The German Energiewende Book


Back-up power

Back-up power: backup power is not a clearly defined term. In general, it indicates that certain power plants need to be maintained on standby in case other generators failed to produce power. In the case of wind and solar, dispatchable backup power will always be required, though this could soon increasingly, in the form of stored excess renewable power. Conventional plants occasionally malfunction themselves and have therefore always required some kind of backup capacity; countries that do not rely heavily on our imports all have a part of their generating capacity on standby almost all the time. In addition, many countries, including Germany, have "reserve capacity" – power plants that only rarely run in case of emergencies. For the German grid, oil-fired power plants are generally reserve capacity.

Baseload / medium load

Baseload / medium load / peak power: baseload power plants are those that cover the minimum amount of power a country needs around-the-clock. For instance, German power consumption rarely drops far below 40 gigawatts (link to kilowatt) even in the middle of the night, so the baseload would be considered roughly the first 40 gigawatts. Power plants that serve this load generally run around the clock when in operation. The medium load is then the load that is generally reached every day. On a normal workday, power consumption in Germany easily reaches 60 gigawatts reliably, so the medium load might be considered the area between 40-60 gigawatts. Power plants that serve this load run regularly but also ramp up and down on a daily basis. The peak load is everything above the medium load. In Germany, power demand rarely rises above 80 gigawatts, so the peak load can be considered from 60-80 gigawatts. Peak power plants run rarely, must be able to ramp up quickly, and may often be idle for days and weeks at a time.

Brown coal/lignite

see hard coal

Capacity factor

Capacity factor: the relationship between a generator's rated capacity (measured, say, in kilowatts) and the amount of energy produced (measured, say, in kilowatt-hours). For instance, a wind turbine with a rated capacity of 1.5 megawatts could theoretically produce a maximum of 36 megawatt-hours a day (1.5 MW x 24 hours) under ideal conditions, equivalent to a capacity factor of 100 percent – the turbine then generates its maximum output all the time. In practice, an onshore wind turbine has a capacity factor closer to 25 percent in good locations, so a 1.5 MW turbine would run at 0.375 megawatts on the average, producing nine megawatt-hours a day. In Germany, the capacity factor of onshore wind turbines is below 20 percent, whereas the capacity factor of offshore wind turbines is estimated to be in the mid-30s. The capacity factor of solar likewise largely depends upon the amount of sunlight and is generally estimated to be between 10 percent and 20 percent. See "full-load hours."

Carbon/greenhouse emissions

Carbon emissions/greenhouse gases/heat-trapping gases: One main reason why the planet Mars is so much cooler than the Earth is that Mars has no atmosphere. Essentially, the Earth's atmosphere acts as a blanket; sunlight that reaches the Earth bounces around in the atmosphere a bit before leaving. In the process, heat builds up instead of quickly dissipating. A number of gases intensify this insulation effect more than others, but to keep things simple, experts express everything in terms of equivalent carbon emissions, with carbon dioxide being the largest factor by volume. Essentially, civilization is taking carbon that has been trapped underground (in coal, gas and oil) and pumping it into our atmosphere, thereby making the atmospheric blanket more effective. These gases are also collectively referred to as "greenhouse gases," a term that has too positive connotations for some – after all, dramatically rising temperatures are expected to have drastically negative consequences, not the pleasant ones suggested by the term "greenhouse." The term "heat-trapping gases" is therefore also used, as is the "overheating of the climate" instead of the more positive-sounding "global warming."

Cogeneration / trigeneration

Cogeneration / trigeneration: When the waste heat of electricity generator is recovered for useful applications, we speak of the "cogeneration" of heat and power. "Trigeneration" indicates that the waste heat is partly also used to provide cooling. Not to be confused with combined-cycle gas turbines, where the waste heat (steam) is recovered to drive a second, downstream generator that produces more electricity, but does not directly provide waste heat as an application. In cogeneration, the waste heat is not recovered to produce additional electricity, but to provide space heating, process heat, etc.

Demand Side Management

Demand Side Management (DSM): also known simply as "demand management." Electricity cannot easily be stored, so the exact amount consumed generally has to be the same as the amount generated. Until recently, our power supply systems were designed so that the supply side was managed to meet demand; our central-station power plants ramp up and down as electricity demand increases and decreases. With intermittent renewables (see dispatchable), however, power supply will no longer be able to be adjusted so easily, so demand will have to be managed. For instance, when there is enough power, refrigerators and freezers could cool down a bit more so they can "ride through" a few hours of lower power production. In this way, peak power demand can be shifted slightly.


Dispatchable: dispatchable power plants are simply those that can be switched on and off and ramped up and down to meet power demand. Gas turbines are the most flexible, though modern coal plants also ramp up and down well. Older coal plants prefer to be switched on and left running near full capacity, as do nuclear plants. Like gas turbines, generators running on biomass are generally quickly dispatchable, but they are the only type of new renewable source that can be considered dispatchable in Germany. Wind and solar are considered "intermittent," meaning that they do not produce power all the time, though power production can be reliably predicted at least a day ahead. Most importantly, wind turbines and photovoltaics cannot be "dispatched," i.e. switched on and off. Aside from hydropower, the only other renewable sources of electricity that are dispatchable are geothermal and concentrating solar power, which Germany does not have in large quantities.

Distributed power

Distributed power: electricity produced by a large number of small generators (solar roofs, wind turbines, etc.), as opposed to a centralized power supply based on a large power stations (not only nuclear and coal plants, but also utility-scale photovoltaic power plants and large wind farms).


Efficiency: the amount of useful energy output relative to the amount input. Not to be confused with the capacity factor. For wind power and solar power, efficiency measures something fundamentally different than for non-renewable resources. For instance, an old coal plant may have an efficiency of 33 percent, meaning that a third of the energy in the coal is converted into electricity, with the other two thirds being lost as waste heat. Nonetheless, 33 percent may sound better than the 15 percent efficiency of an off-the-shelf solar panel. But there is a difference: the coal is lost forever when consumed, so it makes sense to use it as efficiently as possible; in other words, we lose what we use. While it obviously also makes sense to use sunlight as efficiently as possible, with solar and wind we lose what we do not use – the Earth gets roughly the same amount of energy from the Sun every day. Whatever we do not harvest with wind turbines and solar panels is lost forever. This distinction becomes clearer when we keep in mind that the volume of coal power is different depending on whether we count primary energy or useful energy, but the amount of wind and solar power is the same in terms of primary/useful energy.

Energy crop

Energy crop: a plantation whose sole purpose is to provide energy. A crop of corn planted to provide food, for example, is not an energy crop if its waste residue is also recovered and used to generate energy. To stick with the example of corn, an energy crop used to produce biogas is actually harvested before the ears become ripe enough to eat, and the entire plant is used in the process. In contrast, only the fruit – the edible part – is used to make ethanol.


Energy-intensive: In Germany, firms that consume a lot of energy and face international competition are largely exempt from the surcharge to cover the cost of renewable power. To be eligible, companies have to consume at least 10 GWh per year to fall into the category of "privileged industry." In 2011, some 300 energy-intensive firms paid 0.05 cents per kWh to cover the cost of German feed-in tariffs for 90 percent of their power and only paid the full surcharge for the first 10 percent; everyone else paid the full surcharge extra for all of their power. Furthermore, if a firm consumes at least 100 GWh per year and power costs make up more than 20 percent of total production costs, it does not even have to pay the full surcharge for the remaining 10 percent of its consumption.

European Energy Union

The European Commission aims to create a European Energy Union over the next few years to strengthen EU energy security at affordable cost. In all likelihood, only small steps will be taken; there is often too little consensus among EU member states about what specific path should be pursued in the EU's energy policy.

Full-load hours

Full-load hours: Whereas capacity factor is an indication of capacity utilization as a percentage, one also speaks of "full-load hours," an especially useful term for dispatchable generators, which can be switched on and off – such as biomass, coal, natural gas, and nuclear. There are 8,760 hours in a normal year. The number of full-load hours can be used, say, as an indication of how many hours a particular generator needs to run each year to be profitable. For instance, a particular power plant may need 4,000 full-load hours of operation to be profitable, equivalent to a capacity factor of 4,000 / 8,760 = 45.7 percent. If it runs at 50 percent capacity, it would need to run for 8,000 actual hours to achieve 4,000 full-load hours.

Generation capacity

Generation capacity, aka rated capacity: the maximum output a generator can produce under specific conditions. For instance, a single wind turbine may have a rated capacity of 1,500 kilowatts (1.5 megawatts), but it will only produce that much power under strong winds. See "capacity factor."

Grid access

Grid access: one obstacle to the growth of renewables is a lack of grid access. German law specifies that renewable electricity has a priority on the grid, meaning that conventional power generators have to ramp down production. Other countries more easily allow wind turbines and solar arrays to be disconnected to protect the profitability of conventional plants. Furthermore, German law specifies the conditions under which grid operators must expand the grid to provide a connection for wind turbines, biomass units, and solar arrays. Otherwise, investments made in renewables could come to naught if the grid operator fails to provide a connection.

Gross energy/final energy

Gross energy/final energy: gross energy includes energy consumption within the energy sector along with distribution losses; final energy is the energy that reaches your doorstep as fuel or electricity. In other words, losses in production and transport are not included. For instance, gross electricity consumption in Germany was nearly 600 terawatt-hours in 2011, whereas net power consumption was reported at around 535 terawatt-hours. The "missing" 60 terawatt-hours were consumed by power plants themselves or lost in power lines. See also primary energy.

Hard coal/anthracite

Hard coal/anthracite: Anthracite is basically another way of saying "hard coal," just as lignite is another term for "brown coal." Brown coal, which Germany has in large quantities, is the dirtiest kind of coal; it has relatively high water content and hence relatively low energy content; it is therefore not generally shipped over long distances. In contrast, hard coal is more compact with higher energy content, which make it affordable to ship around the world. Hard coal is generally what we imagine as a "lump" of coal. Brown coal is softer. But in practice, there is no clear distinction between lignite and anthracite, which are perhaps best seen as two ranges on a spectrum. Indeed, most of the coal used in the United States is called "bituminous" and has a slightly lower energy content than what Germans would call hard coal.

Kilowatt vs. kilowatt-hour

Kilowatt vs. kilowatt-hour: 1,000 watts is a kilowatt. Likewise, 1,000 kilowatts is a megawatt; 1,000 megawatts, a gigawatt; and 1,000 gigawatts, a terawatt. A hair dryer that has "1,000 watts" written on its label consumes a kilowatt of electricity when it is on full blast. If it runs for an hour, it has consumed a kilowatt-hour. Likewise, an appliance that consumes 2,000 watts when it is on will consume 1,000 watt-hours (or a kilowatt-hour) when it runs for 30 minutes. The terms "kilowatt" and kilowatt-hour are commonly confused, but the terms refer to completely different things. If you need a memory aid, think of kilowatts as horsepower – the amount of power your car's engine can provide. Horsepower is then equivalent to kilowatts – the engine/appliance's potential. But your car rarely runs at full horsepower, and most of the day it stands around doing nothing to. So think of kilowatt-hours – the work done, as opposed to the potential – as, roughly, the number of kilometers driven.

Merit order

Merit order: indicates the order in which power is bought from power plants on the market. The merit order means that the most expensive plants currently producing determines the price of power on the power exchange. Power plants are ranked and switched on in the order of their "marginal price," which is basically the cost of operation (especially fuel); it specifically does not include the cost of plant construction, for instance. In the case of coal and nuclear, a plant is expensive to construct but relatively inexpensive to operate, so such plants have relatively low marginal prices and therefore run for a large number of full-load hours. In contrast, natural gas turbines are relatively inexpensive to build, but natural gas is expensive in many parts of the world, so gas turbines run for a fewer number of hours when natural gas is more expensive than coal, as is the case in Germany – but not, for instance in the UK. Renewable electricity has a priority on the grid and therefore is not ranked by price. The effect of renewables is therefore the same as lower consumption; the most expensive peak power plants run less often, thereby lowering the price on the exchange.

Passive house

Passive house: a highly efficient building (residential or otherwise) that "passively" uses solar heat (sunshine) to drastically reduce the need for "active" heating and cooling, such as from an air conditioner and heating system. Passive houses are able to do without central heating systems. Increasingly, old buildings can also be renovated to fulfill the standard. In warmer climates, passive houses can also be built largely to offset cooling demand.

Primary energy

Primary energy: the amount of energy put into a supply system, as opposed to the "useful energy" that the supply system outputs to consumers. For instance, the tons of coal fed to a coal plant are considered primary energy, whereas the electricity that leaves the plant is considered secondary energy. For instance, a coal plant with an efficiency of 40 percent consumes 2.5 times more primary energy (coal) than it produces in the form of electricity (secondary energy). For wind and solar, there is no difference between primary and secondary energy. See efficiency.

Retail Market

Typical retail power consumers include households and small businesses. These power purchasers have low-voltage grid connections and consume relatively little electricity. They also generally pay the highest prices because they have been "captive" up to now, meaning that they have had no affordable alternatives to electricity from the grid. The growth of renewables - and in particular solar with storage - is changing that situation worldwide.

Smart Energy

When IT is combined with energy consumption devices and power generators of all sizes, we speak of "smart grids" and "smart meters." Electricity has to be generated in the exact amount of simultaneous consumption; otherwise storage is needed. Data can be used to adjust consumption and production levels - such steps are also possible in households. For instance, refrigerators and air conditioners could switch off temporarily to "shave off" peak demand. When power consumption drops to a lower level, these units could then stay on a bit longer.

Spot / day-ahead market

Spot / day-ahead market: Power can be bought and sold in long-term agreements, the most common model for the bulk of electricity in free markets like Germany. But because actual power demand cannot be exactly estimated 18 months in advance – the term sometimes applicable for power purchase contracts in Germany – the remainder is purchased on the power exchange, which consists partly of a spot market for relatively immediate purchases and the day-ahead market, for purchases the next day. The day-ahead market is especially interesting for renewables like solar and wind, which depend on the weather – and that can only be reliably predicted within 24 hours.

Wholesale Market

Just as other commodities, electricity is sold on both wholesale and retail markets. In Germany, big buyers of electricity (for example industrial companies and retail power sellers, etc) and the big sellers of electricity (power plants) can sign power purchasing agreements directly, but a significant amount of electricity is increasingly sold on the spot market (wholesale market) in Germany. Spot market prices generally determine what prices can be arranged in direct purchasing agreements, which - in Germany - generally last for a few years.