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New offgrid system

PostPosted: Fri Mar 02, 2018 2:25 pm
by offgridQLD
Starting with a blank page again designing a offgrid system for our new home in South Australia.

My initial thaught was to just mimic my old system I ran in QLD with some minor tweaks. Main components of the old system below.

16x 400ah calb lifepo4 cells
8000w pv (spit between two 4000w arrays)
Two midnite classic 150 charge controllers (one for each array)
selectronics PS1 6000w inverter
MPPsolar 4000w backup/shed inverter
kabotaJ108 desle genset (auto start)

Tweeks to new system if I was to mimic it again.

More PV 10,000w split ne/nw most likely ground mount this time.

Use sp pro series inverter (better specs more options than older ps1 I had)

Consider not bothering with the backup genset (didn't get used in old QLD system) though I should see out a winter in SA first :lol:

Using a different BMS than last time (latest batrium system would be on the cards this time)

Though I have been thinking this could be a opportunity with a blank page to try something new. I was perhaps considering the SPpro ac coupled to a fronius 8kw inverter and perhaps even a pair of LG CEM RESU10 batterys.

The advantages I could see in this would be a very simple install for the AC coupled inverter (way less fusing and cable runs along with no double charge controllers needed along with all the wiring fusing of Dc coupled)

The advantage in the LG RESSu10 would be a OEM battery with integrated BMU. Most likely better warranty support and perhaps better quality. No need to make enclosures again, wire up BMU, cell monitors and all that.

The disadvantages I can see is I haven't checked but the LG RESU10 has a max output of 5kw continuous. I would need to know if this is doubled when linking two RESU10's together or if it only doubles the capacity and not the max output to. As 5kw max would be a deal breaker. anyone know?

Perhaps one other disadvantage with a OEM battery system would be if there is a issue its not so user survivable. not easy to just swap a cell out like the calb/winston cells . Perhaps wouldn't be as easy to monitor individual cells. That said my electric car is now 6 years old without any need to tinker with the battery.

So over all my thoughts are should I go AC coupled this time and should I give a OEM battery a go this time.

Re: New offgrid system

PostPosted: Sat Mar 03, 2018 7:12 am
by australsolarier
hello Kurt,
good to hear from you again.
the midnite classic takes easily 6kwp, no worries.
yes ac coupling the selectronic sp pro is way easier to wire up. but also much more expensive, unless you have the relevant licenses. the fronius with the special software is probably much more expensive than the normal fronius.
they give you 10 years warranty on the LG CEM RESU10 batteries. i would think you would double the 5kw to 10 kw. and if you have 2 of them, there is some redundancy if one fails.
it all depends if you want to tinker or just have it ready made.

looking forwards to seeing how it all progresses.

Re: New offgrid system

PostPosted: Sat Mar 03, 2018 8:59 am
by australsolarier
LG CEM RESU10 cheapest price online i could find is 8220$ .
it seems when you connect two of the LG CEM RESU10 batteries it needs a box in between that sets you back another 500 odd dollars.
and bizarrely you need a rj45 crimper to connect the rj45 plug after the net work cable is threaded through the hole in the case.

Re: New offgrid system

PostPosted: Sat Mar 03, 2018 10:22 am
by offgridQLD
Yes it boils down to value and what the system is like to live with. The Fronius Primo 8kw is just under the 3k mark retail from what I can see. Two classic 150's are just over 2k .

What I found with my last system was wiring a large 40 panel+ array into 2s configuration sure has you wishing you could just run a bunch of panels in series. Expense in cable, plugs and quality isolation/fusing sure added up. Though I agree working over 120vdc has you paying some one to install it. Though there could be some benifits in that being able to aply for the REC on the install.

I did see the LG cem RESU10 for $7300 online $14,600 for two + 500 for the RESU Plus Battery Expansion Kit . $15,100 total.

400ah Winston cell x 16 is $11,500 then another $300 or so for bolts and interconnections, cover-compression plates and around $1000 for a good BMS and contactors a so around $13,000 with a bit of headroom.

$2100 differance for a OEM turn key solution. it's getting close enough to start considering. Though as mentioned if that 5000w max continouse output doesn't double when you conect two togeather then its not the battery for me.

Re: New offgrid system

PostPosted: Sat Mar 03, 2018 11:21 am
by australsolarier
that fronius primo 8 probably has to be bought from selectronics, indirectly , as it has a special software in it. i suppose davidg would know more about the price for the selectronic certified fronius.

Re: New offgrid system

PostPosted: Sat Mar 03, 2018 4:09 pm
by tom rickard
If you are looking to DIY the DC side, the RECBMS coupled to a SMA Sunny Island is going to be a lot simpler than using the Batrium system. I have used both.

I would stick with LiFePO4 over LiNMC, if you are looking for a commercial solution check out the BYD B-box.

The system you had looks fine to me!

Re: New offgrid system

PostPosted: Sat Mar 03, 2018 5:09 pm
by davef
Thought I would head over the LG site and have a look at these batteries.

Three statements caught my attention:

*Charge time should not be longer than specified in the manual.
*When the cell is not charged after long exposure to the charger, discontinue charging.
*Battery must be charged at operating temperature range 0 ~ 50℃.

Interesting that the third item agrees with other statements that I have read, ie charge only between 5C and 45C.

The first two points sound like two interpretations of same "charging condition"

Can anyone clarify or point to a more comprehensive document? Specifically why are there some time limits imposed on charging?


Re: New offgrid system

PostPosted: Sat Mar 03, 2018 6:22 pm
by davidg
australsolarier wrote:that fronius primo 8 probably has to be bought from selectronics, indirectly , as it has a special software in it. i suppose davidg would know more about the price for the selectronic certified fronius.

Their only slightly more than a "std" fronius, but worth it. Particularly with an SP pro it works a treat. I upgraded my old 4 x 2 kW inverters to one on 8.2kw fronius units when one of the 2kw units failed well out warranty. Easy conversion with the four strings took longer to make all tidy than the install.

Re: New offgrid system

PostPosted: Tue Mar 27, 2018 11:34 am
by offgridQLD
I thought it would be worth while taking a step back to crunch some numbers with the various options to power our new home.

It's been interesting living temporarily in a grid connected home without any solar this year. living much the same as we did in our offgrid home. As in charging our EV and running the same appliances within in the home. No workshop loads but more Aircon loads to ballance it out. We have a power bill around $500 pr quarter $2,000 PA in this situation.

I have a good idea of what it takes to build a good offgrid system that just works without compromise to live like we are now. Ballpark $35,000 large array, lithium batterys and quality power electronics. As most know the biggest thing to consider in a offgrid system is the battery bank. Near on $12,000 for a calb - Winston 400ah - 48v bank lithium bank (just the cells). I have resonable confidence I can get 10 years service from the battery bank.

Using this time frame. I have a ongoing cost of $1,200 PA over 10 years for the battery bank replacement cost.

Comparing this with the Grid I would have $300 pr 1/4 to spend on electricty (current bill is $500 incliding daily survace charge) So I have a $200 pr 1/4 saving Offgrid (assuming the bat bank is the only repeated replacement item). Though I am $35,000 out of pocket for the offgrid system. Yes $12,000 of that is included in the first 10 years for the battery. $35,000 divided by $800 pa = 43 years of paying the $800 short fall. 33 years once you take the first 10 years battery life out. That said assuming you put that $35,000 into the bank at 3% PA $1,050 pa interest.

So from a economics stand point I'm struggeling to justify offgrid. I think in situations where the grid is going to cost the same or more to connect to as a off grid system then that evens things out a little. Though even then with the very low cost of 5kw grid connect systems now days that could break down the bulk of the consumption charge then. I'm sure that the grid would still be less expensive even if they were the same cost to connect to connect.

My thinking is there are are two cases where it's economically viable. One being extreme cost to connect to grid (several Km from grid massive cost to connect) Two would be potentially a situation where you had the bulk of your consumption overnight and a grid connect system would be of little benefit without battery's. The latter would only offer break even or a small advantage.

Me being just over 100m from the grid with a transformer sitting unused just a trench and cable away from being on the grid Im finding it hard to justify going offgrid. Thinking a 5kw grid tie on the house and perhaps use my 4kwh of portable calb cells with a spare PIP4048 and some seconhand PV on the shed as a island backup offgrid system. Just so I to can be smug and switch to offgrid the few times a year we have a power outage.

Re: New offgrid system

PostPosted: Tue Mar 27, 2018 5:56 pm
by australsolarier
a few things i like to add to your calculation:
the money you pay for electricity is AFTER you have been taxed on your income. (and there is much more. in germany they estimate their 30cents/kwh turns into 1.30 euros after you add all the social contributions and taxes)
the income generated from your installation is tax free .
electricity charges will go up.

we buy many things we do not calculate the economic monetary return: cars, smart phones, computers, holidays, etc. it is just taken for granted that this money is basically gone with very small economic monetary return.

in my situation the island system is not for the financial return in the first place, but it is a retirement investment, a hobby, proving other people it can be done, going ahead with the good example etc.
in my case it generates a small financial return, 400$ aus per year.

i myself found it extremly difficult to do the financial calculation. there are too many variables. interest rates, electricity prices, inflation, currency exchange, retirement laws, not to mention power use will go up with overpowering solar generation, simply because it is available.

and not last, you do not have to make a commitment. simply go with the selectronic compatible fonius grid feed inverter and you can add the rest later.