The charge of the battery storage brigade - turnkey energy storage
Grid-connected, battery-based energy storage systems have many beneﬁts, including renewable energy integration, enhanced grid capacity and improved power quality. Recognising these advantages, some of the world’s largest power equipment OEMs are developing turnkey energy storage products.
Timeshifting: the ability to store something for consumption at a more convenient time. Great for watching your favourite television shows. Ideal for energy, too, but sadly we are not at a stage where it is widely timeshifted via a programmable box. At least, not yet.
One battery manufacturer, Saft, is actively working towards such a solution. The French firm is participating in a number of projects aimed at moving solar photovoltaics (PV) with energy storage systems (ESS) from feasibility in the laboratory to feasibility on an industrial scale. One such project is Franco-German Sol-ion, which also involves solar PV manufacturer Tenesol, string inverter specialist Voltwerk, German utility E.ON and a number of academic institutions, including Zentrum für Sonnenenergie-und Wasserstoff-Forschung (Centre for Solar Energy and Hydrogen Research, ZSW). The project, which has financial backing from the French and German governments, was initially conceived with the German Federal Government’s decision to augment its national feed-in tariff regime with a self-consumption tariff from 2009. This incentive was axed during the latest amendments to the Renewable Energy Sources Act (EEG), but the timeshifting concept remains pertinent as many countries move towards a post-incentive solar world, where exporting power to the grid becomes less lucrative and self-consumption at times of peak demand (and therefore high prices) makes more economic sense.
The project will see the installation of 75 solar PV + lithium-ion battery ESS units in France and Germany, which makes it the largest such R&D project in Europe. Ten of these have already been installed in the various institutes and partners participating in the project, while the remaining 65 will be deployed in households. In Germany, they will mostly be installed in the Bavarian town of Schwandorf, where there is a high penetration of solar power. In France, they are mostly going to Guadeloupe, a French département in the Caribbean, as well as mainland France.
The Sol-ion systems comprise of four of Saft’s Synerion 48E lithium-ion modules, each with a capacity of 48V and 2.2kWh, a 5kWp string inverter and a battery converter. The unit’s energy management system (EMS) controls the overall system state and chooses the mode of operation, for example using PV for selfconsumption, to recharge the battery, for storage or for export to the grid.
The Sol-ion systems deployed in Germany, however, are optimised for selfconsumption and are therefore configured to prioritise household loads. Surplus energy is sent to the batteries until fully charged, and only then is the excess power fed to the grid.
Initial test results from one installation at ZSW’s site in Widderstall, Germany, showed a fairly consistent boost in self-consumption of approximately 40% during 11 days of testing in November 2011 (see page 31). On 18 November, for example, solar PV self-consumption with storage was 85%, of which 45% was delayed use. By comparison, the site self-consumed just 45% of solar PV output with an identical set-up minus the ESS on the same day.
According to Michael Lippert, head of Saft Energy Storage, these early results are in line with projections. He explained, ‘In our calculations and simulations we expect to shift self-consumption by 30–40% to 70% overall over one year. This includes what we call natural self-consumption – when production coincides with consumption – which is around 30%’. Self-consumption will naturally vary in different months of the year. ‘You would probably have 100% self-consumption in January due to shorter days. If you produce just 2kWh a day in January, most of this will be used.
‘On other days, the capacity of the energy storage system will be inadequate and the battery system will be fully discharged and recharged in a day, while other days may see only a 10% discharge. Over the course of a year, the batteries will cycle at 60% a day on average. This is why we think lithium-ion is the best technology for energy storage batteries, as it can cope with this high variability of discharge.’
Of course, they say the same thing about lithium-ion for electric cars. And with the greatest will in the world, not to mention billions of dollars of government funds, electric cars have struggled to find a market, mostly because of the high cost of lithium-ion batteries.
Lippert says costs will come down once the systems are mass produced. Saft’s recently commissioned US battery manufacturing plant in Jacksonville, Florida, will make up to three million cells a year, but it will be some time before the cost will come down to the company’s target price of €400/kWh for ESS lithium-ion batteries.
Saft is not the only company planning to bring to market timeshifted solar power via lithiumion batteries. In July 2012, solar PV manufacturer Kyocera began shipping its solar PV + ESS system to households in Japan. The package, which features a 4.03kW PV array with a 7.2kWh lithium-ion ESS made by Samsung will retail for the tidy sum of ¥4,926,000.
Distribution and investment
Lippert acknowledges that the uptake for ESS from solar PV producers will be limited in the short and medium terms due to the high cost. Furthermore, large scale solar power producers have so far shown little interest in storage, as feed-in tariffs have incentivised them to export as much as possible. So while the Sol-ion test results have shown some promise for residential users for self-consumption, the primary takeaway from the project for Lippert is the drastic reduction in power fed into the grid, which on some days fell to zero. ‘From the grid point of view that’s the target,’ says Lippert. ‘If you reduce the exchange of power, you reduce the fluctuations and perturbations of integrating solar energy with the grid.’ Grid stability is key to the adoption of energy storage for large-scale solar and other renewables and is the reason why leading power equipment manufacturers are developing their own grid-scale ESS.
Big on storage
But energy storage batteries do not start and end with lithium-ion. US firm GE Energy Storage has placed a large bet on sodium nickel chloride being the winner in the race to provide cost-effective batteries for the global energy storage market, which it estimates could be worth US$65 billion by 2020.
The firm has built the largest non-lead acid battery manufacturing plant in its home nation in ystem. GE’s global research centre looked at all the available battery technologies and decided on sodium nickel chloride as the most viable solution for energy storage. Firstly, while lithium-ion has a higher power density, sodium nickel chloride has a higher energy density. Lithium-ion, therefore, is better used in short duration applications. For power needs over a longer period, GE decided that sodium nickel chloride is the best bet.
Secondly, sodium nickel chloride is seen as an inherently robust and simple chemical technology. Sodium chloride is, of course, salt, which is highly abundant and cheap. While more expensive than lead-acid batteries, sodium nickel chloride has greater cost-effectiveness on a mass-produced scale than lithium-ion, the company says.
For large solar applications, GE sees a niche for Durathon as a 1MW energy storage system with the capability to produce that power between two and four hours a day. Rick Cutright, GE Energy Storage’s Director of Product Management, says, ‘If you go through the trouble of installation, the cost of the breakers, the switchgear and the inverter, then I don’t see too much logic in connecting grid-connected battery systems with a capacity of less than 1MWh.
‘A two-hour capacity gives you a battery storage system of reasonable size with black start, load levelling, uninterruptible power and other functions. With a four-hour capacity you can start thinking about time-shifting.’
To rapidly bring down the costs, GE is focusing hard on a modular, scalable architecture using the same cells, battery modules and control systems across the range of system sizes that it will install. Cutright states that the market for energy battery storage systems starts at US$1,000/kWh, which GE can achieve, more or less, at present, but that at US$500/kWh the market will really take off.
Alstom eye opportunities
French power equipment OEM Alstom believes there is a good business case to install ESS to manage demand in cities that have a shortage of power capacity and where the installation of new cables is problematic and expensive. Laurent Schmitt, Vice President of Smart Grid solutions at Alstom Grid, says an increasing number of distribution network operators (DNOs) and other grid companies are exploring installing ESS and critical grid nodes as a way of avoiding grid expansion.
Schmitt believes that within 10 years, a strong competitor within the sector will be able to install around 100MW of gridconnected energy storage systems per year. While Alstom has no intention to build batteries itself, it is currently in discussion with five strategic partners in the USA, Europe and China, all of which are purely battery manufacturers, in order to develop storage products. ‘We plan to offer different technologies at a size of 1–10MW, or two to eight hours’ capacity,’ says Schmitt.
‘We believe that both sodium sulphur and lithium-ion have a role to play in the grid, as well as vanadium redox flow in the future. The technology deployed depends if you want to shift demand on a daily basis or whether you want to stabilise power quality at various times of the day. Each grid and each node will require different technologies. We intend to package various battery technologies with our power electronics on a turnkey basis to high and medium voltage grid operators consistent with their specific grid codes.’
However, warns Schmitt, the current problem with grid-connected ESS is that the business model is not clearly defined. ‘Current projects are merely technological demonstrations. While solar and wind farms have had an impact on price volatility, at the moment the price spikes are not regular and, therefore, hard to predict in terms of cash flow.’ Price spikes themselves will not be sufficient to justify their installation, adds Schmitt. Furthermore, the other benefits of these systems, such as power quality improvements, need to have a revenue stream to be viable. As much as technological improvements and cost reductions, Schmitt believes the success of grid-connected ESS depends on regulators deciding whether it is the role of regulated grid companies or deregulated generators to be mandated to install them.
‘As with smart meters, it would be more natural for grid operators to install ESS because the benefits can be shared across the entire grid. However, it would require some recognition that regulated DNOs can be a market participant in intra-day transmission system dispatch, which is normally managed by the market. This is something new.’ One such regulated DNO, UK Power Networks, sees ESS not just as a tool for smoothing load profiles, but also as an alternative to network reinforcement. In May 2011 it commissioned a grid-connected ESS at a substation near Hemsby in Norfolk, UK.
Eight stacks of 13 Saft lithium-ion batteries with a total capacity of 200kWh are connected to a 600kVA voltage source converter made by ABB, which converts AC power from a nearby 2.2MW wind farm into DC to be stored in the batteries and converted back to AC for the grid. UK Power Networks believes ESS could defer investments in network reinforcements such as transformers and is considering installing a 1MW system on a large substation in need of reinforcement in the coming years.
Clearly there are a number of challenges to overcome before ESS are integrated with the grid, not least the cost. But the world’s largest OEMs are backing it. They can’t all be wrong, can they?