Leveling solar

As readers of pv magazine will know, the use of battery storage systems is quite well-established in off-grid PV installations. “They’re typically used in telecommunications and industrial applications, as well as remote villages, to provide reliable power,” said Bryan Godber, Trojan Battery’s VP of renewable energy. What is new is using battery storage in the grid to do things like maintain power quality, peak shift, and provide bridging power at pre-defined times, with an eye to easing integration of solar PV. What is also new is the sale of battery storage systems in the residential segment to maximize self-consumption of PV power, with the long term goal of taking pressure off the grid that could be created by decentralized renewable energy production. In this department, Germany is leading the way.
Given the hype about storage it might seem like it is as important to PV as “higher efficiency” and “cost reduction” has been for the industry, but that might be overstating things. A clue about storage’s importance to PV was provided in a presentation by Henning Wicht of iSuppli at PVSEC 2011 where it was pointed out that grid parity is at hand, but he’s not forecasting a “boom” as a result. Wicht said in his presentation that on the microeconomic level the investment case is not an “easy one,” mentioning low cost storage as being “unavailable.” He also listed the costs of grid supply and management and the costs associated with decentralized production affecting the investment case. But “much more important” than these factors, in his view, are the macroeconomic political aspects and the influence of traditional energy suppliers that “fight against solar.” So the cost of storage is a factor, but only one of several.

Grid-connected battery storage

The cost involved in using battery storage is one reason that there is so much interest in lithium-ion (Li-ion) battery solutions. These advanced batteries are believed to be longer lasting and safer, and require less space and less maintenance, but what makes them the most promising is that they have the potential to get a lot cheaper, especially once the electric vehicle market starts to create demand in high volumes.
In fact, prices are already coming down. SolarWorld, for example, used lead gel batteries in the first version of its Sunpac residential battery storage product because, compared to Li-ion, they were cheaper. Now however, SolarWorld has R&D underway on lithium batteries. Its engineers are in discussions with local suppliers. “I have observed prices (…) decline by 50 percent in the past two years. Competition amongst suppliers and higher demand are the drivers,” said Milan Nitzschke, SolarWorld’s spokesman.
Elsewhere, Trojan Battery, which has been making deep-cycle flooded batteries, as well as other glass mat and gel batteries, for 85 years, identified the potential and recently formed a strategic alliance with Palladium Energy to develop lithium-based battery packs to address several market applications, including renewable energy.
It might seem that this is all mushrooming of late, but it’s actually been a long time coming. Saft is one of the early market entrants. “Saft is now on generation three of serial production of Li-ion batteries for grid connected storage and it has just received its first serial order for a large system for a community installation in the U.S.,” said Holger Schuh, Sales Director North Europe, Saft. The entry of international battery manufacturers into the U.S. market can be seen as validation of the French company’s decade long research and development and market priming.
Saft has prepared a whole range of energy storage solutions from residential to megawatt-sized grid-embedded solutions. For the residential market it developed a complete system solution with Conergy’s Voltwerk including inverter. The commercial launch is planned for the first quarter of 2012.
The “VS 5 hybrid” includes an 8.8 kilowatt hour (kWh) battery, which provides enough energy to increase the self-consumption of a homeowner’s PV installation from about 20 to 30 percent, up to 70 to 80 percent, and to supply the main household load for several hours in case of a grid black-out, according to Schuh in an interview with pv magazine.
In the megawatt class, Saft works closely with the big international power transmission and distribution companies like ABB and Siemens for PV and wind solutions. In these larger applications, battery storage is located in the transmission network, distribution network, or at the point where the PV power is interconnected to the grid. “All three options are possible, it really depends on the application,” commented Schuh.
It should be noted that grid-connected energy storage is already an established practice amongst utilities. There are more than 125 gigawatts of installed grid-connected energy storage technologies deployed worldwide, with a comparable amount under development, according to the California Energy Storage Alliance.
Batteries are just one technology available for storage. “Battery storage solutions in the grid can be used for load leveling, peak shifting, grid stabilization and backup systems,” said Jochen Lenck, Sales Manager, Samsung SDI Company Ltd, in an interview with pv magazine. For bulk power management, pumped hydro and compressed air energy storage (CAES) are used, according to Saft.

Trials and demonstration

Battery solutions are being deployed in a good number of utility trials and pilot projects, clearly anticipating both a drop in cost of battery solutions, and an intent to avoid the use of fossil fuel grid-management alternatives.
Typically, the purpose of a demonstration or trial is to prove a solution for a clear technical requirement, or to demonstrate a short and clear return on investment where PV power is grid-connected. (See table on page 72: Selected PV projects and battery storage solutions. This short list enables a bird’s eye view on current trends and reasons to use battery storage.) A common goal for storage and PV is grid stabilization in transmission and distribution systems to smooth intermittence.

“Reliability is an issue when fog or clouds, for example, causes swings in PV power output. Battery storage is part of the solution,” said Chris Campbell, Vice President of Marketing and Business Development at A123 Systems Energy Solutions Group in a phone interview with pv magazine. A123 Systems has deployed 34 megawatts of Li-ion battery storage solutions in renewable energy plants to date, expecting to triple that by the end of the year.
ABB Smart Grid’s spokeswoman confirms the technical requirement with respect to renewable energy by pointing to three of its recently announced grid-integrated battery storage projects, all exploiting Li-ion batteries. Two of the projects involve wind and one is hydro power generation, located in Sweden, UK, and Switzerland, respectively. The storage systems are located in the power distribution network.
Beside these examples, battery storage can solve several upcoming issues in island networks, particularly grid stabilization or grid support. “If there is a local concentration of volatile and intermittent renewable power generation, such as PV, and the local grid is also constrained, then battery energy storage systems can effectively be deployed,” said ABB’s spokeswoman.
SunPower’s Carl Lenox, principal engineer, agrees in principle that island grids and micro-grids that incorporate a very high penetration of PV or planned high penetration, may find storage to be an “attractive” option if needed to supplement the flexibility from the other generators in the system.
Saft’s installation with Tenesol in Guadeloupe is illustrative of a solution that economically provides grid support during peak demand periods. It involves 14 sites with 2.5 kilowatts peak PV and 11 kWh Li-ion batteries (which replace fossil generation to cover peak demand). “With a grid feed-in at peak periods, one hour in the morning and three hours in the afternoon, and a battery efficiency of 97 percent, the expected return on investment is six to ten years, depending on [the] cost of peak power,” said Saft’s Schuh.
Elsewhere, in Hawaii, for example, several battery storage solutions from Xtreme Power are being deployed specifically to deal with renewable energy integration issues. Another example is a project undertaken by Younicos to test battery storage solutions for the Azores island of Graciosa, which is aiming for high penetration of solar and wind power generation and independence from fossil fuels.
Battery manufacturers believe that island networks can inform various industry players about the impact of renewables, particularly solar, on grid management. “The kinds of issues that utilities are running into on the islands where there is a lot of solar PV capacity foreshadow what might happen in other mainland markets,” said A123 Systems’ Campbell.
Germany was able to reach such a high renewable penetration because it had a very “solid” power grid, but Campbell points out that not all regions have such a power grid. “For example, Italian authorities may force grid operators to install storage due to weakness in the grid infrastructure,” said Campbell.
And even with a strong grid, a case can be made for battery storage at the edge of the grid. “Once renewables pass the 20 to 30 percent threshold either country wide or locally, battery storage makes sense. It is either that or upgrade the network,” said Saft’s Schuh.

Regulatory hurdles

There are hurdles still to be overcome besides cost reduction. The local regulatory and accounting rules often have to be amended to enable battery storage to compete on a level playing field with conventional alternatives such as gas peaker plants. “It is critical to enabling a return on investment for the large-scale utility segment. In the U.S., the FERC is currently working on such changes,” said ABB’s Smart Grid division spokeswoman.
Deregulated markets, such as Europe’s, are a challenge when it comes to selling battery storage solutions because it is more difficult to capture all the potential value from the investment. “In the U.S., the utilities can capture all the value streams, but in Europe it’s divided between the various players, from grid operators to sellers and it is an issue to understand who makes the investment,” said Holger Schuh, Saft.
Some of the value streams for utilities, or ways that the utilities can derive a return on investment in battery storage systems include: matching generation with demand, enabling peak shaving for both generation and demand, avoiding and/or delaying grid upgrade investments (cost avoidance), and profiting from utilizing variable tariffs . “The SOL-ION project in Germany demonstrated that a battery solution enables the avoidance of costs associated with grid upgrades, substitution of conventional ancillary services, and substitution of conventional peak power generation using fossil fuel plants,” explained Schuh.

Co-location questions remain

As several of the examples cited here indicate, battery storage systems do not necessarily have to be co-located with PV generation. There are two technical reasons to co-locate battery energy storage with PV: capacity firming and ramp control, according to ABB. At issue is the cost and efficacy. “Storage should be sited where it will provide grid services most cost-effectively,” said Carl Lenox, SunPower Principal Engineer, who explained that it is known that aggregating the variability of many PV systems, along with variability of load and of other variable generation sources, like wind, results in total system-level variability that is much less than the simple sum of each.
Lenox said that variability is uncorrelated mathematically, especially on short time scales, and over fairly short distances in the case of PV. “Controlling the ramping behavior of two adjacent PV plants with batteries might mean that you have a situation where one battery would be discharging while the other was charging, simultaneously,” said Lenox. The short term changes in output would otherwise at least partially cancel each other out. “Obviously, this is a very inefficient way to deploy energy storage,” said the SunPower engineer.

Residential solutions in Germany

Where it could make sense to co-locate battery storage with PV is in grids, weak or strong, to maximize the economic value relative to variable energy prices, one example being the self-consumption feed-in tariff. In such an environment, energy management on the premises or in community networks adds value to the PV plant in order to do things like time-shift the mid-day peak power generation. “We are keeping our eye on that, but right now battery costs are significantly higher than the value that would be provided by such an arrangement, and there [are] a number of other barriers to work through,” said SunPower’s Lenox.
Tariff pricing structures or FIT conditions, such as dynamic pricing, or firm capacity requirements, contribute to the attractiveness of storage. A flat rate for energy input into the grid, at any time of day, at any ramp rate and power, won’t enable a return on investment for the customer. “Right now it is difficult to make a business case for placing storage in the home in the U.S., and community segments. However there are several pilots underway,” said A123 Systems’ Campbell.
One country where FITs and conditions are almost aligned is Germany. “Opinions changed in 2009 with the new FIT in Germany. Home-owners could achieve a better profit if they consumed the power they generated. It is now more profitable to enable self-consumption than selling energy back to the utility,” explained Volker Wachenfeld, Executive Vice President, Off-Grid Solutions at SMA.
Vendors such as SolarWorld and Solutronic market battery storage systems as a way to help cut the electricity bill. Based on today’s rates, a homeowner can expect to have cost savings of about 350 euros a year, with a PV plant battery storage package as opposed to “no solar,” according to Uwe Scobel-Freimüller, Solutronic’s director of sales, marketing and administration.

Supply chain and markets

Any new technology in the solar PV sector must be low cost and competitive. It also has to be an integrated solution because there is a whole host of software, electronics, and components that need to be supplied along with the battery for management and interconnection to existing systems. It requires systems integration know-how and supplier R&D contracts.
A123 Systems, which was a pioneer in this respect, has had to provide a lot more than just a battery. It developed techniques for system integration, advanced control systems, and professional services, such as maintenance contracts. It also had to make the business case to the grid operators. Consequently, A123 systems offers not only the physical plant, but also business modeling know-how and experience.
An integrated solution means R&D partnerships. Solutronic co-developed its battery storage solution with EWE subsidiary E3/DC GmbH, a systems integrator, which in turn partnered with the Sanyo business unit for the 5.4 kWh battery technology.
SolarWorld, which confirmed with pv magazine that it has sold about 100 Sunpac systems to-date, partnered with SMA for the inverters and Hoppecke for batteries. SMA in turn has R&D ongoing with several battery vendors, including LG Chem, Dispatch Energy, Sony, and Saft.
For each battery supplier, SMA must perform research and development. “The R&D is not on chemicals, rather it includes the software and how the inverter talks to the battery. You have to understand how to deal correctly with the battery management system,” said Volker Wachenfeld from SMA.
The R&D goal in this respect is to guarantee a long service life of the batteries. “To achieve this, the cells in a battery block have to be balanced periodically, so the available charging or discharging current has to be ‘agreed’ [on] between [the] inverter and battery management system,” explained Wachenfeld.

Conclusion

It looks like battery storage can and will be a part of the solar PV landscape, initially at the edge of the distribution grid in homes and commercial installations, but also in time within the grid itself providing various PV-related services. “We’re still in the time of pilots. Trials and demonstration installations are to be expected over the next two years,” said Bryan Godber, Trojan’s VP of Renewable Energy.
As the supply chains get established and volumes are low, costs are still on the high side for grid-connected residential and commercial markets.
In many ways the situation with lithium battery storage is similar to solar photovoltaics in its early years, particularly the optimism about the path to lower cost and scalable solutions. And everyone reading this knows how surprisingly quickly that trajectory unfolded.