Plug in balcony solar UK , just a Lidl question

[denso13]

, if there is never any export, that issue will never arise.

Is that technically possible though?

 

[ericmark]

Is that technically possible though?

Yes, as the export is from that circuit to rest of house, not just export to the grid where there is a problem.

 

[JohnW2]

... if there is never any export, that issue will never arise. ...

Is that technically possible though?

It would be difficult, if not impossible, to ensure, 'technologically', that there would never be any export (not like DC, where one could simply put a diode in the incoming grid supply!). However, what I was suggesting is that, particularly in UK (climate-wise), these small bits of solar kit are probably unlikley to produce more electricity than is actually 'needed', such that there would be nothing 'left' to export.

However, perhaps what you are implying, there could not be a guarantee that export wouldn't happen sometimes (sunny days with low electrical loads) - but, as I said, 'they' might just possibly choose to 'overlook/ignore' that if they felt that the amount of export was likely to be 'negligible'. I suppose they could strengthen that approach by 'banning' the use of batteries with such systems, since that would presumably markedly reduce the chances of export (since lowest loads, hence greatest scope for export, will usually occur during the hours of darkness).

 

[denso13]

However, perhaps what you are implying, there could not be a guarantee that export wouldn't happen sometimes (sunny days with low electrical loads)

I'm wondering the opposite really, I think, the new product standard has yet yo be released. Could they be designed with a guarantee not to export.

British Gas, for one, seems to be implying this. I'll post a link in a bit, I'm on a train!

 

[JohnW2]

I'm wondering the opposite really, I think, the new product standard has yet yo be released. Could they be designed with a guarantee not to export.

Have I not already given my answer (right or wrong) to that - which, in my post you're just quoted, said ...

However, perhaps what you are implying, there could not be a guarantee that export wouldn't happen sometimes (sunny days with low electrical loads) ...

I previously wrote "difficult or impossible" but, on reflection, think that it's probably impossible. As I see it, in order to be able to power any of the local loads (within the property), the output voltage of the inverter would have to be slightly higher than the grid voltage - and if that is the case, then at least some electricity (even if only a tiny amount) is, I think, bound to be exported.

The only way I can see that any PV system could be 'guaranteed not to export' would be to not have it connected to the grid at all - i.e. just like a standalone generator with local loads plugged into it, and no connection to the property's electric installation or grid.

However, even if it were possible, I don't think it would satisfy the likes of eric, who (particularly if they have expensive batteries) seem to regard the ability to be paid for significant export (rather than just powering some local loads with 'free' electricity) as being one the main attractions of any PV setup.

British Gas, for one, seems to be implying this. I'll post a link in a bit, I'm on a train!

That will be interesting - since, as above, if you are correct it sounds as if they are talking about something which currently seems to me to be technologically impossible

Kind Regards, John

 

[mikehammer69]

Indeed. Until very recently, I had always assumed that 'traditional' RCDs (without markings) were all 'unidirectional', and that 'bidirectional' was a relatively new-fangled concept which had arisen as a result of electricity export.

However, having just found a number of bog-standrad RCDs (RCCBs) on my shelves which are 20+ (quite possibly 25+) years old, which appear to be about as 'bidirectional' as they could be, I'm definitely coming to wonder whether there ever have been (at least, 'this century') any that were actually 'unilateral'.


Yes. Even with the additional switched contacts for the test button circuitry (which seems to be what is done to make a device 'bidirectional') there will still be a potential problem with 'lengthy presses of the test button) if (due to being faulty) the device fails to trip when it should - and it would require a fair bit of additional complexity to address that possibility. As I've suggested, it may be felt that since such a device is 'already faulty', and hopefully will be replaced since it did not respond to the test button, that this is not a issue to worry about?

Yes, but as I've said, if the device does trip when it is meant to, that is not a problem - since having the electronics permanently powered (for years/decades) is precisely what the devices are used to experiencing in-service.

A possible problem arises if (due to being faulty) the device fails to trip after the electronics has detected a residual current which should result in a trip (since it is not impossible that the electronics uses more current in that situation) -- but, as I have said (unless, I suppose, the devices became much more complex) I find it hard to see how that possibility could be addressed (just as with the 'test button problem'), even in a device said to be 'bidirectional'. If the device does trip when it should, then any residual current will vanish, so that the electronics should return to their 'normal' state (in which being continuously powered is not a problem).

I said it before but my assumption was that new bidirectionals would be switching the line pole at both ends

That disconnects the internals and the test button

 

[JohnW2]

I said it before but my assumption was that new bidirectionals would be switching the line pole at both ends .... That disconnects the internals and the test button

It would, but I don't think that would be a very good (or necessary) way to achieve what is needed, since it would involve 'unnecessarily' having two sets of contacts in series in the main current path through the device (potentially carrying a high current).

The same could be achieved with a slight modification of the one I recently illustrated, without introducing that issue. That had a third pair of contacts which disconnected the test button circuitry when the device tripped - so, if one were concerned (as I've said, I think probably unnecessarily) about the electronics remaining powered after a trip, one could simply also power the electronics through that third pair of contacts.

However, as I've said, I'm not convinced that is really necessary since, once the device has tripped, there can no longer be any 'residual current', so the 'still powered' electronics are in no different a position from the situation they usually live with for years/decades.

There are, at least theoretically, potential issues if (due to being faulty) the device fails to trip when it should (due to pressing test button or a real residual current) - but that is true with both 'unidirectional' and 'bidirectional' devices (albeit for different reasons in the two cases) ... but it's difficult (at least for me) to see what one can do about that. However, if the device is 'already faulty' (as shown by failure to trip), and therefore hopefully will be replaced, maybe that is not regarded as a cause for concern?

 

[denso13]

Have I not already given my answer (right or wrong) to that - which, in my post you're just quoted, said ...

However, perhaps what you are implying, there could not be a guarantee that export wouldn't happen sometimes (sunny days with low electrical loads)

It was just a question, "could there be a guarantee", as in, could it be ensured that there would be no export (to the grid).

That will be interesting - since, as above, if you are correct it sounds as if they are talking about something which currently seems to me to be technologically impossible

Not explicit, but neither a simple yes either.

Plug In Solar Panels Explained: What UK Households Need to Know

Plug in solar panels could be on sale in the UK within months. Learn how they work, new safety rules, potential savings and what the Government’s changes mean for homes.

www.britishgas.co.uk

 

[ericmark]

Sorry, seem I have not explained very well.

Two different questions, one about export to grid, and the other reverse flow through the RCBO.

I'll start with RCBO first, this house has 14 RCBO's in the consumer unit, plug in solar would likely feed in through one RCBO and out through the other 13 RCBO's the feed in RCBO needs to be bidirectional as most of the daylight hours the current will be going in the reverse direction, even if not exporting to the grid.

As to export to the grid, my iboost+ and I am sure there are many other products, can detect export, but I want it to charge battery first, so I can set it to export 100 watt, 150 watt etc, before it starts to use the excess, with 6 kW a 100 watt is nothing but with only 800 watt, to switch in an immersion heater does seem a little pointless.

The same charging a battery, to charge a battery with 1 to 450 watts, seems an expensive option for very little gain, charging with 1 to 4.5 kW is very different.

The idea of off-peak is the same, got to use enough to be worthwhile, looking at round figures 8.5p off-peak for 5 hours and 32p for 19 hours with a constant load would be 27p average. So unless a reasonable amount moved off-peak to peak, it can cost more.

So the debate, is if worth having such small solar panels grid tied? Feeding a battery pack which can't feed into the grid likely yes, but with the ability to feed into the grid, not sure worth the effort.

As to Plug-in solar panels – what are they, and how could they help cut your energy bills? By British Gas Energy. This is the firm who told me repeatedly that the reason I could not be paid for export was I had filled in their forms in the wrong format. The real reason was I needed a second MPAN number for export, and on changing to Octopus I got this within 2 weeks and started to be paid for export, so I take what British Gas says with a pinch of salt.

 

[JohnW2]

It was just a question, "could there be a guarantee", as in, could it be ensured that there would be no export (to the grid).

Sure - and as I have pointed out, I had previously written (and you had quoted) ...

... there could not be a guarantee that export wouldn't happen sometimes ...

Is that not an answer (at least, my opinion of the answer) to your question?

Not explicit, but neither a simple yes either.
View attachment 415902

Plug In Solar Panels Explained: What UK Households Need to Know

Plug in solar panels could be on sale in the UK within months. Learn how they work, new safety rules, potential savings and what the Government’s changes mean for homes.

www.britishgas.co.uk

Thanks. I'll have a look when I have some moments and will then probably comment again. However, the little bit you've quoted seems to suggest that, at the least, they probably share my suspicion that export is not really a part of the thinking about these things - at least not initially?

 

[JohnW2]

I'll start with RCBO first, this house has 14 RCBO's in the consumer unit ...

Fair enough, but the situation is obviously a bit more complicated/'unpleasant' with RCCBs, since (if one just 'plugs in' the PV kit) the RCD through which current from the PV inverter is flowing will also be protecting several other circuits.

... plug in solar would likely feed in through one RCBO and out through the other 13 RCBO's the feed in RCBO needs to be bidirectional as most of the daylight hours the current will be going in the reverse direction, even if not exporting to the grid.

Sure, whether there are RCBOs or RCCBs, current from the PV will only flow through one device, the flow through all others be in the 'usual' direction (from supply towards load)

even if not exporting to the grid.

As I've been writing to denso, is that ("NO export to grid") actually possible? As I understand Mr Kirchoff, current from the PV inverter can only flow ('backwards') through the one RCD connecting it to the CU's busbar if the output voltage is slightly greater than the voltage at he busbar, which in turn will be the grid voltage (as seen in installation). If the output of the inverter is at slightly above grid voltage then it is surely inevitable that at least some (even if very little) current will always be 'exported', isn't it (again, per Messrs Kirchoff & Ohm)?

As to export to the grid, my iboost+ and I am sure there are many other products, can detect export, but I want it to charge battery first, so I can set it to export 100 watt, 150 watt etc, before it starts to use the excess, with 6 kW a 100 watt is nothing but with only 800 watt, to switch in an immersion heater does seem a little pointless.

This seems to be introducing a new goalpost (iboost+), which I don't know much about, and I doubt will be any relevance to users of whatever 'plug-in solar' we may end up with in UK. I can but presume that what you describe is achieved by some fairly clever electronics controlling he immersion (or, indeed,battery charging). I don't know much about what goes on, 'control-wise' within the inverter but I would assume that (again, per Messrs Kirchoff and Ohm), for a given inverter output, the only way of controlling how much gets exported is to (usually manually) switch local loads on and off?

 

[denso13]

Is that not an answer (at least, my opinion of the answer) to your question?

I've read it a few times.

However, perhaps what you are implying, there could not be a guarantee that export wouldn't happen sometimes (sunny days with low electrical loads) - but, as I said, 'they' might just possibly choose to 'overlook/ignore' that if they felt that the amount of export was likely to be 'negligible'.

I thought/think that you meant I was implying "there could not be a guarantee that export wouldn't happen", when I was just asking a question. I do understand your answer to the question though.

 

[ericmark]

Mr Kirchoff

Oh, that takes me back, there was another as well, but can't remember his name.

The way iboost+ monitors import/export could be used with solar inverters, so no need to open the CU, but these seem to be the norm which need mounting in a box, the IHD (in home display) keeps flicking between the two screens, however, solar and battery is very different to just solar.

With just solar, only thing which can happen to excess, is for it to be exported, there is no need to measure, as nothing you can do with it.

With solar and battery, measuring is essential, and the import/export line on the graph will be flat until battery either fully changed or discharged to the set limit.

But with these

there is no back feed, the solar and mains can both feed the socket on the front of the unit, it is grid tied, but no way it can back feed, and legal today. It is basic an UPS unit with added solar.

 

[JohnW2]

I've read it a few times. .... I thought/think that you meant I was implying "there could not be a guarantee that export wouldn't happen", when I was just asking a question. I do understand your answer to the question though.

I think you now understand what I have been writing, which is what matters - but I'm still a bit confused!

I never thought that you were 'implying' anything, since you appeared to be just asking whether there could be a guarantee that export would not happen - and I had previously expressed my view that there could not be such a guarantee (which seemed, at least to me, to be an answer to your question )

 

[JohnW2]

... The way iboost+ monitors import/export could be used with solar inverters, so no need to open the CU ....

Sure, it's obviously possible to measure the magnitude and 'direction' (import/export) of electricity moving between the grid and the installation- that's obviously how metering works!

With just solar, only thing which can happen to excess, is for it to be exported, there is no need to measure, as nothing you can do with it.

True, but you can control whether or not any significant amount gets exported by switching on/off the local loads. As I've said before, it looks to me as if one can't avoid exporting some (even if only a very small amount), unless one disconnects either the grid or solar, since if they are both connected, if the voltage from solar is high enough to preferentially feed loads, then it will presumably also be high enough to export at least a little?

With solar and battery, measuring is essential, and the import/export line on the graph will be flat until battery either fully changed or discharged to the set limit.

That's sort-of true - but, again, one may well be able to 'control' the situation (altering amount being exported) by switching on/off local loads as well, of course, by 'controlling' the battery charging.

... but with these <image> there is no back feed, the solar and mains can both feed the socket on the front of the unit, it is grid tied, but no way it can back feed, and legal today. It is basic an UPS unit with added solar.

I would need to look a bit to understand exactly what it is doing. Can the mains really (directly) 'feed the socket on the front' - or is it the case (as with a UPS) that the 'mains' (grid supply), when available, can (after conversion to DC) feed the inverter which, in turn, 'feeds the socket on the front'?
How is the 'grid tying' achieved?