Thanks, QueenBee!QueenBee wrote:RegGuheert wrote:Thanks, Marktm! That sounds very useful!
While I'm a fan of microinverters, this is one feature they currently do not offer.
It can be done easily enough just not cheaply. I have a friend who really wants to do this but I don't think he ever will as it just costs too much.
http://www.outbackpower.com/index.php/a ... c-coupling
http://www2.enphase.com/global/files/En ... ystems.pdf
I actually have a 2 kVA 12V Outback inverter and 800 Ah of SLA batteries (badly sulfated down to 200 Ah, but I am now slowly recovering their capacity). While I can certainly build such an arrangement using the parts I have and some additional safety equipment, I have to say that I think SunnyBoy has done some things that Enphase never has (to my knowledge). Specifically, rather than simply dropping off in a grid overfrequency event, the SunnyBoy inverters linearly reduce their output power as you increase the frequency of the source above around 60.5 Hz. This is particularly attractive to grid operators since these inverters will gradually reduce their generation in an oversupply event.
This also allows a clever control scheme that the Sunny Island inverters take advantage of to allow their grid-connected inverters to run islanded. I assume their TL SunnyBoy units use a similar scheme.
Since the SolarEdge inverters control the optimizers directly, I suppose they use their own methods for modulating PV production.
Unfortunately, to my knowledge, Enphase microinverters do not seem to have any concept beyond "harvest as much energy as possible". The underlying assumption being that the grid can accept whatever electricity the microinverters can produce. This makes operation of such an AC-coupled system with Enphase microinverters somewhat "fiddly".
Frankly, I'm more inclined to simply use my LEAF and/or SLA batteries with 12V inverter(s) to ride out a storm unless there was a long-term outage. Then I might consider trying to use my Outback Inverter to bring the PV array into service.
It would be nice if Enphase would make using the PV in a backup situation easier. One simple solution would be to create a mode for the inverters which matches the SunnyBoy output power versus frequency curve to allow use of Enphase inverters with a Sunny Island inverter. I guess there is no chance of that since it violates the NIV principle (Not Invented Here).
I suspect there will be something coming from Enphase fairly soon now that they have bi-directional inverters, AC batteries and advanced control schemes available with their Envoy-S.