An update on SMA. After chatting to battery installer experts, SMA's Sunny Island poses the same issues as other solutions. In our case, with the existing solar array, anything we do will need to be AC coupled and take control of the SolarEdge inverter for zero export and frequency shifting for power control. But we're continuing to look and think of solutions and workarounds. 

I know that since we're in a first world country with a very reliable electricity grid there isn't a direct need for solutions like this, but I'm surprised there aren't more out of the box options to accomplish this. I'm also humoured by the fact most battery solutions that can recharge from PV (when the grid's working) are actually called off-grid solutions. In practice, they are anything but when the grid is actually down. 

I can't help thinking your log burners and a very manual solution using a diesel generator (using HVO from your tank) and some extension leads would be a good and reliable emergency backup. Perhaps don't even bother running the oil heating and focus on what electrical appliances you want to absolutely keep running in an emergency for a finite number of hours or days. 

Completely separating the emergency solution from the normal operation may be an option. 

I haven't given it any thought in the past, but a combination of our log burner, very small  campervan, portable marine 12v fridge/freezer and diesel generator we could easily last a week. The 12v leisure batteries in our campervan are nearly always charged up. We have a portable battery jump-starter for the van that we would use to charge up phones etc. We wouldn't bother with the broadband router, just hotspot from my mobile. For now at least we could use the gas bbq. Far from elegant i admit.

If we were to get weekly intermittent short  complete outages i can image other systems involving batteries. But even then the risk of empty batteries when you really need it? For an emergency system using batteries i think the batteries are likely to be unusable for normal operation, else you can't guarantee electricity when the grid is down. 

Be really interesting to see what suppliers offer. 

Posted by: @editor

An update on SMA. After chatting to battery installer experts, SMA's Sunny Island poses the same issues as other solutions. In our case, with the existing solar array, anything we do will need to be AC coupled and take control of the SolarEdge inverter for zero export and frequency shifting for power control. But we're continuing to look and think of solutions and workarounds. 

I know that since we're in a first world country with a very reliable electricity grid there isn't a direct need for solutions like this, but I'm surprised there aren't more out of the box options to accomplish this. I'm also humoured by the fact most battery solutions that can recharge from PV (when the grid's working) are actually called off-grid solutions. In practice, they are anything but when the grid is actually down. 

Hi Mars,

I wonder if your battery installer experts are fully aware of all the SMA products. From reading the details of the Sunny Boy Storage system, the following is stated to be possible. 

Reliable power supply–even in the event of grid failure

Reliable electricity supply

• Integrated Secure Power Supply provides electricity to individual loads manually from the battery even in the event of a grid failure
• Optionally with an automatic transfer switch for full power supply to the home from the battery and PV system on all three line conductors in the event of a grid failure
• Power in the battery-backup operation of up to 8 kW is sufficient for all standard loads
• 5-year warranty

With the high protection class IP65, it can withstand even harsh ambient conditions and is therefore also ideally suited for outdoor installation.

You may wish to have a look at the following:-

https://www.sma.de/en/products/battery-inverters/sunny-boy-storage-37-50-60.html

@derek-m, a fair point. There's a lot of information I need to get through in the days ahead and I've been reliant on "expert" feedback to cut some initial corners. I will do some of my own reading and see if I can make any progress. I simply can't believe that some sort of solution doesn't exist. I have contacted SMA but they haven't replied to me yet. I will read the doc you uploaded now.

@derek-m, I'll ping this back to the installers and see what they say:

• Integrated Secure Power Supply provides electricity to individual loads manually from the battery even in the event of a grid failure
• Optionally with an automatic transfer switch for full power supply to the home from the battery and PV system on all three line conductors in the event of a grid failure

I'll give them the benefit of the doubt and say they may not know much about SMA. Seems everyone's interested in flogging Powerwalls, Givenergy and SolarEdge.

What I'd love is a battery system that we could switch to supply critical loads during a power cut. As we're not on mains water if we have no power then we have no water...

I wonder if the hassle of adding switching and cabling to critical devices would be more or less hassle than "just" enabling the whole house to switch to battery..?

Thankfully the 10 day power cut we had back in 1987 seems to be a thing of the past even with the most recent storms, unless that is you live a long way out in the sticks...

@ken the issue isn't a switch, the issue is that a battery/inverter has a peak output; for example my current setup is only 3.2kw (48v x 75amps). So you can have a circuit, but it cannot exceed that peak output or it just wont work.

https://midsummerwholesale.co.uk/buy/sofar-storage/sofar-eps-chint-nc1-2508 - a power chint for power cuts

It just means you need have a new consumer unit installed with "critical loads" - you'll also need batteries, which you keep full, as a backup for that circuit. No use having a system if the battery is empty!

Posted by: @ken

What I'd love is a battery system that we could switch to supply critical loads during a power cut. As we're not on mains water if we have no power then we have no water...

I wonder if the hassle of adding switching and cabling to critical devices would be more or less hassle than "just" enabling the whole house to switch to battery..?

Thankfully the 10 day power cut we had back in 1987 seems to be a thing of the past even with the most recent storms, unless that is you live a long way out in the sticks...

 

Hi Ken,

From what I have read recently, the German company SMA have a facility on their Sunny Boy Storage system, where by flicking a switch it will provide power to selected loads (of up to 16A at 240v) during a power cut. This will continue until it is switched off or the batteries are discharged.

@derek-m @editor

you might want to check out the battery specifications before getting too bogged down -

I note that the EPS has a maximum of 16A - as noted on page 3. Therefore even if you had big capacity, you are pretty limited on what it can actually run. Just worth noting!

I'm no sparky but I'd have thought 16A would be sufficient to cover the inrush current for a well pump, that 3500W isn't it? 

@ken the battery wont be 240v - it'll be 48-52v I expect. I didn't dive into the exact schematics, but I'd be surprised if it was a 240v battery

Posted by: @batalto

@ken the battery wont be 240v - it'll be 48-52v I expect. I didn't dive into the exact schematics, but I'd be surprised if it was a 240v battery

Hi Batalto,

The output is from the inverter and is 16A at 240v A.C.