Category Archives: Articles

Re-purposing old coal mines as pumped hydro storage facilities

Energy storage is a necessary component of practical solar or wind energy systems. Without storage, a passing cloud or a day of calm winds could result in the lights turning off.

This article from discusses a proposed energy storage system that may be used to complement wind energy in Central Pennsylvania. The Bucks County-based Merchant Hydro Developers wants to convert 21 out-of-use anthracite coal mines into pumped storage facilities. When power is less expensive, intermittent wind power will be used to pump water into an upper reservoir. When energy prices rise during the middle of the day, the water will be released into the lower reservoirs of the mines, spinning turbines on the way down to generate a consistent and predictable flow of power.

Pumped hydro storage already accounts for the vast majority of stored energy in the world including 97% of the energy storage in the United States. The coal mine reservoir solution is unique because it is a closed system. Most pumped storage draws from flowing bodies of water  (e.g. rivers) and released the water back into the same system.

Offshore Renewable Energy Systems in Singapore

Nanyang Technological University (NTU) is constructing four offshore hybrid microgrid systems in Singapore under the Renewable Energy Integration Demonstrator-Singapore (REIDS) initiative. The microgrids will include over 3,000 square meters of solar panels; their first customers will include fish hatcheries and nurseries in Singapore.

Read more from Asian Scientist Magazine at:

Image credit: Asian Scientist Magazine

Research Developments Could Lead to More Efficient Lightbulbs

The BBC recently published this report that gives an overview of new research conducted at MIT which may make traditional incandescent bulbs even more efficient than modern LEDs. The method required covering the base of the bulb with a nano-engineered material that reflects some of the (otherwise wasted) energy back into the bulb where it is emitted as visible light.

IEEE Milestone: Virginia Smith HVDC Converter Station

IEEE Milestone Honors the First Interconnection Between Two U.S. Power Grids

IEEE has recently honored the Virginia Smith High-Voltage Direct-Current Converter Station, completed in 1988, as an IEEE Milestone. The station was the first of eight HVDC stations that connect the eastern and western AC grids in the United States. These interconnections allow power to flow east and west through the county, increasing the flexibility and reliability of both grids.

The Virginia Smith station, named after Nebraska’s first woman in the House of Representatives, can transfer up to 200 megawatts of power. The full article is available online here.

Update: NordLink – IEEE Spectrum

In December, IEEE Spectrum published an article on the now-underway NordLink project, which will result in a new high-voltage direct-current (HVDC) link between Norway and Germany. A new Spectrum article reveals that the project is on schedule to be completed in 2019, and will travel a total of 623 km, making it the longest HVDC line in Europe. And with a 1400 MW capacity, it will also be the most powerful HVDC line in Europe.

The new Spectrum article highlights the three primary incentives for the project, from and electrical point of view:

Firstly, the HVDC converters have the ability to connect two non-synchronized grids, thereby linking the frequency of the two separated electrical zones represented by the Nordic and continental grids. Secondly, the HVDC connection makes it possible to transmit electricity over long distances with minimum losses. In fact, it is not even possible to transport alternating current (AC) over long distances subsea due to capacitive losses. Finally, the VSC-HVDC converter stations have full STATCOM (Static Synchronous Compensator) functionality to support the AC network at the Norwegian and German point of common coupling.

You can visit the official ABB site on Nordlink here.

Powerwall: Tesla’s Home Energy Storage Solution

Tesla’s Powerwall announced

Last month, Tesla Motors unveiled their new Powerwall battery packs for home and commercial use, and in less than a month, they’ve already sold out through mid-2016.  With such staggering sales numbers in less than a month, Tesla’s Powerwall units have already made significant headlines in financial news, but the impact on how we operate the electric grid will certainly make headlines after units begin shipping this summer.

There are two basic purposes for the the Powerwall batteries. The residential user can use a 7 kWh  daily-cycle battery, coupled with solar panels on their roof, to store excess solar energy during the day, and to purchase and store cheaper electricity from the utility company at night. Commercial users are typically more interested in
(possibly an array of) 10 kWh units for back-up/reliability applications. In this capacity, the batteries can provide uninterrupted power to the customer when the local utility experiences an outage. Smaller operations may use a Powerwall array as a cleaner, smaller alternative to on-site diesel generators.

How will distributed storage impact the grid?

The immense capacity of Tesla’s Gigafactory suggests that they have no intentions of slowing down production or shipments for quite some time. Utilities and grid operators must now ask themselves how batteries from Tesla and other competitors will impact distribution systems. Peak-shaving has long been a goal of operators, but control over storage units is now shifting to the customers, downstream of metering devices, where it will essentially be invisible to the distribution operator. Furthermore, if many customers install batteries that follow the similar rate-based charge/discharge schedules, the utility will see a large shift in when real power is demanded from the substation. This could cause power factor issues during the day, (when potentially less real power then normal is demanded), or thermal rating violations at night (when pre-set control settings are no longer reasonable for an unusually large demand). These questions are further complicated by the stochastic elements related to distributed generation devices (i.e. solar and wind), which, when viewed in tandem with the widespread storage, can result in a substation demand profile being completely different between one day and the next.