Hedges said:
I think they do when they are meant to play with batteries. Enphase combines their microinverters with a battery inverter. One of the guys here (Ampster?) says he uses their microinverters with Skybox.
We’re going pretty far OT, but what the heck, it’s my thread, right?
The DC-coupled stuff has the benefit of being pretty-much open-standard. Any MPPT SCC can charge a battery alongside any other MPPT SCC and any battery-powered inverter or inverters can convert that stored battery energy to AC power. No walled gardens.
As a general rule, the AC-coupled world is more proprietary.
So I’m interested in any non-proprietary solution to AC-coupled PV charging, but in particular what I’d be interested in is an efficient AC-coupled battery charger with sensors which supports zero-export by:
1/ monitoring PV production and self-consumption so that any production in excess of consumption is used to charge battery as long as battery is not full (charger needs to be bigger than PV array). This means that during the day when PV is active, all self-consumption is supplied by the Microinverters or the grid as long as the battery is still charging.
2/ if battery is full and PV production exceeds self-consumption, either throttles-back Microinverter generation (back to needing open communication standards) or shuts down Microinverter generation by blocking grid signal. DC-coupled SCCs throttle very easily by increasing string voltage above Vmp and all the way to Voc if current needs to drop to zero. Throttling is tougher and not yet as mature with microinverters.
If you or anyone knows of anybody working on non-proprietary smart AC-coupled battery chargers like this, please let me know.
Hedges said:
I favor string inverters. Microinverters have to replicate all or part of the functionality in every inverter (part if another box performs other parts of UL1741 function.) I think efficiency can be higher with string inverter for this reason. But the difference between say 97% and 99% doesn't matter much in terms of power production (2% difference). It should help reliability - 3:1 difference in heating, and getting inverter off the roof to a shady location. I think Enphase is still able to deliver good MTBF by overdesigning, and of course a couple failed is just a percentage reduction in output while waiting to replace.
I’ve got NEP dual-microinverters which have run for 6 years now without a hiccup. Exceedingly effective at dealing with any shading (MPPT per panel) and 96% conversion efficiency. The only issue with Microinverters is when you need to throttle them back (brute-force shut down works but probably not good for lifetime, smoother/gentler throttling is still evolving).
I paid under $1000 for 3kW of microinverters which include Rapid Disconnect functionality, so lower cost than all of
Hedges said:
You can get a string inverter with 3 MPPT, so it can have 3 different length strings. However, I like to have parallel strings of multiple orientations and the inverter I'm thinking of (Sunny Boy 7.7 kW -41 model) has limited current per MPPT. I would have to parallel all MPPT (which is allowed) to over-panel with 1.5x or 2x rating using the latest high wattage panels. So for me, a single MPPT works as well. But it won't do well with two strings where one is 50% shaded, something that separate strings would handle.
Yeah, that’s the challenge of my new array. 10 panels with a shifting 5-panel shadow progressing it’s way across the array all morning-long. 60% production is easy because the shade is gone 40% into the day.
But getting back as much of that list 40% as makes sense is the challenge.
Half the panels are unshaded at any point in time, so a full parallel string would get me back at least half of the lost 40% (which was my original plan).
Parallel arrays require a great deal of current (lots of money for wires and wiring) so I’m looking for a solution with 3 2S or 3S strings that can get me close to the same ~20% loss from shading (without costing more that it would be worth).
2 more panels in another part of my roof gets me another ~20% power, so anything I spend to squeeze 20% more power out of the partially-shaded section of roof needs to cost less than that...
Hedges said:
It looks like Solar Edge with its optimizers supports a single string of multiple angles and a battery backup is available. This may support your > 2:1 current output.
SolarEdge only works with SolarEdge, so that’s a non-starter for me. In addition, both the optimizers and the string inverter are expensive and U’m just looking to charge a 24V/48V battery, not invert power.
But if solar edge offered a cost-effective smart PV battery charger with optimizers, I’d consider it...
