Great question.

I am just about to get a battery and want to mount 2 panels (800Wp) on the wall. 2 panels will give an Voc of about 80V so won't fire up most normal hybrid inverters (some will but not ones I am looking at). So, how do we safely connect them to the house electrics?

 

These are intended to plug in, so do. Grid frequency is picked up on the power cable not the ct's. Imagine a ct wire failure, mains failure just turns the whole kit off.
Measuring is phase and frequency.

To much info here

How do grid tie inverters sense the mains phase and quality and at the same time feed current into it?

Grid-tie inverters synchronize the phase and also check the quality (frequency, magnitude) and shutdown in case of errors to prevent what's called islanding, i.e. to prevent feeding current to netw...

electronics.stackexchange.com

 

It gets the grid frequency from the mains voltage at the plug, not from a CT. As far as the normal DC and AC isolators are concerned, 30 V is unlikely to cause a huge arc, or electrocute somebody. Although it shuts down almost instantly, it boots up very slowly (when happy?).

 

Ok, so why do my other inverters need CTs?

 

Panels just arrived… and I think I may have made a minor measurement error. Two of these won’t fit, unless I block a window. I might be able to squeeze one in between the drainpipe and the window, perhaps. You can see how bright the sun is, shining directly at the wall, with no shading, so it is a good place to put panels. Maybe smaller ones though… I thought these were about the same size as a door.

 

Did you get Planning Permission for those? I think you need to, esp on the front of the house.

 

The CT is nothing to do with measuring frequency. As the name Current Transformer implies, they measure current. The AC voltage and frequency can be directly measured by the inverter, since this can be assumed to be the same everywhere within your house, so needs no external sensor. The inverter will use the CT to measure the power going through your meter. It does this by multiplying the instantaneous voltage and current then integrating the result across several complete AC cycles.

I'm not an electrician and can't advise on how to connect these whilst complying with regulations.

 

Presumably with no CT the plug-in panels will just blindly generate their maximum power the whole time, even if that results in an (unmetered?) export to the grid? I guess you may want some kind of separate control system to turn stuff like an immersion heater on to absorb some of the power instead of exporting it for free.

 

I already have batteries, I installed them last year. I had solar installed a decade ago, but it wasn’t until I got an EV and a smart tariff that I started making best use of the solar and cheap rate, with batteries, fully electrified home with no gas supply, and now more solar. I don’t have an export meter, and I won’t run these through the old FiT generation meter, so it won’t affect those payments.

 

For the EcoFlow and other balcony systems they just plug and play. No CT clamp or load monitoring required. Any excess just goes back to the grid for nothing.

now- on my system I have a Shelly 3em monitoring the house load - and this integrates with the EcoFlow sw and an EcoFlow battery so I save excess to the battery (until it’s full) and the battery can discharge along with the solar to match the house load. All up to a max of 800w - which is what the inverter is rated for.

for the power stream there are quite clear instructions as to which order to plug everything in. This is for the sake of the inverter not a safety issue iirc.

finally @Rbrian you have my sympathies with the panel size - I did the same - thought f*ck me they’re huge when they arrived! I just managed to shoehorn them into a spot.

 

now- on my system I have a Shelly 3em monitoring the house load - and this integrates with the EcoFlow sw and an EcoFlow battery so I save excess to the battery (until it’s full) and the battery can discharge along with the solar to match the house load. All up to a max of 800w - which is what the inverter is rated for.

Can you give some clues about how this works, please. I have the HA EcoFlow cloud integration going with it's 57! entities, but I think you must be onto something else.

 

CT'S are the way the various parts of the system know how the house is importing or exporting and enable charging of batteries and divertion of power for water heating as well as limiting import if needed.
The other use is making fancy graphs of usage

The balcony solar has no ct's for control so will just provide some power to the house.

 

If you already have an export tariff presumably any excess is still exported in the normal way and we get the payment for it?

 

Yes, the smart meter export register has no clue where the export is from, Solar roof or battery or balcony solar or your biomass generator....

 

Does anyone have a link to a good plug-in inverter that would work for a single panel? Ta.

 

As long as the panel is within spec.

https://www.amazon.co.uk/ECOFLOW-PowerStream-inverter-800W-Waterproof/dp/B0C49HY214?dib=eyJ2IjoiMSJ9.2j9bXw_H32x9xFay4Iy62YDnxRO0oaNQTmoMCl2mkMTdDFEJnUkCo5_5Uy7aAoGfuodvG-FfmnKznJ2r7i-NG-FC05t3bYGsh-wq0BgTiOxA_j-XPyWmeijh8kiljbFPmSaC3sQgxXscF9hj8FIMhiY9rs3i-5d-Pmy9yHP4WsDfcukHINUGEdgUvG69XNazQGAM-nWV_-JCRaWH6s23laRqb1GnQDEAHmJn9c6bLS8CoXMjaswon_raLCxe6eUOJegu-O6736FZlQL2oEdtuWhU-kcC99j3sNkn-5vHk9I.o5NsH8cBtWQ6STG9_coY3zvDjtFM_NPJVk2FCOhsxvk&dib_tag=se&keywords=powerstream&qid=1743670441&sr=8-1

Edit:
I have only one 440 W panel connected, the other connector is just left unwired. I expect to limit at 400 W at some stage due to reflected light from a wall, and light from below, but expect it to cope. I am up to 360 W peak at the moment from a horizontal panel.

 

As others have posted, frequency synchronisation is done from the supply voltage to the inverter. It happens very quickly as soon as the inverter is connected to AC. The reason for the Sofar requiring the AC to be powered up first is so that it doesn't start up initially in emergency power supply mode. In order to configure itself it needs to start up in grid connected mode.

Ok, so why do my other inverters need CTs?

They are there to monitor the grid import/export current. Some inverters don't need these, for example our main 6kW PV inverter doesn't have any CT connections.

 

As far as I can tell, installing a grid-tied micro-inverter plugged in to a standard socket is not legal in the UK.

Are people saying it is? I am not arguing, just trying to get to the bottom of what we can and cannot do.

Any posts to show one way or the other please?

 

It's not illegal, in as much as there isn't a specific law that states that you cannot do it, AFAIK.

Anything that connects to an outlet and that isn't a fixed bit of kit is classed as an appliance, so not a part of the electrical installation. This means that if, say, you had an electrician around to do an EICR then they would just ignore it in all probability.

As soon as you start delivering power to the grid from your home, though, then you become bound by the regulations that cover grid tie devices that can export, so the equipment has to comply with the provisions of either G98, or if it has a power of greater than 3.68kW, G99. In all probability these microinverters do comply with G98, so there's not an issue there. There is a very minor issue in that you're supposed to notify your DNO if you have a G98 export limited device.

In all probability, these micro PV systems rarely export to the grid, they mostly cover base load. I'd frankly not be overly bothered about them in that respect, given that any grid export is going to be pretty small.

The main safety issue is whether or not there is a possibility of the plug becoming live when the system is exposed to the sun and its not plugged in. The manufacturers have included a rapid shutdown to prevent this though, although I have to say it still makes me feel a wee bit uncomfortable, relying on a bit of code inside the thing to keep it safe.

 

If I only had one 500W panel any feed back to the grid will be small... probably < 200W most of the time. Would the DNO even know about such a small export? Would they care?

 

I doubt they'd ever notice or care, TBH. I have a rapid stop on one of my lathes, which essentially uses regenerative braking to make the machine stop quickly. When it does that it exports a few hundred watts for a second or two. This sort of braking system isn't unusual on larger machine tools.

 

One of these Ecoflow batteries charged from a couple of Solar panels might be a cheap way for me to get my shed off-grid.

I could easily run an extension lead and keep it as an entirely different supply for some of the higher load kit but if I can run the alexa thing, lighting and a dehumidifier off grid it would definitely be worth it.
The alternative would be to charge the battery overnight (keeping it grid tied) but I'm not clear if that's doable.
So if I had one of these microinverters in place which charged one of their batteries can the battery supply power via it's sockets while it's actually charging?
If @motmot has clarification on how the system hangs together and where things plug into it might be useful.
Am I right in thinking the microinverter doesn't have an output for sockets but assumes the only draw would be from the household wiring rather than from the sockets on the battery itself?

Clearly any additional solar to charging the battery might go towards appliances in the house as well as in the shed with surplus being exported.
Grid tied or off grid might not be easily mixed but my hope was to have the battery supplying most shed loads, charged by solar but also a charge from the mains overnight which is where I'm doubting if the battery can take a charge and be used at the same time.
Maybe I should get the coloured pens back out.

Gaz

 

One of these Ecoflow batteries charged from a couple of Solar panels might be a cheap way for me to get my shed off-grid.

You need to unpack and use the air fryer you bought ages ago, Gaz. No new toys until you've gone through the old ones.

 

@Peirpoint delta 2 power station (battery and built in inverter - and can take a 400w panel - is about £500 give or take (discounts come and go). I’d stick with a cable to the shed.

 

The money isn't an issue but I'm thinking about having the shed completely independant because it then gives me a useful space if the house was off for some reason.
TBH I've been looking at these battery things on wheels which can charge from an EV charger for several years now and the price has been in the range of several grand.
I'd have to have seperate sockets for things like the table saw, big angle grinder and my welding equipment (I imagine).

I'm guessing though that it might be better to just use the house power this year and see how it goes, need to keep the money earning interest while they still pay it.

There's a nice hammer I've seen so I'll stick to cheaper stuff while I can,

Gaz

 

Some panels absorb certain frequencies and some absorb others. If you could put a transparent panel that absorbs one range of frequencies in front of a panel that absorbs a different range of frequencies then it might just work.

 

I read about panels which work at night, those as a transparrent stick on sheet would be worthwhile even if they knocked daytime generation by a few percent.

Another 100 years and they'd be laughing at our quaint tech.

Gaz

 

Since I don't have solar at this house I was also thinking of sticking a big 400 odd watt panel up here on the south facing garage roof with a micro inverter for some baseload goodness as well a bit of fun. Looking at ITS there is a minimum order for most panels. The recent sale of my HP Microserver would cover the kit. Decisions decisions Cheers!

Edit. Baseload is in the very low 100 watts whilst WFH.

 

I've posted a screenshot of it before when you asked last time. I don't know the exact regs off the top of my head but I do remember there was a lot of discussion on Twitter about it and it was one of the reasons Ecoflow changed their wording. At one point they were heavily advertising it on Twitter and Facebook and then backtracked on the plug in element in the UK. I'll see if I can find the screengrab again.

 

The curious thing here is that the wiring regs (i.e BS7671) don't apply to anything other than the fixed electrical installation. Stuff that plugs in is the homeowners responsibility. Certainly ESQCR applies inasmuch as the requirement to notify the DNO applies, as it does with any sub-16A per phase connected generator.

One consequence of Ecoflow having changed their wording is that the wiring regs will then apply to a hard wired microinverter. Not very onerous, just means having a dedicated circuit with RCD and overcurrent protection, but because it is a new circuit it also means that Part P applies (in England and Wales).

 

Here we go:

 

Here we go:

View attachment 207910

Got you, this is that reg in full :

Note that this regulation in full makes it clear in the first sentence that it applies to a generator that is installed.

However, as mentioned previously, if a balcony solar system is not installed, i.e. it's not fixed, then the wiring regs do not apply as it would no more be a part of the electrical installation than a TV or any other plug-in appliance.

 

I guess the loophole exists as the wiring regs never intended anyone to plug in a genset to a socket in the first place? Most cables that I know if that would allow you to do something like that (be it home wiring or EVs etc) are generally not professionally made and known as widowmakers for a reason.

 

We would need to see the official definition of 'generating set' I guess but all definitions I've seen would include solar in that, as similarly mentioned many times in a G98/99 application. Seems to be an unintended loophole if you can call it 'not installed'. After all a standard generator could just be plonked on your drive, but I suspect they would call that fixed in this instance.

 

No, it's nothing at all to do with that. It's simply the boundary between what forms a part of the electrical installation and what does not.

To give an example. Say I'm asked to do an EICR. I inspect and test the installation, as required, to ensure it complies with the regs that were in force when that installation was installed. In the process I find a 13A plug with bare conductors hanging out.

What can I do?

The regulation-based answer is absolutely nothing, other than unplug it for my own safety It's not a part of the wiring installation and I can just ignore it. If all is well I can issue a certificate that states that the installation is safe and compliant with the regs.

In reality, of course, I'd point the problem out to the home owner and strongly suggest they get it fixed. You could argue that having exposed conductors in a place where they can be touched is a breach of the wiring regs, and it would be if it was on the fixed installation side of the outlet. Because it's on the consumer side it is not, though.

 

I suspect that EcoFlow started shipping the unit with a connector (to the unit) with bare wires so that it was no longer a ‘plug in’ unit - thus they’re trying to make the user not just plug it in. That I suspect is then dodging the liability. Though they do then also ship them with the three pin connecter too!!

personally I think this is flawed logic as this is sold to diy-ers and you’re more likely to get an issue from someone wiring it in badly (even from not putting a plug on it properly!) than if it’s just plugged into a socket. Lowest common denominator etc…

 

I agree, even though plugging it in goes against every instinct I have, it's undoubtedly safer than some dodgy DIY'er trying to wire a cable to a some cobbled together junction box.

 

Yes - I thought about wiring a spur off a ring (in the cellar - all nicely exposed to work on) and adding a bipole switch in a box to the cable to the inverter. Then figured it would probably be less risky just to stick the plug in the socket..

 

I saw a video on solar installation, normal hybrid inverter... not a micro-inverter, and they said that we need to switch the RCBO in the CU to a bi-directional RCBO... is that something that a solar installer would do? Is it something that we might want to do if installing a micro-inverter (plug-in or wired)?

 

They will fit a whole new circuit. An RCBO only protects one circuit, so they should fit the correct one. They probably won’t change an RCD, however, which on older installations is shared by several circuits. An RCBO combines an RCD and an MCB.