Hybrid Ouback Skybox with Nissan Leaf batteries

[Ampster]

I have an existing Grid Tied solar system and want to use the Skybox for the following:
- Shift loads so that all my solar production gets credited at the Peak Rate.
- Have a backup in the case of a power outage.
- AC couple the Outback inverter to my Grid tied system so that during a power outage the additional capacity if that system can supplement my back up.
I have the Nissan Leaf battery modules from another project. I had thought about a Tesla PowerWall but believe i can bring this system online for less than the cost of a PowerWall, before incentives and rebates.

[J.P.M.]

If you want to do what I think it sounds to me like you might want to do (storing off peak generated power and feeding the grid from storage at peak hours) , the POCO may have something to say about it. Have you checked their NEM rules ?

[Ampster]

I already have a NEM agreement for my existing GridTied system. I don't see the value of having another. I also won't be adding any solar panels initially. I have a source for more Nissan Leaf modules and I will be incrementally adding capacity until I can get through the peak period without using anything from from the grid during that time period.
I am still doing the analysis on whether to use the energy generated by my existing Grid Tied system to charge the batteries, or charge from super off peak rates. In summer my peak rate is $0.47 per kWhr vs $0.13 super off peak.

NB: after reading @JPMs post again, I realize I should have clarified that I do not intend to sell back power that I have stored. I do intend to peak shave, load shift and long term add additional non grid tied solar, to reduce my overall consumption.. That often results in load departure from the grid.

[J.P.M.]

I already have a NEM agreement for my existing GridTied system. I don't see the value of having another. I also won't be adding any solar panels initially. I have a source for more Nissan Leaf modules and I will be incrementally adding capacity until I can get through the peak period without using anything from from the grid during that time period.
I am still doing the analysis on whether to use the energy generated by my existing Grid Tied system to charge the batteries, or charge from super off peak rates. In summer my peak rate is $0.47 per kWhr vs $0.13 super off peak.

I assumed you do already have an NEM agreement. My point was not to have another NEM agreement. Since I don't know what your NEM agreement looks like and since some NEM agreements exclude or disallow arrangements that allow storing grid power in batteries during off peak times for use at peak times, or modify agreements if storage is part of the arrangement, I am only suggesting you might want to check it out before you assume anything.

[Ampster]

My NEM 2.0 agreement limits the amount of solar panels I can add and it only allows me to be grid tied with the existing Solar edge inverter. Further it requires me to pay Non Bypassable Charges for any power I consume during each one hour interval. The installer did that paperwork. I did two earlier NEM applications and they are a pain. In my unique circumstances I see no financial benefit to going through those steps. You are correct, that a NEM agreement would not let me charge my batteries from the grid at $0.13 and sell back to the grid at $0.47. All I need to do this install is a building permit to store that power. What I do behind the meter is my business aa long as I don't sell it back. If If I shed load, or divert load because i run my critical loads panel off my new inverter, all my solar generation goes to the grid at on peak rates. Plus I don't pay peak rates for what I use after the sun goes down.

If there is something I am missing I am open to suggestions and i assume you are familiar with NEM agreements in California?
I clarified my earlier post to make it clear that I only intend to remove load from the grid and not sell back power that I have stored at cheap rates.
Incidentally I had a Powerwall on order and the Self Generation Incentive Program incentive was attractive but it came with limitations and the constant excuses for the backordered Powerwalls convinced me to go in this direction.

[jflorey2]

I have an existing Grid Tied solar system and want to use the Skybox for the following:
- Shift loads so that all my solar production gets credited at the Peak Rate.

You mean to offset your usage at peak rate times, right? If so OK but it won't save you money long term.

- Have a backup in the case of a power outage.

Generators are generally a better choice for that. However, the Skybox will also allow you to do that by adding storage.

- AC couple the Outback inverter to my Grid tied system so that during a power outage the additional capacity if that system can supplement my back up.

This is doable but is not easy. You need at least one relay that can disconnect your solar generation when the battery is close to fully charged.

I have the Nissan Leaf battery modules from another project. I had thought about a Tesla PowerWall but believe i can bring this system online for less than the cost of a PowerWall.

That is a lot of work. You will need a BMS, and will have to figure out how to integrate the BMS into the Skybox. There aren't many lithium chemistry batteries yet that work with the Skybox.

[Ampster]

....OK but it won't save you money long term.

Generators are generally a better choice for that. However, the Skybox will also allow you to do that by adding storage.

This is doable but is not easy. You need at least one relay that can disconnect your solar generation when the battery is close to fully charged.

That is a lot of work. You will need a BMS, and will have to figure out how to integrate the BMS into the Skybox. There aren't many lithium chemistry batteries yet that work with the Skybox.

How much money I save depends on how much I use. Remember in summer my peak rate is $0.47 /kWhr. If I save 1000 kHrs per year I get my money back over 15 years

I can't achieve my other goals with a generator and that is why I prefer to use storage supplemented by solar than maintain a generator. It is a personal preference. Your mileage may vary.

I am very familiar with relays. That is my fallback if I can't get CAN communications to work with the BMS. If I can't get Outback's AC coupling to control the grid tie inverter when the grid is down I will use relays there triggered by high voltage battery signal to knock the grid tie inverter off line.

I am retired and one of my hobbies is this kind of electronics. Yes, it will be a lot of work. Any ideas on how to make it simpler? I already have an Orion BMS and it is already configured from another project for this battery chemistry.

I am not sure I agree with your statement about Lithium chemistries not working with Skybox. You maybe thinking of package systems like SimpliPhi or LG Chem where the issue may be the communications between the Skybox and the integral BMS of those systems. Lithium is easier for me than FLA or AGM. It requires just a constant charge voltage, the correct Amperage and a BMS to control or cutoff the charging and discharging. No float just a simple voltage setting. My previous system was a Radian and I used LFPs for a while before I switched to the Nissan Leaf batteries which I think are NMC. The Radian didn't care what the chemistry was. Am I missing something?

Thanks for the feedback. It is always important for me to check my assumptions. That is the value of forums like this.

[Sunking]

OK you are going down a dark democrat road of insanity. Here is a parable of what you are doing or wanting to do if I understand you correctly.

Two Jewish Tailors, Abe, and Ruben, are standing out in front of their shops talking biz. Abe sells his suits for $800, and Reuben sells the same suit for $400.

Abe the conservative ask: Reuben how much does it cost you to make a suit?

Ruben answers: Same as you $600.

Abe ask: How do you stay in biz selling for a loss?

Reuben the democrat says: I make up for it in volume selling more than you do.

You are Reuben. In the end it will cost you over $1 to make a Kwh, and you sell it for 15 cents. You need to buy more batteries and panels to step up production and go bankrupt faster like Reuben the democrat.

[Ampster]

OK you are going down a dark democrat road of insanity........

Thanks for the encouraging words. Is there something wrong with my goals?
I am not sure how you calculated the cost of the energy I will produce? Are you costing both my grid tied system (sunk cost) or the cost of the Skybox and the rest of the system (batteries & BMS) that I already have?

I am on a TOU rate and a NEM agreement that pays me $0.47 in summer and $0.37 in winter. I currently have the ability now to do some load shifting. This additional inverter will only enhance that ability and give me a hedge against further shifts by PG&E of the TOU time periods. Plus I get backup and with AC coupling can extend that backup time by utilizing the grid tie system when the grid is down.

What am i missing?

[Ampster]

........... In the end it will cost you over $1 to make a Kwh, and you sell it for 15 cents. ........

I don't know how you assumed $1.00 per kWh without knowing what my system will cost. To give us a common set of facts to discuss let me explain what I anticipate my costs to be. Initially this will be a hybrid system without solar panels. Later if my needs exceed the capacity of my existing system I was thinking of adding 3K of solar panels. Over 20 years they should generate approximately 72,000 kWhrs of electricity. If I add the cost of the skybox ($6,000) and the cost of 3kW in solar panels and hardware ($4,000) the total system cost will be $10,000. If I assume the system has a life of 20 years that system could generate 72,000 kWhrs. So the cost of the energy generated by that system over 20 years would be $0.14/kWh. Since that system will not sell any power to the grid it is hard to quantify a number for what I will sell it for. What I do know is that at peak summer rates of $0.47/kWh I am going to saving money by taking that load off the grid.

[Mike90250]

.......

What am i missing?

Battery replacement costs. If you cycle the batteries to sell power, you wear them out, Then you buy new ones, and your cost savings fly out the window

[SunEagle]

I don't know how you assumed $1.00 per kWh without knowing what my system will cost. To give us a common set of facts to discuss let me explain what I anticipate my costs to be. Initially this will be a hybrid system without solar panels. Later if my needs exceed the capacity of my existing system I was thinking of adding 3K of solar panels. Over 20 years they should generate approximately 72,000 kWhrs of electricity. If I add the cost of the skybox ($6,000) and the cost of 3kW in solar panels and hardware ($4,000) the total system cost will be $10,000. If I assume the system has a life of 20 years that system could generate 72,000 kWhrs. So the cost of the energy generated by that system over 20 years would be $0.14/kWh. Since that system will not sell any power to the grid it is hard to quantify a number for what I will sell it for. What I do know is that at peak summer rates of $0.47/kWh I am going to saving money by taking that load off the grid.

You did not figure in the number of sunless days you will be getting in those 20 years or the depreciation of the panels over that time to produce anywhere close to nameplate wattage.

If you live in an area where your electric costs more than $0.40/kWh you certainly can get a good ROI for a grid tie system. It all depends on how much you use and how much good sun you get. But with a battery system unless you get them for free you will end up spending more than what they will generate in kWh.

New battery technology has brought down the price of systems and may have some type of payback but at today's prices most batteries will cost you more than $0.50 for each kWh they can generate over their life.

[Ampster]

Battery replacement costs. If you cycle the batteries to sell power, you wear them out, Then you buy new ones, and your cost savings fly out the window

Okay, if I buy more Nissan Leaf batteries at $200/kiloWatt and I replace them every 8 years. Assuming I use 50% of their capacity every day. 14kWr costs $2800 and stores 7kWh per day for 360 days per year for 8 years. That means the cost of 20,100kWhr stored is $0.139/kWh. Add that to to the previous cost above means that total cost per kWh is still only $0.28/kWh. That is still cheaper than my peak rate of $0.47 in summer plus I have a hedge against inflation, I have backup and the satisfaction that I am only paying the minimum fixed charges to PG&E.

[Ampster]

You did not figure in the number of sunless days you will be getting in those 20 years or the depreciation of the panels over that time to produce anywhere close to nameplate wattage.
.............
New battery technology has brought down the price of systems and may have some type of payback but at today's prices most batteries will cost you more than $0.50 for each kWh they can generate over their life.

Here is my math so you can tell me what I did wrong or whether my assumptions are correct. I looked up my location and installation specifics on PVWatts which gave me a factor of 1438 times nameplate to estimate my annual production. That is consistent with the production guarantee my installer gave me on that system. In 10 months since it has been installed my system is on tract to exceed that projection. To be conservative and account for degradation I only used a factor of 1200 for my calculation above.

If I could get batteries at $0.50/kWh I would buy a megaWatt of those. Perhaps you mean $0.50/Watt? Still, that makes my price of $0.20/Wat for used Nissan Leaf modules a good deal.

As calculated in the post above, the cost of my battery storage is $0.139/kWh. That is significantly below your estimate of $0.50/kWh. How did you calculate that number and what assumptions did you make? Is that the total cost of ownership of FLA batteries?

[SunEagle]

I looked up my location and installation specifics on PVWatts which gave me a factor of 1438 times nameplate to estimate my annual production. In 10 months since it has been installed my system is on tract to exceed that projection. To be conservative and account for degradation I only used a factor of 1200 for my calculation above.

As calculated in the post above, the cost of my battery storage is $0.139/kWh. That is significantly below your estimate of $0.50. How did you calculate that number and what assumptions did you make?

Unfortunately your calculation is based on a paper estimate and not real time usage. The big question is, will any of those Li battery systems provide the rated kWh each day and last 8 years that they say they will. I do not believe they will yet. They are too new a battery technology to have a proven track record.

My $0.50/kWh is based on current FLA type battery costs, kWh output and cycle life. While an FLA might not last very long, it still costs much less then any professionally installed Li battery systems. Heck even the Powerwall2 is about $9k to $10k installed.

But you might find used batteries for less. The key term is USED. Can you trust them?