I’m planning an extension of mv PV system and pondering whether to go with a MPPT RS450, or whether to go the cheaper AC coupled route.
So – are there any efficiency curves for the MPPT RS, like there are for the Multiplus?
My main concern is the winter, where my current AC coupled PV produces a few hundreds of watts and the conversion losses (via Multis to the battery) are big. The MPPT RS datasheet indicates a maximum efficiency of 96%, but what can I expect at about 380V and 0.5A or less on an overcast winter day?
For a bit of background: the current system is an ESS with 3 phase MP-II 3000, 10kWp of east-west solar on a north slope with no direct sunlight in the winter, AC coupled, and with maybe 5kWh per day in december.
I now will fit a second roof with PV, 18 panels or about 8kWp, and I’ll either get a string inverter, which would be cheaper, or a MPPT RS450/100, if that significantly increases the amount of energy that makes it to my battery.
I’m not concerned about summer; I’m aware the MPPT RS would limit PV output to about 5.6kW, and feeding in the DC-coupled PV via the Multis incurs additional losses, but at the current feed-in tariffs it will not make much financial difference, while not having to buy from the grid in winter will.
So – are there any efficiency curves for the MPPT RS, like there are for the Multiplus?
But just add this if it helps at all.
I am living off-grid in the UK with 25kWp of solar, over-paneled to combat those challenging winter months, presents a unique set of circumstances. For the past two to three years, my three RS450/100 MTTP’s have been managing the charge of my 90kW AGM batteries, and generally the system performs admirably.
While most days provide sufficient solar energy to fully recharge the batteries, there are inevitably a few overcast periods each year that test the system’s limits. The variable nature of UK winters, where cold, sunny days are a blessing and mild, wet days a curse, adds another layer of complexity to the equation.
It’s a constant balancing act, but that’s part of the off-grid life. Feel free to ask if you have any specific questions about my setup or experiences.
A cloudy(ish) winters day below, on just one of my three RS450/100
The RS range boost PV voltage to about 400V, the DC bus voltage.
And from there, it either generate AC-OUT (but that’s not your case) or transform it to battery voltage, through a High Frequency converter - which is very efficient.
So, in your case, with 380V PV, it almost transfer it directly to DC bus, with almost 0% loss and from there convert it to battery voltage.
So the loss of boosting from 380V to 400V is almost nonexistent and only the low voltage conversion will influence efficiency.
