Looking to enhance my existing solar setup by adding storage & continuous supply when grid power down

[stephenc1]

I'm so glad to have found this forum as I hope it will help me to further enhance my existing setup.

The pasted image below shows my setup which was installed nearly 10 years ago and because I'm in the UK, I benefit from ROC's payments which is where I not only get to use the free power I've generated, but also get a grant for it which last year meant I received over £800 for the 3,798 kWh generated as well as just over £200 for the 1,275 my system exported to the grid.

My equipment includes -

Solar panel model - Sunpower 327
Inverter model Samil 3680tl
Smart meter Landis + gyr E110
Eco-eye
Smart Immersion controller

There are 2 big improvements I'd really like to make -

1 Because my solar (understandably) won't provide power to the house when there is a power failure in the grid for safety reasons, I'm trying to figure out a way to change this so that if the power goes down as it sometimes does during storms etc, that I will have some power providing of course the sun is shining.

It was explained to me during installation this could not be done because of the risk of power being sent back to the grid during a failure which could potentially electrocute workmen working on the line, but I'm wondering now is it not possible to install some sort of switch or relay somewhere to prevent this?

2 I have a Smart Immersion controller which heats my immersion when the threshold of 1000 Watts is being generated, meaning that it simply heats the water rather than sending the power back to the grid, but I'm wondering if this controller might be able to charge a back up storage system and if so what type & where? For example, could it be some sort of battery pack in the hotpress beside the hot water immersion?

I'd really appreciate some help with this project - thanks in advance and apologies if I've posted to the wrong forum. If so, could I respectfully ask the moderator to move it please.

 

[DIYrich]

Replace the samil with a deye or luxpower inverter that can take a battery.

You could use a chargeverter to charge a battery (instead of heating water), but then you have the problem of converting the battery power to ac power.

 

[Luk88]

You could replace an inverter with one that has a battery and on-grid capability, but depending on availability it may just be a bit too expensive. Especially that the inverter will have to be sized to power your entire house's peak load (unless you can live without certain appliances at grid off situation).

Personally I find a solution that contains something like Victron MultiPlus II with a battery. AC coupled to ther existing on-grid inverter much more appealing. I only decided against it, because I'm going a full DIY route as it even cheaper then.

Victron Multiplus II is a "grid forming" device. You connect your existing on-grid inverter to its output alongside any loads you need powered during a grid outage. The grid connection goes to the input.

When the grid is on Victron is smart enough (with a sensor) to charge the battery with only excess solar. If the grid goes down Victron will switch to its generation in about 20ms and power its output from the battery. To the on-grid inverter this looks like a normal grid, so it generates power to the loads and for battery charging.

If the battery is full and there are no big loads Victron will raise the AC frequency ever so slightly to signal to the on-grid inverter to hold on and not feed in as much. It is the same mechanism the utility grid uses to tell your inverter "stop pushing power, we have too much".

I find this a very elegant solution. If Victron Multiplus II was cheaper I'd definitely choose it. I really like that you can also connect them together if you want for more power, or program 3 to run in a 3 phase setup.

The only disadvantage of this setup is in an event of extended power outage with no sun if your battery gets drained a "deadlock" occurs. If the sun starts shining the battery is still dead, Victron doesn't produce energy which keeps the on-grid inverter off and the whole thing just stays off.

People have various solutions. A small DC charger alongside the on-grid inverter, just to "boot" the battery back up. Also a petrol/gas AC generator can be used to start the system or to top it up if necessary.