Waste Not or SOC% ?

[gblass1]

Hi all

My System:
Midnite Classic 150
Whizbang Jr.
System voltage 24V
6 panels for a total of 900 watts
4 Interstate 235AH 6volt batteries
1000 watt grid tie inverter
2500 watt 24v to 110v inverter

What I'm trying to do is once the batteries are close to fully charged turn on AUX1 to turn on the 1000 watt grid tie inverter.  On a sunny day the panels will just about keep up with the GT inverter but will still pull a little power from the batteries.

From what I've been reading it looks like I have 3 options to accomplish this, Waste Not, SOC% or Diversion.  I have been reading up on the "Waste Not" mode but still can't wrap my head around how it works and how it differs from "Diversion" mode.  SOC seems simple enough to set  it to turn on at say 95% and turn off at 90%.

I'm guessing this is a fairly common issue and would like to know what others have done. 

Thanks in advance.
George

[Westbranch]

Option 1 should be to get about 600 more watts of PV so there is no draw from your batteries....maybe even a bit to float the batts.

[gblass1]

Thanks for the reply Westbranch

Aside from this system I have on the Classic 150 I have 24 panels on my roof hooked to a 5kw grid tie inverter. 

This small system is kind of an experiment with the intention of eventually going completely off grid.  My plan is to split the 24 panels into 2 strings of 12 and get 2 Classic 200's.  Right now I'm just trying to understand all the modes the Classic has which will help me in designing my new system.

Thanks again.
George

[zoneblue]

You can do oppurtunity loads on both aux1, and aux2. Aux2 uses PWm to modulate the load, which is exactly what you do not want for a GTI. Aux2 is also tied up by the WBjr. Aux1, is just on an and off, which is more what you need.  Wastenot should be fine, although this will tend to switch on and off as the sun comes and goes. SOC, might be a better route there, because it will cycle less, if you can tolerate a bit of battery use.

We trust that your GTI is permited...

[gblass1]

zoneblue thanks for the reply.

I just tried the SOC% today and it worked better than Waste Not that relies on voltage.  I have an on at 99% SOC and off at 97% SOC.  Even on a moderately sunny day like today it would kick the 1000w GT inverter on for about 45 minutes at a time.  I'm guessing that in the summer it will probably stay on the majority of the day.  It may take some tweaking of the % on off but it looks like it going to work out just the way I planned it.

As for the GT inverter being permited, the 5kw system is professionally installed and signed off by the utility company and local zoning dept.  The 1000w inverter is 110v backfeed style that needs to see 60kz utility grade power to operate.  There is also a manual disconnect on the outside of my house so if the utility needs to turn off the solar they can.

[tecnodave]

Gblass,


Just because you have a valid grid tie permit for your 5kW system does not make a plug in unit legal!

YOU ARE RISKING EVERYTHING DOING THIS!!!

If there is an incident you will be held liable!

Several years ago I was paid to completely remove a totally hacked solar system form a house something like you describe.  There was a professionally installed 3 kW system totally legal, but a newer owner hacked the system and added lots of Chinese grid tie inverters , an incident happened where the non legal grid tie inverters did not disconnect and provided the Sunny Boy legal system with the needed 60 Hz.   A nasty incident occurred, cause was traced and the utility company removed the electrical service to that property......house went into bankruptcy.....red tagged.....bank sold property as-is......utility company would not even remotely consider reconnecting electricity until all solar was removed!........two year battle to get house back on market and livable.

End result  I got $800 for 2 days work and 12 good panels, sunny boy grid tie inverter, and lots of junk panels and trash to haul away.....part of the deal was to get the electricity restored to NEC compliance and clear the red tags.


Just saying.......Chinese plug-in grid tie inverters are not legal in the states under any circumstances.

Dave

[CDN-VT]

I have seen the same up here & just note it in my mind .
Good point Dave
VT

[tecnodave]

VT,

I see stupid in electricity all the time, I was referred by a building inspector to help a self taught electrical expert........he had the whole house wired with 16 ga zip cord......one circuit feeding everything......wow....no concept of how to make it work......I gave up on him....he was too smart for me......the house was never finished....permit jerked!    Stupid beyond belief and knows he is right!
Ok what ever you say!

I guess that they had good deal on stupid pills....

Dave