Electricity is a critical source of energy for today’s modern societies. With global population set to grow to close to 10 billion by mid-century (from about 7.5 billion as of this writing), increasing urbanization and billions needing more electricity access to climb out of poverty, the global demand for electricity is projected to only increase. Electricity grids around the world will need to grow and increase, while at the same time, continue to provide reliable, on-demand services.
This post will discuss three requirements for reliable, on-demand electricity services and also address the topic of deep decarbonization of electricity generation (climate scientists tell us we need to reduce carbon dioxide [CO2] emissions quickly). Electricity generation sources that can meet at least two of these three requirements will then be examined. For deep decarbonization, the International Energy Agency recommends CO2 emissions to not exceed 100 grams CO2 emitted per kilowatt-hour (CO2ge/kWh). Each electricity generation CO2ge/kWh number is taken from the median here.
Three electricity requirements are:
1. Must be produced and available 24-7-365
Some examples of 24-7-365 electricity requirements are: hospitals, personal care homes, refrigerators, water pumping and purification, sewage treatment, street and traffic lights, electric fans in furnaces, air conditioning, Internet, computer data centres, police and fire departments, air traffic control, 24-7-365 industry, animal farms etc.
Minimum electricity demand generally occurs at 3 or 4 am and peak demand generally occurs about 7pm, after arriving home from work and school to prepare meals, watch TV, turn on lights, etc (peaks can also occur earlier in the day due to air conditioning). In California, minimum demand is usually at least 18 gigawatts (GW) and peak is about 36GW. In Alberta, Canada, on July 1, 2017 minimum was 8.1GW, peak on June 30, 2017 was 9.9GW (in winter, this peak would likely approach 11GW as the latitude is greater than 49 degrees. The city of Edmonton, and its metropolitan area, has a population of 1.3 million and is at 53.5 degrees latitude).
2. Electricity supply must match demand or consumption at all times
As we saw in point one above, electricity consumption varies throughout the day and electricity grid operators must ensure electricity supply operates accordingly. Therefore, electricity generation sources that are capable of dispatchable operations (sometimes referred to as load following or flexible) are critical (they can adjust their power output supplied to the electrical grid on demand). Storage could alleviate the neccessity of electricity supply needing to match demand (storage will be discussed as one of the sources).
3. Tight tolerances for frequency and voltage
Electricity is delivered by grids in the form of alternating current (AC) and this electricity needs to be at 50 or 60 hertz and 120 or 240 volts, depending on which part of the world is being referred. AC generators that operate in synchronization with each other are required in order to meet these tight tolerances for frequency and voltage. A clear, concise explanation of the requirement of synchronous generation sources for grid operations is provided here (well over 90% of electricity generated globally is provided by synchronous sources). A simulation of synchronous generation sources operating together is done by Bellingham Technical College in these four videos (five minutes each). From the article “What’s wrong with the electrical grid” – “for an AC power grid to remain stable, the frequency and phase of all power generation units must remain synchronous within narrow limits. A generator that drops 2 Hz below 60 Hz will rapidly build up enough heat in its bearings to destroy itself. So circuit breakers trip a generator out of the system when the frequency varies too much. But much smaller frequency changes can indicate instability in the grid. In the Eastern Interconnect, a 30-mHz (0.03 hertz) drop in frequency reduces power delivered by 1 GW”. Not only do electricity grid operators purchase electricity from electricity generators, some also pay for synchronous generation, known as ancillary services. California electricity grid operator is seeking bids for frequency response (automatically detect under-frequency and autonomously ramp its output without receiving a market signal or manual instructions). It is hoping “the effort will head off an issue expected to become more problematic as California moves to fulfill its ambitious renewable energy mandate”
The following electricity generation sources meet at least two of the above requirements.
Nuclear (12 CO2ge/kWh)
Nuclear can provide 24-7-365 electricity generation, as can be seen on any electricity grid with nuclear, for example California (view any “output data” file) and many countries in Europe (it provides about 10.5% of global electricity generation). It generally shuts down once every 18 months (spring or autumn) for refuelling.
Its generators are synchronous and therefore also meets this requirement. Nuclear is controversial with its pros and cons (and misconceptions), all well articulated by Sense about Science here. For mostly economic reasons, nuclear is generally operated in “always on” mode, but it is capable of being dispatchable, for example in Germany and France. Nuclear may not be the best source of dispatchability, but the future does hold some promise in this regard via small modular reactors. Perhaps the best source of dispatchability is…..
Natural Gas (490 CO2ge/kWh)
Natural gas meets all three requirements and is a growing source of electricity generation globally (number 2 source). For example, one can see California’s electricity grid is dominated by natural gas. It is a controversial source, but because it meets the three requirements and is for the most part, cost competitive, it is growing. An alternative could be renewable natural gas (capturing methane from landfills and burning it, instead of allowing it to accumulate in the atmosphere), but its contribution is currently almost non-existent.
Coal (820 CO2ge/kWh)
Coal meets all three requirements, is the number one source of global electricity generation and continues to grow, primarily because it is relatively inexpensive and is able to meet all three requirements. It is high in CO2 and pollution emissions, so it would be ideal if as much of it as possible can be replaced with a cleaner source with similar characteristics.
Hydro (24 CO2ge/kWh)
Hydro generally meets all three requirements, but weather conditions, such as drought, impact its output. For example, in California, hydro produced twice as much in 2016 than 2015, without any change in capacity. Other issues with hydro is that it generally is not near where the electricity is consumed, so long distance high voltage transmission lines must be built, requiring resources such as concrete, steel, aluminium, copper and finances which can be in the billions of dollars. There are biodiversity issues such as sediment collecting against the dams, releasing methane into the atmosphere, and negative effects on wetlands and coastal habitat. Hydro produces almost 17% (see figure 04) of global electricity.
Biomass (230 CO2ge/kWh)
Biomass meets all three requirements, but there are environmental issues with it, such as pollution and CO2 emissions. Trees harvested to burn to generate electricity is also an issue as trees are a carbon sink and take quite some time to grow and be an effective carbon sink.
Diesel can meet all three requirements, but it is expensive and is generally only used in remote areas, such as islands and locations well off the grid.
Geothermal (38 CO2ge/kWh)
Geothermal meets all three requirements “Geothermal power, in particular, operates the most efficiently when it runs continuously without interruption; however, some geothermal plants can load follow and depending on the engineering of the plant can provide other flexible system needs”. The 24-7-365 requirement can be seen to be met on the California grid with a steady output of just over 1GW. Geothermal today produces very insignificant amounts of electricity on a global scale. It has geographic limitations, but there are some areas that seem well suited, including California (future global potential projections vary widely).
Storage (~24 CO2ge/kWh based on pumped hydro?)
There is currently about 165GW of storage capacity globally, of which 98% is pumped hydro. Storage is technically not a source of electricity as it depends on generators to charge it and therefore does not meet the 24-7-365 requirement, but it can “allow for the decoupling of energy supply and demand, in essence providing a valuable resource to system operators”. It is dispatchable and pumped hydro is capable of synchronous generation. Storage has a long way to go to be a globally significant source of electricity, as can also be seen by this trial in California and this 2020 target of 200 megawatt-hours set in New England (summer minimum is about 12GW and peak is about 19GW, peak in winter would be higher).
As can be seen, it will be very challenging to provide access to electricity to everyone around the globe on a reliable, on-demand basis. An indicator of reliability is capacity factor and an example of that are these USA Energy Information Administration reports. Levelized cost of electricity can be a useful metric in choosing electricity generation options, but it has serious limitations. System value is also useful, as it accounts for dispatchability. (Great explanation of LCOE, dispatch, etc here). Due to CO2 emissions, climate change, ocean acidification, etc. deep decarbonization could be considered a fourth requirement of electricity. All sources will be required for deep decarbonization, including low CO2 emitting, non-dispatchable, non-synchronous sources, but the challenges with them need serious consideration.
Feel free to add to the conversation on twitter @tder2012