SmartRE Charging/Selling

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SmartRE Charging/Selling

Postby ejerrym on Fri Aug 07, 2009 8:09 am

Since all the solar power goes through the charge controllers to a common DC bus, how does the system continue to sell power in the grid tied mode once the batteries are fully charged? When my off-grid system batteries are charged my charge controllers shut off (essentially). I realize the grid would be seen as a load which would keep the MX-60's on, but how are the batteries protected from overcharging? How is the charge cycle stopped? What am I missing?
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My RE system: 24 x 175 W Shell Solar (SolarWorld) panels (4200 Watts total) divided into two arrays each configured as 6 parallel strings of two panels. Two MX-60's and two VFX3648 inverters charging a 48VDC Hup Solar-One battery bank. 15 kW diesel back-up generator.

Re: SmartRE Charging/Selling

Postby tallgirl on Fri Aug 07, 2009 8:12 am

The "SellRE" voltage regulates the amount of available charge current to the batteries. If you set SellRE too high, it's like they are being run in "Absorb" mode too much. If you set SellRE too low, it's like they are being undercharged all the time.
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Re: SmartRE Charging/Selling

Postby ejerrym on Wed Oct 07, 2009 8:03 am

Thank you for the clarification TallGirl...that makes sense. When operating in battery back-up mode (the grid is down) would 100% of the PV current be available for battery charging or would the charging function still be limited by the "SellRE" setting?
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Joined: Mon Dec 29, 2008 6:20 am
My RE system: 24 x 175 W Shell Solar (SolarWorld) panels (4200 Watts total) divided into two arrays each configured as 6 parallel strings of two panels. Two MX-60's and two VFX3648 inverters charging a 48VDC Hup Solar-One battery bank. 15 kW diesel back-up generator.

Re: SmartRE Charging/Selling

Postby SteveHiggins on Thu Oct 08, 2009 6:54 am

The answer to your question is "it depends"

This is a battery based Grid tie system, hopefully you purchase a battery based system on the advice if you lost power you would at least have backup when the grid was down. If that is the case, the problem with battery based Grid Tie is it's only as efficient as the battery bank will allow.

The problem with this is the larger the battery bank or the age of the battery bank can severally affect sell back efficiency. My guess depending on the size of the battery bank, you will see 75-90% of the Pv power being sold back into the grid.
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Re: SmartRE Charging/Selling

Postby verdigo on Tue Jun 16, 2015 12:01 pm

Looks like an ancient thread but what I do is check my mate for the difference in actual battery bank voltage and temperature compensated voltage. Then I set my sell RE voltage at temp compensated float voltage and my battery bank floats all week, and then I do a full absorb on the weekend. My charge controller is a Classic 150 and it tries to make it to absorb any time the sun is shinning but the inverter's sell RE set point holds the voltage at float.
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