Smart grids support network stability by helping to establish a balance between power generation and demand. In conjunction with energy storage devices, they enable distributed energy producers to be integrated into the grid on a large scale.
Energy generation once was a simple matter of having power stations produce electricity that was consumed by households and industry. Rooms were kept warm with gas or oil heating systems and cool with air conditioners. Energy suppliers offset fluctuations in demand by starting up gas-fired power plants or using pumped-storage electrical power stations. As a result, there weren’t really any unwanted fluctuations in electricity production.
But power generation has become more complicated since many countries began to focus on renewable sources of energy. Whereas Germany had several hundred large and medium-sized power plants 20 years ago, it now has almost 2 million energy producers, including roof-mounted solar panels, wind turbines, and biomass facilities. Households, buildings, and industrial facilities are increasingly turning into “prosumers” — consumers who also produce energy.
As a result of these developments, smart grids are becoming necessary to safeguard the transmission and distribution of electricity from a growing number of fluctuating sources. Smart grids help to increase energy efficiency by incorporating prosumers (examples include buildings and, in the future, electric cars) and balancing supply and demand as much as possible.
Smart grids are particularly important for the sustainable management of energy in urban areas. They require all of the electricity market’s components to communicate with one another, and they incorporate large as well as small decentralized power generation units and consumers into an overall structure. Smart grids regulate power generation and prevent network overloads by ensuring that only as much electricity is produced as is actually needed. In addition, demand management processes can be used to minimize peaks and balance energy supply. For example, cooling systems can be shut off for short periods, elevators can travel more slowly, and industrial power demand can be scheduled to take place when energy supplies are at their highest level.
Throughout the world, Siemens is already using smart grids to optimize the balance between the supply and demand of electricity. This is also happening in Germany. An example of this is the village of Wildpoldsried, which generates six times as much electricity from renewable sources as it consumes. A smart grid ensures that fluctuating energy supplies from solar, wind, and biogas facilities don’t threaten the stability of the network. Software agents from Siemens regulate the interaction between energy consumers and producers within the village’s smart grid.
The Road to Energy Storage
Because electricity generation from renewable sources fluctuates with weather conditions, energy storage devices will increasingly be needed to store surplus electricity from the smart grid for hours, days, and even weeks, if necessary.
Pumped-storage power plants are a proven storage technology with a high level of efficiency. They use surplus electricity to pump water into a higher-lying basin. When more power is needed, the water flows downwards to drive turbines that generate electricity. Unfortunately, there aren’t enough places that are suitable for pumped-storage power plants — at least near urban areas.
That’s why Siemens is working on the development of alternatives. For example, surplus electricity can be used to generate environmentally friendly hydrogen in electrolysis plants. The hydrogen can then be used to power fuel cell vehicles, for example. The next step would be to use a catalyst to generate methane from hydrogen and carbon dioxide. This synthetic natural gas could then be fed into the natural gas network, stored in underground caverns, or converted back into electricity by gas turbines. Moreover, electricity can be temporarily stored in the batteries of buildings and electric cars. Siemens is conducting research in all of these fields.
One storage solution that is already available is the modular energy storage system Siestorage. It buffers short-term — seconds or minutes-long — fluctuations in output from renewable energy sources. Siestorage is based on lithium-ion rechargeable batteries, and the large version of the system fits into a normal shipping container. It can store 1,000 kilowatt hours of electricity, which is about the average daily power consumption of 100 households. The Italian power company Enel (link to Enel article) recently powered up the first Siestorage installation, which has a capacity of one megawatt. Enel is using it to research how voltage can be stabilized in its medium-voltage grid.
Combining Energy Sources
One of the major challenges associated with renewable energy is that it is often produced far from where it is needed. This is especially true of wind turbines. As a result, the white giants in places such as the North Sea are increasingly being switched off when there is a lot of wind but little demand. The full potential of renewable energy sources thus remainsout of reach . To prevent this from happening, the electricity has to be either stored or transported along long-distance transmission lines to areas where energy is in demand (link to HVDC/power transmission article).
Multimodal energy systems might also be used in the future. These systems combine various types of energy into a single unit. Instead of being fed into the grid, electricity can be converted into thermal energy such as heat or cold, or into chemical energy such as hydrogen or methane. These types of energy can also be transported, stored, and used. By employing existing gas networks and storage devices for this purpose, operators can reduce costs and increase the flexibility of energy systems.
However, the electricity can also be used to heat water that is then channeled into district-heating distribution systems, for example. In hot regions, it might instead make sense to do the exact opposite and create a central cold-storing system using cold water or ice. Such a system could reduce the need for air conditioning which, with its high levels of peak demand, strains power grids. Such heat and cold-storing systems are often cheaper to create than energy storage devices.
This article is republished by permission from Siemens, Pictures of the Future, siemens.com/pof.