Cost: Another critical part of the design of a battery is not the actual battery itself, but the space the battery operates in. The impact of incremental costs of necessary added systems required for safe operations is significant. In most cases, and in our earlier designs, things like fire safety, fire detection, gas detection, gas extraction, cooling and emergency ventilation were left to other contractors and not included in the cost of the battery system. These so-called add-on systems are actually critical to the performance of a battery and are not optional, but in most cases battery suppliers will leave these added costs to the ships builders.
Our approach became more holistic and covered all parts of the battery system as our design evolved, which means less added cost per kWh and more integrated engineering. Our next evolution in development is to validate the design of our core modules to withstand an A60 battery test. Validation of this test will eliminate the need to build an A60 enclosure for the batteries.
To put this in context, one of our integrator partners determined that the typical added cost of a battery system could be as high as $275/ kWh for a total battery installation, this cost comes on top of the cost of the batteries themselves. It is essential that integrators and end customers always understand the overall system costs to allow decisions to be made on return on investment based on the actual installed system costs not just the battery cost.
In fact, SPBES is not
completely immune to this cost; our liquid cooling requires chillers sized to meet the power demand of the system and our gas extraction system must be correctly vented, but instead of $275/kWh, we face a cost typically of $20/kWh for the added components and to meet all performance requirements.
Another benefit of SPBES CellCool liquid cooling is the ability to actually predict the life of our systems. Air cooled systems are
62 | The Report • March 2020 • Issue 91
SPBES 1MWh battery located inside a 20-foot ISO shipping container.
very dependent on the ambient battery room temperature to be able to manage the overall life of a lithium battery, and they are very fickle. Even a small increase in ambient battery room temperature will affect the temperature of the lithium cells and can have a significant reduction in calendar life.
In contrast, liquid cooling
maintains the temperature of the cells at a fixed range and we can eliminate the impact of ambient temperature on the performance life of the cells.
As system life continues to be in the 10-year range and with many operators seeking longer-life solutions, eliminating temperature as a variable goes a long way to meeting lifespan requirements. There are still a large number of factors that will influence battery life, but temperature is by far the most impactful.
System Size: Another area where we have seen a significant evolution both in the use of cells and the design of a battery is size. Cell manufacturers have significantly improved energy density over the last ten years. By increasing the energy density of the lithium-ion cells, a significantly smaller system can be created. For example, a system with 88kWh per module versus a battery that has 65kWh per module has already achieved 35%improvement of weight and space required for an installation.
As long as the cycle life meets the lifetime need, this is a huge improvement. In my experience, increases in energy density tend to a reduced cycle life.
The other significant feature of any system is the percentage of energy available on a continuous basis. On our first-generation air-cooled design, the continuous rating was about 70%. This meant that if we needed 1MW of energy, we needed to have about 1.4MWh of capacity to operate at 1MW load. This meant a larger, heavier system that was also significantly more costly to install and maintain. If we assumed that the battery system cost $100/ kWh, then a 1.4MWh battery would add $140,000 to the capital cost of the system – and does not even consider the ongoing performance and financial impacts of the increased size, weight and maintenance!
A liquid cooling system allows SPBES to use significantly more of the battery capacity. This really means we can greatly reduce the size and the associated costs of the battery. In our case, the battery can now operate at an average continuous rate (charge and discharge) of 300%. In the example above, a 1MWh system can now be met with a 350kWh battery; much smaller, much lighter, and much less costly to install, with only a $35,000 budget needed (if the necessary costs were $100/kWh).
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