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Renewable Energy Questions/Discussion => Automation, Controls, Inverters, MPPT, etc => Topic started by: frackers on February 24, 2017, 05:40:45 am

Title: Regulating battery charge rate on AC coupled system
Post by: frackers on February 24, 2017, 05:40:45 am

Like many I'm moving towards using the benefits of a grid tie inverter with its MPPT and a low frequency inverter to interface my solar panels to my batteries.

Also like many I want to make sure I don't cook the batteries!!

So far I have 2 x 5kw inverters, each has 2 x 2.5kw trackers in it and my first thought was to switch the DC feed into the inverter to give me 4 charging levels (the value of which depends on the amount of sun at the time). The obvious problem is breaking the 350V DC that is running at up to 8 amps without getting a fireworks display.

My present thought is switching large incandecent lamps in series with the panels to current limit them to regulate the amount coming out of the grid tie, into the LF inverter and hence to the batteries. Something like the 375w heat lights (I'm in a 240v mains country by the way!) but I'm unsure of the panel/inverter characteristics and whether I'll end up with more than the rated voltage across the bulb.

The switching will be less onerous but I've no idea how the whole system will behave.

Ideas?

Title: Re: Regulating battery charge rate on AC coupled system
Post by: oztules on February 24, 2017, 03:35:35 pm

Mosfet switching...... 8 amps is small beans for a lot of fets nowdays.... even at 500volts or more..... .3r typically available.......... parallel for lower rdson.

Or you could just switch the ac off, which will give you 2 stages with just a relay. ( my favourite )... or get hold of 4 inverters, and use relays again. s/h grid ties are becoming very cheap


........oztules

Title: Re: Regulating battery charge rate on AC coupled system
Post by: eraser3000 on February 25, 2017, 08:20:37 am

Buy an SMA GTI and then just send a modbus register everytime you want to adjust watts out.
Tell it 2000 it wont put out more than 2000, etc...

Eraser

Title: Re: Regulating battery charge rate on AC coupled system
Post by: frackers on February 25, 2017, 01:28:04 pm

Buy?

Title: Re: Regulating battery charge rate on AC coupled system
Post by: lighthunter on February 25, 2017, 03:18:43 pm

 ;D  I love your sense of humor!

  You can always add (or subtract) a productive load, I hate to waste a moving electron. :)

Title: Re: Regulating battery charge rate on AC coupled system
Post by: frackers on February 26, 2017, 01:27:27 am

That's so true - I plan to have the generation side talk to my irrigation system as that is the greatest gobbler of power (2MWh a year just for direct flow from the well pump - what goes via the holding tank probably accounts for another MWh).

Title: Re: Regulating battery charge rate on AC coupled system
Post by: Pete on February 26, 2017, 02:40:54 am

Gee Frackers that is a serious irrigation system you have going, 8 kwh a day is pretty chunky. Are you a fish farmer or something?