diy solar

diy solar

Help converting an existing grid tie system to battery TOU shaving

My system is AC coupled and it works as described.
Interesting. I was under the impression Grid Support only worked when the battery voltage was above the Grid Support threshold setting when operating in a DC coupled situation. I'll have to experiment with the settings and see what happens.
 
AC coupling is a great way to leverage your existing GT system. I installed mine behind the meter with just a building permit because I did not want to involve PG&E. Mine is connected to a separate critical loads panel and set for self sufficiency. I added additional solar but programmed the hybrid inverter to not export more than my PTO allows. That is possibly how @goldserve could do it if he finds a hybrid that allows external CTs. That way he would not have to have a separate critical loads panel.
 
BTW, When you say "works as described" I'm not sure which section of the rather poorly written Schneider operating guide you are referring to. I found some of the information not only confusing but conflicted in some cases. In any case, Thx for the tip.
 
(That is possibly how @goldserve could do it if he finds a hybrid that allows external CTs)
Thats what I'm doing with PG&E as well. Using CTs on a 200 amp service that does not export any power to grid.
also using batteries to not use any power during expensive TOU hours as well as all thru the darkness hours
The Sol-arc is great at this but they come at a price.
 
My Skybox has an option for external CTs and now that Outback has come out with the Mojave, Skyboxes may be available for bargain prices.
 
With Sunny Boy, you can AC couple to either Sunny Island or Sunny Boy Storage battery inverter.
Sunny Boy Storage supports TOU shaving etc. It also requires commercial high-voltage battery (expensive)
Sunny Island I don't think has particular shaving features, but could disconnect from grid and run off battery, connecting to grid if too low.

I don't think you can save vs. utility rates by adding batteries. Consider purchase price of battery, usable capacity, anticipated cycle life. Calculate cost per kWh. I believe that exceeds even peak rates for some commercial batteries. Some cheaper, possibly fly-by-night brands might pencil out. DIY battery will too.

I put PV cost at $0.025/kWh (over 20 years), batteries at $0.50/kWh (big name lithium & AGM), $0.25 (FLA), down to $0.05 for DIY.
I think adding excess PV is a better deal, so long as you have net metering and peak rates are only 3x to 4x off-peak.
Once credit is reduced to 25% of off-peak, it stops making sense. Only use-it-or-lose-it.

Batteries are OK where you don't mind paying $0.50 to $2.50/kWh for small loads like telecom.
I also use them for one night's backup, and to make an island grid alive when utility is down so PV can power my house.
 
BTW, When you say "works as described" I'm not sure which section of the rather poorly written Schneider operating guide you are referring to. I found some of the information not only confusing but conflicted in some cases. In any case, Thx for the tip.
I was referring to what I said in the previous post:
That's load shave, sure but you could also use "grid support" and program it to push current out to the grid. You could set this at 0.1 amps and it would take you down to 0 import. I've got mine set up to export 1 amp minimum for the entire "peak" TOU time.

Interesting. I was under the impression Grid Support only worked when the battery voltage was above the Grid Support threshold setting when operating in a DC coupled situation. I'll have to experiment with the settings and see what happens.
Battery voltage must be above "grid support voltage" that is correct.
Battery voltage must also be 0.5 volts above "recharge voltage."

Having AC coupled or DC coupled solar doesn't matter.

The issue with Schneider and AC coupling and Grid tie is that it won't look at grid current to adjust charging or initiate charging based on anything but battery voltage. It won't initiate charging at a set time, or grid current.
That's why I don't recommend it for AC coupled solar, unless you're willing to custom program something yourself. I'm using a raspberry pi and GXMnow is using a PLC.
It doesn't work off the shelf.
 
I discovered that same issue, the Schneider will only Peak Load Shave down to 0.5V above recharge voltage so it will not trigger a Bulk cycle. Funny thing is, some of the older literature from Schneider seems to indicate that in the past peak load shave would continue down to LBCO +2.0V.
The Modbus map is published so it looks like all that is necessary is to send a 1 to address 0x0165 the next day or whenever you want to start a charge cycle. I would be interested in how you are doing it since I'm a bit of an amateur with the RPi.
 
I think we're getting pretty far off topic for the OP.

I don't know what's at modbus address 0165 (I'm away from that computer), but yes, modbus control is simple and works. That's what both myself and GXMnow are doing.

Here's my build thread, the link it to about where I started working on the PI.

Here's GXMnow's thread, it's a long one:
 
Many thanks to the great discussion here. I didn't mean to say the Outback Skybox was outrageous in price but I think the Solark is bordering that.

After looking at my wiring a bit more, I think I can easily put a critical loads panel beside the main service panel and re-use the 10awg wiring to the current Sunnyboy inverter.

What I would do is replace the sunny boy with the Outback Skybox so the two strings of PV would connect to the MPPT controller, AC in would come from main panel and critical loads will be connected to the loads output. Some additional questions I have now:

1) What software to quickly draw out connection diagrams with assets for panels and hybrid inverters?
2) Do the two solar strings have to be identical in panel configuration, same voltage as I read the MPPT is just a single controller
3) When there is excess solar, will power be pushed back into the grid on AC IN if the demand on the Loads is met?
4) If I want to minimize but not eliminate grid export, do I still need the CT connection on the incoming house AC?
 
I was referring to what I said in the previous post:



Battery voltage must be above "grid support voltage" that is correct.
Battery voltage must also be 0.5 volts above "recharge voltage."

Having AC coupled or DC coupled solar doesn't matter.

The issue with Schneider and AC coupling and Grid tie is that it won't look at grid current to adjust charging or initiate charging based on anything but battery voltage. It won't initiate charging at a set time, or grid current.
That's why I don't recommend it for AC coupled solar, unless you're willing to custom program something yourself. I'm using a raspberry pi and GXMnow is using a PLC.
It doesn't work off the shelf.
I am a programmer and EE by trade, and was curious if you accomplished hacking the SI's over can to do peak shave. Since in lithium battery mode the data is all fed from 500kbps canbus using SMA-NET. ID's 0x355 are required for SOC/SOH but voltage can also be fudged to potentially allow for peak shaving use as you can override the data using raspberry pi or use a microcontroller w/ canbus support to send can data every 100ms to the SI's. Can ID 0x356 has battery voltage, battery current and battery temperature. These ID's are all defined from the pylontech battery bms which feeds the data to the SI's in LI mode. It would seem that these values could be fudged to present an overvoltage condition to trigger TOU grid feedback if you could determine how much overvoltage sent would trigger backfeed in terms of amps. My other idea was to buy a bunch of cheap microinverters - like older enphase - the business next door to me has buckets of them from older solar roof tearoffs. Wire them up to a 110-240v relay on each 110v leg and toggle them on/off with relay board on the ac side using a microcontroller or rasp pi. This would allow you to grid backfeed in 150-170w increments. It would take a bit of effort but totally would allow a legal way to backfeed the grid off of lithium, agm or lead acid banks @ 48v and would be UL certified too in terms of the grid interconnect.
 
I've got a Schneider inverter, not SMA. So I don't think I'll be much help to you.

With my Schneider, I can program grid shave or grid feedback pretty flexibly using the standard web interface. No need for CAN hacking the Pylontech messages.
 
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