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DuncanCunningham
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 9:15 am

LKK wrote:I installed a Tesla Powerwall 2 with a SolarEdge system. The system works well. During the day excess solar power is first used to charge the battery and when it is fully charged the power is sent to the grid using a net metering power purchase agreement. When the sun goes down the power is first drawn from the battery via an integrated 5 kw inverter and when it is depleted, power is drawn from the grid.

If the grid fails the Powerwall isolates itself from the grid and uses its integrated inverter to supply a 240 VAC signal to the SolarEdge net tied inverter to allow it to function in backup mode. There are two subpanels in my system, one for backed up circuits the other for unbacked circuits. The criteria used to decide if a circuit is backed or not is the power capacity of the integrated inverter. It will handle 7 is peak and 5 is continuous, you have to decide which circuits you want backed based on their power consumption and the capacity of the battery. The subpanels are next to each other so it is relatively easy to move a circuit from one subpanel to the other. In my system I backed all the 120 VAC circuits and put all the heavy load 240 VAC circuits in the unbacked side. I should add when the system is operating normally the battery supplies power for both subpanels when solar power is not available.

The battery capacity is around 13.6 kwh. You can set the amount of usable capacity in the Tesla app. The battery is liquid cooled. The Tesla app has been very useful showing power flows between the solar, battery, home and grid in instantaneous and accumulated power over different periods.

The main advantage of the battery for me is rate arbitration. With solar I'm forced on to a time-of-use rate schedule where the main daylight hours are classed at off peak and late afternoon and evening hours are the peak period. Off peak is around $.25/KWH, peak is double that at $.50/KWH. So instead of sending excess solar power to the grid, it makes much more sense to store this power in a battery that becomes active during peak hours. This could save up to $7/day on a 14 KWH battery. The new net metering rates being forced on new solar users without this battery, is in my opinion totally useless.

Here in California a Self Storage rebate is being offered which significantly offsets the cost of the battery.


I was lucky, i installed my solar array when they did like for like net metering.. so anything I put in I get back at the same rate. They could change that I think, at anytime to suit them. so this setup is the best, the one you have. I'd do it. But since our power company has a flat rate all day each day.. not much of an incentive to do such a system yet. I'll have to watch closely to see what happens. right now the grid is my battery but they've been harping on about it some recent mailings to the city, which pretty much calls residents with solar 'thieves', though they don't go as far but it's implied.
Last edited by DuncanCunningham on Fri Sep 29, 2017 8:28 am, edited 1 time in total.
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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 10:26 am

LKK wrote:I installed a Tesla Powerwall 2 with a SolarEdge system.

What model SolarEdge is that? So that's it? Panels on the roof, Tesla Powerwall 2 and the SolarEdge box?
LTL
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LKK
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 10:43 am

LTLFTcomposite wrote:
LKK wrote:I installed a Tesla Powerwall 2 with a SolarEdge system.

What model SolarEdge is that? So that's it? Panels on the roof, Tesla Powerwall 2 and the SolarEdge box?


(12) LG 335N1C-A5 panels with AS P400 Solaraedge optimizers.
Solaredge SE3800HD Inverter
Tesla Powerwall AC battery

The Powerwall comes with a Tesla Gateway which acts as the brains of the system directing the powerflow between all the components. I don't have line item pricing but I believe the Powerwall and Gateway was around $7500 all of which is applicable towards the Federal Tax credit.

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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 12:22 pm

LKK wrote:(12) LG 335N1C-A5 panels with AS P400 Solaraedge optimizers.
Solaredge SE3800HD Inverter
Tesla Powerwall AC battery

The Powerwall comes with a Tesla Gateway which acts as the brains of the system directing the powerflow between all the components. I don't have line item pricing but I believe the Powerwall and Gateway was around $7500 all of which is applicable towards the Federal Tax credit.


Thanks. Looks like those panels are about $325/ea, the inverter is about $1100 and the Powerwall is $7500 so $13k - 30% - $9k, not counting anything for installation or other components. At .50/kwh I can see these quickly become no-brainers, at .11/kwh it's a lot tougher to get them to pencil out.
LTL
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RegGuheert
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 12:54 pm

LTLFTcomposite wrote:At .50/kwh I can see these quickly become no-brainers, at .11/kwh it's a lot tougher to get them to pencil out.
Comparing the cost of a system which will likely last over 25 years (except for the battery) to TODAY's price for electricity often leads to incorrect conclusions.

I recently purchased new grid-tied microinverters to REPLACE existing functioning inverters which have used seven of their 15-year warranty. I suspect these inverters will not outlive their warranty by much, so I decided to extend the warranty by 17 years with this purchase. Using the following calculations, I convinced myself that this purchase was better than any Roth 401k investment we could make today.

Data:
- Electricity currently costs $0.12/kWh here
- The solar array being upgraded produces about 4000 kWh of electricity each year
- The warranty on the current inverters continues through the end of 2025.
- The warranty on the new inverters is good through the end of 2042.
- The new inverters cost $1100 installed.

Assumptions:
- Basic (no TOU) net metering will be in force through 2042. (We live in the country and growth here is quite limited by law.)
- All warranties are honored by the manufacturer through 2042.
- The old inverters will fail shortly after the end of the warranty period. (This is the shakiest assumption here, since they could fail just BEFORE the end of the warranty period, in which case all would become new again.)
- The price of electricity in January 2026 will be 50% higher than it is now, or $0.18/kWh. (This MAY be aggressive, but I think it will be close.)
- The price of electricity in December 2042 will be 100% higher than it is now, or $0.24/kWh. (This is likely a conservative number.)
- The photovoltaic panels last until December 2042. (These panels where installed in 1999, so that implies a 42-year life. Time will tell.)

Calculations:
- Average cost of electricity between January 2026 and December 2042 is $0.21/kWh.
- Total value of the electricity produced between January 2026 and December 2042 is $14,280.00.

In other words, I expect my $1100 investment today to yield over $14,000 dollars between the years 2026 and 2042. I don't know of any financial investments which I can confidently expect to yield such a return.
RegGuheert
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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 1:21 pm

Maybe I'm jumping to conclusions here too quickly but it looks like the backup power/storage capability is more than doubling the cost of the system vs simple grid tied. Considering that such outages really are quite rare I'm probably better off just spinning up the Honda generator to keep the fridge going in such situations. Who knows, a storm could easily damage the panels and that's what I'd be doing anyway.

Still, if it was just a matter of getting a fancier inverter to enable upgrading the system later to have backup capability it might be worth considering. Years ago we had an RV with a 2kw inverter and it was pretty amazing what you could run off four golf cart batteries. Do we really need a fancy $7500 powerwall? I suppose the difference there is while that might give me some backup capability it wouldn't do much for not pulling power after the sun goes down.
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BrockWI
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 1:40 pm

I started small, with 2 marine batteries and an inexpensive inverter. then added a few panels. We now have 3kw of solar, 8 L-16 batteries and a xantrex XW6048 inverter with most of the house on that electrical subpanel. The problem is you have to piece most of this together yourself or pay someone a good chunk of change to do it. Basically our system is what you are looking for but not something most people could setup or maintain.

Most of the time it is less expensive and a lot more straightforward to just go with a small genset. We have a Honda EU2000i and after trying over a dozen gensets or 20 years I would strongly recommend just skipping the rest and pay for a good one, the quietness of it alone is worth it, not to mention fuel economy and reliability.

Or take a look at this thread

viewtopic.php?t=13097

You already have the 24kWh pack ;) But again get a good quality inverter to start with.
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 3:07 pm

BrockWI wrote:Most of the time it is less expensive and a lot more straightforward to just go with a small genset. We have a Honda EU2000i and after trying over a dozen gensets or 20 years I would strongly recommend just skipping the rest and pay for a good one, the quietness of it alone is worth it, not to mention fuel economy and reliability.

Sounds like good advice and I should just stick with the generator. After fighting with a big box store POS generator after storms back in 2004 I upgraded to a Honda EB5000. That performed well after storms in 2005 but mostly sat around ever since. It was a tank, like 275 lbs; I just recently sold it and got an EU2000. Less is definitely more in this situation. At least I managed to get it right on the third try :-)
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Beardedjeff
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Re: Solar for grid tied AND backup - where to begin?

Thu Sep 28, 2017 2:02 pm

Great question! I had the same needs/wants and actually just had my grid-tied PIKA system commissioned a week ago. I have 7.45kw (21 panels) from Seraphim with the Pika inverter, grid-tied. Their battery setup is done with Panasonic and is super easy to integrate later, its literally 2 wires plus a sub-panel with your backed up loads. I hope to add it in a year or so to allow grid-down usage.
The other nice part was their flexibility with operating modes when the battery is connected. I can set it up to give priority to sending excess to grid, never send to grid, priority to keep battery always charged, or self supply where it will use entirety of battery before tapping back into grid.
I was also looking at the Solaredge Storedge system with a powerwall but ultimately was swayed by a few things:
- Powerwalls are all but impossible to get in the US, they're only NOW starting to be somewhat available, mostly in mandated states.
- The Pika setup is a simpler system. There is no additional auto-transformer for battery backup needed, the one box does it all
- Both the Pika and Seraphim panels are made in the USA. I personally talked with the guys at Pika and they were very helpful.

Check out my production here!
http://profiles.pika-energy.com/jeff

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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Thu Sep 28, 2017 5:15 pm

Beardedjeff wrote:Great question! I had the same needs/wants and actually just had my grid-tied PIKA system commissioned a week ago. ...

Thanks for the reply, great info there. So do I understand correctly, you got the Pika inverter with backup capability, but you didn't buy the batteries yet? How much additional did the backup add-on capability cost?
Did you consider the Schneider Conext box?

Lots of articles in the press here about how you can't use solar during an outage. Many are written to convey a narrative it's the evil power company keeping control over the masses. No doubt a bunch of people read the headlines and take away confirmation they're better off not having gotten solar.
LTL
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