Does anyone have a Tesla Powerwall (or another type of battery system)?

[Halcyon]

Just a simple question. If you have one meter, you produce 10 KWh during the day turns in one direction, and use it at night, turns in the other direction, it will show 0 the next day, right? So you would pay 0. But you claim, that you have a more elaborate payment scheme. I guess you have more than 1 meters then? Maybe it is not even called net metering.

We haven't used meters that "turn" for many years. Everything is electronic and readouts are via LCD display, Ethernet, RS232 and/ir IR. Everything is done in one single meter, including time-of-day billing (peak/off peak rates) if that's the type of plan you're on. These are also known as "smart meters".

There is nothing elaborate about it, homes with PV here are connected to the grid and import/export is measured using a net metering scheme. That is, whatever you don't consume is exported back into the grid as excess. That is called "net metering". The payment in which we receive back from the energy retailer is known as a "solar feed-in tariff".

There are no if's, but's or maybe's about it. Even if you look up the definition of the word "net" in a financial/accounting sense, you'd come to the same conclusion. The tariff may be equal to the import price (in some countries), but in the case of Australia, it's far less. You can still have a solar feed in tariff on a gross metering scheme, however these days, it makes no sense to do that. Don't confuse metering with tariffs or payment arrangements, they are two different things. At one stage, I wasn't getting a feed-in tariff at all because of a paperwork screw up, that didn't change the fact that I was still on a net metering system.

Nothing personal, but I'm going to side with the electrical distributer, government and manufacturers on this one and trust that they are using the correct terminology.

For your benefit, I've attached a photo of my meter/distribution box (sorry about the lighting).

[Someone]

Based on the original Powerwall 1 (which had approximately half the capacity), the system would pay for itself within the 10 year warranty period. This was based on a 4KW PV system + Powerwall available in January 2016 for under AUD$15,000 and the average solar generation in Sydney AU on a 4KW system is about 15.6kWh per day (averaged across an entire year). Most parts of Australia have higher generation (the highest being Alice Springs at about 20kWh per day).

You'll need to show your working for that, it doesnt sound like it could profit alone. Even with the poor tariff structure you have at the moment:

I'm sorry, but you are using the term "net metering" wrong. Maybe even the DSO uses it wrong. In net metering, if you export 10 KWh during the day, and buy back 10KWh during the night, you pay 0.

I don't think so. Here's some maths using my current rates:

Export 10 kWh = 67c credit
Import 10 kWh = $2.40 charge
Import - Export = $1.76 out of pocket.

As you said earlier, you have to take into account the lower feed-in tariff. In this example, the proceeds from my export don't equal or outweigh my total outlay. This is by definition what the word "net" means.

The 50%/50% split is a reasonable assumption for the storage, so you'd need to have a 10 year system cost less than 1.76*356*10 = $6400

Don't see the profit yet! You already said better tariffs are available to make it less attractive. Also the Panasonic quote at half the storage size is already costing more than this. You'll be betting on electricity prices (and the grids energy arbitrage ratio) increasing more rapidly than other investments. With all the blustering from the government about the energy sector I wouldn't be investing on such assumptions.

[Monittosan]

Any reason why you're not building your own powerwall?

This field of electronics isn't my area of expertise. Plus I'm not licenced to touch/work on anything at 240v.

Upgrading to an inverter that supports a battery (hybrid compared to grid tied or purely off grid)and making your own lithium battery from used cells mite be another option if you have the time.
Extra low voltage under 120volt DC doesn't require a licence to work on.     

[Brumby]

Just to clarify one very obvious difference in how two people are using the term "net metering".

One is using it on a "point in time" basis and the other is using it in reference to an extended period.  Interestingly, both of these usages refer to a value determined by the net flow of electricity - it's just the time scales that differ ... and that difference is significant when it comes to the electricity bill.

For the "point in time" approach, when the net flow of energy is out to the grid, this is credited to the household at one rate - and when the net flow of energy is coming in from the grid, it is charged at another rate.  There is price differentiation between exporting to and importing from, the grid that changes with each and every change of the flow of electricity.  This requires either a Smart meter or two meters to be installed.

For the "extended period" approach, there is no interest in the instantaneous direction of energy flow, just a simple arithmetic difference between the kWH that flows out to the grid and the kWH that are drawn from it.  Here, the price differentiation is only visited once - at the end of the billing period.  This only requires a single meter - and if it is an old fashioned electromechanical induction meter, there is no need to even change it.  This has got to be the cheapest implementation at the utility end of the exercise.  All they need to do is allow for readings to go backwards in their billing system - in case the solar installation is a net energy exporter over the billing period.

The difference in overall electricity pricing can be quite significant, as this post describes:

I'm sorry, but you are using the term "net metering" wrong. Maybe even the DSO uses it wrong. In net metering, if you export 10 KWh during the day, and buy back 10KWh during the night, you pay 0.

I don't think so. Here's some maths using my current rates:

Export 10 kWh = 67c credit
Import 10 kWh = $2.40 charge
Import - Export = $1.76 out of pocket.

As you said earlier, you have to take into account the lower feed-in tariff. In this example, the proceeds from my export don't equal or outweigh my total outlay. This is by definition what the word "net" means.

[Brumby]

Any reason why you're not building your own powerwall?

This field of electronics isn't my area of expertise. Plus I'm not licenced to touch/work on anything at 240v.

Upgrading to an inverter that supports a battery (hybrid compared to grid tied or purely off grid)and making your own lithium battery from used cells mite be another option if you have the time.
Extra low voltage under 120volt DC doesn't require a licence to work on.   

My understanding - and I admit I might be lacking here - is that if you have any device hard-wired to the mains, you must be properly licenced.  I take this as not only including an inverter - but anything hard-wired to the inverter, such as a battery bank.  The only way around this is to have your own system, electrically isolated from and independent of grid-connected mains.

[Gregg]

Here is a 24 volt string of C&D brand 1212 Amp Hour at 8 hour rate on a friend’s off grid system.  I did all of the major wiring to the inverter and Pelton wheel.  The Pelton wheel is connected to a brushless automotive style alternator that outputs 17 amps at 27 volts 24-7.
A big resistor dumps the excess as heat to keep the powerhouse dry.  The battery room is separated from the powerhouse with a fire wall.  A 3500 watt inverter supplies all the AC power.

[Red Squirrel]

Here is a 24 volt string of C&D brand 1212 Amp Hour at 8 hour rate on a friend’s off grid system.  I did all of the major wiring to the inverter and Pelton wheel.  The Pelton wheel is connected to a brushless automotive style alternator that outputs 17 amps at 27 volts 24-7.
A big resistor dumps the excess as heat to keep the powerhouse dry.  The battery room is separated from the powerhouse with a fire wall.  A 3500 watt inverter supplies all the AC power.

Nice!    Those telecom batteries are quite impressve.  We have 4 strings here of 3800ah ones.   For those curious each one of those is 2 volts.   In telecom we use 48v so we'll have several strings of those, 24 per string and they float at 54v.  You can make a metal tool disappear if you make it touch two terminals. (I would not recommend that)

Has anyone tried running a washing machine or central A/C system off an inverter?  If I wanted to put my whole house on battery I imagine those two loads would be the most challenging to power because of the startup draw.   

[Jeroen3]

Modern washing machines use motor drives. They don't have a lot of inrush anymore.
Central A/C I don't know, but the indoor units in the office also use drives.

[tszaboo]

Just to clarify one very obvious difference in how two people are using the term "net metering".

One is using it on a "point in time" basis and the other is using it in reference to an extended period.  Interestingly, both of these usages refer to a value determined by the net flow of electricity - it's just the time scales that differ ... and that difference is significant when it comes to the electricity bill.

Yes, exactly. The one I'm describing, the net metering is for extended time. When it is instantaneous, it is always "Power Purchase Agreement". I looked up "gross metering" since it is an unknown term, and only Australian websites come up? Anyway, I'm going to accept that it means something else on the other side of the planet, and I cannot force a country to say potato instead of potato.
But then please accept, that net metering means something else for anyone outside Australia. Sorry, I got little personal, since I work for a company, installing smart metering for solar panels and green energy in general, and handling database for it, and such.

[rstofer]

For PG&E (California), Net Metering means net at the end of a 12 month period.  Throughout the period, the utility bills for a metering charge only (about $5/mo) and, at the end of the term, the net of generation and consumption is settled up.

My 8.5 kW array was more than adequate to provide my annual consumption and that creates a problem since I buy the solar energy on a Power Purchase Agreement of $0.15/kWh.  But PG&E only settles up at about $0.04 (IIRC) so I don't want to be a net supplier.  In fact, the Public Utility Commission rules state that I can't be a net supplier.

Still, it was nice to avoid the $0.36/kWh Tier 3 charges (consumption well above Lifeline).  Having a battery car made it an even sweeter deal because I was driving for $0.03/mile.

Alas, we moved and our roof isn't conducive to installing solar again.  Bummer...

At some point, the utilities are going to force Time Of Use billing and On Peak will go well into the evening.  In this case, batteries might make sense.   If you can just slide through until Off Peak things will be much cheaper.  Or, get a system large enough to be able to stay off the grid entirely.

The utilities hate solar and, in Hawaii, there is a 4 year wait to get permission to install solar (that has changed but probably not improved, see linked article below).  This in a place that is all sunshine!  The problem is the Tier rates.  The lowest (Lifeline) tier is intended for the economically challenged and is subsidized by the higher tiers.  It isn't until the upper tiers that the utility makes enough money to maintain their system and, by definition, solar eats away from the top tier down.  It becomes increasing difficult to afford maintenance as people move out of these higher tiers.

It's awkward:
http://www.pbs.org/newshour/bb/switched-rooftop-solar-move-hawaii-long/

[metrologist]

I was looking for where I read that solar battery technology still costs ~$0.15/kWh for the batteries alone. There are inefficiencies in the charge/discharge cycle, and in both the solar charge controller and inverter. In practice I think one never realizes the full potential of the battery due to less than ideal operation and mfg issues. Add on installation and maintenance costs and I think off-grid systems are a net loss or break even at best.

I started experimenting with a small panel and have discovered that I cannot win anyway I try. I am now considering running DC devices directly from the panel to create air circulation and heat.

[rstofer]

When the vast majority of your energy is bought at $0.35+/kWh, batteries may help.  Given a sufficient sized array.  In the end, all batteries do is allow a time shift between generation and consumption.

There is also the possibility of building a cabin where electricity simply isn't available.  A real off-grid application.

[Gregg]

Has anyone tried running a washing machine or central A/C system off an inverter?  If I wanted to put my whole house on battery I imagine those two loads would be the most challenging to power because of the startup draw.

My friend does have a 20 year old washing machine that works fine with his inverter that isn't true sine wave as well as a refrigerator.  Cold beer is #1 priority so when the refrigerator is full of food the spring that feeds the Pelton wheel is 40 degrees F and becomes the beer cooler.  Hair dryers are strictly forbidden but the coffee maker is not.
The flooded batteries are actually UPS batteries and were replaced under warranty because the post seals leak.  My friend doesn't understand batteries so I do the maintenance for him.  The battery terminals need to be cleaned every 3 to 4 months, but the price for the batteries was right.

[metrologist]

When the vast majority of your energy is bought at $0.35+/kWh, batteries may help.  Given a sufficient sized array.  In the end, all batteries do is allow a time shift between generation and consumption.

There is also the possibility of building a cabin where electricity simply isn't available.  A real off-grid application.

In my area, there is tiered pricing:

$0.20 to 10kWh/day
$0.28 to 40kWh/day
$0.40 over 40kWh/day

I think the pricing model provides incentive to use less energy, and I keep my average use to around 80% of baseline. I’m having a hard time justifying solar at all, especially given your earlier comments. I expect the power companies to change things to cut the legs off this option, if tariffs don’t do it…

For the OP, this is how I would look at it, just taking a rough stab at it…

Usage: 20kWh/day
Cost:  23c/kWh
Production: 6.7kWh/day
Return: 6.7c/kWh (soon to go up to 12c/kWh?)

Net use is then 13.3kWh/day at a daily cost of $3.059.

The pricing on the Tesla battery system I saw was $11k and I think to determine the value we need to take the difference of what electricity costs vs return, or 16.3c/kWh.

Production is only 6.7kWh/day and if we assume 100% efficiency all around, then that presents a value of $1.0921/day. It would take over 27 years to make up the cost of the battery (but that battery is larger than can be fully charged). The cheaper battery system was listed at $9k and would take over 22 years to make up, and it is a little smaller than what could be charged.

[tszaboo]

Don't see the profit yet! You already said better tariffs are available to make it less attractive. Also the Panasonic quote at half the storage size is already costing more than this. You'll be betting on electricity prices (and the grids energy arbitrage ratio) increasing more rapidly than other investments. With all the blustering from the government about the energy sector I wouldn't be investing on such assumptions.

I dont think it actually makes sense to be an early adapter for this kind of system, if you loose money (degradation of battery) with each charge. If electricity prices go up, you can install a battery system later. Prices are likely to drop, and reliability and number of charges are likely to go up in a future system. Imagine, they finally start mass producing aluminium-ion batteries, and prices are halved.

[hendorog]

Tesla powerwall is too large, and therefore too expensive for what I need:

I use spot price power which is expensive at peak times and cheap off-peak. It can be very expensive at peak time.
Therefore need a small battery to cover the peak time usage only.

The other issue with the Powerwall seems to be the additional costs pushing the price up.

The local energy company Vector quoted about NZD 17K including all costs. Tesla's website says 10K, but excludes install, shipping, inspection and their tax calculation is obviously wrong (and they call it VAT instead of GST). Teslas 10K is already 1500 more than the equivalent USD price.

[Halcyon]

From my figures, I've worked out that the Tesla Powerwall 2 (including cost of installation) will cost (over 10 years and taking into account 3% capacity decrease each year) about 23.18c/kWh which is roughly around the price of energy from the grid.

The Panasonic LJ-SK56A is even more expensive to run at 52.71c/kWh.

With those figures in mind, unless the price of battery technology drops, it doesn't seem all that worth while. I think investing money in more energy efficient appliances and air conditioning units with inverters will yield larger savings.

[hendorog]

Maybe mentioned or already considered but you can use the free solar power by dumping it into things - instead of feeding it into the grid:
e.g.
Cool/heat the house - so it gets to the desired temp faster when you get home and you have less solar.
Run the fridge/deep freeze
Heat the spa
Heat the pool
etc

Much lower capital cost than batteries and so payback is faster.