Energy Matters Forums

[gpigeon]

I currently have a farm shed with 55 x 180W REC panels on it feeding 2x SMC5000TL inverters. Shed usage is absolute minimal so come the end of the GFIT the income from this system will be drastically reduced and hardly worth changing it all to net.
I am also in the process of building a new house which will be off grid, so my plan was to move around 5kW of the panels plus one inverter to the new dwelling early next year. I will then buy a Sunny Island and a battery system.
Current household usage is around 14kWh/day (separate from the "solar shed" mentioned above)but this will reduce to maybe 11kWh/day because I will not be running a pool pump. The 10KW shed system over the last 6 years has produced a min. of 16kW per day and a max. of 57 kW/day.(average over a month) so presumably a 5kW system will produce half that.
So, my question is what size battery will I need?
I note that the LG Chem battery off ebay is about 6.4 kWh expandable to 9.6 and 12.8.
It looks to me as if say 5.5kW (half the 11kWh) consumed over a 12 hr period without any additional input would be beyond the capability of a single 6.4 kWh battery. Correct????
What is the normal factor for calculating battery storage capacity required?

My consumption may be a little higher than usual because I am running 2 fridges and a freezer. This will not change in the new house. By my calcs those 3 items alone use about 3.75 kWh /day. Not sure where the other 10.25 kWh goes to.

[Helipos]

So, my question is what size battery will I need?

Simple, how many days in a row do you get with minimal solar inputs? (eg. no sun)
How many of those days do you want to go without having to either change your usage or having some other form of input ie generator?

[Tracker]

And there is the RedFlow battery system.. which can he charged and then left FOREVER (Almost) to cover abnormal.times.. but, at what price....

No idea what a LG battery is...
..bottom line is we are all trying to come to terms with Jan 1, 2016..
And it is not being helped with the reports of offers of cheap battery system incentives ..
Oh for a crystal ball..
..

[davidg]

I currently have a farm shed with 55 x 180W REC panels on it feeding 2x SMC5000TL inverters. Shed usage is absolute minimal so come the end of the GFIT the income from this system will be drastically reduced and hardly worth changing it all to net.
I am also in the process of building a new house which will be off grid, so my plan was to move around 5kW of the panels plus one inverter to the new dwelling early next year. I will then buy a Sunny Island and a battery system.

As good as SMA is when used on grid or "grid mutlimode", I'd suggest Sunny islands may well be problematic off-grid even though they are in general a reliable product. #just saying, the marketing makes them out to be much better than they really are, maybe it's changed in the last while but ....................

Is the house on the same farmland the shed is on? if so there is no need any panels at all, thats simply an installation/wiring issue, anyway a shed is great place for a system to live on/in.

So, my question is what size battery will I need?

That's really a design question, without the full load profile it's a bit like asking how long is a piece of string, the requirements for when the grid is involved is different to being independent of the grid.

I note that the LG Chem battery off ebay is about 6.4 kWh expandable to 9.6 and 12.8.

As above

It looks to me as if say 5.5kW (half the 11kWh) consumed over a 12 hr period without any additional input would be beyond the capability of a single 6.4 kWh battery. Correct????6

Sorry it's quite not that simple

What is the normal factor for calculating battery storage capacity required?

load profile required

My consumption may be a little higher than usual because I am running 2 fridges and a freezer. This will not change in the new house. By my calcs those 3 items alone use about 3.75 kWh /day. Not sure where the other 10.25 kWh goes to.

Complete load profile still required.

[gpigeon]

Thank you for the replies to date. The new house is on the same property as the "shed" but 1 km distant so connection is not possible.
Yes, I see that a "load profile" is necessary to fully analyse future requirements. Unfortunately I don't have this yet so have just been looking at approx. requirements.
The minimum daily output in April 2016 was 6.2 kWh (from 5kW of panels) and there were 3 days in a row with less than 9 kWh. That is better than I thought! The minimum monthly output for the whole system over the last 6 yrs. was in Feb 2013 so I will try to download the daily outputs for that month and see how many "low" days in a row there were.
So, it would look as if a +/- 6kWh battery system may just supply my needs providing I modify my power usage a little.
How often (roughly) do you other "off grid" guys run your standby generators?
What type of charger do you use via that generator?
Thanks again for your input.

[BruceM]

Gotta remember most advice from those on here will be from registered electricians and installers that do everything by the book. By that I mean start with the 99 steps to ensure EVERY thing is taken into consideration.
This is the very best way to do it. Especially if they are doing it for some George Street millionaire!
For some of us wishing to 'get our hands dirty' it's sufficient to start with the proverbial "ball of string" but don't cut into length .... ever!
Build it in a way that you can simply roll out more string ... (panels, batteries & maybe inverters)
In my opinion there the 2 distinct different ways to go.
Even Gordon has rolled out more string .... several times in fact!

[Gordon-Loomberah]

How often (roughly) do you other "off grid" guys run your standby generators?
What type of charger do you use via that generator?

I went 2 years without using a generator after installing 21kWh of LiFePO4 battery, and that included using ~12kWh/day average over winter. I have much larger energy use these days, due to running 2 aquaponics systems (with over 400 rainbow trout), so generator use has increased somewhat. Generally I have to use it in heavy overcast weather that lasts more than one day. The past 2 days are a good example- Saturday was mostly cloudy to overcast with a late storm, and under yesterday's heavy overcast and rain, 6.5kW of PV only produced 2.1kWh. This morning it is foggy, but mostly sunny so far, so solar is doing the charging

Usage varies from not at all in the usual fairly sunny weather here, to up to a few days in a row in extended periods of overcast/wet weather. Run times may be from half an hour up to 12+ hours in a day (like yesterday).
The charger is only a 25A 48V Lithium battery charger (the largest I could find), run by a 2.3kW gas powered generator, so not really enough for my current rate of energy use, meaning long running times. but I'll soon be experimenting on modifying a 24V alternator to see if I can get high enough voltage from it to charge at 54V.
If you have a suitable alternator, IMO it is best to directly charge your battery with that, rather than using a 240V generator + charger, which is much more expensive than a motor + alternator, and is what I used for many years when I had a 24V battery.


... now where did I put my spare ball of string?

[jules]

What's a "generator"?

[Gordon-Loomberah]

A device that converts mechanical energy to electrical energy

as in hydroelectric generator, wind turbine generator, or what is being asked about here: diesel, petrol, gas or biofuel powered generator

[jules]

Sorry Gordon, I was being slightly facetious. I have a generator but I haven't used it since about 1985, so it might not actually generate any more if the mice have got into it.