Tweet
For whoever cares, the new SMA rapid shutdown box has been released. It has two independent channels allowing two strings to be combined into each channel. If you want independent MPPT control of 3 strings then you'll need two boxes. I got a quote for $292 for the box and $50 for the stop switch. If you have 2 or more boxes, the stop switch control signal is daisy chained between them so just one stop switch is needed.
-
-
This is good news for those who want the ability to have some power when the sun is shining without any battery or associated equipment. Huge added value there in my opinion. Unfortunately they may be a day late and dollar short on getting this to market - it needed to be out over a year ago to respond to the 2014 NEC and provide resistance to the move toward module level electronics. Future NEC's may say the shutdown has to be under the module which will make this product no longer compliant. Not having to manage string lengths opens up the installation market to simplified designs, and much less studious installers that come with it may be the end of residential string inverters.
Commercial buildings still have to comply with rapid shutdown, and MLEs are the simplest and likely least expensive way to comply there too. This hurts the value proposition of arrangements that could use solar to keep buildings limping along in an extended grid outage (limited life safety functions support like lighting and minimal ventilation). Rapid shutdown requirements as written are short sighted in my opinion and the unintended consequences will eventually result in more harm than reasonable protection from an on-site power generation source which is what makes these systems so unique.
I'd be curious to know what percent of the market don't understand their system won't help them in any way if the grid is down. Similarly, how many people just don't care.
Thanks for the pricing data. -
The NEC is pretty clear that for the Rapid Shutdown requirements are that the voltage being generated by a solar pv array must be less than 30 volts more than 5 feet inside a building or more than 10 feet from the array. So I am guessing that the SMA box is mounted within that 10 foot distance of the array and communicates with the main string inverter near the power panel.Comment
-
I don't think it communicates with the string inverter. You have to wire the indoor/remote "emergency power off" switch to the rooftop box. This provides the shutoff at the box that gets located at/under the panels. It is run of the DC available from the system. Most other rapid shutdown solutions would automatically disconnect at the roof box if grid power is lost - something not desired if you want the Secure Power Supply operational when the sun is shining but grid is down (no batteries required).Comment
-
That's right, it's simply a contactor relay box powered from the array and deactivated by a first responder hitting the stop switch. It's operation is independent of the grid being up or down.
It seems kind of stupid to have to have this, but it's NEC 2014 compliant and since my system is finally going up soon I'm assuming I'll be grandfathered in should NEC 2017 require deactivation of all of the modules individually. I only hope now that SMA or anyone else keeps making string inverters for the US market 10-20 years down the road. If not, I guess I can eventually switch over to an MLE system without having to replace the wiring between the array and the inverter.
-
Comment