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DIY Battery Storage


Fly100
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Hello all,

 

I have access to some free batteries ( 6v 100ah ) and would like to consider the chance for some sort of Solar Storage. I currently have a Solar Edge SE5000H-RW000NNN2 connected to 6.2 Kw of Panels. The inverter also connects to an immersion controller which sends spare power to an immesion heater.

 

What sort of extra equipment do I need as Id like to cost this before talking to Electrician about installing etc to consider if this is cost effective.

Many thanks in advance.

 

Fly

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I have often thought about such a system, but it won't be off the peg parts and it won't be a job for an electrician, more a job for an electronics boffin.

 

In my case I have a home made PV dump controller based on an Arduino.  so I would add to that to turn on a charger when there is surplus to charge the batteries.

 

The same Arduino might as well turn on a grid tie inverter to discharge the batteries when import is detected.  The only bit of that I had not solved was an off the shelf grid tie inverter that lets you set the output power.

 

It is the cost of batteries that has stopped me experimenting with this.

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3 hours ago, Fly100 said:

I have access to some free batteries ( 6v 100ah )

 

Interesting. Free is hard to pass up on. As for how to use them I can't see how you could really do it without some practical electronics knowledge. Like ProDave says, it's not so much a job for a sparks as for an electronics engineer. Doubtless there are a few who fit both descriptions but I don't know how you'd find one. Basically you would need a way to charge the batteries - wired in a series string to match the output of your PV array. But that could be several hundred volts so you might not  have enough batteries. But if you did then you would need a way to limit both the charge current and final voltage. If such a system were in place then it could be as simple as a couple of Silicon Carbide Schottky Diodes to merge the battery bank with the PV array to continue powering the invertor after the sun has set.

 

The annoying thing (for you I imagine) is that everything could be done with simple switches and a multimeter plus a couple of diodes all for under £20 but you would be the guy in charge of the switches! 

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4 hours ago, Fly100 said:

have access to some free batteries ( 6v 100ah )

How many ..? As this will alter what you may want to do with them or how you make things “work”. 

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30 minutes ago, PeterW said:

How many ..? As this will alter what you may want to do with them or how you make things “work”. 

 

I was going to get 8 ( 48v ) with a couple of spares. My interest is not to run the cooker or high load stuff its to cover the base load of the house at night mainly. For instance as sit her now TV on etc im drawing approx 400 watts. The drops to 250w ish over night. Thats what I would like to cover.

 

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Would it not be easier to run some dedicated circuits from a standard pure sine wave  inverter and plug in appropriate loads as required.

Use the inverter diverter to activate a battery charger.

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4 hours ago, Fly100 said:

connected to 6.2 Kw of Panels

OK. So assume that at over 4kwp you had to request permission from the DNO? Bear in mind that anything A/C coupled that is a generator adds to your total grid-tied generation / output, so, for eg, if you had a 4.8kw battery system and your 6.2kwp PV installed at the same time, you'd have been then asking for permission to connect 11kw of grid tied 'A/C coupled' generation.

I'm not 100% sure where anyone stands adding this retrospectively or DIY / other, but it is ( technically ) something which you should be asking for permission to connect / add AFAIK.

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48 minutes ago, Fly100 said:

The drops to 250w ish over night.

What is taking that much?

 

How old are these free batteries, or in other words, why are they free?

Some SunnyBoys had a settable relay in them that could be used to divert load.

Could you charge them with 4 or 8 half decent car battery chargers? (I don't know enough about the chemistry of lead acid batteries to really comment).

Can you run some of a dedicated load of a cheap inverter, or even DC (with appropriate switching)?

Edited by SteamyTea
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1 hour ago, Fly100 said:

 

I was going to get 8 ( 48v ) with a couple of spares.

 

 

Are these heavy lead batteries or lithium batteries?

 

If lead then you only have 1.6 kWh of daily usable capacity in that bank.

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1 hour ago, Fly100 said:

 

I was going to get 8 ( 48v ) with a couple of spares. 

 

Oh, here was I thinking you might have scored somewhat more than that. That makes it quite a bit more difficult. As a massive series string, they could have had similar characteristics to the PV output and parallel up quite easily. But the relatively lower voltage you have requires some serious power conversion and that's never cheap.

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With 8 batteries (or 4 strings of 2) you can get 400Ah at 12v but that’s not that much capacity. A decent Victron charger inverter is  going to cost you at least £400 to make it grid connected.


Do you have some sort of outbuilding that you could make “off grid” and use them for that ..? Stick a couple of cheap panels on the roof of it and for change of £250 you’ve got a full off grid storage and charging solution for the batteries. 

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10 hours ago, Radian said:

 

Oh, here was I thinking you might have scored somewhat more than that. That makes it quite a bit more difficult. As a massive series string, they could have had similar characteristics to the PV output and parallel up quite easily. But the relatively lower voltage you have requires some serious power conversion and that's never cheap.

 I miscalculated that Ah and series does not total up, but I have access to a pallet full of batts so more is not a problem.

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12 hours ago, SteamyTea said:

What is taking that much?

 

How old are these free batteries, or in other words, why are they free?

 

CCTV

Alarm

Nas Boxes

Wifi Thermostat in every room

Smart sockets

Switch

AP's

 

All adds up.

 

As for free batts, they have been installed 6 months and now removed, project ended and the disposal is chargable.

Edited by Fly100
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2 hours ago, Fly100 said:

 I miscalculated that Ah and series does not total up, but I have access to a pallet full of batts so more is not a problem.

What's the maximum DC output voltage from your PV array? If you don't  know, I'm guessing it's split it into two strings, so how many panels per string?

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7 minutes ago, Radian said:

What's the maximum DC output voltage from your PV array? If you don't  know, I'm guessing it's split it into two strings, so how many panels per string?

11 panels per string ( 22 in total ).

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5 minutes ago, Fly100 said:
13 minutes ago, Radian said:

What's the maximum DC output voltage from your PV array? If you don't  know, I'm guessing it's split it into two strings, so how many panels per string?

11 panels per string ( 22 in total ).

So around 500V then.

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1 hour ago, SteamyTea said:

So around 500V then.

More like 400V I think. SE5000H-RW000NNN2 has Max. input 480V, nominal 380V which would be a sensible design choice. So 55 off 6V batteries in series as a minimum before a buck regulator would be needed. Based on a full absorbtion charge voltage of 7.2V the PV array could charge up to 396V at the natural current limit of the array (<13.5A looking at the spec of the invertor) then get disconnected at this threshold using a relay driven by a comparator. If this was a changeover contact: Bat <- PV -> Invertor then another changeover: Bat <- Invertor -> PV could switch in at dusk to run off battery. Alternativley the use of a Diode Or could do most of the switching but a charge termination circuit would still be necessary.

 

Probably not going to happen though as 55 batteries won't fit on a palette.

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