We are installing the below off-grid system for a client and would like some advice on controlling a 3kW immersion heater as a dump for excess solar when the batteries are fully charged.
16.2kWp Solar
15kVA Quattro
30.4kWh BYD Battery Box Premium LVL Batteries
Smart Solar MPPT RS 450/200
2xLynx Distributor M10
26kVA Generator with electronic governor and alternator
We understand that the Cerbo GX has a relay that can be used to control an external contactor for the immersion heater, but as the site supply is 230V (created by the Quattro), we have concerns that the voltage spike created by the contactor when it switches off, may cause the Cerbo relay to be welded shut.
We have read that a snubber may be able to prevent this happening, but does anybody have experience of this and recommended unit?
I have searched around a little more and found that Shelly provide a contactor relay for direct integration with Victron which should simplify the process.
Their is a webinar about this on the 22/04 with Victron & Shelly I believe.
Any relay (as the shelly) will not work as it switches “hard” (on/off) but there is a Fronius Ohmpilot and a MY-PV which are proportional, the MY-PV is way more advanced than the Ohmpilot.
Check this link to a topic I made some time ago about an installation we test test things all the time since 2012.
Read it from top to bottom carefully, the advantage is basically that your frequency stays in place (50.05-50.20Hz instead of 51.00-53.00Hz), and to set your clocks every week or so.
That test install has 100KWh batteries, 4200Ah at 24V, yes lead acid, and has basically no “overkill” on panels, only 8KW, so there the gain is very low, as the topic explains.
But, if you “overkill” your solar inverters, yes, it pays off (but it takes many years), but still, a single vacuum CRK12 (about 2KW) panel from Wolf will outdo easily 5000-6000Wp VP panels for hot water, as there on that site 8 are mounted and catch in those round tubes, with reflector below, from sunrise to sun down, instead a VP, these have a 95+% efficiency and a VP not even 30% seen over a full sun day (as these are flat glass), that efficiency is the hot water temperature rise, not the panel efficiency, ok.
When it rains, VP production is zero, CRK12 is then producing easily 40-50 degrees of water, tested since 2012, and frequency controlled hot water since 2016.
In one of my homes we have 1 CRK panel with a 300 liter SS tank, always hot for 4 grown ups to shower, build in 2015, we save 500 liter of gasoil a year due to that panel, and the install was only 2200 euro, calculate, within 3 years back in the pocket before and now within 2 years (as such install is now still the same price) with the Trump actions…
The client is installing an oil based heating system to cover the majority of the heating and hot water requirement for the property (we are not undertaking any of this work), so the immersion heater in the cylinder is just to back this up and also act as an extra dump for excess solar generation when the battery storage reaches a set charge level, say 95% soc so the MPPT RS does not have to throttle down production.
The Wolf CRK12 look like good units and may suggest to the client to look to incorporate this into his heating/HW system to reduce the use oil as the savings you mention look good.
I have been discussing this with Shelly and we may be able to use some of their products to switch a larger contactor for the heater. I’ll let you know what the end result is.
Thank you for the reply and link to your article, very interesting.
I think we will have to use a smaller contactor, like the Shelly, to act as an intermediary between the Cerbo and a larger contactor supplying the immersion heater. As you note, we will programme the Cerbo relay using node red to switch the relay on and off depending on the battery soc.
This will not be the primary source of heating the hot water as there is an oil heating system being installed, but hopefully will reduce the oil usage a little and save the MPPT RS ramping down the solar production unnecessarily.