New "off-grid" installation in urban (grid-tied) setting...

ElectricLove

We had solar at one of our previous homes and loved it, back then you could get huge utility rebates off the installed cost and so we went with an installer and did a 5kW system (limit of rebate), it cost us about $12K out of pocket (after tax credits and rebates, etc) and was installed for us with a SMA 7kW inverter in case we want to expand it later a bit... 

Well, fast forward 10 years and our present house is quite a bit larger and energy bills are killing us!  (over $500/mo) We decided to strive for net-zero energy independence and being both on a budget and a do-it-yourself type of guy I'm taking on this project all on my own!

We have about 1200 sqft of flat roof (pitched 6 degrees South) where we are currently installing everything.  We found 27 used Sharp 170W panels and bought them as well as 16 230W "Jetion" panels (unused).  We also acquired a couple Xantrex XW inverters and an XW PDP as well as 2 Xantrex 60A MPPT charge controllers and 2 MidNite Classic 250V charge controllers.  I am a battery guy and love the Lithium Iron Phosphate technology, light-weight (easy to work with), energy dense (not too much space), clean (no corrosion/acid) and long-lasting.  To me all those pro's are worth the premium price (and when you factor the price in terms of cost per kWh stored and retrieved from the battery over its entire life, it is actually not a premium price but is cheaper!); so I went with Ohmmu Group 31 Lithium batteries, we have the Gen. 1 set now which are 12.8V and 100Ah (we want to upgrade to the Gen. 2 when they come out which are 150Ah and same size/voltage!)

I decided to do the install in phases:

1st phase: install all of the AC-side stuff; New sub-panels (2 of them), PDP (with dual-inverter breaker and maintenance bypass breakers) and XW inverters and Xantrex SCP.  Had to buy a lot of 4 AWG wire to finish this but got it all done in a day.
2nd phase: Add a battery bank; I found the best batteries possible since this will be so critical to our system.  We installed Ohmmu Group 31 batteries and I built a wooden rack to hold 24 of them, currently we have 20 installed which gives us 25kWh of usable energy (Lithium Iron Phosphate batteries so we can discharge them down to 20% or so and still get many thousands of cycles out of them!)

After these two phases were complete we were able to start doing load-shifting.  We are set up to charge our battery bank up from 11pm-5am when we get EV-super-offpeak rate from SRP of around $0.045/kWh.  Then at 2-8pm we do "load shedding" mode which uses the battery bank to power our house (rather than pay the "peak rate" of $0.25/kWh).  This process allows us to off-set around 20kWh of peak energy cost with the offpeak cost, at about $0.20/kWh ($0.25 - $0.045) that means we save $4.00 per day utilizing this method! (weekdays only) $20/week and ~$1000 per year.  The savings is off-set by the cost of the batteries though, it was about $14K in batteries to get 25kWh, so that is a 14 years pay-back.  HOWEVER, the bigger benefit is we now have a higher level of comfort throughout the day, we no longer turn our AC's off during peak-time and so the house doesn't climb too high in temperature.  So although we won't get our money out of it for 14 years (and if we replace the pack at that time we will never really get our money out of it) we will get benefits from it starting immediately!  And, when we disconnect from the grid a battery pack will be absolutely necessary to make it through the night, so there is that benefit too...

3rd phase: reroof (needed it after inspecting it, the asphalt was all worn away)
4th phase: install feet (roofing tar underneath during lag-bolt install and again another layer of roofing tar over the top and around the foot after mounting)
5th phase: install racking and panels for 4 strings which will feed Xantrex Solar Charge Controllers (16 Jetion panels, 4 strings of 4, 2 strings in parallel to each Xantrex)

At this point we will have 3.7kW of solar feeding the battery bank (and house), we expect to gain about 18.5-22.2kWh of energy per day from this solar bank.  Now is when the savings starts to build, if we capture 20kWh of energy per day at an average rate of about $0.10 (accounting for peak-load shifting happening with battery bank already) that is another $2.00 per day (365 days per year), which is $730 per year in cost savings.  Add that to the $1000 and we are up to $1,730 per year.

6th phase: install feet, racking and panels for 5 strings of Sharp panels (2 strings of 6 feeding one of the MidNite Classics and 3 strings of 5 feeding the other MidNite Classic);

At this point, this adds another 4.6kW of solar feeding the battery bank (and house).  We expect to gain 23.0-27.6kWh per day of energy from this bank of solar panels.  Again at an average rate of about $0.10 and 25kWh per day that gets us $2.50 per day more savings.  Annually this means $912.50, add that to the $1,730 and we are up to $2,642.50 in total energy savings (if this is all we did).  Our total system cost for all this equipment is around $8,000 plus the $14,000 for batteries for a total of $22,000.  If we deduct fed tax credit from that cost we get to $15,400.  If we save $2,642.50 per year we are at a 5.8 years payback on the system, after which we will be ahead $2,642.50 every year that we don't have to spend more money on repairs/batteries/etc.

This is a lot of information and thank you for anyone who was interested enough to read it all, I'd love to hear feedback from others going through this same process and what they foresee as the costs/savings/ROI/etc to this entire project...  I assume most "off-grid" style installations are done in a truly off-grid location where it is the best option for energy, certainly my situation is unique in that we live in the city and are connected to the grid...  We want to do this to protect ourselves from increases in cost and also allow ourselves the ultimate freedom of potentially one day cutting the cord from the power company and being energy independent within the city!  Also we have had a couple brown-outs in our area over the last 2 years and we are now immune from those!  

I'd also love to hear folks thoughts on doing an "off-grid" system where we won't be selling any power back to the grid vs a traditional net-metering installation.

clockmanfran

Yes, we have Grid utility,  large old House and several holiday buildings, yet with a BIG change over switch we are then off Grid. We keep the Grid utility for night use as the utilities gives huge discounts for 7 hours during the night-time.

Please remember that insulation of your home is very Important.  As we have restored our 8 buildings we insulate them to Passive House Standards.

I know of several /many other folk around the World doing the same and cost effectiveness should be looked at long-term ie 15 to 20 years.

However If you have a professional installation & install, then the cost saving figures do not add up.

I have found in the past a clash of cultures between our sustainability concept and the truly Off Gridders who have no access in getting a utility supply.

I have published a Chapter on Off Grid in my recent book, empirical evidence on cost effectiveness and installation equipment & Types, and I would be willing to post the few pages here on this forum. But I would require The moderator on this Forum to approve it.

I have a habit of ruffling the feathers of professional Installers.  

ElectricLove

Our home is cinder-block construction for first floor and I believe timber on second floor (2x4) but stucco all the way up.  I don't think we will be able to add any insulation to the walls but our windows are old (single pane, aluminum frames), however we have wood shutters that sit 4" away from the glass that can be closed off completely creating a second barrier to the heat they let in (we keep them shut during hot times).

The only place I can conceive of adding insulation without breaking the bank (windows/doors would be around $20K per the last quote we got) is to do more blown in insulation in the attic.  It is a very small attic in this house, only 2-4' height throughout, it is not pleasant to enter and work in but we could get some skinny helper to go up there and help us blow insulation into the entire thing and create a more dense barrier.

What do you think?  I'm guessing the attic insulation was never improved in the house since it was built (70's), is it worth doing?

Also, we did replace one of our AC recently so we now have a 19SEER and 15SEER system (upstairs/downstairs), we hope to see reduction in consumption from that next summer...

What I would love is to be able to take our home totally off-grid with the 8.3kW of solar we are doing now or maybe add another 5kW (we already have an inverter waiting for this task) of solar and go totally off-grid at 13.3kW total solar (and expand battery bank to 50kWh)...  But I don't know if that'll be enough juice!

mcgivor

Quiet the ambitious project, be aware projected energy savings may not be reflected in actual results, with so many variables it's best to be conservative in estimating.

Being a "battery guy" I'm surprised by the use of drop in replacement type Lifepo4 as opposed to using prysmatic cells which are around 35% to 50% the cost depending on cell manufacturer, many drop in replacement type use multiple small cells in a parrallel series arrangement to provide 12V nominal. Are the batteries allowed to be configured in series? The website says they are compatible with all 12V systems but no mention of higher nominal voltages, admittedly I didn't do an extensive search.

Insulation of concrete blocks can be achieved with styrofoam on either the inside or outside depending on which is the most accessible, either with panels or spray. Regarding air conditioning 19 and 15 SEER are pretty low by modern standards but if it's what you have it may be economical to use what you have, for now at least.

Will limit comments so as to not overwhelm, thus leading to confusion, which is so easy in a forum with the delay in response due to different time zones.

BB.

ClockManFran,

Please feel free to post your excerpts. No problem with good/accurate information that is posted on topic.

-Bill "moderator" B.

clockmanfran

Thanks Bill.

Its just a few concise pages without getting to bogged down with minutia , but its all there.

Electriclove if you can insulate do so, every little bit helps.

If you have any questions about my few pages please don't hesitate to ask.

However, I am in Europe and follow the local electrical codes, and its important for your install to also follow your local electrical codes.

I trust this helps?

ElectricLove

@mcgivor
I didn't want to build my own battery bank with LFP cells, I wanted something with built-in BMS and already done for me.  With LFP cells I don't see getting much of a warranty while the Ohmmu batteries have a warranty from the manufacturer if I need to use it.  I've worked with LFP cells before in EV's and also in other projects and I am now a strong believer in buying them already assembled for me unless the price is drastically better.  However these Ohmmu batteries ran me about $565 per kWh, which really isn't a bad price, if I went the LFP cell route I don't think I'd get much better price per kWh.  How much did you spend on your 400Ah LFP cells? (I'd suspect about $750 per cell, which is about $585 per kWh...)

mcgivor

ElectricLove said:

@mcgivor
I didn't want to build my own battery bank with LFP cells, I wanted something with built-in BMS and already done for me.  With LFP cells I don't see getting much of a warranty while the Ohmmu batteries have a warranty from the manufacturer if I need to use it.  I've worked with LFP cells before in EV's and also in other projects and I am now a strong believer in buying them already assembled for me unless the price is drastically better.  However these Ohmmu batteries ran me about $565 per kWh, which really isn't a bad price, if I went the LFP cell route I don't think I'd get much better price per kWh.  How much did you spend on your 400Ah LFP cells? (I'd suspect about $750 per cell, which is about $585 per kWh...)

The cells I use are 100Ah used in 4P 8S arrangement, each cell cost $65 or $200 per Kwh, including shipping and BMS  $240 per Kwh, this is roughly double what I paid for 400Ah in FLA not including core value. They have been in service for a little over a year now, I didn't really need them but wanted to gain some experience before my LA bank needed replacement, lesson learned, I'll never use LA again.