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Why batteries need to be a full fledged architectural entity
James Kempf <kempf42@...>
So I think you need to separate out batteries (as bulk power storage devices, not for powering electronics) from microgrid controllers in your architecture. Here are the reasons:
1) These kinds of "hidden" components often turn out to pose problems over time from a practical standpoint. For example, vendors look at them as an opportunity for differentiation, and engineer proprietary "lock in" protocols that then turn out making interoperability more difficult and systems more expensive. You mentioned today about the microgrid controller having an algorithm for leveling charging and discharging, what about if I have a better idea for an algorithm and want to substitute it, but the manufacturer has coupled their microgrid controller tightly to their battery? Such algorithms are an active area of research in the home energy management controller space today. I am facing this problem right now with my Enphase inverters, Enphase won't tell me what protocol their microinverters use to talk to the controller (other than PLC, but that's Level 1).
2) Batteries and other storage devices are being proposed for use in demand response types of situations. If the battery is hidden under the microcontroller, each microcontroller would individually need to co-ordinate with the utility for its batteries. I think you want the building energy management system to do that. Otherwise, your hierarchical model, where the microcontrollers just communicate point to point, would be violated.
2) While they are not widely deployed today, there are other classes of equipment that are similar to lithium batteries for bulk power storage, in the sense that they can serve as loads when power is abundant and cheap and sources when power is scarcer and more expensive. Examples are flow batteries, where the charged and discharged electrolyte are kept in separate tanks, flywheel storage, and bidirectional fuel cells or a combination of an electrolyzer and a fuel cell,. I have seen startups working on all of these concepts, and one even has a product that uses hydrogen for seasonal storage (unfortunately it only stores 500 kwh and isn't available in the US). Is the architecture going to model all of these kinds of devices as a battery and hide it under the microcontroller? While it might seem a bit far fetched (and doesn't come under the category of single building nanogrid), how about if my neighbor and I trade hydrogen rather than electrons? His solar makes more power in the summer when mine is shaded and mine makes more power in the winter, so he agrees to sell me hydrogen in the summer and I agree to sell it to him in the winter.
So I recommend rethinking the design, and separating out bulk power storage devices into its own architectural entity.