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Old 06-05-19, 12:27 PM   #9
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Location: Georgia
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Hi Steve;

I'm finding some conflicting reports about the switch.

As I understand it the IQ8 can run independent of the grid, but to do that in accordance with the 2017 NEC it still requires a microgrid interconnect device, now known as a MID.

Enphase calls their MID Enpower. It consists of a transfer switch, neutral forming transformer, and controller.

If I understand it correctly the anti-islanding feature is adequate for a grid tie that shuts down with the grid. A system that produces power when the grid goes down still requires NEC mandated physical isolation, similar to the requirements for a generator. The Enphase MID looks like it is going to be expensive because there are no cheap workarounds for a safety rated transfer switch and neutral forming transformer.

It might be possible to eliminate the transformer if only 230V loads are applied. One would still end up with a system where licensed contractors, permits, inspections, and PE-stamped engineering drawings could double the overall cost of a small array. There would be some economy of scale, but not in my area where grid tie PV systems are limited to 10KW.

Battery prices are still going up. Now that PV panels are the least expensive part of a DIY system I think the next thing to do is eliminate the batteries. Using the IQ8 to power loads that can be switched in and out based on what the PV's are producing seems the best way to accomplish this task. DHW can be heated and stored. Hydronic heating water can also be heated and stored. Window shakers or a small minisplit can run continuously during daylight hours to take some load off the primary HVAC. None of these loads have to be connected to the grid. Take out the cost of switches, batteries, and permits and there would be plenty of money left over to buy more panels and IQ8's.

CrankyDoug is offline   Reply With Quote