With renewable energies on the rise, there is a growing need for high-capacity energy storage. One possible solution is the “virtual power plants”.

People all over the globe depend on batteries for power. We're also increasingly seeking renewable resources to supplement rising power demands. Unfortunately, modern batteries have been insufficient to effectively store the energy harvested from renewable sources on large scales. In order to address this challenge, the evolution of the battery may be about to take a large step forward.

In this article, we'll review historical batteries, the power storage challenges that modern power grids face, and introduce the concept of a virtual power pxlant.

 

The History of the Battery

Depending on who you ask, you will get different answers to the question “What was the first battery?”  

Benjamin Franklin is credited with the modern discovery of electricity as well as coining the term “battery” in 1749 when connecting multiple capacitors together in parallel.

Some archaeologists, however, believe that the first battery could have been in existence 2000 years ago. The “Baghdad Battery” is an artifact discovered in modern Khujut Rabu (Iraq) consisting of a ceramic jar, a tube of copper, and an iron rod. Some have theorized that the device (when filled with an acid) was used as a battery for electroplating gold onto metals but other scientists have said that there is no evidence of electroplated gold from this era. However, counter-arguments suggest that gold museum pieces have been assumed to be solid gold as no museum in their right mind would dissect a gold trinket from 2000 years ago.

 

The Baghdad Battery. Image courtesy of Irønie By Ironie [CC BY-SA 2.5]

 

51 years after Benjamin Franklin’s battery, Alessandro Volta invented the voltaic pile which consisted of copper and zinc discs stacked separated by a moist cloth. The cloth was soaked in brine which provided an electrolyte between the copper/zinc discs and the result is a voltage difference across the pile; the voltaic pile was the first wet electrochemical battery. This was likely the world’s first true battery. 

Some history-savvy reader may bring up the Leyden jar as a contender for this title. Invented in about 1746 by Pieter van Musschenbroek, the Leyden jar is a glass jar that incorporates metal coating and brass elements to store electricity until it is given a discharge path. Unlike the Leyden jar, however, the voltaic pile can provide a consistent voltage and current.

Since the voltaic pile, batteries have gone through a massive transformation using different chemistries and materials. The lead-acid battery (invented in 1859) was the world’s first rechargeable battery. The nickel-cadmium battery was invented in 1899 and the 1990s saw the commercialization of nickel-metal hydride battery.

It can be argued, however, that the single most important battery technology, commercially made available in 1992, was the lithium-ion polymer battery. Not only are lithium-ion batteries one of the most energy dense battery technologies, they are also capable of releasing their energy very quickly (similar to a supercapacitor). This has led them to be found in a range of devices including laptops, smartphones, and even car batteries.

 

Lithium-ion batteries have changed portable devices. Image courtesy of Aney [CC BY-SA 3.0]
 

Batteries have come a long way and have found their way into most devices but one area remains battery-free: the power grid.

This is theoretically about to change with several companies teaming together to create the world’s first virtual power station. But before we look at what virtual power stations are we need to look at the issue with some renewable power sources.

 

The Problem of Power Grids

All electrical grids around the world, no matter where they are or who runs them, have the same problems. Electrical generation is most easily achieved with 3-phase dynamos but then having three phases means that each phase needs to be balanced correctly. Electrical distribution is much safer at voltages such as 12V but this would result in unimaginable currents and therefore large energy losses so voltages in the region of 500kV is used.

Power plants could be made to be very efficient by always operating at the same rate—but to prevent overloading the grid, power station outputs need to be carefully regulated.

While some renewable energy sources such as hydroelectricity can easily be regulated and are consistent, other sources are not. For example, solar energy is only available during the day and reaches peak efficiency on non-overcast days and wind energy is only available when there is a breeze. But the inconsistency of these sources is compounded when electrical energy supplied to the grid cannot be stored. This means that in the event of a windy night when power consumption is at its lowest, wind farms can generate electricity which does not go to use.

What makes the problem even worse is that renewable sources are very easy to turn off/disengage whereas coal and gas are not (as they have steam boilers with industrial scale fires that take time to start and stop). This means that when the grid needs to quickly reduce power station outputs (to prevent overload), they are more likely to disconnect renewable power plants. Interestingly, nuclear power plants are the single most difficult plant to “turn on and off” which is why their power output is effectively constant (see the GB National Statistics Grid Status Below).

 

Image courtesy of Gridwatch

 

Storing energy on these large scales is a large challenge to tackle. What is a virtual power plant and how does it propose to solve these issues?

 

The Virtual Power Plant

In its simplest form, a virtual power plant is a system whereby the grid can store excess power for future use when demand increases. Unlike electrical generation, virtual power plants can instantly output power to the grid to respond to changes in the power line frequency and voltage which can help to make power stations more efficient (as they are not required to rapidly change their power outputs, which results in downtime of generators).

But virtual power plants will also be instrumental in renewable power as they will be able to store excess power generated by wind farms and solar plants when there is little demand and then supply power when the renewable sources of energy are minimal (such as calm days or at night). 

 

Image courtesy of Next Kraftwerke

 

Integrating a virtual power plant is not as obvious as you may think. Simply connecting a battery to the grid would have a negative effect as the power draw from the battery would increase the overall demand and therefore require power stations to output more power. Instead, the battery banks need to be charged when demand is lower than the power being produced. This requires coordination with power generation companies and the virtual power plant.

Next Pool, a developer of virtual power plants, have developed algorithms that not only determine when battery banks should be charged but also when to discharge them back into the grid to maintain the power line frequency to within 200mHz. This communication, however, requires power companies to purchase “charging space” from the virtual power plant but this cost is lower than the cost of power cycling power stations.

One market in particular that will heavily benefit from virtual power plants is the European Power Grid. By EU law, the EU must obtain 32% of its energy from renewable sources by 2030. Since solar energy is only available during the day and wind is not constant, the power grid will 32% rely on sometimes sporadic sources. However, the use of virtual power plants will enable renewable power plants to generate more than that is needed during times of plentiful energy and then supply energy when those energy sources are absent.

Two companies, Eneco and Mitsubishi Corporation, have teamed up to build Europe’s largest battery bank for use as a virtual power plant. Located in Germany, the system will have a power capacity of 48MW and a storage capacity of 50MWh. While this power capacity is small on the scale of power plants (a typical coal plant can produce 600MW of power), it can power up to 5000 homes.

 

Conclusion

Virtual power plants are still in their infancy but will play a key role in electrical grids of the future. While renewable power is better for the environment and has inspired a great deal of technological development, it will need a higher level of dependability to gain true popularity. For that to happen, energy storage needs to scale smartly.

 

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