Off-grid system - 960W of 12v PV goodness - now what???

[Outbackshackhack]

Hi everyone, My name is Michael and I live in NSW Australia, at a place called Cootamundra. We get good sun hours, but I don't know actual statistical data (not that anything is consistent about the weather these days!).

I have been using a 100% off grid setup for almost 2 years, comprising 4x 120W 12v panels, 6x 2v 525Ah flooded batteries (ex-pallet truck) (used and tired but still giving 40%) which is lasting about 2-3 days. Charger is a Sidewinder 40A PWM. The batteries only ever charge at up to 270W according to the LCD display, and the batteries are showing signs of suffering - each month the available capacity seems to be lower than the month before, although not a rule. I feel the need for equalisation, but this setup just does not provide the power to get the batteries gassing well.

I am about to add an additional load of about 400W x 6hrs per day (office) which is computer, LED screens and lights. I guesstimate power usage to be in the order of 4000w per day.

I am going to assume winter sun hours to be around 4.5. Summer won't really be relevant as I will need to run aircon which will have to be mains powered. I don't have mains yet, but will get it before the warm weather in 6 months time or so. It's a tough call, going off-grid solar when the grid is (will be) there, the cost of solar is soooo expensive compared to mains power, but it is fun!

I have my eye on some new batteries that are rated at 1000Ah as they are a good price, but 1000Ah is a bit overkill for my needs - but the price is right - about $3000. I am not really liking the idea of an 80 amp charger though ($800) but unless I go 24v, I don't see any other choice. 2x 40A charger cost about the same as 1x 80A charger.

Also considering MPPT as my existing 40A charger is PWM.

So I have several options, not the least of which is to spend my $$$ on beers & smokes instead of batteries and just go Grid . But let's just humour me and consider other options as well...

1. keep existing panels and batteries and upgrade controller and maybe add some panels.
2. add panels, replace batteries with new ones and a new charge controller.
3. what else?

Getting new batteries means superseding the old ones and to do what? seems a waste to chuck them out when they can still offer 3 or 4 kW for a while yet. Same with the controller. I am suspecting that doubling the panels will not do much if the batteries won't take the charge.

So, any ideas then on where to go from here? I don't mind throwing the bucks at the system, as it is a hobby and an adventure and I do love bad investments

Cheers

Mike

[Naptown]

How about a grid tie system when you get mains.
the cost will be much less than a battery system, will produce more electric than your existing or enlarged battery system will.

[Sunking]

You really ought to rethink this. Taking Air Conditioner off-grid is insanity. I know you guys down under pay unreal amounts to the POCO for power of about $0.30/Kwh AUS but going off-grid will cost you in excess of $2.00/Kwh AUS. [...]

[Outbackshackhack]

rethinking...........

I hear what you are saying, although I never said I wanted to run aircon off the solar, although I could do it - as you say, in less than 10 years I will have to start replacing expensive bits, well before any of it has paid for itself.

Well I started with solar for cost reasons, with a pair of 20W panels and 2 truck batteries and it grew into 480W from there. Now I must rethink the whole thing. It is a real shame because I have loved running off solar - every time I turn an appliance on I feel all warm and fuzzy inside (and that's not due to earth leakage in case you're wondering).

Solar will also be way quicker to get my office up and running, as the mains will take a month or two to get sorted (trenching, tradesmen etc).

I'm being pulled in two directions - one of logic and common sense and the other of fun and exploration. Trenching is starting on the weekend. I have conversations going on with battery people, too, although I feel that side of things slipping away.....

A grid tie system is my ultimate, to have the best of both worlds, so perhaps I will start thinking along those lines now...

Thanks fellas.

[Sunking]

Solar will also be way quicker to get my office up and running, as the mains will take a month or two to get sorted (trenching, tradesmen etc).

I'm being pulled in two directions - one of logic and common sense and the other of fun and exploration.

OK think of it this way. You are in biz for yourself right? What is the most important aspect of running a biz?

I am a small biz owner myself and like anyone in biz the most important thing is making money. Otherwise you are not in biz. So how do we make money? One of the most important ways is controlling cost and keeping them as low as possible to maximize profits. It enables you to undercut the competition and get their biz.

[...]

[Outbackshackhack]

well you know people love to "go broke" over their hobbies, (gambling, drinking, cars, water sports, cycling, go-carts, horses, home theatre, audio, tools and workshop and many more).

Consider a fellow who loved the movie The Fifth Element so much he designed a home theatre setup from the ground up and in the end spent nearly 100k on an extension to his home, plus all the best audio and visual technology and created a system he loved and enjoyed every time he used it (perhaps 8 hours a week).

Or another fellow who bought a ski boat and then year after year spent thousands on equipment and maintenance, but always loved it and looked forward to every other weekend and trip away.

Let's not even get into what a waste of money cars are. Nobody would be silly enough to spend unwarranted money on cars would they?

I can easily justify spending the money on a solar setup, and money doesn't even come into it and it won't send me broke - in fact if profits aren't spent - they get taxed! And a solar setup would be a tax write-off. Sadly I'd get no rebates because I have mains available at the street. My issue is with logic and emotion. I guess a big upgrade to the solar system is silly and I can spend the money on panels only and a grid-tie setup, but I want to keep my current system operational.

So, let's take another gander at the sitch - I have some tired batteries that still put in a good day's work and I'd like to keep them healthy. what can I do to my existing setup to enable me to keep the batteries going, such as extra panels (won't go to waste) or a new charger or what?

[Sunking]

So, let's take another gander at the sitch - I have some tired batteries that still put in a good day's work and I'd like to keep them healthy. what can I do to my existing setup to enable me to keep the batteries going, such as extra panels (won't go to waste) or a new charger or what?

Well first thing replace the batteries and upgrade to a MPPT controller.

Next is a sanity check on battery capacity. At 1000 AH 12 volts the minimum panel wattage is 960 watts to deliver a C/12 charge rate of 80 amps. FLA batteries require a minimum of a C/12 charge rate and no higher than C/8 (125 amps on a 1000 AH battery.)

With that said it would not be advised to operate at 12 volts and demands an upgrade to at least 24 volts. A 24 volt battery @ 500 AH = 12 volts @ 1000 AH

[Outbackshackhack]

Agreed, Sunking - 12v is much too hard if I go bigger batteries and I would certainly look at 24v before I did anything and have been doing just that over the last few days. I could get 24v 395Ah for just over $2k and could stretch that to 500Ah for a little more. Another 480W of panels would be $800, 80W charger $800, new 2500W inverter $1000, plus cabling etc. Something around $5k and that would provide enough power for the home & office, sans aircon. So $5k to provide around 50c/day of power usage, or around 25 years worth of power that may need another 2 or 3k spent on upkeep in less than 10 years. Of course, with mains connected, power usage goes up by at least double, so actual usage on mains are twice as much as on solar (that's an estimate, but with unlimited power available from mains, we know the lights and aircon etc stay on longer than they would on solar). In reality and so long as parts behaved themselves and were looked after, I would think 15 years of service from a solar system would be enough to say it paid for itself. 10 years is a bit sad. And none of us knows what replacement bits might be available in 10 years - super-dooper batteries or fuel cells could be well worth the money in 10 years.

However we digress again - the last question I asked was what can I do to keep the existing batteries healthier?

[Naptown]

Grid tie is the really only way to go. Much more bang for your dollar. OK AU dollar

Ok so take a budget of 5k grid tie
spend 1500 on an inverter
3500 on panels
3500 should get you almost 2 k + the 960 you have.
Now you are almost at 3KW
Grid tie you can be at over 80% efficient
Battery will be 50% at best

So based on a 4 hour sun day average 3KW x.8 x4 x365 = 3504 KWH per year
Same budget except it is 2 KW as I subtracted the batteries from the budget.
2 KW x.5 x4 x365 = 1460 KWH per year less than half.
Now cycle in battery replacement every 5-7 years depending on the quality and care.

[Outbackshackhack]

Yeah I can't argue with that - the money is much better spent on panels than anything else.

$5k might get me 3000w worth of panels, which might nett something like 6 or 7MW pa., or about $1300 pa, so they pay for themselves in just a few years and continue to provide that income for another 20 years! So $5k worth of panels can get maybe $30 income over their life. whereas $5k worth of off-grid system never pays for itself and has to be replaced in 10 years.

OK, so aside from my other question above, I have read here that grid-tie panels are different to battery charger panels - can I get some more explanation on this pls? Is it really worth paying the extra for grid-tie panels?

[Naptown]

Yeah I can't argue with that - the money is much better spent on panels than anything else.

$5k might get me 3000w worth of panels, which might nett something like 6 or 7MW pa., or about $1300 pa, so they pay for themselves in just a few years and continue to provide that income for another 20 years! So $5k worth of panels can get maybe $30 income over their life. whereas $5k worth of off-grid system never pays for itself and has to be replaced in 10 years.

OK, so aside from my other question above, I have read here that grid-tie panels are different to battery charger panels - can I get some more explanation on this pls? Is it really worth paying the extra for grid-tie panels?

What you will find is that grid tie 60 cell panels are the best value out there. Actually less than the off grid. BONUS!
Simply because they are more common and in greater supply.

[Sunking]

OK, so aside from my other question above, I have read here that grid-tie panels are different to battery charger panels - can I get some more explanation on this pls? Is it really worth paying the extra for grid-tie panels?

The difference is the cell count or voltage. Panels made for battery systems are 36 cells, while Grid Tie panels start at 54 up to around 80 cells.

As for pricing I am not certain about AUS, but globally Grid Tied panels are quite a bit less expensive on a $/watt cost. There is not much demand for battery panels, so they cost more.

[Outbackshackhack]

OK, so the OP is a bit superseded now, but I reckon I will go with the following:-

1. connect mains up for office, forget solar for that.
2. keep solar for home, but improve to ensure health of existing batteries.
3. potentially add panels to grid for income. Need permanent structures to install them onto though..... or a free-standing frame of sorts.

So number 2 still needs addressing please.

[Outbackshackhack]

The difference is the cell count or voltage. Panels made for battery systems are 36 cells, while Grid Tie panels start at 54 up to around 80 cells.

As for pricing I am not certain about AUS, but globally Grid Tied panels are quite a bit less expensive on a $/watt cost. There is not much demand for battery panels, so they cost more.

haha I just looked online at the FiT (feed-in-tarriff) for my area and it is presently 0c/kWh! Other energy providers are offering as much as 6c/kWh. Industry suggests that 8 to 10c/kWh is the approx. cost to produce a kW and that is likely to become the FiT here in Oz.

FYI cost per kWh is 20.6c for the 1st 730kWh and well as 48c per day service availability charge.

Those numbers above are going to change all over the place in the next few years, but certainly my original guess of getting 20c/kWh Fit is way out, and that $1300 pa has turned into a fluffy cloud of smoke. At 6c FiT at 3500kW/pa comes to a whopping $210 for about $5k investment taking 23 years to pay off at that rate.

Suddenly no solar option is financially viable

[Outbackshackhack]

Just an aside - when one looks closely at the cost to produce small scale solar power, it's just nuts compared to mains. Which doesn't make solar expensive, but rather mains is unsustainably cheap and always has been. It is incredible how much energy is stored in fossil fuels and if we knew that going in (or rather if AG Bell knew that) then the price per kWh might have been much higher from day 1. This really shines a light on the true cost of electricity generation and why our "current" system cannot last, and explains why the change to renewable energy is so difficult.