In-Home Storage: The Virtual Power Plant

Rapid Growth

Solar and wind are considered the most popular renewable resources across the world, but due to their intermittent and unpredictable nature, utilities are still relying on natural gas and coal. However, when renewable technologies are combined with energy storage they smooth out load fluctuations and have the potential to significantly impact the generation mix.
Total energy storage deployment has increased dramatically in the past few years because of low-carbon, clean energy policies, and is anticipated to grow even more in the near-term. By 2022, GTM Research expects the U.S. energy storage market to reach 2.5 GW annually, with residential opportunities contributing around 800 MW.


Source: GTM Research

How Does It Work?

Energy storage works as a three-step process that consists of extracting power from the grid, solar panels, or wind turbines, storing it (charging phase) during the off-peak period when power prices are lower, and returning it (discharging period) at a later stage during the on-peak period when the prices are much higher.


For electric vehicles (EV), most of the charging happens at night and during weekends, when the prices are comparatively lower, and vehicles are not used that much. As EVs continue to enter the mainstream market, they would increase the off-peak prices and contribute to load shifting.
Energy storage devices and EVs can complement each other or they may be competitive. But energy storage is the key element for EV charging during on-peak hours.

Different Market Players

Residential energy storage has been a holy grail for companies like Tesla, Panasonic, LG, Sunverge Energy, and Orison with lithium ion (Li-ion) batteries as the leading technology type. Now with plug-in electric and hybrid vehicles on the rise, automobile companies Tesla, Nissan, Mercedes Benz, BMW, Renault and Audi have also joined the residential market to integrate EV charging stations, battery storage and rooftop solar that in essence has a residence operating as a virtual power plant.
Beginning in December of last year, Arizona Public Service Company deployed Sunverge Energy’s energy storage hardware coupled with advanced, intelligent energy management systems that predict future load requirements and solar generation. Additionally, Tesla is enjoying significant market share, shown recently by Vermont-based Green Mountain Power’s launch of a comprehensive solution to reduce customer electricity bills using Tesla’s cutting edge Powerwall 2 and GridLogic software.
A few other utility companies, especially in Florida and California, are also exploring residential energy storage programs, as shown in the figure below.


Source: Hawaii PUC; General Assembly of Maryland

So, what are some other current thoughts about the pros and cons of in-home energy storage?

  • Energy storage reduces load fluctuations by providing localized ramping services for PV and ensuring constant, combined output (PV plus storage).
  • Improves demand response and reduces the peak demand.
  • Extra savings for customers through net metering systems and end-user bill management.
  • Reduces reliance on the grid; the customer can generate and store the energy during severe outages also.
  • Disposal of Li-ion batteries is not easy, and they are difficult to recycle
  • Automakers, like Nissan and BMW, are implementing second-life batteries, thereby reducing the durability and reliability of the product.


Concluding Thoughts

Clearly, a wider acceptance of energy storage resources would be a game changer in the U.S. power sector. Utilities, consumers, and automakers are profiting from this exponential growth of energy storage. With an increasing number of companies using artificial intelligence and machine learning algorithms for energy management systems, the synergy with energy storage creates a perfect, smart, personal power plant which has tremendous potential to change the landscape of the energy industry.

Filed under: Clean Power Plan, Hydro Power, Power Grid, Power Market Insights, Power Storage, Renewable Portfolio Standards, Renewable Power, Solar Power, UncategorizedTagged with: , , , , , , , , , , , , , , , , ,

Large Scale Battery Storage

Some emerging technologies pave a bright path for the future of Large Scale Batteries

As we move towards more renewable energy sources and away from fossil fuels, we will need new technologies to capture energy production as well as provide new ways to store and deliver power. An ongoing issue with solar and wind production is the inability to predict exactly when you can produce and dispatch power. Additionally, we are seeing more interest for generating, storing, and time-shifting power in other ways to meet environmental goals. Large Scale Batteries are an exciting step toward meeting, and supporting, some of those goals.

While we don’t know what the future will bring, there are some forecasts that predict substantial drops in the cost of the various storage technologies as there is more adoption into the marketplace. Among these, in 2014 Citigroup analysts predicted a drop in battery storage costs to $230/kWh by 2020 and a further drop to $150/kWh in the years after that. Whether it is from the reduced cost or simply an increased need, Navigant Research forecasts worldwide battery storage to grow to almost 14 GW by 2023.

Wordwide forcast of battery storage capacity

Graph 1: Source

These potential reductions in costs could even lead to some ‘grid defection’ as the economics change and become less of a hindrance for adoption.

Lowest current and projected battery cell price by type

Graph 2: Source

Tesla founder Elon Musk has been working with lithium-ion technology both for vehicle battery and grid-level storage for over five years. Li-ion is a familiar battery type, typically a pair of solid electrodes and an electrolyte, and has been around for a long time in smaller applications… Tesla (and other companies) is currently testing larger scale battery installations, currently only for households and businesses. In the future they are looking at becoming scalable for utility systems. Some advantages and disadvantages to Li-ion are:


· High-energy density

· Low maintenance

· Low self-discharge


· High cost to manufacture

· Limited number of charging cycles (They age and will need to be replaced.)

· Heat generated during use graph

Figure 1: Source

Meanwhile others are pursuing what is known as “as “flow battery” technology. This is aptly named, in that it contains two liquids that flow next to each other, separated by a membrane, and as they move past each other create an electrical current. These batteries use two electrolytes in separate tanks, which are then pumped into a central stack. The central stack has an ion-conducting membrane that captures the electrons as the two liquids are pumped through the stack. Currently, most new flow batteries use a membrane containing vanadium. Some advantages and disadvantages to this technology include:


· Electrolyte solutions are safe, non-flammable, and non-corrosive

· The two electrolytes are compatible and easily rechargeable

· Expected to handle many more cycles than Li-ion batteries


· Maintenance cost of the tanks and pump system are high

· Overall cost is higher $/KWh than Li-ion

· Low energy density

· The volume of space that the tanks may take up Figure 2

Figure 2: Source

A promising hybrid of these two technologies is also being tested, using solid materials in two separate tanks with an electrolyte fluid that passes over them. The solid material can be lithium-based, while the flow of the liquid then conducts the electrons to the cell stack. Although still in testing, this looks to combine the scalability of flow batteries with the power density in Li-ion batteries.
Electrochemical Society Figure

Figure 3: Eletrochemical Society Source

The need for large scale energy storage will continue to grow as we move forward with renewable energy sources making up a larger portion of our energy generation. The inconsistency of renewables’ generation and the need for maintaining a stable grid will necessitate some form of storage. These are just a few of the most promising utility scale battery technologies that are currently available. Skeptics could argue that technologies like GTs or hydro which are currently used to firm up intermittent renewables will continue to do so in the future. That may be likely in some cases but those current technologies have their own issues. There are environmental and locational issues with hydro; there are pipeline access and saturation issues with small gas. Whatever technology moves us forward it seems apparent that battery storage will be an integral part of that future.

Filed under: Power Market Insights, Power StorageTagged with: , , ,