Use surplus only for the boiler

DIY
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1

Hello,

I’m hoping to get some help with the following problem:

I have an off-grid system consisting of:

  • 2 × Trina Solar PV modules, 430 W each
  • Battery storage (DIY, made from 6 solar batteries)
  • Cerbo GX
  • Smart MPPT 100/50
  • SmartShunt 500 A
  • Smart BatteryProtect (not yet installed)

The system cuts off the PV modules fairly early because the batteries are fully charged.

How can I use the surplus to heat the hot-water cylinder?

Of course, I’m still missing a DC-to-220 V inverter for now.

But what else is missing? And is the Cerbo sufficient for this? What would I need to configure?

The hot-water cylinder specifications: 220 V, 1,600 watts

2

There is only one solution to find the value of the surplus: Vary a load and observe the Battery current. If it sinks, lower the load. If not so, increase the load. And so on.

3

How do you intend to get 1600W out of the two panels?

But if you connect both panels in series, giving you around 100V, the heating element should then be around 300W

Some heating elements don’t particularly like DC, though — in that case, use an inverter, followed by a transformer

4

@adw93

Add
1x MP2 3000
1x Shelly
1x Wi-Fi or LAN

Then you can use Victron’s “opportunity loads” to have the boiler switched automatically.

5

another way if there are absolut no shadows: Make a additional heater with many in serial wired diodes. The total forward voltage should be a litte lower than th MPP voltage of the warm Modules at MPP Current at maximum irradiation. In parallel to the PV input of a MPP it will only take the surplus. If the MPP needs power, it will slightly drop the PV voltage . So the diodes will more and more block the current.

6

In an off-grid system?

7

off-grid doesn’t mean no comms..

8

How is the system supposed to know how much PV power is available when off-grid?

There must be a reason why Victron is now selling the Mini PV measuring cell.

9

Yes, you’re right.

I’ve already thought about that too. The idea was to add another two PV modules and, if necessary, limit the boiler to, say, 800 watts with a power controller… but for now I’ve written down what I have, to see what else I need.

10

If there is a gx and pv it is still making forecasts based on the location. Accuracy may vary but it still does it.
VRM is also tracking your trends.

11

I’ve already thought about the MPII as well; it seems to be a real all-rounder.

  • With a meter in front of it, it can achieve zero export
  • Without a meter, it feeds the power back into the grid
  • And in off-grid systems, it at least replaces the inverter (and apparently it can also switch an output)
12

With Opportunity Loads, you configure the SOC at which controllable loads are switched on and the priority in which they are added. Shelly is supported for switching AC loads.

You can also configure switching hysteresis.

MP2, as according to the author there are not yet any „DC inverters“ available for 230 V AC.

It also provides the option of retrofitting AC PV or a generator. Of course, any inverter will work too. However, the MP2 gives you greater flexibility.