New Member New System in Tempe, AZ

[sscherer2030]

Thank you for having me, we are in Tempe, AZ

Putting together and currently in the process of DIY install for a off-grid scale/capable system in our urban setting.

So far we have gathered 8.3kW of solar panels (1.6 installed now)
10.5kW of XW inverters (all installed)
4 Solar Charge Controllers (all installed)
20 Ohmmu 1.2kWh battery packs (25kWh total); these are Lithium Iron Phosphate, awesome batteries!

We plan to add another 5kW or so in solar and double the battery pack capacity and hope that brings us to the ability to go ahead and cut the cord with SRP, our local electric company...

Any ideas or thoughts, we would love to hear!

[Ampster]

Do you have any consumption numbers? Are the inverters hybrid and capable of grid tie and off grid?
I have been using Lithium batteries for ten years. Some of that is in EVs but my main use of my house inverters has been for backup and load shifting. If my utility keeps changing the rates and messing with my TOU periods it may be economical for me to use less and less of the grid. It will be nice to hear your experience with you progress toward you goals. I am thinking about increasing the size of my pack. I couldn't find any information on Ohmmu batteries. What has your experience been so far.

[SunEagle]

Hi sscherer2030 and welcome to Solar Panel Talk

Sounds pretty ambitious building an off grid system. I am curious as to what your POCO charges you for electricity. Most people have a hard time saving money going off grid instead of using a grid tie or hybrid system. Hopefully you will come out ahead of the game.

[sscherer2030]

What is POCO? Power Company? Makes sense, correct me if wrong...

we pay $0.05 off-peak and $0.25 on-peak.

It’s more about the “power” or energy independence and controlling/fixing our energy costs for the next 30 years. However we have had months where we pay over $500 for energy, so the budget to get to zero is somewhat large...

Our consumption ranges from 10kWh in a day up to 150kWh in a day. 150kWh is when we charge both of our EV from low to full and run both AC all day in Arizona summer heat.

We know to go fully off-grid will require new energy consumption strategies too, such as charging the EV on certain days or not at home during peak summer times. Also newer higher efficiency AC and more insulation in the attic will both help...

[sscherer2030]

Oh, Ohmmu batteries; www.ohmmu.com/group31

[Ampster]

Oh, Ohmmu batteries; www.ohmmu.com/group31

Thanks, that is $565 per kwhr. which is the best price I have seen for those kind of self contained Lithium batteries. Lets hope the price keeps coming down.

[sscherer2030]

No problem, they are local for me too (Tempe). I got the 12V battery for my Tesla from them and established a relationship with them, I think they are new on this scene (solar) but have been doing the Tesla batteries for a few years. I thought the intro price was pretty good and per kWh it’s quite good for Lithium Iron Phosphate. Thought about doing a torn down Tesla battery pack (buy chunks off eBay) but these were easier to work with in terms of wiring and building a rack and just look safer than buying batteries from a crashed car to me...

[azdave]

Sounds pretty ambitious building an off grid system. I am curious as to what your POCO charges you for electricity. Most people have a hard time saving money going off grid instead of using a grid tie or hybrid system. Hopefully you will come out ahead of the game.

I always felt SRP rates were pretty reasonable so it seems odd to see you developing an off-grid plan for the future when the grid is not expensive, nor unreliable around here. I would not consider for one second building an off-grid system, even if I had 30 years to make it pay for itself. I live in Gilbert with SRP and in Mesa before that and it was not a slam dunk decision to invest the money in buying a grid-tie. Are you doing this for environmental reasons because I can't see you saving any money this way.

[sscherer2030]

It isn't about saving money exclusively, though I do think in the end we will, it is about 2 main things:
1. Energy Independence; we will not be subjected to cost increases in future, don't have to "play games" with the energy company. We get to be the decision makers for where 100% of our energy comes from and for us that has value.
2. Environmental reasons; we drive electric vehicles not because they are the cheapest way to get from A to B but because we feel they are the cleanest and most environmentally friendly mode of transportation possible, however the thought that some of our driving may be powered by polluting energy sources (even though it is WAY less than any gas/diesel engine) has always been a little bit of a sore spot on the "perfect system". Well, if we are 100% solar household and off-grid then we are totally in control of what energy powers not only our home but also our driving.

So, I actually contributed to a book called "Driving to Net Zero" which was about some of the early EV and solar adopters and our efforts to go "net-zero" in terms of carbon emissions. This concept has stuck with us and we see the opportunity to get our household and driving both to net-zero by doing this "off-grid" system. Sometimes doing the "right" (for us) thing is not the cheap thing or the best way to save money.

However, on to the costs, fortunately I am a very capable DIY guy. I redid our entire roof prior to installing the solar and am just finishing up the 2nd and 3rd phases of solar installations up there. Doing it myself is great because it goes back to our reason #1 (energy independence) and not relying on anyone outside to maintain/service/repair/etc our system. It also saves a ton of costs. I acquired all the solar panels and inverters through OfferUp/Craigslist. We bought the batteries from an awesome local company, Ohmmu Energy (www.ohmmu.com/group31) and they aren't terribly expensive (though they are Lithium and admittedly they are expensive). All in we will spend:

1. Inverters, Panels, some wiring, PDP, accessories: $5,500
2. Installation materials (Unistrut, mounts, nuts/bolts, etc): $2,300
3. New roofing (tar, rolls of roofing): $1,100
4. Battery Bank (wiring, rack and 24 batteries): $16,000
5. Wiring (PV wire, some AC side wiring, breakers): $600

So, our total out of pocket expenses are $25,100 (not accounting for any related tax credits). Currently our annual energy bill is about $3,000; this puts our "break-even" point at 8.5 years out (8 years if you don't count the roofing which should have been done either way). I don't consider 8 years a bad pay-back period and 10 years from now we will be ahead by $6,000 and looking back saying "why didn't we do that sooner". We don't know how long our battery pack will last but we certainly expect a minimum of 10 years using it at about 25% every day with a few times a year where we actually run it down to "low". In 10 years I expect the replacement cost to be quite a bit less.

If we account for tax credits ($1K AZ state and about $7K FED) it shaves almost 3 years off the payback timeline.

So, although this isn't a "get rich quick" formula or an uber-thrifty idea and it does take weeks of labor from me and quite a big out-of-pocket expense up-front I also don't consider it a bad investment, it is a green and environmentally friendly way to go and in addition to that in the long-run it is also a financially sustainable and genuinely good investment!

Now, I can't fully advocate it for others because let's face it, who else is going to do all of the work themselves? And solar companies need to make their money. I think if you run the numbers assuming a solar company does the entire installation/project for you and use these same batteries we used you are probably at about $40K in cost, minus $13K in tax incentives puts it at $27K and a 9-years break-even point... I still think that would be a worthwhile way to go and SRP currently has an energy storage rebate that a licensed installer can qualify for (worth about $3K) so that would bring it back to an 8-years break-even if one went that route...

[sscherer2030]

One of the things I noticed when I first started shopping is the battery banks. We actually started this journey when the SRP energy-storage incentive post card came to us.

We got quotes for installing battery banks and after taxes and installation it was about $18K to do 2 of the LG Chem Resu 10kWh batteries and about $20K to do 2 of the TESLA PowerWalls (27kWh). Neither of which would qualify for any tax credits if we didn't also install solar (and install that solar with the same company of course). We decided we wanted the batteries to be less complicated and easier to work with than these massive/heavy battery packs, Resu and PowerWall are both very large and very heavy which makes self-install impractical. PowerWall can be installed on its own but the Resu require an additional inverter. PowerWall uses AC to charge the battery bank and then converts it back to AC on the way out, resulting in round-trip efficiency losses.

To us the ultimate solution is a battery that is a smaller form-factor which can be scaled up/down as needed really easily, these Ohmmu units are about 25lbs and don't have any fancy cooling/installation requirements (aside from the obvious don't install them outside and don't get them wet), I can carry 2 batteries at a time easily so I knew I could build the battery bank with these all on my own and not break my back doing it. They are also straight-forward, just simple 12V batteries, wire them in parallel for more Ah and series for more V, if we got an inverter that runs on 24VDC we can wire that way if we got an inverter that runs on 72VDC, we can do that too! (consider when these inverters fail and need replacement, 10 years from now if we find 72V inverters it would be nice to be able to use them!).

Cost per kWh being a factor to consider as well:

PowerWall (x2 w/ install): $20,000 / 27kWh = $740 per kWh
Resu (x2 w/ install): $18,000 / 20kWh = $900 per kWh
Ohmmu (x24 w/ install): $16,000/ 25kWh = $640 per kWh

Lastly, Ohmmu uses Lithium Iron Phosphate chemistry which is well known to be much safer than the chemistry of the PowerWall or Resu and also to be more robust and last longer. We shall see in time but we are optimistic that our system's batteries will last much longer than a PowerWall or Resu system would and that results in a lower cost per stored/retrieved kWh, which is ultimately the real cost to consider.

This line of reasoning was the start of us moving away from the traditional route and going to a DIY system where we can achieve all of the benefits we feel are most important and do so at the best possible cost.