The World's #1 Renewable Energy Network for News, Information, and Companies.

Energy Storage Offers Tailored Grid Solutions, But at What Cost?

The grid must maintain a full balance between generation (supply) and load (demand) at all times. In small-scale networks, imbalances occur more often and are generally more difficult to manage when compared to large-scale networks that often incorporate interconnector links.

Tackling Imbalance

Any imbalance situation between generation and load must be counteracted instantly in order to prevent wider issues, which can include a grid blackout in a worst-case scenario. In order to cope with larger amouts of distributed energy, networks should consider introducing or expanding energy storage to meet higher grid stabilizing demands and energy surpluses.

All power-generating sources, renewable and non-renewable, are characterized by specific inherent technology and operating features. In classic conventional electricity systems such as coal or nuclear, plants provide baseload energy because their operating output levels can only be varied gradually. Much faster-reacting natural gas-fired power plants are therefore necessary for managing rapid network demand fluctuations.

Utilities recognize and address the characteristics of each energy technology. For example, in Europe wind farms produce the bulk of their yield during autumn and winter, whereas PV plants yield best in summer and inherently do not produce during night hours. Combining these two complementary sources in an electricity network offers some grid stabilization and other benefits without actual storage.

The Stability Phenomenon

Biomass plants that burn sustainable dry fuels like wood pellets fit into the baseload category, whereas liquid biofuels can add to both baseload and fast-response variable capability. Geothermal has also been proven to be both a baseload and responsive technology. Combining biomass and geothermal with wind and solar in a single network inherently adds storage capacity through the contained energy in the biomass and geothermal resources.

Public discussions about network stability and grid disturbance often overlook the fact that fluctuations in demand are an inherent system phenomenon independent of the generating resource. There will always be demand differences during daytime and night hours, on work days versus weekends, between months and seasons, and during special events like electricity demand peaks during football match breaks. 

Wind power is wrongly blamed as a primary electricity network disturbance that endangers stability. PhD research conducted under specific Dutch conditions showed that “natural” network demand fluctuations are far greater compared to the variability caused by wind power. The study also showed that a need for energy storage would only arise when wind capacity, as a share of total generating capacity, exceeds around 33 percent — it currently stands at about 4 percent. Nevertheless, below we explore some potential energy storage applications that could work in parallel with wind power.

Hydrogen Technology

Rather rudimentary “island” wind-diesel systems comprised of one or more fixed-speed stall-regulated turbines and diesel generators do not incorporate energy storage, and wind surpluses are simply “burned” via a dump load. More sophisticated modern wind-diesel systems that include modern (active) pitch-controlled variable-speed wind turbines do not require dump loads.

A highly sophisticated island power plant developed by German turbine supplier Enercon and Norwegian energy company Norsk Hydro during 2003/4 represents the other end of the technology spectrum. This unique stand-alone wind and hydrogen renewable energy system was installed in Utsira municipality, Norway in the winter of 2004/2005. The plant produces hydrogen through an electrolyser with excess wind energy. When there is insufficient wind, it releases the stored energy again as electricity via a fuel cell and hydrogen combustion engine. In contrast, last year German utility E.ON introduced a power-to-gas unit, which feeds hydrogen into a regional natural gas system.

However, this technology does have a major disadvantage. When converting wind electricity via electrolysis into hydrogen and back into electricity via a fuel cell, there is a huge cumulative efficiency loss estimated to be in the range of 45 to 55 percent.

Response Time

Enercon’s containerized stand-alone system contains (up to) 900-kW wind turbines, in-house flywheel storage technology and a power management system, plus a third-party master synchronous machine, diesel-generator sets, and battery storage.

The benefits of flywheel storage include minimal efficiency loss and rapid response time, but there has yet to be a large-scale commercial breakthrough for these systems mostly due to cost. Battery storage, too, is still expensive.

A potentially interesting battery option is to reuse discarded electric car batteries in a wind power and PV energy storage application, which is currently being studied by Germany’s Münster University. It might also be possible to use surplus wind power for charging car batteries on a large scale, which together with smart grids might create a new energy storage form (vehicle-to-grid storage).

In mountainous regions with favourable geographic conditions for creating large elevated water storage basins, it may be possible to combine large-scale coal/lignite/nuclear power generation with pumped hydro storage for a long-term storage solution. In situations where electricity supply exceeds demand, surplus energy is used for pumping water from a lower level into the higher-level basin. When power demand exceeds supply, water from the basin is released to driving a hydro-turbine. However, its combined efficiency loss is at least 15 to 25 percent, and some sources claim cumulative losses of 30 percent and higher. 

Adiabatic Research

Compressed air is another storage option that has been studied for many years. From an energy efficiency point of view, adiabatic compression, which takes place without the exchange of heat, is the preferred process. When compressed air is stored in underground enclosures such as caverns, there might be competition with alternative uses including carbon capture and storage (CCS) or natural gas storage. 

Integrated Technology

In early 2013 GE unveiled a 2.5-MW wind turbine that incorporates battery storage capability in the power converter’s DC bridge. Here, AC generator power is converted into DC and back to 50Hz/60Hz AC grid power. The solution offers short-term energy storage to help ensure reliable, predictable power, according to GE. The actual installed storage capacity depends upon local grid/market conditions, including whether or not utilities are prepared to pay for increased grid stability with voltage regulation.

Energy storage requires careful analysis, which should at least consider grid stability requirements, energy efficiency loss, and lifecycle-based investments set against overall cost savings.

Lead image: Turbines and Transmission via Shutterstock

RELATED ARTICLES

Microgrids

Coast to Coast and Across the Electric System, Microgrids Provide Benefits to All

Dick Munson, Environmental Defense Fund At the most obvious level, microgrids could disrupt today’s utilities and their regulated-monopoly business model, because they challenge the centralized paradigm. In a nutshell, microgrids are localized power grids that ha...
Lead image: Earth with solar and wind. Credit: Shutterstock.

What's In A Name? That Which We Call A Solar Microgrid Is By Any Other Name A Solar Installation

Paula Mints A few years ago in a solar marketing department near you an enterprising executive had an epiphany: the word “microgrid” could be adapted to describe any system of any size and then used to confer a marketing advantage. Mor...
Tesla New Energy Storage Sales

Can Tesla's Battery Hit $1 Billion Faster Than the iPhone?

Tom Randall, Bloomberg Tesla’s new line of big, stackable batteries for homes and businesses started with a bang. The reservations reported in the first week are valued at roughly $800 million, according to numbers crunched by Bloomberg. If Tesla...
Le Cheylas pumped storage plant scheme. Credit: Alstom.

A Solution to Intermittent Renewables Using Pumped Hydropower

Nathalie Lefebvre, Marie Tabarin, and Olivier Teller, Contributors Integrating large quantities of renewable generation with low-carbon technology will require the development of large flexible carbon-free generation and storage assets. Over the last 40 years, numerous large capacity pumpe...
Eize de Vries worked from 2001 to 2010 as Wind Technology Correspondent for Renewable Energy World magazine and rejoined the publication again in 2013. He also works as a Technology and Market Trends Consultant for Windpower Monthly and WindStats ...

CURRENT MAGAZINE ISSUE

03/01/2015
Volume 18, Issue 3
file

STAY CONNECTED

To register for our free
e-Newsletters, subscribe today:

SOCIAL ACTIVITY

Tweet the Editors! @megcichon @jennrunyon

FEATURED PARTNERS



EVENTS

Doing Business in Brazil – in partnership with GWEC, the Global Win...

Brazil is one of the most promising markets for wind energy.  Ranke...

EU PVSEC 2015 (European PV Solar Energy Conference and Exhibition)

The EU PVSEC is the largest international Conference for Photovoltaic re...

Communication: Webconnect Plug & Play Installation Webinar

Get to know the fastest and easiest communication and monitoring device ...

COMPANY BLOGS

EU PVSEC 2014 extends its Scope

Added focus on application and policy topicsAbstracts for conference con...

EU PVSEC 2014: Call for Papers Receives Great Response

More than 1,500 contributions apply for presentation in AmsterdamScienti...

Hawaii Solar Industry Enters Uncharted Territory

Post originally appeared on the GreenLancer Blog by Ardelia Lee In...

NEWSLETTERS

Renewable Energy: Subscribe Now

Solar Energy: Subscribe Now

Wind Energy: Subscribe Now

Geothermal Energy: Subscribe Now

Bioenergy: Subscribe Now  

 

FEATURED PARTNERS