V2H recommendations

One of those "balcony solar" boxes which disconnect if there is no mains power, to act as an UPS ?

Battery systems often have an 'emergency' power output, that is driven when the grid goes away. Strictly not to be connected to the upstream grid, but appliances can be connected there. There may be a changeover so the appliances are normally powered from the grid (not via the inverter) but it switches to the inverter if grid power drops out - you can buy suitable transfer switches for £20 on ebay.

I think some of the 'portable power station' boxes just run their sockets from the inverter all the time, which avoids having a changeover but is more designed that the power input is intermittent (eg solar panels or camping trips). In that case you have continuous losses in the inverter (and continuous heat next to the battery, which may reduce its lifetime).

Theo

They will shutdown the "to grid" output when islanded, but they you can use the 13A sockets to run stuff (fridge will survive long enough for you to notice, but then how long are powercuts nowadays?

How do you avoid back-feeding the grid in that situation? I'd suggest it would be more viable to have a change-over switch on the input to your CU so that you can isolate the grid, or to use a battery system that does that automagically (I assume, but don't know, that they exist). I have a change-over switch for generator (or V2L) input but would hope to find a battery that automagically switches if I go that route. OOI, since installing the switch there have been no power cuts of more than a few minutes, and since buying a snow blower there has been no snow ... so they have worked well :-)

Because such "balcony inverters" only send to the house/grid on a single output when they detect the grid is "up"

But they can power one or more sockets (e.g for a fridge or computer+router) when the grid is "down"

Aha! So they act like a UPS (and only power things directly connected to them), but solar-powered ... ?

The technology required to make them feed your house mains rings is quite complex.

And dangerous if you start backfeeding the grid from them when the grid is supposed to be dead.

Your UPS gets around this by detecting a dead grid and not feeding it, but the downside is you can't backfeed a live grid.

Converet8ng one or more rings to run off a battery when the whole grid is down is rather complex and expensive.

My sister in S Africa has such a setup, but its only cost effective because in general the grid is down around 20% of the time, as the government investment in it does not match the free electricity that the (township) community extracts with crocodile clips.

And her electricity demand is very low. Hot water is solar, there is no central heating and the cooker has to be a wood barbecue when the power is out And no washing of clothes until the power resumes. The fridge stays on as to the two computers and the TV screen.

That's what these so-called "balcony" inverters are aiming to simplify.

I've never seen any UPS that can send power back to its input.

I have a radial in my study that runs in dado trunking for all the IT kit which is wired to the UPS C19 outlet (the UPS has a C20 inlet, so in the event of a dead UPS I can bypass it with a C19/C20 extension cable)

That does not mean that it cannot be done , In practice you have to have a whole house UPS that actually disconcets its input under battery/solar, but can backfeed when mains is present

If I gave enough of a s*it I might do something similar. Power cuts of several hours duration are a regular occurrence...but in reality I don't especially care.

I generally go shopping ....

Not really. Spend 17 quid and one of these upstream of your CU:

Grid goes in top left, battery inverter goes in top right. You join bottom left and bottom right together and they feed the CU.

The motor (green terminals) is wired so that the left side contacts are closed if there is grid power. If grid power is removed, the motor turns over to the connect the right side contacts. If grid power returns, the motor breaks the right side contacts and then makes the left side contacts.

There are also 3 phase versions with each side having 4 contacts instead of

2. > And dangerous if you start backfeeding the grid from them when the grid

This is a rotary transfer switch, so the mechanical rotation means there is break before make - it is physically impossible to make both side contacts together. It may take some seconds to switch over though, so may not be ideal for appliances which don't like that short dropout.

Installing one of these is max an hour's work, just screw it to the wall and connect up the terminals. If the battery has its own overcurrent/RCD protection and isolation then you can install it on a ring downstream of the grid MCB/RCBO.

Now, whether you want to fit this particular piece of Chinesium or look for something with more safety certifications is up to you, but these are in operation in a lot of countries.

More awkward is if you don't want to changeover all the CU, but exclude certain things (eg cookers and water heating). Then it gets more invasive - perhaps need to split everything in two CUs and only one is on the changeover switch.

Theo