Direct and alternating current
Alternating current (AC) is electrical current that changes its direction periodically and repetitively. Often energy supply is AC-based. AC-current flows through high voltage power lines and reaches consumers through the power socket. In Europe and most countries in the world, the current changes direction 50 times per second – i.e. with frequency of 50 Hertz. Direct current is an electrical current that does not change in strength or direction. DC is used in flashlights and other battery-powered devices.
Electrochemical storage – batteries – is the best current storage technology. Batteries are reliable, commercially and industrially viable. Lithium-Ion-, Vanadium-Redox-Flow and Sodium-Sulphur batteries in particular can already help on a large-scale, demand-driven integration of sun and wind power into existing grids, thus easing the transition to renewable energy generation.
Inverters convert one form of electricity into another, mostly direct current (DC) in alternating current (AC) or vice versa. There are also DC/DC- und AC/AC inverters. Wind and photovoltaic power generation units produce direct current. Batteries also use direct current. Conventional generators produce alternating current. That is also the historic reason why our grids and most electric applications require alternating current. With the power provided by DC batteries, our software allows inverters to form grids just as (or even more) stably as conventional generators.
Lithium-Ion batteries are particularly well-suited for short-term storage, i.e. minutes or hours. Since they have a very high energy density, they need little space and can also be easily integrated into homes as well as distribution grids. They are also ideally suited to balance large short-term fluctuations.
There is a great variety of different Lithium technologies and suppliers. Thus, Lithium batteries are built with different properties - durability, safety, energy density and performance capacity varies. For portable applications, i.e. cell phones and laptops, Lithium batteries have been available for a long time. The production capacities developed for electric mobility batteries can be very well used for the assembly of Lithium-Ion batteries for stationary applications.
Power and energy
Power and energy are the most important concepts in the energy industry. It’s easy to confuse them. Energy is power times time. Power is the amount of electricity that flows at a given point in time. Energy measures how long that power is provided. To illustrate, compare electricity to water: The volume of a water tank determines its maximum energy capacity, the diameter of the tubes leading in and out determine the maximum power.
Pumped hydro storage
Pumped hydro storage is a sensible way to save excess energy. Unfortunately, there is not enough water everywhere. Also: Pumped hydro storage only makes ecological and economic sense in certain natural surroundings: This includes a certain natural slope and the possibility to build a water dam with relatively minor construction. In most places including Germany the potential for pumped hydro has almost been exhausted.
Sodium- Sulphur batteries have a high storage capacity. These high temperature batteries are therefore especially well-suited for balancing the daily fluctuations of wind and solar power generation. Since the founding of Younicos, we have been working closely with the Japanese company NGK that manufactures Sodium-Sulphur batteries with an especially high energy density and many life-time cycles. Globally, this is the only industrially manufactured battery that has been successfully tested in daily use for more than 13 years now. Given enough demand, this technology could be easily industrialized even further. The commodities required are not only non-toxic, but also widely available.
Vanadium Redox Flow batteries
Vanadium-Redox-Flow storage systems are next-generation batteries. They do not self-discharge. That makes them ideally suited to store energy over long periods. Since this energy carrier does not age or wear, the batteries have a nearly unlimited durability – with very limited maintenance required. Power and energy capacity can be scaled independent of each other according to need.
Voltage and frequency
Voltage and frequency are the most important determinants for a safe and stable energy supply. Almost all grids use alternating current and frequency. For electrical applications to use power safely, it needs to have a certain frequency –in Europe and most other places 50 Hertz, but 60 Hertz in some places like North America.
Today, alternating voltage is produced by large generators that power rotors which turn 360 degrees. This creates voltage with changing polarity, i.e. a sinus wave. To produce 50 Hertz in a 230 Volt grid, a rotor turns 50 times per second.
Power is often measured in Watt (W), Kilowatt (kW), Megawatt (MW), Gigawatt (GW) etc. Energy is often measured in Watt-, Kilowatt-, Mega- or Gigawatthours (Wh, kWh, MWh, GWh). The units are separated by a magnitude of 1,000, thus: 1 GW = 1.000 MW = 1.000.000 kW. If a 1-GW coal power plant runs at maximum capacity for a whole day, it produces 24 GWh of energy. Germany uses 1.600 GWh of energy per day, average power production is thus ca. 67 GW. The maximum load is about 80 GW.