DC coupled Storage and Export

[Johnnyt]

I have a 10 kWp array and a 6kW inverter with 2 x 9.4 kWh dc coupled batteries.

A feature of this is when PV production is over the rated output of the inverter I can charge the batteries with excess using uninverted dc direct from the array.

My batteries will take a max charge rate of 7 kW.

I use octopus flux to export with the max export rate available between 4 and 7pm.

A feature I have found is to export at the full rate 6kW less the house load whilst using the surplus to charge the batteries.

i can get the best of both worlds export max export during sunny weather and full export at the peak time.

These screenshots should illustrate the options.

As soon as my battery if full I lose the facility and any excess is clipped.

The alternative is to dump power into my UVC but I can get 16p and kWh export upto 4pm and 26p from 4 to 7 and my gas costs me 6p a kWh.

so it makes sense to heat the water off gas

Much manual involvement but it seems to work well.

Is this a feature with othe systems or just particular to SolarEdge?

 

[sharpener]

Will have a similar issue as am planning to move to Octopus Cosy when the HP is installed. There is a school of thought which says that rather than prioritising battery charging from PV it is more cost-effective to export to the max at 15p on Octopus Outgoing and then charge the batts at 7.5p during the cheap periods if you have to.

 

Sounds like what you are doing.

 

The economics are also discussed by Michael Podesta here. The profit seems however to rely on the cost of increased use of the batteries being disregarded as it is already a sunk cost.

 

I have 3.68kW of panels on an AC inverter and 3.24 on a DC MPPT, but max export is constrained by the DNO to 3.68kW. So when it is sunny it makes sense to delay charging the 10kWh of batts until the 3.68kW limit is being reached, this means the marginal cost of charging is then zero as generation would otherwise have to be curtailed. Problem is that if it then clouds over the batteries never get fully charged from the PV. However it still works out cheaper, as above.

 

On 22/06/2024 at 13:14, Johnnyt said:

Much manual involvement but it seems to work well.

Is this a feature with othe systems or just particular to SolarEdge?

 

Victron Dynamic ESS is supposed to integrate all that with weather forecast and control all this automatically but still has various teething problems reported. Also it relies on integrating your usage over time so if you go away for a while does not work well. There is a ?Polish software package which is reputedly better and has a "holiday" mode, but more complicated to program, sorry can't find the link ATM.