Powerwall: The Arrival of Home Battery Backup System

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oragne lovre
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Powerwall: The Arrival of Home Battery Backup System

Post by oragne lovre »

I've for a while waited for an affordable, small home backup battery that can store power generated by my solar panels. It seems the solution has just arrived tonight

http://www.engadget.com/2015/05/01/tesl ... l-battery/

Since I'm with Solar City, I plan to contact it to see which type of Powerwall I need, what the total cost of installation is, and how long it takes to recoup the upfront cost.
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harikaried
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by harikaried »

It looks like the main benefit is indeed for owners with solar as excess energy generation would otherwise be wasted and night time relying on the grid.

Another type of benefit would be for people who could store excess cheaper energy to use at peak/expensive usage. This would allow owners to not need to worry about adjusting energy consumption behaviors.

It would seem that electricity companies could use these batteries to do the opposite: store cheap energy to then release at peak times for higher prices. This avoids needing to build additional power sources to satisfy peak usage. Similarly, I wonder if these companies would provide any incentives to have homeowners install batteries to reduce peak load to avoid needing to acquire batteries themselves.
madbrain
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

A bit non-plussed about this :
You can reserve a Powerwall right now on Tesla's site. The device will also be available via distributors, with the 10kWh version offered to installers for $3,500, while the 7kWh model will cost $3,000. This doesn't include the cost of a DC-to-AC inverter to work with your home. (Solar cell customers will already have that inverter.)
This is not always true. I have Enphase micro inverters with my solar system, not a monolithic inverter.
It won't be possible to use the Powerwell with those micro inverters.

Even for those who have monolithic inverters, the rating might not be high enough for both the PV and the Powerwall.

For example, if one wants to send solar power to the grid, while at the same time depleting the battery to send power from it to the grid as well, then the inverter would need to be big enough for both the solar PV panels and the Powerwall.

This is actually what I would want to do, given that peak electricity rates coincide with sunshine hours.
However, the total wattage from PV varies depending on the time of day. There might be a way to deplete the battery slowly during the day if the peak hours are long enough, during the time the PV are not maxing out, without buying a bigger monolithic inverter.
But this would need some kind of regulator to avoid exceeding the monolithic inverter rating.
But it's not possible at all with micro-inverters. Those won't work with a Powerwall.
Last edited by madbrain on Fri May 01, 2015 5:44 am, edited 4 times in total.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

harikaried wrote:It looks like the main benefit is indeed for owners with solar as excess energy generation would otherwise be wasted and night time relying on the grid.
With a net metering plan, you get paid by the electric company for that excess solar energy.

It's never really wasted - it just goes to your neighbors, who will be paying the electric company for it, even though it doesn't have to generate it.
In the US, with time of use rates, the peak power prices often coincide with the times the sun shines, so there would be no financial benefit for a homeowner to charge an empty batteries from a solar array, instead of sending that power to the grid.

In Germany, it appears that the rates are the opposite - power is cheaper during sunshine hours, but more costly at night.
So over there, people indeed don't want to "give away" their solar power to the power company, and would prefer to charge batteries from solar during the daytime and deplete them at night.

And of course there are other types of generators that have variable hours (wind) for which the situation will vary.
Another type of benefit would be for people who could store excess cheaper energy to use at peak/expensive usage. This would allow owners to not need to worry about adjusting energy consumption behaviors.
Yes, that's the main advantage as I see it - even for those who don't have generators, shifting the hours of consumption would be a benefit.
The article doesn't do a good job of explaining it, though.

I have about 45 kWh of total daily consumption on average (that's without solar generation), so if I wanted to shift all of it from peak to off-peak, I would need about 5 of these devices. There are some 20 kWh days and some 80 kWh days too.

In practice I rarely have much net consumption during peak hours, except when it's raining, and even with 10-12 kWh net grid consumption per day, the net electric bill is already zero due to favorable time of use rates for solar, so there is no cost left to offset.

I could still use a battery to charge cheaply at night, and discharge during the daytime during peak hours. This might allow consuming a bit more grid electricity, maybe 15-18 kWh per day, and still keeping the electric bill 0.

The backup feature is really uninteresting to me as the grid seldom goes down here.
It would seem that electricity companies could use these batteries to do the opposite: store cheap energy to then release at peak times for higher prices. This avoids needing to build additional power sources to satisfy peak usage. Similarly, I wonder if these companies would provide any incentives to have homeowners install batteries to reduce peak load to avoid needing to acquire batteries themselves.
These batteries are far too small and too expensive to be cost effective for power companies, though.
They only make sense for the homeowners who are paying high per kWh price that include both generation and distribution.
The main cost to the power companies are distribution rather than generation.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by angelescrest »

Keep in mind the powerwall is the home product, while the powerpack is for use by businesses, and is much more robust. They powered the entire launch event last night with their powerwall packs.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by bpp »

That's a pretty interesting price point. A day's worth of electricity storage for $3500? Only question would be how many charge/discharge cycles it is good for. But getting very interesting!
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by TomatoTomahto »

Interesting. I am #6,xxx in line for a Tesla Model X. I was discussing the charger installation with the electrician. Our "whole" house generator won't back up the charger, but I wonder if there's a nice way to combine the charger, battery, and generator into a robust and resilient system. We shall see, but I'm intrigued.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by Epsilon Delta »

madbrain wrote: This is not always true. I have Enphase micro inverters with my solar system, not a monolithic inverter.
It won't be possible to use the Powerwell with those micro inverters.

Even for those who have monolithic inverters, the rating might not be high enough for both the PV and the Powerwall.
I don't see how you could reuse an inverter even if it's big enough. The solar array puts out one voltage, (which should change due to peak power tracking) and the battery uses another voltage (which will vary due to state of charge and charge/discharge).

Just because they're both DC doesn't mean you can just connect them to the same bus. Even if the voltage is close enough that they don't energetically self-disassemble you're going to lose efficiency if you don't control the voltages separately.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by barnaclebob »

There really isn't much point to this as a money saver unless you aren't on net metering.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by indexfundfan »

"Powerwall is a home battery that charges using electricity generated from solar panels, or when utility rates are low, and powers your home in the evening. It also fortifies your home against power outages by providing a backup electricity supply."

I think one way the Powerwall might work is that this will sit between your solar grid and DC-AC inverter. During sunshine hours, it gets charged directly by DC (no DC-AC conversion needed) from the solar panels (those on micro-inverters are out of luck here). Then in the evening, it supplies DC power to the inverter that converts it to AC.

At no time would both the solar panels and the Powerwall be feeding their maximum power output into the inverter.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by Epsilon Delta »

indexfundfan wrote:I think one way the Powerwall might work is that this will sit between your solar grid and DC-AC inverter. During sunshine hours, it gets charged directly by DC (no DC-AC conversion needed) from the solar panels (those on micro-inverters are out of luck here). Then in the evening, it supplies DC power to the inverter that converts it to AC.

At no time would both the solar panels and the Powerwall be feeding their maximum power output into the inverter.
You can't do this unless the voltage of the solar cells matches the charging voltage of the battery. Since both of them vary quite a lot this is unlikely. Not all DC is the same. A DC-DC converter is pretty much the same complexity as a DC-AC converter.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by dolphinsaremammals »

There's apparently push back building from utilities about net metering. Whether they will be successful, I have no idea. But I read an article about that somewhere. The more solar systems at homes, the more annoyed money they lose harder it is for the utility to manage the power.

The more independence of the grid the better, in my view. If I weren't too old, I'd love to have a house built that incorporated that type of thing.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by indexfundfan »

Epsilon Delta wrote:
indexfundfan wrote:I think one way the Powerwall might work is that this will sit between your solar grid and DC-AC inverter. During sunshine hours, it gets charged directly by DC (no DC-AC conversion needed) from the solar panels (those on micro-inverters are out of luck here). Then in the evening, it supplies DC power to the inverter that converts it to AC.

At no time would both the solar panels and the Powerwall be feeding their maximum power output into the inverter.
You can't do this unless the voltage of the solar cells matches the charging voltage of the battery. Since both of them vary quite a lot this is unlikely. Not all DC is the same. A DC-DC converter is pretty much the same complexity as a DC-AC converter.
Can a battery pack tolerate different DC voltages during charging?

I think some information is missing here. How does the Powerwall work? Anyone knows?
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by dolphinsaremammals »

What do they mean by backup applications vs. daily cycle applications?

It just occurred to me that if this will keep the electric pump for my baseboard heating system working, 99% of my worries about power outages in the winter will be gone. The frig and lights I don't care about. But it would have to do that for a week or so, not the few hours the site mentions. But if the only power being drawn is from the presumably wimpy (I'll have to check that) pump, it should last awhile.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by mmmodem »

Some back of the envelope calculations here:
I own a plug in electric vehicle and have a time of use rate plan with PG&E. I do not have solar.

Peak cost is ~$0.30/kWh. Non peak cost is ~$0.10/kWh.
Displacing 10kWh every day from peak to non peak would save me $2 a day or $730 a year.
The payback on a $3500 10 kWh power pack is 4.8 years + whatever installation costs.

That is not bad. I would only need 1 10 kWh pack ecause I use about 550 kWh a month.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by hicabob »

A good dog and pony show by Elon explaining the Powerwall
https://www.youtube.com/watch?v=yKORsrlN-2k
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oragne lovre
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by oragne lovre »

mmmodem wrote:Some back of the envelope calculations here:
I own a plug in electric vehicle and have a time of use rate plan with PG&E. I do not have solar.

Peak cost is ~$0.30/kWh. Non peak cost is ~$0.10/kWh.
Displacing 10kWh every day from peak to non peak would save me $2 a day or $730 a year.
The payback on a $3500 10 kWh power pack is 4.8 years + whatever installation costs.

That is not bad. I would only need 1 10 kWh pack ecause I use about 550 kWh a month.
Your back-of-the-envelope calculations are easy to understand. If Powerwall warranty is 10 years, then it looks financially sensible to have it.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by autolycus »

Epsilon Delta wrote:
indexfundfan wrote:I think one way the Powerwall might work is that this will sit between your solar grid and DC-AC inverter. During sunshine hours, it gets charged directly by DC (no DC-AC conversion needed) from the solar panels (those on micro-inverters are out of luck here). Then in the evening, it supplies DC power to the inverter that converts it to AC.

At no time would both the solar panels and the Powerwall be feeding their maximum power output into the inverter.
You can't do this unless the voltage of the solar cells matches the charging voltage of the battery. Since both of them vary quite a lot this is unlikely. Not all DC is the same. A DC-DC converter is pretty much the same complexity as a DC-AC converter.
The press reports I have seen all indicate that a DC-DC converter is built-in to the Powerwall unit. So at least that problem seems to be already addressed within the product. The DC-AC inverter is not included though.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by ivyhedge »

oragne lovre wrote:Your back-of-the-envelope calculations are easy to understand. If Powerwall warranty is 10 years, then it looks financially sensible to have it.
There will be folks, businesses, and even small local providers for whom/which this works, and for whom/which it does not (at least, at first).

What it was not, however, was the ridiculously grandiose "solve everything every night" claim that Musk's detractors predicted it would be with their collective ignorance.

Indeed, the only element of the presentation that irked me was the delay of the broadcast: I am paying for that today!
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by BL »

Are we going full circle on this home electricity thing? This is nearly the 100th anniversary of the Delco Home power system. Dr Delco writes:
In 1916, Kettering founded the Domestic Engineering Company and introduced the Delco-Light electric plant to bring the wonders of electricity to homes, farms, and businesses in rural America. Joining with battery and appliance manufacturers, Delco-light offered a complete electric power system for “flameless lighting”, “running water”, and convenient labor saving equipment and appliances. It was an immediate success and a new 300,000 sq. ft. factory employing thousands was built in Dayton, Ohio. The Delco-light plant was sold nationwide through a sophisticated dealer and installation network. The success created an entire industry to supply farm electric plants to rural and remote homes, businesses, schools, churches, small towns, resorts, and even yachts. In the late 1920’s sales would surpass 325,000, over 150 companies were offering farm electric plants to compete with Delco-Light, and the market was estimated at 2.5 million units. In the early 1930’s, nearly 2 dozen companies were producing wind generators to compete or be used with farm electric plants. Several hundred companies throughout the country were manufacturing appliances, equipment, and batteries, or selling, installing, or servicing farm electric plants and equipment. The Rural Electrification Act of 1936 would change the market forever and end this vibrant industry in a short period of time. The companies would convert temporarily to support the WW II effort before changing to related markets or closing down and being lost and forgotten as America moved on.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by Epsilon Delta »

dolphinsaremammals wrote:What do they mean by backup applications vs. daily cycle applications?
It says the backup application is designed to cycle weekly compared to the daily cycle.

Rough approximation (real numbers will be different)
backup application power = 10kWhr / (3.5day * 24hr/day) ~ 120W
daily cycle power - 7kWhr/12hr = 580W.

There could be all sorts physical differences that account for this. Different cell construction, cooling, parrallel/serial arrangement of the cells, thickness of internal wires, different power electronics. Basically the backup model uses more of the space (or cost) to store energy in the module and less space (or cost) to move energy in or out quickly.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by TimeRunner »

SolarCity is providing additional details too: http://www.solarcity.com/newsroom/press ... -across-us

and more details in the SolarCity Blog, "A breakthrough in the affordability of Solar Battery Systems": http://blog.solarcity.com

I especially like this quote from the Blog:
"I believe the best grid design is one in which utilities embrace distributed energy resources. However, when utilities and regulators impose solar-specific charges on their customers, or burden homeowners with unduly long system interconnection delays, utilities risk mass customer defection from the grid via solar battery systems.

In Hawaii, people are frustrated with utilities for having put a hold on rooftop solar in their territories. We hear often from people seeking a solar battery system that will allow them to sever ties from their utility completely. As I’ve written before, we don’t think this is optimal for the grid. But when the choice is between being grid-connected without solar or being off the grid with rooftop solar and a solar battery system, the choice is clear. As a result, SolarCity plans to offer an off-grid solar battery system to eligible customers in Hawaii beginning in 2016."
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by randomguy »

ivyhedge wrote:
oragne lovre wrote:Your back-of-the-envelope calculations are easy to understand. If Powerwall warranty is 10 years, then it looks financially sensible to have it.
There will be folks, businesses, and even small local providers for whom/which this works, and for whom/which it does not (at least, at first).

What it was not, however, was the ridiculously grandiose "solve everything every night" claim that Musk's detractors predicted it would be with their collective ignorance.

Indeed, the only element of the presentation that irked me was the delay of the broadcast: I am paying for that today!
Factor in buying an invertor, installation, and the financing cost and it is a bit borderline. For people with an inverter or installing solar it is probably a better deal.

Yes Mush oversells stuff quite a bit. But I wouldn't be shocked to see pretty much every new house have one of these and some solar panels in 10 years (i.e. time for the cost of both to be cut in half and for the cost of electricity to go up 30%). The are some advantages to a distributed system like this versus monolithic generation so I expect some small fraction of grid (call it 20%) to shift towards it.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by kolea »

TimeRunner wrote: I especially like this quote from the Blog:
"
In Hawaii, people are frustrated with utilities for having put a hold on rooftop solar in their territories. We hear often from people seeking a solar battery system that will allow them to sever ties from their utility completely. As I’ve written before, we don’t think this is optimal for the grid. But when the choice is between being grid-connected without solar or being off the grid with rooftop solar and a solar battery system, the choice is clear. As a result, SolarCity plans to offer an off-grid solar battery system to eligible customers in Hawaii beginning in 2016."
I live in Hawaii and I don't know anyone who has PV and is clamoring to go off the grid. What most people here want to do is sell their excess power back to the grid, but the local power company will not let them do that except under certain conditions.

Home storage that removes a PV system from the grid does not help promote solar power. People who live in sunny areas like Hawaii can make money by selling power to the grid. This encourages more people to install PV. But that only works if the grid is forced to accept the power. The technical problem is that solar power is too unpredictable for the grid. But the solution to that is for the grid to store it. Why should every homeowner have to buy 1000's of dollars worth of batteries to make up for a regulatory problem with the local utility? Tesla is selling grid-storage also, and the utility companies should be accommodating home PV systems by deploying grid storage.

BTW, home storage is not new. Lead-acid or Gel batteries have been available for years. Their cost is about 40% less than Li-ion and they last longer. But they are bulky and heavy.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by novicemoney »

TwoByFour wrote:
TimeRunner wrote: I especially like this quote from the Blog:
"
In Hawaii, people are frustrated with utilities for having put a hold on rooftop solar in their territories. We hear often from people seeking a solar battery system that will allow them to sever ties from their utility completely. As I’ve written before, we don’t think this is optimal for the grid. But when the choice is between being grid-connected without solar or being off the grid with rooftop solar and a solar battery system, the choice is clear. As a result, SolarCity plans to offer an off-grid solar battery system to eligible customers in Hawaii beginning in 2016."
I live in Hawaii and I don't know anyone who has PV and is clamoring to go off the grid. What most people here want to do is sell their excess power back to the grid, but the local power company will not let them do that except under certain conditions.

Home storage that removes a PV system from the grid does not help promote solar power. People who live in sunny areas like Hawaii can make money by selling power to the grid. This encourages more people to install PV. But that only works if the grid is forced to accept the power. The technical problem is that solar power is too unpredictable for the grid. But the solution to that is for the grid to store it. Why should every homeowner have to buy 1000's of dollars worth of batteries to make up for a regulatory problem with the local utility? Tesla is selling grid-storage also, and the utility companies should be accommodating home PV systems by deploying grid storage.

BTW, home storage is not new. Lead-acid or Gel batteries have been available for years. Their cost is about 40% less than Li-ion and they last longer. But they are bulky and heavy.
All what you say is true but if the power company wants to change the terms of NET metering (pay less for PV generated energy) or eliminate NET metering altogether than the equation changes and IMHO favors some sort of battery system as an adjunct to solar panels. As you know Hawaiian Electric wants to sell out to mainland based Nextra who is on record of opposing tax credits for home based PV. They are in favor of utility owned solar farms so solar generated energy will be included in the grid.

My point is the economics of battery technology is dependent on what the utily company wants to or will do.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by kolea »

novicemoney wrote:
My point is the economics of battery technology is dependent on what the utily company wants to or will do.
Agreed. But utility companies are beholden to the public because in general they don't have competition. The local utility commission can force them to implement procedures that will promote PV. This is primarily a regulatory problem.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by TimeRunner »

The cost of every kWh keeps rising, and meter costs, distribution costs, investment recovery costs, nuclear power decommissioning costs, regulatory costs, etc keep rising even faster. The more we reduce our power use, the less electricity per house the utility sells, so they raise the unit cost and fees again to meet their fixed costs. I very much look forward to being able to feasibly go off the grid. If they took down the neighborhood power poles and lines, that would also be great. (Yes, I know telecomm lines are strung up there too, but a man can dream.) Who would have thought you could have gone without a landline a dozen years ago....
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

barnaclebob wrote:There really isn't much point to this as a money saver unless you aren't on net metering.
Not necessarily.

If you have a time of use plan, but not net metering, it could still work, if the Powerwall can be set to never send power to the grid - ie. just charge the battery during off-peak hours, and discharge the battery during peak hours, but only discharge it up to the amount of local consumption by the house.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by ryuns »

I think the most exciting thing to me is just that is the price and scale we're talking about. Sure, we're only talking about a subset of people who will find much use in this, and many of those are likely to be businesses and others who need to have backup power anyway. But heck, having battery + solar be a reasonable solution for *anyone's* energy needs in 2015 is a serious achievement. These systems are $350/kWh (plus install) for a residential size pack, but get down to $250/kWh for larger scale storage. The price decrease for PV and battery storage is wildly exceeding almost everyone's imagination from even just 5 years ago. There's obviously no telling what the future will hold--it vary well may be that we plateau on cost reductions until new technologies come out. Or maybe we'll keep seeing incremental improvements. Or maybe the technology will change completely. But in any case, I find the progress massively exciting. Whether it manifests itself in more feasible grid-level storage for utilities to bring more intermittent renewable energy online or moving more people off the grid, it's still an encouraging step.

One big caveat: There is still a big issue with wealthy people being able to afford these types of system and poor people not, while the utilities continue to increase baseline fixed costs, which they do in order to recoup losses associated with selling less electricity because of increased use of PV and from losing the very customers who were previously in the highest/most expensive tier of usage. Leasing PV systems to individuals, as SolarCity does, has actually helped this issue somewhat by lowering capital costs, but it remains the case that the wealthy are able to invest the money to save on electricity, while others are not.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by MathWizard »

ryuns wrote: One big caveat: There is still a big issue with wealthy people being able to afford these types of system and poor people not, while the utilities continue to increase baseline fixed costs, which they do in order to recoup losses associated with selling less electricity because of increased use of PV and from losing the very customers who were previously in the highest/most expensive tier of usage.
Ultimately this issue will not matter.

As with any technology, early adopters are the rich, who pay development costs.
Once those are accounted for, we move to costs of production, which are often cheap
when done on an industrial scale.

Think telephones, electrically initially, cars, TVs, Flat Screens, VCRs, GPSs, computers, cell phones, smart phones ...
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

ryuns wrote: One big caveat: There is still a big issue with wealthy people being able to afford these types of system and poor people not, while the utilities continue to increase baseline fixed costs, which they do in order to recoup losses associated with selling less electricity because of increased use of PV and from losing the very customers who were previously in the highest/most expensive tier of usage. Leasing PV systems to individuals, as SolarCity does, has actually helped this issue somewhat by lowering capital costs, but it remains the case that the wealthy are able to invest the money to save on electricity, while others are not.
The less wealthy people probably consume less electricity because they have smaller dwellings.

With low consumption, solar doesn't make economic sense yet. It mainly makes sense if the electric per kWh rate is high. This tends to happen if you have a tiered rate schedule, and higher usage, ie. larger home, meaning wealthier customer.

But even if the rate schedule is flat per kWh with no tiers for high consumption, there is a fixed install cost to each solar system. The install cost is not directly proportional to the size of the system. There are economies of scale with a larger system.

But the biggest issue is for people who don't own their homes, ie. renters. There is no current economic model for solar that works for renters. Even solar leases only work for homeowners. If you are a tenant, the next tenant might have completely different electrical usage. That means the solar system might be undersized or oversized for them. Undersized is not as much of an issue - the tenant could just buy the rest of electricity from the grid. But if it's oversized, the tenant will not be happy.
But ultimately, the solar system is attached to the house. The tenant can't take it with them to their next house. So the tenant won't be the one signing the solar lease. The landlord would have to be.
The landlord will also have to sign the interconnection agreement with the power company. And the landlord will probably need to put the utility account in their name as a result, not in the name of the tenant.

That means the landlord would have to charge the tenant for electricity, both generated by the system, and the amount billed by the power company.
There are additional issues with net metering when "true up" billing happens as the end of the year if the tenant doesn't live in the residence the whole year.
These are a lot of obstacles to solve. They are more of financial/billing nature than technical, however.

I will stop here because we are quite off topic from the Powerwall at this point.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by nordsteve »

Did some analysis of this for some relatives who live in Northern MN and have off peak power available at $0.04/kWh. It doesn't currently have a payback.

Happy to buy power from people who are installing solar, as long as they're willing to pay the fixed costs of having generation capacity around to call on when they need to draw from the gird.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

MathWizard wrote: As with any technology, early adopters are the rich, who pay development costs.
Once those are accounted for, we move to costs of production, which are often cheap
when done on an industrial scale.

Think telephones, electrically initially, cars, TVs, Flat Screens, VCRs, GPSs, computers, cell phones, smart phones ...
Almost all of these don't have high fixed initial installation costs, and are things you can take with you if you move - the situation is a bit different with a Powerwall or solar PV system, IMO.

I agree with your point about early adopters paying for development costs, though. But this isn't going to bring installation costs down.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

TimeRunner wrote:The cost of every kWh keeps rising, and meter costs, distribution costs, investment recovery costs, nuclear power decommissioning costs, regulatory costs, etc keep rising even faster. The more we reduce our power use, the less electricity per house the utility sells, so they raise the unit cost and fees again to meet their fixed costs. I very much look forward to being able to feasibly go off the grid. If they took down the neighborhood power poles and lines, that would also be great. (Yes, I know telecomm lines are strung up there too, but a man can dream.) Who would have thought you could have gone without a landline a dozen years ago....
For me, going off the grid is a pipe dream with solar PV.
The reason is that in the winter, the sun shines much less than in the summer. I have massive net consumption from the grid in the winter, and some excess power in the summer.
I would need a solar system at least 3 times as large in order to generate a sufficient amount of kWh for December/January.
And even then, that's just on a monthly basis, but sometimes during a winter month, it rains for a week and the solar system produces almost 0 power on those days (about 5-10% of sunny days).
The amount of batteries needed would also be massive. We are talking hundreds of kWh or possibly MWh+. I don't see how this could ever make economic sense.
As it is, with a grid tie solar PV system, my annual grid cost is $0 due to net metering . The extra 80 PV panels, as well as all those batteries batteries, would have to cost less than $0 for it to make economic sense for me to disconnect from the grid. And in the summer I would have 3x as much solar power as I need which would be wasted.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by LadyGeek »

This thread is now in the Personal Consumer Issues forum (battery backup).
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

novicemoney wrote: All what you say is true but if the power company wants to change the terms of NET metering (pay less for PV generated energy) or eliminate NET metering altogether than the equation changes and IMHO favors some sort of battery system as an adjunct to solar panels.
Yes, but eliminating net metering, or changing its terms, is not just up to the power company, but also regulators. Regulators also set the hours for peak / off-peak power prices. Ultimately, I believe this sort of battery backup can help stabilize the grid.

But it would need some sort of network so that the utility can decide when is the best time to discharge the batteries, or charge them, in order to minimize the peak number of power plants that it needs to have, and to best utilize the power plants that are online. The Tesla Powerwall appears to be network, but I don't think it's done with controlling access from the utility in mind. But that should be technically possible to implement. It's a bit more difficult to see how the financial incentives would work for it, though, in terms of how much the utility would pay the homeowners to have that ability.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

mmmodem wrote:Some back of the envelope calculations here:
I own a plug in electric vehicle and have a time of use rate plan with PG&E. I do not have solar.

Peak cost is ~$0.30/kWh. Non peak cost is ~$0.10/kWh.
Displacing 10kWh every day from peak to non peak would save me $2 a day or $730 a year.
The payback on a $3500 10 kWh power pack is 4.8 years + whatever installation costs.

That is not bad. I would only need 1 10 kWh pack ecause I use about 550 kWh a month.
A couple of issues with that math :
1) At 550 kWh/month, that means you are only using 18.3 kWh/day. Are you sure you currently have 10 kWh/day of peak usage to displace ?
Peak hours are often daytime hours when the sun shines. If you work and no one is home during the day, you may not have that much peak consumption to offset.
This does not matter if you have net metering. But if you don't - ie. you cannot send power to the grid, or you don't get paid for it - then it would be an issue.

2) Are those per kWh rates for peak and off-peak the same year round ? If you have seasonal rates, you may need to adjust your math.
I find that the electricity rates are much higher in the summer here in Northern California with PG&E. There are no peak rates in the winter, just part-peak and off-peak. Summer has peak, part-peak and off-peak.
See http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-6.pdf
Summer peak rate starts at 32 cents/kWh, part-peak 20 cents/kWh, off-peak 13 cents/kWh.
Winter part-peak starts at 15 cents/kWh, and off-peak 13 cents/kWh.
That is a large seasonal difference, which could decreasing your projected savings by a large percentage.

3) Are those flat rates regardless of how much you consume in each time period, or do you have tiered rates ?
The PG&E E-6 rate schedule has both tiers and time-of-use periods, so they are quite complicated.
The rates I was listing in 2) were baseline. The baseline amount varies both regionally and seasonally in California with PG&E.
The rates get more expensive in higher tiers, so if you are hitting upper tiers and displacing peak usage from a high tier, this might increase your projected savings.

4) you also need to purchase a DC-AC inverter which is not included in the cost. You probably don't need a big pricey one, though.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

Epsilon Delta wrote: You can't do this unless the voltage of the solar cells matches the charging voltage of the battery. Since both of them vary quite a lot this is unlikely. Not all DC is the same. A DC-DC converter is pretty much the same complexity as a DC-AC converter.
Makes sense. I wonder why the article and the Tesla press release bother to mention that solar customers already have a DC-AC inverter, if it can never be reused for the Powerwall. Unless there is some voltage regulator in the Powerwall to allow this to work with an existing inverter. Maybe that is the point of the DC-DC converter which is included.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by airahcaz »

Solely for backup in the case of power outages caused by storms, et.c, can this replace a whole house (e.g. Generac) natural gas generator whose costs are approximately $10K (5 for the generator, 5 for permit, installation, etc.)?
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by madbrain »

airahcaz wrote:Solely for backup in the case of power outages caused by storms, et.c, can this replace a whole house (e.g. Generac) natural gas generator whose costs are approximately $10K (5 for the generator, 5 for permit, installation, etc.)?
Depends how long you want to it to run, and what your peak load might be.
The generator will run for a long time, for days as long as you have natural gas coming in. OTOH the battery might only last a few hours.

The average US home uses 909 kWh per month or 30.3 kWh per day. So assuming it can meet all your peak loads, on average the 7 kWh model would last 5.5 hours, and the 10 kWh almost 8 hours.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by TimeRunner »

In the last year, our peak month electrical use was 503kW last January, lowest month was August 2014 at 305kW. Two house occupants, not much TV watching, energy efficient house and lifestyle. We prefer the outdoors. Going off the grid isn't maybe as big a hurdle for us. YMMV for sure. :beer
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by puma »

For states with net metering and time of use rates, I don't see how this makes any sense for homes with solar. Can't beat generating and selling power at 4x what we pay when we use the power at night.

Availability of this technology may give regulators enough cover to give the power companies what they have wanted for a long time. Do away or cripple net metering. At least for new customers. And Tesla may lobby to make sure that happens.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by kolea »

TimeRunner wrote:In the last year, our peak month electrical use was 503kW last January, lowest month was August 2014 at 305kW. Two house occupants, not much TV watching, energy efficient house and lifestyle. We prefer the outdoors. Going off the grid isn't maybe as big a hurdle for us. YMMV for sure. :beer
The problem for most people is not the power consumption, it is the consistency of solar radiation. We installed PV for a water pump system and the average solar power output in December is about 30% of what it is in June. That is at 45 degrees North latitude. And that assume no clouds. Cloudy days will diminish solar radiation. So if you are off the grid you have to plan for less sun in mid winter, and cloudy days on top of that. The further north you are, the worse it gets. Southern states have it a whole lot easier.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by denovo »

This is certainly an intriguing proposition; especially with a 10 yr warranty. Prices are going down and solar efficiency is going up. I suspect we'll see some massive disruption in the utility sector in the coming years.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by just frank »

My guess is that the two products, 'off-grid' and 'back-up' applications have the same battery pack, and the 'daily cycle' version just uses a reduced cycle range to get longer battery life (more cycles), e.g. 10-80% SOC (thus 7 kWh versus 10 kWh). The backup version is rated for 'weekly', meaning <500 cycles per 10 years (the warranty period), so they can use the full 100% cycle SOC.

The backup product is clearly pitched to folks that would otherwise get a $15-20k automatic, natgas fired genset. If you got 3 backup modules, that would be $11k+ installation, would deliver 6 kW continuous, 10 kW surge, and store 30 kWh of energy. This would be good for 1 day (if you had fossil/gas heating) or 2+ days if you 'conserved'. Since very few outages last more than a day or two (outside of hurricane country), its a compelling product. More 'frugal' people (who might not shell out so much $$ for backup) can get a single module for $3500, wired to their essential loads (sump pump, light, electronics) and make do without AC or with backup heat (wood stove, kerosene, etc). Cheaper/quieter/more reliable than a genny, with a sexy 'badge'.

The 'off-grid' product...I priced out the cost per khW delivered over the course of 10 years (the warranty period), assuming you cycled it 7 kWh per day, and got 13.7 cents/kWh. This might seem high to some folks, but current lead-acid off grid solution easily cost that much or more, with a much shorter cycle life (cheap systems last 2-3 years, expensive last 5-7 years), AND the lead acid systems have maintenance (cheap systems need watering, expensive AGW systems still need to be equalized periodically) and can be killed by careless 'abuse'. This product is very competitive for less tech-minded folks building off-grid systems, and as with the other unit, can be scaled to meet your needs. Think cabin in the woods, small island communities now served by communal diesel gennies, etc.

The cost per cycle, 13.7 cents/kWh is high enough to preclude using these products for grid storage in many markets with TOU rates. I don't think that is the target audience.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by airahcaz »

just frank wrote:My guess is that the two products, 'off-grid' and 'back-up' applications have the same battery pack, and the 'daily cycle' version just uses a reduced cycle range to get longer battery life (more cycles), e.g. 10-80% SOC (thus 7 kWh versus 10 kWh). The backup version is rated for 'weekly', meaning <500 cycles per 10 years (the warranty period), so they can use the full 100% cycle SOC.

The backup product is clearly pitched to folks that would otherwise get a $15-20k automatic, natgas fired genset. If you got 3 backup modules, that would be $11k+ installation, would deliver 6 kW continuous, 10 kW surge, and store 30 kWh of energy. This would be good for 1 day (if you had fossil/gas heating) or 2+ days if you 'conserved'. Since very few outages last more than a day or two (outside of hurricane country), its a compelling product. More 'frugal' people (who might not shell out so much $$ for backup) can get a single module for $3500, wired to their essential loads (sump pump, light, electronics) and make do without AC or with backup heat (wood stove, kerosene, etc). Cheaper/quieter/more reliable than a genny, with a sexy 'badge'.

The 'off-grid' product...I priced out the cost per khW delivered over the course of 10 years (the warranty period), assuming you cycled it 7 kWh per day, and got 13.7 cents/kWh. This might seem high to some folks, but current lead-acid off grid solution easily cost that much or more, with a much shorter cycle life (cheap systems last 2-3 years, expensive last 5-7 years), AND the lead acid systems have maintenance (cheap systems need watering, expensive AGW systems still need to be equalized periodically) and can be killed by careless 'abuse'. This product is very competitive for less tech-minded folks building off-grid systems, and as with the other unit, can be scaled to meet your needs. Think cabin in the woods, small island communities now served by communal diesel gennies, etc.

The cost per cycle, 13.7 cents/kWh is high enough to preclude using these products for grid storage in many markets with TOU rates. I don't think that is the target audience.

Thanks for this excellent post. Perhaps when batteries come down in price as well as hold higher capacity, this will be a legitimate backup power replacement for NatGas generators.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by dolphinsaremammals »

It looks a lot simpler than having a natural gas generator installed, plus it would take up a lot less room, apparently. Probably a lot quieter?
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by airahcaz »

dolphinsaremammals wrote:It looks a lot simpler than having a natural gas generator installed, plus it would take up a lot less room, apparently. Probably a lot quieter?
Perhaps even silent.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by kolea »

just frank wrote: The cost per cycle, 13.7 cents/kWh is high enough to preclude using these products for grid storage in many markets with TOU rates. I don't think that is the target audience.
I am not sure what Musk is doing to tell the truth, other than possibly making some noise. Yes, he is making batteries but if nothing else, those will go in his cars which heretofore used batteries from Panasonic. The use of those same batteries in home, business, or grid-storage is sort of a side show since he is not providing anything that is not already available. GE has been selling Lithium-ion grid storage for a while now and Bosch has had a Lithium-ion home storage unit, and DIY'ers have always had access to Lithium-ion batteries for building PV systems. So Musk is not breaking any new ground, other than perhaps bringing competitive pressure to other vendors. It is a win-win for him since those batteries can always be used in his cars, but if he is successful in breaking into the stationary power storage market, that will be nice too. But Lithium-ion has to get cheaper; it still costs almost 2x what gel batteries cost for PV systems.
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Re: Powerwall: The Arrival of Home Battery Backup System

Post by TimDex »

Quite a few threads discussing this at solarpaneltalk.com. Personally, I think most splashy media introductions like this one should be regarded with skepticism. Tim
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