection of energy at the network connection point and/or at a high percentage of local sustainable production of electricity.

Project steps for a district supply system
Project steps for a district supply system
Energy sector coupling with electricity at the source. (Diagram: ZSW)
Energy sector coupling with electricity at the source. (Diagram: ZSW)
PV storage and own consumption

// PV storage and own consumption

In the household, the use of the electricity generated by the own solar system (own consumption) is limited to 25 to 30 percent without applying additional measures. If electricity consumption is shifted to sunshine hours, it can rise to 30 to 40 percent. In case solar power is used for heating or hot water, which can be done particularly efficiently with heat pumps, one may reach 50 percent. In the commercial sector, significantly higher self-consumption rates can be achieved, even without additional measures.

Battery storage systems can be used to effectively increase the amount of energy consumed by the user. Optimised controls allow the storages to be used for other purposes, such as peak shaving of consumption, grid feed-in or as an emergency power source.

 In the course of projects and field trials, various publications have been produced by ZSW on the subject of own consumption, usage of battery storage and optimised control of devices and storage systems in order to improve the cost-effectiveness of the solutions. With the these simulation tools, methods for optimized control (model prediction) and experiences from field tests, ZSW is well equipped to offer extensive consulting services.

With intelligently controlled devices such as solar power storage systems, thermal storage systems and heat pumps, own consumption of PV electricity can be significantly increased.
With intelligently controlled devices such as solar power storage systems, thermal storage systems and heat pumps, own consumption of PV electricity can be significantly increased.
Solar power and mobility

// PV self-sufficiency of a household with electric car – influence of charging behaviour and use of a local storage

A key factor in improving the CO2 footprint of battery electric vehicles (BEV) is charging the battery from renewable energy sources. Charging a BEV using a roof-mounted PV system in a residential building suggests itself. However, the question arises as to how ffar the PV systems can cover the additional demand. For this purpose, simulations of one year with a temporal resolution of 15 min were carried out. The varied parameters include the household profile, the size of the PV system, the capacity of the storage, the charging performance and the charging behaviour of the electric car. A total of six scenarios for usage and charging behaviour were investigated. It was shown that a relevant amount of solar electricity for e-mobility is only "left over" if the PV system is sufficiently large.

E-mobility otherwise results in only a slight increase in self-consumption, be it with or without a PV storage system. On balance, the annual PV yield should cover or exceed the sum of the consumption for household and electric mobility. With this dimension of the PV systems, about 40% of the demand for household and BEV can be covered by solar power. This result can only just be achieved by charging on weekends and with low charging power, even without stationary storage. However, if charging is to take place daily in the evening, a storage capacity of around 8 kWh is required for a comparable result. With 14 kWh, a solar power share of more than 60% of the total demand is possible, independent of charging performance and charging time.

Full battery cycles and own consumption of a household (10 kWp PV system, main load in the evening) depending on charging performance.
Full battery cycles and own consumption of a household (10 kWp PV system, main load in the evening) depending on charging performance.


Dennis Huschenhöfer

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