The generation of electricity by means of photovoltaics (PV) in connection with the use of wind energy represents a central component for the future energy supply, not only in Germany, but worldwide. The direct conversion of solar energy into electricity is efficient, its application is simple, scalable, emission-free and durable.
PV farms impress with their very low electricity generation costs, which are competitive to fossil power plants if avoided CO2-costs are taken into account. PV systems on house and industrial roofs allow for the lowest land consumption and for the local use of solar power, but have slightly higher electricity production costs. So far, they have contributed two-thirds to PV expansion in Germany and are predominantly owned by citizens, giving them the opportunity to help shape the energy transformation.
The use of facades for PV systems, however, has fallen behind. Façade systems are particularly valuable, however, as there is much more space available for them than for roof systems, particularly in the city centres .
If solar energy is combined in an appropriate way with electrical storage systems and heat pumps and if the sectors electricity, mobility and heat are combined, the local use of solar power increases. This reduces the load on distribution networks and contributes decentrally to balancing generation and consumption.
ZSW supports its customers in the analysis of potentials and develops algorithms for the optimised operation of generators, storages and loads, including a suitable charging management for electromobility. The ZSW experts also offer consulting on the development and testing of appropriate algorithms and devices.
As part of the research project "Facade-integrated photovoltaic systems", the ZSW is investigating, among other things, the properties of building-integrated photovoltaics (BIPV) in comparison to PV roof systems. This applies in particular to CIGS façade systems (with thin-film solar modules based on copper, indium, gallium and selenium, or CIGS for short).
A limiting factor for the use of PV roof systems on industrial and administrative buildings is the competition with building services equipment such as heat exchangers, ventilation systems or solar thermal collectors, which fragment the roof surface as shadow-throwing elements.
In addition, however, there may also be a competing use as a walk-in roof garden or for a locally required roof greening. Often, especially on production buildings, it is not possible to realise a PV roof system because the permissible area load is exceeded. In addition, as the number of storeys increases, the share of the PV roof system in electricity generation decreases, as the energy generated is distributed over more and more storeys.
This is why photovoltaics offers a number of advantages in façades: Due to the orientation of the PV systems, energy production is stabilized. The midday peak typical for PV roof systems is eliminated and the share of own consumption increases, also in the morning and evening hours as well as in the winter half-year. A façade system is therefore both grid-compatible and advantageous for the user. In addition, the PV façade system grows with the height of the building.
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.
Photovoltaic supply of a household with electric vehicle – influence of charging behaviour and usage of 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 far 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.