Expecting the solar panel dc will be in order of 100V or so :  48V battery. :   Dont think unusual ?

That sounds like a quite modest system then (my 2.14kWp PV array often chucks out over 400V on the d.c. side). If you can keep in the ELV range (50V a.c. or 120V ripple free d.c.) that certainly keep things simpler from a shock protection point of view. 48V means quite high currents though.

I guess you'd need a 3kW inverter as a minimum (maybe higher to cope with more than one appliance or larger starting currents) - that would mean 62.5A (assuming 100% efficiency, again optimistic). if that's going through your buried 10mm² (presuming you actually have the CCC for that installation method - which looks marginal at first sight) 10mm² has a voltage drop of around 4.4mV/A/m - so  62.5A over 30m means about 8.25V voltage drop - so probably makes sense to have the inverter along side the battery in the garage, and send 230V a.c. back to the house.

If the PV output to the battery is going through the underground cable you probably need to do a similar calculation (we don't have the numbers to do that yet). I guess it too will suggest the charger will have to be next to the battery - but the losses in the PV cables might still be significant.

OK Know you recommended something before  Can you point me to a supplier for your recommendation .

Suppliers are much of a muchness - so I'd suggest shopping around for a good deal (local availability and/or national delivery prices can often make more difference than the headline price) - so just as a random example - TLC Twinwall ducting (the usual convention is black for buried LV electric cables, other colours indicate other types of services - blue for water, yellow for gas, brown/teracotta for drains etc etc). You also need covers or tape to identify it - e.g. https://www.tlc-direct.co.uk/Products/FMPT103.html buried above it.

   - Andy.

so useful  again  Andy :

62 A   I guess thats estimate battery supply A for inverter  48V battery dc  to invert 240V ac   

solar array output??  :  Sizing of DC cables :( that will have to travel 30m roof to garage but only 15m underground . 

Advice if you can : 

 looked at my sth facing roof  cf other solar panels in the area: Easily get 10 or more panels on it  Sent to my supplier  My supplier has them in two strings with (cant remember now) less than 15aA  DC  max  Didnt give voltage .  What kind of current do we expect from domestic roof panel installations to MPPT chargers ?  Ball park ? 

Overall :  Reckon everyone had enough of this now  Anyway Can I keep in touch with you off this channel to bounced things off :?

Remain committed BUT  : If I dont get the trenches dug before this spring fear  the impetus lost.  So cables sizes first even if over do it."

"Already have grid source: Future uncertain : Let solar add measure of independence    

think Not  the only one

ciao  Ms O 

 looked at my sth facing roof  cf other solar panels in the area: Easily get 10 or more panels on it  Sent to my supplier  My supplier has them in two strings with (cant remember now) less than 15aA  DC  max  Didnt give voltage .  What kind of current do we expect from domestic roof panel installations to MPPT chargers ?  Ball park ? 

Depends on the power output of the panels. My (10+ year old ones) are IIRC 240W peak each, a quick google suggest some modern ones can be around 400W.

P=IV so if that can deliver 15A, for 5 panels in each string, for 240Wp panels that would be 1200Wp so 80V. For 400W panels, 2000Wp so 133V.  Maybe a bit more if the sun is bright and the panels new. That's all assuming the 15A is accurate...

   - Andy.

AJJewsbury said:

some modern ones can be around 400W.

Or more?

andy g kenyon : I will get the data from supplier :  panels proposed are 400w each x 10 in two strings in parallel 

Put that aside  I must still have clear idea to get the cables laid before anything :

Issue  

Earthing of solar panels mounting framework   2 B or not 2 B ?  Protections ?  lets assume pv gives dangerous voltage  See attached diagram  I cannot see any return path for current should eg the +ve somehow short to frame ?   The supply is floating ? Unless the charge controller should be earthed ?  No current flow then no trip disconnect ?  So why do it ?  What if any, protections should buyer add ?  Leave as double insulated ? ( squirrels  with sharp teeth clearly nesting in some solar arrays in my road!  Will insist on anti mounting )

grateful again advice :  Ms O 

PDF

Earthing of solar panels mounting framework   2 B or not 2 B ?  Protections ?

Forget "ADS" style earthing and automatic disconnection as a means of shock protection on the d.c. side of PV - it just doesn't work. PV panels produce whatever current they produce (according to what the sun/clouds are doing at that moment) - there's no significant increase in current just because there's a short-circuit (to earth or any other way). So neither fuses nor circuit breaker are any use for ADS. In theory (and what's often done on a.c. systems with limited fault currents) you could have a N-PE link at the source and use an RCD for disconnection, but RCDs don't work on d.c. so that's a non starter for PV as well. Separated is a bit dodgy as it demands complete separation from other systems - which the battery charger (or conventionally an inverter) is unlikely to achieve to a sufficient standard. So all you're left with is SELV/PELV if the voltage is definitely within ELV range (won't be for a 4kW system), or double/reinforced insulation. So normally double/reinforced it is. If needs be you can add extra mechanical protection (e.g. conduit). You may still want to earth the frames for other reasons though (unfortunately I don't have the latest advise to hand - others here might know).

panels proposed are 400w each x 10

I'm probably getting ahead here, but what capacity of battery are you planning for? My circa 2kWp system can produce anything up to 14kWh a day (mostly a lot less, but I have had 14kWh on a few occasions and only a bit less on a larger number of days and so on) - so I'd guess your maximum could be in the region of 28kWh in a day - maybe more as you're a fair bit further south. I'm guessing the thinking is that it would be a shame to waste the power just because the battery was full. Can you presume that the battery would be discharged at dawn, and or there would be some reliable load during the day? Or would you want a bit more capacity so you could store excess for another day?

Even if we work with wanting say 28kWh usable capacity, most batteries don't like going from fully charged to fully discharged - chemistries differ but I think LiIon generally want to say within the 20%-80% band for a decent lifetime - so you can only use say 60% of the nameplate capacity. Thus to get 28kWh you'd need about 47kWh nameplate. At 48V that's about 980 amp hours (Ah) worth (or nearly 4,000Ah at 12V) .... that's not going to be cheap (or small).

Of course there's room for compromise - work with a lower storage capacity that would take all the generation over say 90% of the year so you're only wasting power on the few sunniest days. All choices to think about during the design process...

That's another plus for the grid-connected approach - any excess you can do something useful with - i.e. export to the grid; and you can be paid for it - I think most smart export tariffs pay in the region of about 15p/kWh at the moment. That can add up over time and helps to soften the capital costs.

Grid connected battery system are typically a lot smaller (mostly to make them less unaffordable) - often sized something in the region of one day's consumption (say 5 or 10kWh) - and there's a lot more to-ing and fro-ing with the grid to make up the differences - exporting on sunny days and importing on dull ones. In effect use the grid as a big (and not too expensive) battery. It might not always be there, but that doesn't stop you taking advantage when it is.

    - Andy.

Put that aside  I must still have clear idea to get the cables laid before anything

and I think you still have the issue with the underground cables if you're running the d.c. PV side through them - the earthed armour approach doesn't work as there's no ADS, and the voltage will be too high for SELV/PELV.

   - Andy.

dear all I, In conclusion I am  taking away There is no virtue in earthing the mounting system of a  dc PV array ? Whether 200V or so or not Since there is no conventional fault protection to dc 

So dont bother . Best is run in protective conduit and fingers crossed . ( Though with all the caveats about burying seems most go to nail it around some fencing as better? 

I wanted this lot to be in my garage firstly out of latest concern LI batteries volatile fire issue ? Does anyone else think house insurance policies will become more adverse if you have one in teh house ?  It will surely happen soon some  ELV car will ignite the issue . 

Anyway so now pondering to build a some outdoor housing closer to the house for this lot . My supplier quoted my £4000 for a proprietary thing .! No way  Any ideas.  But that still leaves another ac cable going to the garage as was goin to do same thing there " Independant sockets /  lawn mower / charge my bicyle battery  etc.   Could think of a changeover switch for that Existing ac cable going to garage. 

A simple outhouse for the inverter batery would greatly reduce trenching  Simple small ( ugly changeover switch for garage might have to tolerate. 

ANDY can I please ask separately on how you sized your system . My supplier ( recipe) has simply sized for a standard off grid whole smaller house.  I dont all that.  In particular how do we estimate recharge times for li batteries 

I still want to go for this anyway . In five years time this system  " Grid /essential independence/ Select at point of use/  will be a regular choice !   Grid is wobbling / EDF nuclear power is cost trebling  Prices for electricity are going up and up. 

ciao MsO 

ANDY can I please ask separately on how you sized your system

It was just the largest we could fit on the available south facing roof space, given the power of the panels available at the time (2010), working around roof windows, a solar thermal panel and shadowing from a possible chimney re-build (which didn't happen in the end, but..)

   - Andy.

In conclusion I am  taking away There is no virtue in earthing the mounting system of a  dc PV array ?

That wasn't the impression I was trying to give. There are potentially reasons other than shock protection from the d.c. side for earthing (or more likely, bonding) PV metalwork. I think you need someone who's read the latest version of Code of Practice for Grid-connected Solar Photovoltaic Systems (I appreciate yours wouldn't be grid-connected as such, but the d.c. side would essentially be very similar). The answer may well still be the same, but it's better to be sure.

I do feel you might be making thinks unnecessarily difficult for yourself. While having what's in effect an off-grid system alongside your normal grid-fed installation is fine in principle, a lot of the details (e.g. remote battery and so running LV d.c. though long and/or underground cables) do create difficulties. By comparison, a grid-connected system would "design out" many of the problems, be a lot simpler to install and I think still have all the features you want (including being able to work when the grid has failed). As an added bonus you'd have your own power available throughout the installation (not just on the special circuit in the kitchen) and be able to take advantage of the grid (e.g. to export excess power, at a profit) when the grid is there. Power wise you could then run a single SWA cable out to the garage and use that both for the battery storage system and anything else electrical (lights, sockets etc., maybe even an EV point in the future). Grid connected battery storage systems (complete with islanding relays to keep your installation running when the grid fails) are commercially as packaged (and type approved) solutions. Maybe give it some thought?

   - Andy.

Andy could you please itemise your system 

1. total wattage PV array  ( assume just simple PV array ) 

2. KW size of inverter 

3. Battery voltage and Ahr capacity *assuming Lithium ?

4.In winter how long do you expect to recharge this battery system  

5. What appliances did you expect to run from your inverter size ?  

Thinking a 3KW inverter rating generally wooudl easily run a washing  machine with surges  and enough  to spare   ? estimate ? 

TO ALL   Earthing of solar panel framing Any other advance please . If none i'll do it any way just belt and braces but  I cant see why .

£75 for COP ??   Anyone else give a verdict on efficacy of earthing  simple dc solar panel metal mounting systems ?  Issue electric shock maybe 200v +  DC  ? Scenario  ?   ( Trying to imagine foreseeable s/c  )  Squirrel has eaten though +ve dc cable of solar array Now died but  attached conducting to metal frame ?  So anyone touching that frame is  surely NOT exposed to shock unless they also grab hold of any exposed negative side of the PV array .?  2 squirrels There is NO current path through the body unless person does that ?   This in  too difficult box to get this installation on the road  OK I will run an earth wire to the roof mounting system  for looks .

Ms O 

Andy could you please itemise your system 

1. total wattage PV array  ( assume just simple PV array ) 

2. KW size of inverter 

3. Battery voltage and Ahr capacity *assuming Lithium ?

4.In winter how long do you expect to recharge this battery system  

5. What appliances did you expect to run from your inverter size ?  

Thinking a 3KW inverter rating generally wooudl easily run a washing  machine with surges  and enough  to spare   ? estimate ? 

TO ALL   Earthing of solar panel framing Any other advance please . If none i'll do it any way just belt and braces but  I cant see why .

£75 for COP ??   Anyone else give a verdict on efficacy of earthing  simple dc solar panel metal mounting systems ?  Issue electric shock maybe 200v +  DC  ? Scenario  ?   ( Trying to imagine foreseeable s/c  )  Squirrel has eaten though +ve dc cable of solar array Now died but  attached conducting to metal frame ?  So anyone touching that frame is  surely NOT exposed to shock unless they also grab hold of any exposed negative side of the PV array .?  2 squirrels There is NO current path through the body unless person does that ?   This in  too difficult box to get this installation on the road  OK I will run an earth wire to the roof mounting system  for looks .

Ms O 

Hi Anne. The earthing and bonding requirements for the array frame depend on the following factors. You need to assess whether the frame is an extraneous-conductive part or an exposed-conductive part, according to the definitions in BS 7671. You also need to determine if a lightning protection system (LPS) is necessary, or if functional earthing is required for the proper operation of the system.

Also, it enables the effective functioning of the d.c. isolation fault detection system within the inverters; it reduces the hazard of electric shock due to leakage currents; and it harmonises the UK practice with the international standards.

Andy could you please itemise your system 

I've only got a simple grid-tied PV system (2.16kWp (9off 240W panels), with a 2000W inverter. No battery. It just supplies the house in general, any deficit automatically made up from the grid, any excess exported. (To some ways of thinking you could argue I use the grid as a battery.)

Overall it generates around 1800kWh per year - although that might average to around 5kWh/day, it's very variable with both season and daily weather. May/June this year were pretty sunny and I was getting around over 300kWh/month (i.e. around 10kWh/day on average) Dec/Jan was rubbish - barely 1kWh/day on average - many days with next to nothing at all - often several days in a run when it's foggy or the panels covered with snow.

If it help, here are a couple of screen shots from my (emon based) monitoring system (it's not the most accurate in the world, but does give an indication). Blue lines show local demand, yellow PV generation (so where there's yellow above blue, I'll be exporting to the grid, blue above yellow means I'm importing).

June-ish:

Dec-ish:

Anne Otis said:

Squirrel has eaten though +ve dc cable of solar array Now died but  attached conducting to metal frame ?  So anyone touching that frame is  surely NOT exposed to shock unless they also grab hold of any exposed negative side of the PV array .?  2 squirrels

Earthing of PV frames question is far more involved than can be communicated in a discussion forum, and has NOTHING to do with damage to DC cables. !

AMK said:

Also, it enables the effective functioning of the d.c. isolation fault detection system within the inverters; it reduces the hazard of electric shock due to leakage currents; and it harmonises the UK practice with the international standards.

i.e. EAWR which applies to most electricians (although not always "DIY") working on PV systems.

Regardless of DIY, the designer of an installation has to ensure safety during maintenance ...

Thankyou again:  Perhaps thats more practical : Achievable  my idea looks too difficult : Still like it has merit.  

Reflect : any chance to protect the planet  We must simply learn to live with less 

All my kitchen appliances would be plugged to off grid . ( bar fridge)  Consumer faces choice every time and a minor effort to do so. Do we really need to run that washing machine now ? Its in your face :  Off grid living I hear is something you get attuned to . Grid tie  ?  Convenience / forget./ Carry on as normal.   Maybe some chance to equal summer winter out :Size this off grid  it to run only two appliances at a time in winter. Abundance in summer Mow the lawn. whatever.

 Remain reluctant to have a lithium battery in the house: That  has forced outhouse and underground  complications. Costing beyond my abilities and suppliers it seems  Oh  Electric bus in wimbledon caught fire recently. First ev car on charge in front of house to catch fire ?  The genie is out the bottle   Sure many must now be considering battery fire risk and so to outhouse.  That area is the too difficult box.    .   So I thank all and especially yourself  for all the opinions and advice. Life is too short .

Now doubtful in both cerebral Hemispheres  Ms O 

Grid tie  ?  Convenience / forget./ Carry on as normal. 

If you can still have the "experience" if you like - e.g. use a smart meter display to see what you're using (both instantaneously and over say a day) and see if you can keep to some limit. Or if you like some financial incentive, switch to an Octopus Agile tariff and see how good you are at shifting your consumptions to times of excess generation and/or low demand.

Size this off grid  it to run only two appliances at a time in winter. Abundance in summer Mow the lawn. whatever.

Very few off-grid systems will rely on PV alone (not at these latitudes anyway) - the seasonal (not to mention daily) variation is huge. Traditionally domestic sized off-grid systems were backed up with a conventional generator, these days perhaps some other renewable that's better in winter - usually hydro or wind.

Electric bus in wimbledon caught fire recently.

Buses and cars are always catching fire - with petrol/diesel ones it's so common hit hardly makes the news (unless it takes out a large multi-storey car park). I suspect in the end EVs will be no worse than what went before in that respect. I take the point you wouldn't want to store 50 litres of petrol inside you house though.

One thought - some of the commercial (grid tied) battery storage products are designed to be mounted on an outside wall - if you've got a nice solid masonry wall without openings near by, that sort of approach might provide some reassurance. Not suggesting you buy one of their unit, but you can be inspired by the principle.

Keep pondering - it took Edison quite a few attempts before getting even a simple filament lamp right, but with determination you get there in the end.

   - Andy.

If you're worried about fires, then either:-

• Go old school and use deep cycle lead acid batteries.  They will be big and very heavy, but as they aren't in a vehicle, who cares.
• Go up-to-date and use Lithium Iron Phosphate batteries, that are far less flammable than Lithium Ion.

Go old school and use deep cycle lead acid batteries. 

Although lead-acid (even sealed ones) have a habit of liberating hydrogen under some conditions - so if indoors need good ventilation to the outside - so still not ideal for a habitable space.

    - Andy.