Elon, I love you... but the PowerWall isn't that great...... yet.

[brianman]

Well, if you add the cost of a UPS (I have a 6 KVA one which cost more than a couple of Powerwalls ten years ago--and the six battery packs have had to be replaced occasionally) it wouldn't fail. Of course, I don't have solar or TOU, and my cost of electricity from renewable sources is less than $0.10, so the calculation won't work for me either, but should I have to replace the current UPS, it would be with a Powerwall. (I have to redo the wall int he bedroom anyway

Yah, this is a fair point. One of the benefits of the solar+battery installation at my current house was moving away from the 3x 2200VA UPS boxes that I had in the old house (which were taking up space, generating heat, requiring battery replacements every few years, etc).

- - - Updated - - -

They [SolarCity] are trying to install on homes that make the most sense right now. Demand is through the roof, so they have to prioritize.

"Solar panels on rooftops" joke observed.

 

[Foghat]

glhs272, that's an interesting question... Peter rive said that CA, NY, and HI may offer storage+pv customers an "aggregation" demand fee for your home power plant. Essentially they pay you a monthly fee for generating your own electricity in order to elevate load from the grid.

so by the very fact you are 100% self sufficient you are alleviating this load perpetually, thus, you can go off grid and the utility will pay you for it... Who needs net metering when you can get more with a demand fee?

If this is how Solarcity is getting Hawaiians off the grid starting next year, very genius if true.

 

[yobigd20]

SolarEdge just made a product announcement - it seems they are working jointly with Tesla on making a brand new inverter that will be available end of 2015 to integrate the Powerwall with PV and tie it in with the grid. SolarEdge Announces Collaboration with Tesla Motors to Offer Distributed PV Storage Solutions

SolarEdge Technologies, Inc. (“SolarEdge”) (NASDAQ: SEDG), a global leader in PV inverters, power optimizers, and module-level monitoring services, announced its collaboration with Tesla Motors (“Tesla”) to provide an inverter solution that will allow for grid and photovoltaic integration with Tesla’s home battery solution, the Powerwall. The joint development by SolarEdge and Tesla builds on SolarEdge’s DC optimized inverter solution and Tesla’s automotive-grade energy storage technology to enable more cost-effective residential solar generation, storage, and consumption for the global market.

“Tesla’s collaboration with SolarEdge unites leading organizations in two rapidly-growing Industries—solar energy and energy storage—to bring homeowners a more cost-effective and integrated energy generation, storage, and consumption solution,” said JB Straubel, CTO of Tesla. “SolarEdge’s commitment to improving the value of PV systems through product innovation, combined with more than 1.3 GW of successful deployments, makes it an ideal partner for Tesla to develop and introduce this new energy storage solution to the PV market.”

The new offering is expected to present a number of benefits to homeowners, from serving as a backup power source in the event of an electrical outage, to maximizing self-consumption, and enabling energy independence.

“Like SolarEdge, Tesla recognizes the need and opportunity to develop innovative solutions designed to lower the cost of solar energy and make clean, renewable energy more feasible for customers around the world,” stated Lior Handelsman, Marketing and Product VP of SolarEdge. “Tesla’s industry leading battery storage technology makes it a natural fit for this endeavor. Together, we are taking the first step towards widespread adoption of integrated solar energy generation and storage in the residential market.”

Designed to manage both functions with just one SolarEdge DC optimized inverter, the solution will allow for outdoor installation and will include remote monitoring and troubleshooting to keep operations and maintenance costs low. The solution will also support upgrading existing SolarEdge systems with the storage solution.

For enhanced safety, the solution is designed to employ SolarEdge’s SafeDC™ architecture, which enables safe voltage levels in the event of inverter or grid disconnection to safeguard workers, homeowners, and firefighters. Additionally, the system will feature integrated rapid shutdown functionality, in full compliance with the National Electrical Code 2014, 690.12 (1) through (4).

The SolarEdge solution is expected to be available by the end of 2015.

also SolarEdge won't be the only one, more here: Initial Tesla partners include utilities, inverters and sales channels | PV-Tech Storage

"Fronius’ Symo Hybrid inverter can couple Powerwall and residential PV together, with the inverter able to control both in a newly installed system. The Fronius inverter can be AC-coupled to ‘retrofits’ – in other words adding Powerwall to an existing system – or it can be DC-coupled to replace the existing inverter."


Inverter makers, utilities and installers line up to partner with Tesla | PV-Tech

 

[smsprague]

I would be okay with the pay back coming close for the green and cool factor.
The value proposition for me would depend on a couple of things.

1. Will my existing SMA Sunny Boy inverter work with the PowerWall.
2. Can I claim the 30% tax credit for the costs associated with the PowerWall and install. I have already claimed a tax credit in the past for my Solar system.

 

[nwdiver]

I would be okay with the pay back coming close for the green and cool factor.
The value proposition for me would depend on a couple of things.

1. Will my existing SMA Sunny Boy inverter work with the PowerWall.
2. Can I claim the 30% tax credit for the costs associated with the PowerWall and install. I have already claimed a tax credit in the past for my Solar system.

There still appear to be A LOT of confusion over how this system is going to operate but it appears that AC coupling is very likely. I have an SMA inverter that I AC couple to a magnum energy off-grid inverter when the grid is down. I get some terrible resonance problems with the two operating in parallel. The level of resonance is highly variable depending on load and the type of load (reactive or resistive). SolarEdge or Enphase inverters might do better when in parallel... I don't know.

 

[CalDreamin]

Pool filter pump is a bulk of summer daily idle usage. It doesn't run all day, but it uses a good chunk when it does.

Though this particular rebate program isn't relevant to your location, it might be food for thought.

 

[strider]

I've been noodling on this for a few days. I am in the process of building a house and so these kinds of things are at top of mind. I am a complete newbie when it comes to solar. But here is something I've discovered recently that drives me crazy. We have 2 Tesla's that need to be charged at night as my wife and I both work full time. We cannot afford to have enough battery capacity to charge both cars and run the house at night so off-grid is not an option for us. So we're planning to grid-tie and net meter. What drives me crazy is that in the event of a grid outage I am without power even when the sun is shining. That nice expensive solar array does nothing without the grid. That sucks. I was looking and the SMA Sunny Boy inverters offer a single 120V/12.5A (1.5kW) plug that is hot when the inverter is isolated from the grid (and the sun is shining of course). So I can run the fridge and charge flashlight batteries and such but that is a far cry from getting the full power of our solar system.

My question to the smart people here, if I had a PowerWall, could I tap into the full power of the solar system (We're looking at 4.1kW) when we have full sun? So I could run HVAC and other things? I realize that once the sun goes down we're down to 2kW from the PowerWall until it's depleted.

From an economics standpoint, wk057 compared the PowerWall to a 2kW Generator which can be had for $800 or so (I have a nice, quiet-ish Honda). But the generator will never produce more than 2kW. If I could use the full output of my solar system (that I've already paid for) during the day that has value.

Thoughts?

 

[brianman]

Two questions for the OP:
1. For your financial modelling of Powerwall and Powerpack, what are you using for degradation estimation?
2. Same question for your 191 kWh system.

 

[yobigd20]

What drives me crazy is that in the event of a grid outage I am without power even when the sun is shining. That nice expensive solar array does nothing without the grid. That sucks.

Is that the case for all on grid net metering systems or just specific to your hardware or your utility or your configuration? I would have thought there'd be a switch to isolate the systems in an event like this so you could go "off grid" temporarily if you have the power being output by the inverter coming off your panels.

 

[wk057]

Two questions for the OP:
1. For your financial modelling of Powerwall and Powerpack, what are you using for degradation estimation?
2. Same question for your 191 kWh system.

1. Using no degradation for my PowerWall numbers.... which makes them look better then they actually are.... which means they're actually even worse than I have estimated.
2. For my 191 kWh setup I've been using an average of data available from Model S users on degradation and based on the loads/cycles estimated for my setup I expect to lose about 1% of original capacity per year.

 

[strider]

Is that the case for all on grid net metering systems or just specific to your hardware or your utility or your configuration? I would have thought there'd be a switch to isolate the systems in an event like this so you could go "off grid" temporarily if you have the power being output by the inverter coming off your panels.

As I understand it this is the case for all grid-connected systems. Something about safety to make sure the system isn't feeding power back into the grid where it could hurt the workers trying to fix the outage. The grid-connected inverters must see the 120V 60Hz on each phase before it will work. Maybe you could run a small generator to "wake up" the inverter? Beyond my skills to try.

As I mentioned I know that the SMA Sunny Boy inverters have a way to isolate and supply that one outlet but I don't understand why you can't use all the capacity of your solar system even if the grid is down.

 

[brianman]

As I understand it this is the case for all grid-connected systems.

All grid connected systems that don't have some degree of battery backup / alternate power.

Think of the grid / battery like the 12V for the Model S. Without it, you're dead in the water.

 

[lolachampcar]

I see PW as enabling UPS functionality (thus PV utilization when the mains go down) and moving us away from legacy 48 Vdc batteries to 350-400 Vdc batteries. Those that would never have considered arbitrage or UPS functionality now have a cost effective and technically/mechanically simple solution that can be bundled with their PV installation. This is enabling technology.

 

[liuping]

As I understand it this is the case for all grid-connected systems. Something about safety to make sure the system isn't feeding power back into the grid where it could hurt the workers trying to fix the outage. The grid-connected inverters must see the 120V 60Hz on each phase before it will work. Maybe you could run a small generator to "wake up" the inverter? Beyond my skills to try.

As I mentioned I know that the SMA Sunny Boy inverters have a way to isolate and supply that one outlet but I don't understand why you can't use all the capacity of your solar system even if the grid is down.

With Enphase Micro inverters they need to see a clean 120V source to output power, but if your backup system disconnect from the grid and supplies that 120v, the inverters will work, and you can have full solar power on your local grid.

It's a little more complicated than that though, as you may not *want* all that solar power. If your batteries are full and you house is using only a moderate amount of power, you have to send the extra potentially 1000's of Watts coming from the panels somewhere. Most system turn off the panels output by removing the 120V signal (or phase shifting the power enough so the micro inverter thinks it's dirty and shut themselves off). Some system use the large load (like a heating coil of the side of the house) to just burn off the excess power.

I believe in more traditional string inverter systems it works similarly, but they have the advantage of reducing panel output gradually as needed, instead of just shutting down the panels al together.

 

[DFibRL8R]

I've been noodling on this for a few days. I am in the process of building a house and so these kinds of things are at top of mind. I am a complete newbie when it comes to solar. But here is something I've discovered recently that drives me crazy. We have 2 Tesla's that need to be charged at night as my wife and I both work full time. We cannot afford to have enough battery capacity to charge both cars and run the house at night so off-grid is not an option for us. So we're planning to grid-tie and net meter. What drives me crazy is that in the event of a grid outage I am without power even when the sun is shining. That nice expensive solar array does nothing without the grid. That sucks. I was looking and the SMA Sunny Boy inverters offer a single 120V/12.5A (1.5kW) plug that is hot when the inverter is isolated from the grid (and the sun is shining of course). So I can run the fridge and charge flashlight batteries and such but that is a far cry from getting the full power of our solar system.

My question to the smart people here, if I had a PowerWall, could I tap into the full power of the solar system (We're looking at 4.1kW) when we have full sun? So I could run HVAC and other things? I realize that once the sun goes down we're down to 2kW from the PowerWall until it's depleted.

From an economics standpoint, wk057 compared the PowerWall to a 2kW Generator which can be had for $800 or so (I have a nice, quiet-ish Honda). But the generator will never produce more than 2kW. If I could use the full output of my solar system (that I've already paid for) during the day that has value.

Thoughts?

The 4.1kW output of your panels is likely a rated peak number so in reality you will see less than that even on a sunny day with ideal angle etc not to mention losses in conversion from DC solar to AC. In reality, cloud cover (fog for you bay area folks:tongue, temperature etc.. causes quite a bit of fluctuation in the output from the panels. Most electronics don't like that. I have a Sunny Boy with the single 120v isolated outlet for use when the grid is down. I bought it for the exact reasons you state (useless panels if grid outage). I tried charging the Model S during the day and was only able to pull about 1000watts before the Model S protested due to voltage drop and stopped charging. In short, it worked but will only be able to very slowly charge a model S (2 miles of rated range per hour) and will likely require frequent resets. Better than nothing. Also, appliances like a fridge have a high peak current draw at initial start-up of the electric motor that might exceed the capability of the SMA. This is why I would like the ability to use the Model S as a source for emergency power supply. Imagine the good PR for Tesla if the bay area has a quake and Model S owners could provide a source of clean emergency power.

 

[yobigd20]

This is why I would like the ability to use the Model S as a source for emergency power supply. Imagine the good PR for Tesla if the bay area has a quake and Model S owners could provide a source of clean emergency power.

If there's a quake CA's going to break off into the ocean anyway. Not really much need for clean power when you're at the bottom of the ocean.

 

[strider]

The 4.1kW output of your panels is likely a rated peak number so in reality you will see less than that even on a sunny day with ideal angle etc not to mention losses in conversion from DC solar to AC. In reality, cloud cover (fog for you bay area folks:tongue, temperature etc.. causes quite a bit of fluctuation in the output from the panels. Most electronics don't like that. I have a Sunny Boy with the single 120v isolated outlet for use when the grid is down. I bought it for the exact reasons you state (useless panels if grid outage). I tried charging the Model S during the day and was only able to pull about 1000watts before the Model S protested due to voltage drop and stopped charging. In short, it worked but will only be able to very slowly charge a model S (2 miles of rated range per hour) and will likely require frequent resets. Better than nothing. Also, appliances like a fridge have a high peak current draw at initial start-up of the electric motor that might exceed the capability of the SMA. This is why I would like the ability to use the Model S as a source for emergency power supply. Imagine the good PR for Tesla if the bay area has a quake and Model S owners could provide a source of clean emergency power.

Thanks. Yeah, I'm not sure how large of a system we would end up with, possibly larger than 4.1. Car charging is low on my list as with two small children I plan to shelter in place instead of trying to travel. I'm thinking more about being able to use the HVAC system which should be less sensitive to voltage fluctuations. I'm surprised that w/ a 13kW array you were still getting voltage fluctuations when only pulling 1.5kW. My electrical knowledge is weak but it would seem to me that the inverter could make up for low voltage due to clouds or whatever with all the extra current and keep the voltage smooth.

 

[yobigd20]

Sort of a silly related question but what happens if your utility company no longer accepts net metering? Does that mean they don't allow grid tie in's anymore or just that they'll still let you tie in but they won't pay you for your excess power "donations"?

 

[lolachampcar]

Florida Power and Light's sense of entitlement seemed to come from my attaching a producing PV system to their grid. If utilities "go after" net metering, I would think they would use the same logic to say you can not attach your system to our grid.

Those looking into the path for grid defection have speculated about this. I believe an inverter system that uses the battery for a UPS function effectively disconnecting your house from the grid presents a scenario where the utility no longer has a say. My production is not attached to their grid at that point as it is either gird or PV and never both.

 

[apacheguy]

As I mentioned I know that the SMA Sunny Boy inverters have a way to isolate and supply that one outlet but I don't understand why you can't use all the capacity of your solar system even if the grid is down.

I have an 8 year old Sunny Boy and it definitely doesn't have any way to isolate. Are you referring to newer systems? I would love to be able to run off grid in emergencies and just run the extra power into the ground. Obviously back feeding is a legitimate concern so there would have to be a disconnect switch and then the excess would just go to ground. Never understood why batteries are necessary for off grid applications.