Batteries and inverters going off grid with solar.

[DenzilPenberthy]

Have a good look through the website of 'Wind and Sun'. They've done tonnes of off-grid installations from houses up to large islands etc. They also are importers and distributors for loads of the good quality manufacturers of panes/inverters/batteries etc.

I recently did a fully off grid set up for some friends using all stuff from Wind and Sun. REC panels, Trojan flooded batteries and Victron inverter, battery charger and battery monitor. Extremely happy with all of it.

For a domestic set-up Victron do all-in-one units which combine MPPT charge controller, Inverter and batteries in one unit. Plus mains and generator AC inputs and switching. Just add panels and a G59 relay to changeover to the grid supply and you're all set to go.

http://www.windandsun.co.uk/products/Inverters/Victron-Inverters/Victron-InverterChargers#.VdMJ1PlVhHw

[DenzilPenberthy]

I should add to that - If you are doing a homebrew system then don't overlook the fact that there are some quite specific requirements for changeover switching between private and public supply and how to manage the earthing of the two systems - see BS7671 for details on that.

Also if you are using several smaller inverters feeding separate circuits then it will be a ball-ache to organise appropriate switching to interlock them from each other and the public supply. Also if they are not able to be synchronised together then bear in mind that you could have circuits which are 180deg out of phase with each other which would leave you with perhaps 480v RMS phase-phase inside a single-phase domestic wiring system which isn't designed to cope with that. (679v peak!)

Aaaaand... it is likely that small cheap inverters will not have sufficient power capacity to supply sufficient fault current to blow fuses or operate circuit breakers within the required times in BS7671

aaand.. probably more cans of worms I haven't thought of yet

[TheElectricChicken]

Also if they are not able to be synchronised together then bear in mind that you could have circuits which are 180deg out of phase with each other which would leave you with perhaps 480v RMS phase-phase inside a single-phase domestic wiring system which isn't designed to cope with that. (679v peak!)

this is nonsense if all wires are connected to the mains.

[DenzilPenberthy]

Also if they are not able to be synchronised together then bear in mind that you could have circuits which are 180deg out of phase with each other which would leave you with perhaps 480v RMS phase-phase inside a single-phase domestic wiring system which isn't designed to cope with that. (679v peak!)

this is nonsense if all wires are connected to the mains.

Did you miss this bit? 

Also if you are using several smaller inverters feeding separate circuits then ... ...

[Aodhan145]

Have a look at the lith-ion storage packs that elon musk [based on the ones he has in Tesla's] is intending to sell for home energy storage

Those Powerwall's are quite impressive. 10kwh for $3,500 if I remember correctly.

For £1200 I can get the same power in lead acid allowing for 50% only discharge....

Doesn't the powerwall do all the solar charging and include an inverter?

Not at that $3500 price -- that's just the battery alone.  http://www.autoblog.com/2015/05/21/what-do-you-really-get-for-7000-tesla-powerwall-home-battery/

Lithium has a tremendous weight advantage, so I understand why it's ideal for use in electric vehicles.  But weight isn't nearly so important for stationary in-home applications.  Lead acid isn't sexy, but it's boring, dependable, and cheap.  And it has an established infrastructure for recycling.  It seems well suited to the job.

Gotta admit, the packaging of the powerwall is pretty, sleek, and curvy, though.

We were talking about just the batteries. Look at the number charging cycles lithium iron phosphate has compared to Lead Acid. Lead Acid are shit. If you want to stick with Lead, Lead Crystal looks better. LFP batteries have massive life cycles.

[Simon]

is the victron inverter grid tied ? quite expensive though but guess it's well build. I was aiming to build my capacity gradually. 1 set of batteries, inverters for just lights and add some panels (My current capacity is just 40W/hour so need to get some decent size panels)

[Seekonk]

Read very few of the posts, but most are into big dumb power.  Any time you use batteries, the cost per KWH used is about 12 cents. With that you can't win economically.  Add to that, most systems are over designed so they can operate without a bit of thought.   Most of the potential energy that can be harvested is wasted.  Making a system smart and scheduling loads will be the next generation of RE.

I live off grid in the summer for many months and use only a car battery out of a vehicle I don't bring with me.  It is used primarily for initial surge current of the fridge inverter.  Storage is not necessary to the massive extent most moronic solar systems are designed to.  Fridge runs real time off solar only during the day, I store cold for night.  Any excess power is converted to hot water at power point.  Currently I divert over 3KWH a day to heat water, more than enough for my uses.  It is possible to operate appliances real time without storing energy if done one at a time under processor control. I have next to nothing invested in all the electronics.

[DenzilPenberthy]

No,it's not grid tied, just a standard inverter. The AC inputs allow battery charging (and AC feedthrough) when running off a generator or plugged into mains AC.

http://www.windandsun.co.uk/media/314351/Victron-EasySolar-1600-Data-Sheet.pdf

If it's like the other Victron stuff I've used then yes it definitely feels like you're getting your money's worth quality-wise. In fact the battery charger I used for my friends' system got replaced FOC recently by Victron as they were recalling some units due to not getting expected performance out of some components (read: probably a dodgy batch of electrolytics, right?). That makes me think that they actually care about their units' longevity and quality. I've not seen any recalls for cheap chinese inverters on ebay

The system I built used all separate components but it required a lot of thinking and design work and a significant amount of time wiring up. If I was doing the whole project again I think I'd definitely use the all-in-one unit. You can add battery and panel capacity incrementally as your requirements grow but it's probably worth generously over speccing the components like charge controller and inverter. It will cost a relatively small amount extra now but will avoid having for example to bin a £300 inverter and buy a £400 one if you want an extra 500VA in the future. e.g. in the system I built It was an extra £30 something pounds to over spec the charge controller so that in the future I could double the number of panels and batteries if necessary.

[TheElectricChicken]

inside a single-phase domestic wiring system which isn't designed to cope with that. (679v peak!)

this is nonsense if all wires are connected to the mains.

Did you miss this bit?

Also if you are using several smaller inverters feeding separate circuits then ... ...

How can you have all wires connected to the mains in a single phase system and still be out of phase ? hello ? how. You have to find an idiot on the scale of you forget your multimeter and so test for 220vAC by touching your tongue to the mains switchboard. really. Draw up a circuit with one phase wiring and show what you mean. You can only do it with a multiphase wiring system at the least,

[DenzilPenberthy]

If you take the time to read Simon's post and my reply he was suggesting feeding separate circuits in his house with separate inverters.

It then becomes several different single phase installations but with no way of ensuring they are all in phase with each other. Imagine the following situation: you are feeding, for example, the upstairs lights from inverter A and the downstairs lights from inverter B. The inverters are not synchronised together so it is entirely possible that the supplies to the upstairs and downstairs lights are 180deg out of phase.

Now think about the double switch at the bottom of the stairs where Switch 1 controls the stairway lights fed from upstairs and switch 2 controls the hall light which is fed from downstairs. The wires that perhaps share a conduit run and the double switch now contain wires with 480v between them which they are unlikely to be rated for.

[TheElectricChicken]

If you take the time to read Simon's post and my reply he was suggesting feeding separate circuits in his house with separate inverters.

yes, sorry, here it is.

I have 4 circuits in my house so I can and will be splitting them down into different inveters.

I get a similar worry when I disconnect the 'lights' circuit at the fusebox to convert it all to 12v for solar installations. It's like, did they do something bodgey ?

[SeanB]

Most mains rated wire is tested to 1kV in any case, as it is the same wire type used for 4 phase circuits in any case. Thus not a worry about voltage, more the accidental connecting of the outputs of different inverters together. The outputs must be separate, both line and neutral wiring, or else you will have issues.

[Simon]

I've seen automotive rated wire that officially only goes to 50V used at 300V, although I did my nut when I found out, but it worked in that instance.

[johansen]

Now think about the double switch at the bottom of the stairs where Switch 1 controls the stairway lights fed from upstairs and switch 2 controls the hall light which is fed from downstairs. The wires that perhaps share a conduit run and the double switch now contain wires with 480v between them which they are unlikely to be rated for.

romax on their website says 300 volts, but when you use romax, you don't have loose wire floating in conduit, so you won't have that problem.

also, the wire sold in europe where 240 is the standard minimum will be rated to 600 volts minimum.

additionally, the THHN wire used in conduit in the states is rated 600 volts.

two unsynchronized 240v inverters is not a problem for a household installation unless you don't know what you're doing or the house is wired wrong. additionally most legit inverters which have a groundable output.. also allow for synchronization.

the inverters which cannot synchronize usually have floating outputs.. or their output midpoint is connected the battery negative terminal.. this latter issue can be a mess to work with.

[Simon]

Actually the cable rating is not a problem anyway in the event of inverters being 180° out of phase. Each conductor is already rated to withstand the full peak voltage in either positive or negative with respect to ground. If two wires have current in them which is 180° out of phase it would make no difference at all as there would be twice the amount of insulation between them. The cables have to withstand a single voltage anyway so that you can handle them without getting a shock to earth. The problem never existed.

[splin]

As for battery lifetime I hear that well treated lead acid batteries can last 20 years. That is why I am only expecting 500 W capacity from a 110 amp battery and if I had 10 batteries that would be 5 kW. I believe the batteries are around £80 although I might get a good deal on 10.

There are lots of leisure batteries Claiming that they can be discharged 500 or 700 times to a discharged state. That is why I would not want to discharge any batteries beyond 50% because I don't see the point in using those valuable cycles and destroying the batteries early.
So my next main problem is to work out what batteries to buy. I don't need anything huge I was thinking around the 110 A mark there are plenty of cheap leisure batteries but are they good enough? I don't exactly want pounds any battery I buy I will just gradually add batteries to the system to make it capable enough.

Simon, I think you will be seriously dissapointed if you buy 110A leisure batteries for £80 hoping to get 500+ 50% cycles. I think you should be happy if you get 200 cycles but 100 might be more likely.  Take a look at this:

http://www.caravanclub.co.uk/media/6552072/technical.pdf

And these shocking tests:

http://www.caravanclub.co.uk/media/13871919/ccmnovtechnical.pdf?type=archive

The 115Ah Trojan 27TMH is £113.5 and claims 600 50% cycles, but the golf cart batteries, and others in the same class, should be better - the T105 is 6V, 225Ah so the same capacity for £119 but claims 1200 cycles, so potentially much better value. I'd be very surprised if you could get anywhere near 1200 cycles though.

A Crown 27DC115 115Ah cost £117 from BimbleSolar and claims 525 cycles @ 50%.

http://www.yhipower.co.nz/downloadhandler.axd?type=2&id=100096&ins=1

Don't know how good they are but the cycle life table looks very suspect showing 300 x 100% DOD equivalent cycles at 20% and 40% DOD, reducing to 262.5 @ 50% DOD then increasing to 350 @100%! You have to wonder if they they just make the numbers up sometimes...

Note: none of the above are recommendations - just examples for comparison.

As to the 20 year lifetime, you might achieve that on the top of the line batteries but T105s are typically expected to last 2-7 years. You might get lucky and get 8+ years but you might  only get 4 or 5, no matter how well you treat them.

Many suggest starting with cheaper batteries as you are likely to kill them while you gain experience.

[Simon]

I'm confused. The listings generally refer to full discharge cycles and that the batteries can take five or 700. Now what you are saying is that these discharge cycles are only to 50%. I thought the whole idea of only discharging to 50% was to never enter that region of discharge that permanently damages the battery and reduces its lifespan. At this point I might as well get car batteries.

[bookaboo]

Some useful info on LA battery choice:

http://sterling-power.eu/support-faq-2.htm

[Aodhan145]

You should watch mjlorton's videos if you haven't yet.

[DenzilPenberthy]

Actually the cable rating is not a problem anyway in the event of inverters being 180° out of phase. Each conductor is already rated to withstand the full peak voltage in either positive or negative with respect to ground. If two wires have current in them which is 180° out of phase it would make no difference at all as there would be twice the amount of insulation between them. The cables have to withstand a single voltage anyway so that you can handle them without getting a shock to earth. The problem never existed.

This problem was discussed some time ago on the IET forum (I think). It really does open a big can of worms. There was someone who was wanting to install some stuff on a farm which had a split-phase supply. i.e. two phases 180 deg apart instead of the more usual 120deg. It's really unusual here.

Aside from the insulation of the wiring which yes, will be fine at 480v (if it's all rated at 600/1000v) - your circuits will still need protection from overcurrent. The problem is that you will find it extremely difficult to find a consumer unit or any accessories which are rated to 480v phase-phase. Three phase boards commonly available here are typically not rated to such a high phase-phase voltage. You could use a separate 1 or 2 way consumer unit for each inverter but then you'll need a lot of wall space to fit one for each inverter plus another one for your incoming mains plus all the contactors or changeover switches plus the inverters themselves. You will find that you have a very significant problem on your hands when you show all of this to your house insurance company if it is not all done and signed off by someone who knows BS7671 inside-out and back-to-front. You will likely then also have a big problem with your mortgage company when you can't get house insurance. Also bear in mind that if you do a homebrew project of this nature that isn't fully compliant with the regs then when you come to sell your house the purchaser would be wise to include the cost of a full rewire in their negotiations.

I fully agree with several commenters above that yes it will work but my point is that if you wan't to do this project properly then there are significant issues with using multiple inverters which are certain to end up costing more than using one large inverter.

I'm not purposefully trying to pee on your fire but I'm just pointing out some issues that might not be obvious at first glance.

[DenzilPenberthy]

Also to open some more cans of worms, your inverters will likely have a floating output (if you use small cheap ones). This will mean some of your circuits will be supplied from an IT system (not a good idea). You will have to modify them yourself to reference the output to earth. Expensive or large inverters will be designed with this in mind and have an internal N-E link which can be fitted. If the rest of your house is supplied from a TNS or TNCS system then you will have to convert it to TT because you can't rely on the electricity company's earth when using your own power. This will mean earth rods, extra cables and an RCD on your mains incomer. Remember to add suitable double pole switching so that your inverters' N-E links aren't there when you switch over to the public supply.

Also you will have some work to do to check that your circuits will still disconnect in the required time when supplied from your inverters. It is likely that they won't because they can't supply enough current. This will mean all kinds of RCDs everywhere and maybe upgrading the bonding conductors throught your house.

cans of worms everywhere!! Sorry! 

[Simon]

Some useful info on LA battery choice:

http://sterling-power.eu/support-faq-2.htm

So basically I need forklift batteries

[bookaboo]

Well basically yes some form of deep discharge battery, there may be other newer options since that article was written but it outlines the basic difference between car batteries and power back up batteries.

[DenzilPenberthy]

Yep. Flooded lead acid batteries are king for this sort of application. It does mean though that they'll need to be maintained with de-ionised water occasionally and you'll have to put some thought into how to safely manage the explosive hydrogen and oxygen they will give off while charging.

I've used these before. Very happy with them.

http://www.trojanbattery.com/product/t-105-re/

Edit: these are part of a range of suitable renewable energy batteries

http://www.trojanbattery.com/markets/renewable-energy-re/

and they have a very handy calculator to work out the required battery bank size based on your loads and how discharged you want the batteries to get. The datasheet for the battery will have a graph of depth-of-discharge vs how many cycles they will last.

http://www.batterysizingcalculator.com/

[max_torque]

Sorry to say, but i can think of very many better ways to "stick it to da guverment" than this!!


Going off grid in the UK is totally pointless waste of money!  Take the same capital, put it in a suitable ISA (tax free) your pension (taxfree) or invest abroad( could be tax free if you have a good accountant.....), or best, use it as a deposit on a BTL property!

Then wait 10 years, retire early, and emigrate to a nice hot country with good beaches and a favourable view on rich british ex-pats..........   ;-)


Take THAT you  pesky Parliamentarians!