Plan: Off grid solar with a Model S battery pack at the heart

[Yoda101]

+1
"Edit: Mods: I somewhat agree that most of the posts by 'electrodacus' and subsequent replies by others and myself relating to those posts in this thread are mostly off topic here. I leave it up you you guys on whether or not it warrants carving to a 'Lithium Iron Phosphate (LiFePo4) vs Lithium Cobalt variants (LiCo*) for Stationary Storage' type spin-off thread. I have no objection either way."

 

[nwdiver]

Using the warranted life is never a good starting point.

I'm sure the original White House solar PV system was warranted only for a decade or so, yet here they are 38 years later, still producing energy for Unity College.

The white house solar panels Carter installed were thermal... not PV...

Anyway; I agree warrantied life is not a good indicator of actual life.

 

[Robert.Boston]

Carter's panels were removed by Reagan; it wasn't until Obama moved in that new panels went up (PV this time).

But we digress.

 

[FlasherZ]

The white house solar panels Carter installed were thermal... not PV...

Anyway; I agree warrantied life is not a good indicator of actual life.

I was quickly hunting down threads and they weren't all clear. I probably should have just left it at solar - but you note my main point, which is that using the warranty to estimate life is a Wrong Move(tm).

 

[scottbiltmore]

WK-
How are you keeping the batteries from overcharging?

 

[wk057]

WK-
How are you keeping the batteries from overcharging?

Currently just have the voltage cut off points well inside the full SoC window. When I get my BMS completed I can tighten that a bit more.

Well, started work to fully test out (in other words, have some fun with) the panels that I'm going to be putting on the roof in a few weeks.

Just leaned (and tied) 6 of them up against the fence inside my pool area (horrible angle and direction) and wired them to a combiner and one of my charge controllers temporarily. While I was taking that picture they were outputting 2.05kW out of a possible 2.61kW rating, so about 79% of rated output facing the wrong direction (about 145 degrees) at a super steep angle (~60 degrees?).

I plan on rotating the panels out, cleaning them, and such so I can get 36 fully tested by the time it is install time. According to PVwatts, this test configuration should yeild about 5kWh per day usable AC power.... which is interesting considering I've had them put up for less than 2 hours and have put 3.3kWh back into the battery bank already according to the one charge controller I'm using for testing. At my inverter efficiency that would be about 3kWh usable AC... from less than 2 hours of sun....

All of that said, I'm pretty happy with the test so far.

As a bonus... can kind of better visualize how freaking huge this ground mount array is going to be. 11x larger than this test setup. :scared:

 

[oneday]

Sounds like you better start pricing wire to your neighbors. I wonder how the planning department would deal with a multi parcel electrical permit.

 

[lolachampcar]

The utilities will call him a utility and shut him down I suspect.

 

[Johan]

Currently just have the voltage cut off points well inside the full SoC window. When I get my BMS completed I can tighten that a bit more.

Well, started work to fully test out (in other words, have some fun with) the panels that I'm going to be putting on the roof in a few weeks.

Just leaned (and tied) 6 of them up against the fence inside my pool area (horrible angle and direction) and wired them to a combiner and one of my charge controllers temporarily. While I was taking that picture they were outputting 2.05kW out of a possible 2.61kW rating, so about 79% of rated output facing the wrong direction (about 145 degrees) at a super steep angle (~60 degrees?).

I plan on rotating the panels out, cleaning them, and such so I can get 36 fully tested by the time it is install time. According to PVwatts, this test configuration should yeild about 5kWh per day usable AC power.... which is interesting considering I've had them put up for less than 2 hours and have put 3.3kWh back into the battery bank already according to the one charge controller I'm using for testing. At my inverter efficiency that would be about 3kWh usable AC... from less than 2 hours of sun....

All of that said, I'm pretty happy with the test so far.

As a bonus... can kind of better visualize how freaking huge this ground mount array is going to be. 11x larger than this test setup. :scared:

Sounds like you'll be getting way more than 5kWh per day from those when properly mounted. Perhaps the number you got was an average for the whole year, including winter time and cloudy days?

 

[nwdiver]

I plan on rotating the panels out, cleaning them, and such so I can get 36 fully tested by the time it is install time.

Your panels didn't come with cut sheets from the factory? I've always gotten a sheet with performance specs for each panel.

 

[wk057]

Sounds like you better start pricing wire to your neighbors. I wonder how the planning department would deal with a multi parcel electrical permit.

The utilities will call him a utility and shut him down I suspect.

lol. I don't really have any plans to power neighbors. I'll be happy, in year 1, if I can power myself 99.9% of the time.

Sounds like you'll be getting way more than 5kWh per day from those when properly mounted. Perhaps the number you got was an average for the whole year, including winter time and cloudy days?

Yeah, in my haste I actually screwed up my input and reading of PVwatts. It estimates 11.5 kWh per day. Today I got 14.6 kWh.

Your panels didn't come with cut sheets from the factory? I've always gotten a sheet with performance specs for each panel.

View attachment 77055

They have factory specs, but as with all panels, they're overstated for real world for sure.

 

[wk057]

Data from today's full testing of six panels. Got cloudy the last couple hours of the day. 14.6kWh collected. Peak 5 second output average of 2,375 watts (91% of rated).

Edit: I can only assume my full setup with 102 panels will work at least as well. This would be 17x the power, so 248.2 kWh for today. As of right now, 83% of the day is over and: KWH USED SINCE MIDNIGHT: 71.088 kWh

I did just get home from a reasonably long drive, which will add ~40 kWh to that... but still.

 

[llavalle]

What's the model of your panels wk057?

I won't be able to generate as much electricity in here (Cold Canada!) but I would find it poetic to be able to charge my car using solar electricity!

 

[nwdiver]

What's the model of your panels wk057?

I won't be able to generate as much electricity in here (Cold Canada!) but I would find it poetic to be able to charge my car using solar electricity!

I believe those are SunPower 435w panels; B Grade Panels have recently become available for $0.64/w from Sun Electronics.

 

[miimura]

I can only assume my full setup with 102 panels will work at least as well. This would be 17x the power, so 248.2 kWh for today. As of right now, 83% of the day is over and: KWH USED SINCE MIDNIGHT: 71.088 kWh

I did just get home from a reasonably long drive, which will add ~40 kWh to that... but still.

Will you be getting interconnect permission for the solar so that when your batteries are full you can put the excess into the grid? If not, have you formulated a plan for something useful to do with the surplus? I suppose if you don't come up with anything better, you could heat the pool

 

[wk057]

They are the SunPower E20 435W panels, part SPR-E20-435-COM

 

[InTheShadows]

Currently just have the voltage cut off points well inside the full SoC window. When I get my BMS completed I can tighten that a bit more.

Well, started work to fully test out (in other words, have some fun with) the panels that I'm going to be putting on the roof in a few weeks.



Just leaned (and tied) 6 of them up against the fence inside my pool area (horrible angle and direction) and wired them to a combiner and one of my charge controllers temporarily. While I was taking that picture they were outputting 2.05kW out of a possible 2.61kW rating, so about 79% of rated output facing the wrong direction (about 145 degrees) at a super steep angle (~60 degrees?).

I plan on rotating the panels out, cleaning them, and such so I can get 36 fully tested by the time it is install time. According to PVwatts, this test configuration should yeild about 5kWh per day usable AC power.... which is interesting considering I've had them put up for less than 2 hours and have put 3.3kWh back into the battery bank already according to the one charge controller I'm using for testing. At my inverter efficiency that would be about 3kWh usable AC... from less than 2 hours of sun....

All of that said, I'm pretty happy with the test so far.

As a bonus... can kind of better visualize how freaking huge this ground mount array is going to be. 11x larger than this test setup. :scared:

Pvwatts takes weather into consideration. It's average monthly sun hours that it calculates from. If it's sunny all day on the equinox you could get 8-9 sun hours.

 

[wk057]

Got the "cloud effect" a few times per day. Those six panels hit almost 2.9kW output at a couple of points. That's 111% rated output. Yummy!

And to top off the day, my permits for my roof mounted portion of panels was approved today.

Figure I'll share a few somewhat web-sanitized excerpts from the plans I submitted for permitting.

Install for the roof panels planned for the last week of the month. Exciting!

 

[nwdiver]

Test Request;

I was hoping you'd be willing to share some data... do you know what the charge/discharge efficiency of your system is? I'm trying to talk a friend into storing energy instead of exporting it but we need to know how many kWh you get back from what goes in. He get's paid $0.075/kWh exported and charged $0.13/kWh imported... trying to figure out how much he'll save by storing instead of exporting. Thank you.

He would likely get the exact same setup as you (slightly smaller).... (ok, more than slightly smaller).... :redface: though he'll be charging from the grid instead of from charge controllers.

 

[wk057]

Test Request;

I was hoping you'd be willing to share some data... do you know what the charge/discharge efficiency of your system is? I'm trying to talk a friend into storing energy instead of exporting it but we need to know how many kWh you get back from what goes in. He get's paid $0.075/kWh exported and charged $0.13/kWh imported... trying to figure out how much he'll save by storing instead of exporting. Thank you.

He would likely get the exact same setup as you (slightly smaller).... (ok, more than slightly smaller).... :redface: though he'll be charging from the grid instead of from charge controllers.

Numbers relevant to what you're asking about:

The inverters can charge from the grid at about 90% efficiency. The input to the batteries at this point is within 1-2% of output, depending on charge rate (faster charging = more loss, slow charging could approach close to 0% loss).
The inverter output in grid tie mode is also about 90% efficient.
Wiring and other misc losses will be 1-2%.

So, 0.9 * 0.9 * 0.98 * 0.98 yields about 77.7924% round trip efficiency. We'll round down to 75% for simplicity. Not sure what numbers you're looking for beyond that, though.