Alternative solar supply available at point of use Domestic kitchen

hello  welcome to the show  Chris  Most useful to address specifics  PV generation can be fully utilised ? Sound a little corporate speak  ?

Lets give it a go  Questions 

Sun and moon: If moon  there is no PV ? Mostly you have nothing in  peak hours.?  Just grid  ? Unless you have storage battery ? 

Ok so you have to charge it ?  Is that PV by day ?  Or is it also grid charge in case :Is that Off peak electricity for that ? Can we believe that ? 

And how exactly do you size that battery capacity ? 

Grid tie So now you must have import export meter ? AND G9 xx anti islanding in case of power cut ?

Your installation  costs and kit are rising ? 

Excess solar energy If you have it would surely just waft around your home system hopefully being absorbed by some standby thing you have left on during the day ? 

Its chance? 

EV charging is irrelevant ? Just another  load on system .  Anyway I am in the city no point of having a car at all 

And now we must face how we see the future cost of electricity You cant really think its going to come down ? . Possible power poverty ? 

Submit with my scheme the consumer has control  System  KWhr  size can be much smaller Can always expand if wanted

If theres a power cut this system is still on line  No anti islanding required .

Makes full and clear use of PV availability  No hidden  small print. Summer and Winter.  Scale for winter summer is abundance   

Measure of real independence  ?  Its simple  :  sense ? 

All comments welcome as ever . Useful to be specific in criticism  

ciao 

Ms O 

Sparkingchip said:

Research how grid tied systems work and how manufacture's have designed equipment to ensure that PV generation can be fully utilised, as a grid tied system will be far more practical and efficient.

Agreed!

 Anne Otis 

Research how grid tied systems work and how manufacture's have designed equipment to ensure that PV generation can be fully utilised, as a grid tied system will be far more practical and efficient.

Take for example the settings on this electric vehicle charger when it is controlled by a bidirectional current clamp on the meter tails.

1. Fast - Charger will work at full capacity
2. ECO - 6A will be provided from the grid and any excess solar power will be sent to the charger
3. ECO+ - Charger will only use excess solar (requires 6A excess to start the charge)

Option 1 will ensure that the vehicle is fully charged at a specific time, utter regardless of the time of day or the weather, it will use all the available PV generation and only draw what is required from the grid over the level of the available PV supply, so nothing may be drawn from the grid on a sunny day when there is little other usage around your home, depending on how the charging is regulated.

Option 2 will ensure the car does fully charge, but you cannot predict when it will be fully charged, because the total charge time is dependent upon the PV generation. 6 amps is the minimum charge rate for an EV, they will not charge below that, it will take whatever is available from the PV, so if 6 amps is available from the PV that is where it will get it from it will not take it from the grid, but will then ramp the charge up to make use of any additional PV generation, which might only be a couple of amps or may be more.

Option 3 will never take anything from the grid, but there is no guarantee the EV will charge at all on some days particularly if you are using other loads, there is inclement weather or it is dark.

The design of the EVSE is practical and allows for the best use of electricity from PV without separating the system into grid and off-grid.

support.projectev.co.uk/.../4411132985747-How-to-use-Solar-mode-on-your-Project-EV-Car-Charger

 Andy have you ever done this ?

Not exactly - I've had some involvement with UPS systems (for IT server rooms) though, so some of the principles are familiar.

guess it is expensive to test an earth rod  Would this be required as part of final sign off ? 

If you've got a grid supply, with a bit of care, a rod can be tested using an ordinary loop tester (something every domestic electrician should have). There is a bit of debate about a suitable value - the traditional (BS 7430) advise was a (somewhat arbitrary) 20Ω - which can sometimes be difficult to achieve, but some more modern text books are more flexible and you might get away with something closer to 200Ω for simple setups like this. I think the electrical energy storage systems code of practice covers this.

Does solar panel mount  system also require earth . ? 

That's probably a "it depends" answer.  A few years ago the answer was "almost certainly not " - as the d.c. was either extra-low-voltage (<50V)  (so no earthing required for shock protection) or if higher voltage was protected by double/reinforced insulation (so again no earthing required) - I gather than the thinking has moved on a bit now (with all sorts of other considerations coming into play, from lightning to EMI to modern transformerless grid-tied inverters that don't necessarily provide separation from a.c. side) so sometimes the answer might now be different. I think it's covered in the PV code of practice, but I don't have the latest version to hand.

Was figuring on laying both dc and ac cables underground as 10mm for all. 30 + meter distance  Trying to be sure /only want to trench once

There's a simple method to make sure you dig once - install a duct (I like "twinwall").  A size or two larger than you think you need. You can then draw in additional or replacement cables at a later date.

d.c. underground (as I hinted earlier) might be a bit of a issue. Not because it's d.c. but because it's usually part of an unearthed system. Normally underground cables need an earthed armour or similar -  the idea being that if they're hit by digging tools and damaged though to a conductor (which is surprisingly easy to do - as I once demonstrated with a steel wire armoured cable and a simple garden fork) - it'll short to earth and trigger off normal 'automatic disconnection of supply' to make it safe. If the system is unearthed that doesn't happen ... which might be a problem. (We have similar problems with d.c. PV cables concealed in walls - and the usual fix of using a 30mA RCD doesn't work either).  In theory an insulating duct with mechanical protection can be used instead of earthed armour, but the same level of safety needs to be achieved - which is difficult to demonstrate given it might have to resist anything from a garden fork to a mole plough to a JCB. There are possibilities, depending on the details (like the actual voltages and methods of shock protection in use) but the details will need working out. Some will require separation from "mains voltage" a.c. cables (So maybe two ducts, at least 6" apart?).

The "all a.c." grid-tied approach (PV just has a local inverter, battery system has its own charger & inverter locally to itself) does make life a lot easier in these sorts of situations.

PS " Point of USE select  system :  Figure only  have to size Kwhr system for max load( not add up total)  Probably washing/mc  + a bit 

Don't forget the earlier points about starting currents - the grid supply is naturally very tolerant of little surges in demand (since everything is backed up by the almost limitless national grid) so such considerations are very often overlooked - little inverters without a mains backup have no such margin - and many will sulk or shutdown completely with relatively small overloads, however temporary.

   - Andy.

Andy  ! OH  Bingo ?  Attach my updated visual in line with andys suggestion .  Andy have you ever done this ? Is this a common dual supply solution ?  All comments welcome please : 

Two  points

guess it is expensive to test an earth rod  Would this be required as part of final sign off ? 

Does solar panel mount  system also require earth . ? 

Was figuring on laying both dc and ac cables underground as 10mm for all. 30 + meter distance  Trying to be sure /only want to trench once 

thanks again.   Ms O 

PS " Point of USE select  system :  Figure only  have to size Kwhr system for max load( not add up total)  Probably washing/mc  + a bit 

Ms O PDF

thankyou chris     Hoped my diagram explained :One appliance has only one plug ?  So you only have one opportunity to plug it in Grid or Inverter socket  Cant do both  But Both can be live .  Sun or moon   but I do envisage battery storage  solar charged for inverter  Benefit  Direct point of Use : I only have to size the  KWhr system for the max load  Not add up all as with changeover switching    Smaller battery/ inverter . Still fingers crossed for earth system solution  ciao  Ms O 

OK, here's my attempt at a diagram (it's not intended as a full design or even a recommendation, just what I think you're suggesting - so as to keep the discussion on track).

Andy:  Dear All  Frustration from some I can see Forgive : " Why reinvent the wheel ? " >>   How and why this solution See end of this post.  BUT remain very grateful for all comment adverse or despairing hope they keep coming 

If nothing else and this thread becomes a general discussion of earthing / earth rods ./  car charging earth rods / 100 various earth rods now nearly touching  in the street? : I would much appreciate such an educational opportunity  Where actually does the current flow This proposal perhaps a ready  focus .  Gosh : in living memory when boys were told to go out and pee on the old GPO earth rod so the phone would work .

Andy thankyou so much for this reply   Yes  A diagram would simplify the outlook. for comment : Look forward to that.I attach my own visual so we can all visualise the approach so far  . Can send in ppt if useful. I know there are many kinds of inverter  I have not bought anything yet.  Still need to cost it..

Why this approach : Wanted to go solar and some verision  off grid/ battery  looked more appealing if not cost effective and simple.

Accidentally saw a USA video Generator back up: Changeover style This kit seemed to have individual switches for  each existing circuit to switch it from  grid to generator.  Looked great   Ah now in UK doesnt exist:  we have large power changeover switches. So switching a range of chosen circuits :Grid or Generator   All or Nothing : Like it or not

So here I have pondered a solution so its not all or nothing > It is User selection  AT POINT OF USE> Off grid is always a matter of opportunity and weather forecast. ?   So here we can choose target appliance to match power available .  Winter or summer Coould choose a smaller battery / inverter if I select what to run . And its so simple 

In my home kitchen is by far the largest electricity user  Suspect most. So it make sense to concentrate the opportunity there . And time is right My old kitchen ripe for revamp.     Do hope we can find a way. Let you know how it all goes if we do  Ms O 

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Chris Pearson said:

Why do you want to "break new territory" when there is a well trodden path?

Cost, potentially.

Also possibly the fact that some products on the market currently have some in-built functionality that doesn't easily, or  fully, align with Chapter 82 of BS 7671 ?

I really do think that you are making things very difficult for yourself. OK, I stand in the kitchen and look at a double (white) socket with toaster and kettle. You want a red socket (they must be distinguished somehow) next to it. The sun is shining and now what? Do I have to unplug both appliances and switch them over (even though it is mid-day and I am not going to toast bread) or can I leave one in each?

Why do you want to "break new territory" when there is a well trodden path?