I am in the concept design stage of a nominal 12kW off grid solar installation and I am posting this to hopefully get some answers from independent reviewers. I am not confident that advice from installers is independent, accurate, and up-to-date.
I have experience with Victron solar equipment on a sailing vessel and am very happy with it for many years. Now for the house…
I have North facing (southern hemisphere) roof area that can support 18 x 670W panels, I.e. about 12 kW @ STC. I researched Enphase microinverters for off grid installations and even with the IQ8 the Enphase commitment to off grid was not loud and clear. My panels should not suffer from shading so I returned to a DC coupled concept. Is this in any case more efficient than DC - AC- DC- to batteries followed by another conversion to AC?
My attached schematic below shows all components but is this optimal? I am particularly interested in comments on:
the concept in general.
recommended MPPT controllers.
Configuring the MPPT’s to generate max output at all times. The batteries will be in self-management mode.
How to manage the surplus power seamlessly when the batteries are full. Is there a way to regulate power to (for example) one or more SCR power controllers whereby the MPPT’s are at max output and the batteries are not contributing to the non-critical loads. Simply switching loads on/off digitally is not the elegant solution I am looking for. PID control with 4…20 mA control signals?
I look forward to all feedback.
Thanks
Hi Marc,
Thanks for the advice. I have one Multiplus but need three for the future 3 phase. I saw a tech brief somewhere which advised that a 3 phase synched Multiplus config requires 3 matching units, same manufacturing year, and clearly the same firmware. I am not sure I can add 2 new ones to this existing one.
Your advice regarding incompatibility was unexpected. I assumed I could connect it to a Lynx distributor and power a separate load circuit. Any workarounds?
The existing Multiplus II was purchased April 2024. The installation of new equipment won’t take place until Q2 or Q3 2025. Purchasing 2 new units now may ensure compatibility, but rules out possible product upgrades and price improvements. There has been a significant drop in prices over the last year or two. A small dilemma.
I think the MPPT 250 is not compatible with the 6 modules in series, because 6x Voc is 276V.
With lower tempeatures the voltage is increasing (at -10°C to 303 V). The MPPT calc recommends the RS450. But the MPPT/100 is a bottleneck with only 100A output current.
How high is your AC-load?
If there is a high Standby you could tie one or two arrays to a AC-inverter to use the power direkt from the PV-array.
I have the north side (Germany, northern hemisphere) DC-coupled to charge the battery in the morning. When tomes gows by and the sun moves to south the AC-coupled PV can handle the AC-loads directly and export the exess power to the grid.
