batteries and .....

[shine]

Does anyone have any experience with Storz batteries? (battery and charge control - BMS together)?

Additionally, If one builds an off grid system with plenty of panels to generate the needed power do you have to have a battery to use the power directly via mppt and inverter? I do not care about operating after dark.

 

[gnubie]

You can get off grid units designed to work without a battery. Check the MPP Solar range for just one brand, there are others of course.

 

[Hedges]

SMA's newer Sunny Island are meant to be grid-tie, but have a "secure power" feature that produces 120 VAC up to 2000W if enough PV available.

My grid-backup system does have a relatively small battery, but operates major loads direct from PV. The battery provides a reference AC signal for the grid-tie inverters, plus starting surge.

What do you want to operate? I've been thinking that it should be possible to power a VFD with PV panels, and use a control loop to vary 3-phase motor speed according to available power (maintain target voltage). That would be better than just curtailing production to match a fixed load.

 

[shine]

SMA's newer Sunny Island are meant to be grid-tie, but have a "secure power" feature that produces 120 VAC up to 2000W if enough PV available.

My grid-backup system does have a relatively small battery, but operates major loads direct from PV. The battery provides a reference AC signal for the grid-tie inverters, plus starting surge.

What do you want to operate? I've been thinking that it should be possible to power a VFD with PV panels, and use a control loop to vary 3-phase motor speed according to available power (maintain target voltage). That would be better than just curtailing production to match a fixed load.

I am working on the design of two projects. I do not want to be tied to grid on either project. power company is independent CoOp and pays nearly nothing for power back and is a real hassel with permitting to tie in.
1- small cabin, currently using 552.8 kWh per month (most all of the power needs are during the day) Evening needs could be supplied by grid.
2- wood working and machine shop - daytime operation only.

 

[Hedges]

Unless you've got VFD on the motors, start-up surge is typically 5x label on the motor, can be more.
So if you've got a 2 HP motor rated for 20A, 120V, you might need > 10 kW of PV with sun overhead to start it.
Maybe enough capacitor on an inverter would do it?

If it's in your budget, a transformer-type battery inverter from SMA, Outback, Schneider should be able to run the motors.
Some systems may need a battery big enough to accept peak charging current from PV. Mine doesn't because PV is AC coupled not DC, small battery works.

Another way to go is zero-export wired like grid tie. It monitors grid connection and adjusts PV output so never feeds back to the grid. But grid seamlessly provides any power PV doesn't, including starting surge. EnPhase offers that, I'm not sure who else.

 

[shine]

Ok you gave me many thing to think about. Too late now. but I may have questions later. Thanks