Tesla Powerwall

[LordFlathead]

Has anyone looked at the Tesla Powerwall?



So they are going to offer 7kw as a daily supply or 10kw as a standby supply. Thinking about going solar? Well you can generate your own electricity then bank it. You can charge your Powerwall with your PV array OR by using cheap rate E7 over night then use it in the day.



This means it is possible to be completely "off grid". I absolutely loathe the energy companies standing charge - billed even if you use nothing.

So what do you have to factor in? Well that is £2300 for the 10kw unit and that has a suggested 10 years life span. You can buy big high-end storage batteries (like Rolls, Crown etc) that are guaranteed for 10 years and more but they are huge by comparison and still very expensive. Tesla has created a new market - a scalable system that can be stacked as more energy storage is required.

Sadly there is not much in the way of technical details, but their specification says the voltage of the array is between 350-450 volts.. not quite sure how they arrive at that figure because you would need a solar panel string of 30 panels to get that voltage and then one failure would stop the lot from working. If charging from home electricity you would then have to convert AC to DC and step up the supply at the same time.. this is not the most efficient way of doing things but without a full specification I can only guess on how it is configured.

I've just put my name down and reserved one as I am currently building an off-grid solar system and was struggling with the unsightly mess that is 12 large batteries. I've already 15 panels from Bimble Solar as they are doing un-framed 235w panels for £60 which has to be bargain of the century. I'm planning on putting 7kw down one side of my garden. That should see me permanently off the grid but I have quite a way to go.

I wonder if anyone will buy the Powerwall and tow it behind their Leaf in a trailer as a range extender

Anyone else interested in a Powerwall?

[oop north]

I have some interest - but we have a wind turbine not solar (strictly we have one third share in a wind turbine). Not sure if will work with that - and although I am considering a tesla model s it isn't near the top of the list at the moment due to its restrictions (no towing ability and need a decent sized 7 seater and the range isn't quite there for me)

[oop north]

Have just done some quick mental maths - we haven't measured it directly but I have estimated we use about 40% of what we produce (about 23,000 kWh a year) so saving buying 60% of that back (total consumption across three houses is about same as total production) would pay for the cost pretty quickly. So if we could get it to work even on our one third share it would pay for itself within around five years...

[onedsla]

I like the idea but it sounds too expensive to justify at that price point, which I'd imagine will be double the quoted £2.3k by the time it's installed domestically.

We use a similar idea at the moment, with a device diverting the excess solar energy generated into the hot water tank to cut down on gas consumption. From a 2.4Kw array, about 30Kwh has been diverted into the hot water tank in the past 7 days, but can be as much as 9-10kw on a long, sunny day when we're not using significant amounts during the day.

I'm not convinced 'normal' amounts of domestic PV arrays will safely provide enough energy to allow homes to go off grid and avoid the standing charge- A few gloomy winter days and I'd imagine the batteries will be empty (especially if you are charging your Leaf Tesla at home). That said, combined with a tariff which doesn't have a standard charge, it may make financial sense.

[blueacid]

There's one detail in the spec which might present a problem and that's the maximum power it can supply: around 2.3kw

Or, in other words, you need to tuck your peak use under 10 amps if you're going to go completely from a powerwall. For a smaller household that might be okay but in the morning if you boil the kettle while someone else is using their hairdryer, there's just not going to be sufficient power.

Now that's easily worked around, for sure, but it's still a consideration.

[LordFlathead]

oop north said:

Have just done some quick mental maths - we haven't measured it directly but I have estimated we use about 40% of what we produce (about 23,000 kWh a year) so saving buying 60% of that back (total consumption across three houses is about same as total production) would pay for the cost pretty quickly. So if we could get it to work even on our one third share it would pay for itself within around five years...

Exactly my point. Early adopters either pay a premium or reap the benefits; and much like EV's there will not necessarily be free charging for ever. I think the sooner we can get our head around home generation and fuelling your car from your PV, the more chance we have of getting it to work. You don't need to pay through the nose for your PV install to be accredited because you are charging batteries and not feeding the grid. Once the big 6 energy suppliers realise that a lot of people have had enough of being held to ransom with ridiculous energy prices they might start to offer favourable charges.

onedsla said:

I like the idea but it sounds too expensive to justify at that price point, which I'd imagine will be double the quoted £2.3k by the time it's installed domestically.

We use a similar idea at the moment, with a device diverting the excess solar energy generated into the hot water tank to cut down on gas consumption. From a 2.4Kw array, about 30Kwh has been diverted into the hot water tank in the past 7 days, but can be as much as 9-10kw on a long, sunny day when we're not using significant amounts during the day.

I'm not convinced 'normal' amounts of domestic PV arrays will safely provide enough energy to allow homes to go off grid and avoid the standing charge- A few gloomy winter days and I'd imagine the batteries will be empty (especially if you are charging your Leaf Tesla at home). That said, combined with a tariff which doesn't have a standard charge, it may make financial sense.

You could be right about your costings.. that is just one Powerwall and does not include the inverter or management systems. I am guessing that as the voltage is 350 odd they have chosen that figure to enable you to purchase a bespoke inverter from them as most string sizes are 48 volts for an installation that size.

The Powerwall system is scalable (that's where they will make their money) then it doesn't so much depend on your PV array but the size of your storage banks. If you had excess storage, then you can dump the excess into your heating (as you are doing) which is really just acting as a current shunt. Don't forget that if you have adequate storage you can bank your heating energy even during the winter months but this is also dependent on the size or your array.

With 235 watt panels available currently from £66 the future prices can only drop meaning the overall cost of production dropping substantially as competition grows.

I posted this thread because I wondered how many others were evaluating different ways of gaining from PV; it's great to get some feedback from those that already have PV/EV.

blueacid said:

There's one detail in the spec which might present a problem and that's the maximum power it can supply: around 2.3kw

Or, in other words, you need to tuck your peak use under 10 amps if you're going to go completely from a powerwall. For a smaller household that might be okay but in the morning if you boil the kettle while someone else is using their hairdryer, there's just not going to be sufficient power.

Now that's easily worked around, for sure, but it's still a consideration.

It is and that is why they've prices the Powerwall competitively. One would imagine that if you want to become "grid-less" then you would need a few packs in series to deliver the current. A bit of ohms law dictates that the higher voltage the lower the current so their circuits would become more efficient at that voltage and scaling them up would provide huge gains in both efficiency and available current.

I foresee a whole new market in low voltage domestic appliances; particularly 48 volts as this not only provides massive safety advantages (under ELV regulations) but also provides plenty of power (amps). The more you think of the grid being a dinosaur, the more you can see a new future in lower voltage technologies.. watch this space because its coming!

[rudebhoy]

Doesn't ohms law state higher the voltage the higher the current for same resistance????

[LordFlathead]

rudebhoy said:

Doesn't ohms law state higher the voltage the higher the current for same resistance????

Nope, ohms law states the opposite; the higher the voltage the less the current and vice versa. Hence why most medium sized and above PV installations use 48v rather than 12v for their string size (a string is a group of panels in series - 12v x 4 = 48, rather than four 12v panels in parallel giving 12v).. the cable size is much bigger at 12v because it needs to shift current.

Also the charging technology (MPPS) provides a higher "over-generation voltage" and that means the charger is more efficient, by up to 30%.

Still cannot fathom why they use 350 volts though as you would have to step up the voltage from a single phase supply and there would be inherit losses by doing so.

If anyone else can shed some more light on this anomaly I would love to hear the theories no matter how wacky.. it doesn't make much sense to me at that voltage.

[enginearin]

LordFlathead said:

Nope, ohms law states the opposite; the higher the voltage the less the current and vice versa.

Errr... no it doesn't your making some approximate description of a constant Power system:

In a DC system Volts = Current x Resistance or equally Current = Volts / Resistance

So for same resistance you will get twice the current for twice the voltage

100V / 100Ohms = 1A and 200V / 100Ohms = 2A

In an AC system things are more complex as you have impedance as opposed to resistance leading to consideration of power factors, frequencies and such like... but we wont worry about that.

Power = Current x Voltage

1A x 100V = 100W and 2A x 200V = 400W

Thus your battery charges more quickly as Power is increased by increasing voltage into same resistance

[rudebhoy]

I=V/R Bigger V leads to bigger I . Its not rocket science

[LordFlathead]

enginearin said:

Errr... no it doesn't your making some approximate description of a constant Power system:

In a DC system Volts = Current x Resistance or equally Current = Volts / Resistance

So for same resistance you will get twice the current for twice the voltage

100V / 100Ohms = 1A and 200V / 100Ohms = 2A

In an AC system things are more complex as you have impedance as opposed to resistance leading to consideration of power factors, frequencies and such like... but we wont worry about that.

Power = Current x Voltage

1A x 100V = 100W and 2A x 200V = 400W

Thus your battery charges more quickly as Power is increased by increasing voltage into same resistance

Oops spot on! In my defence your honour it was late and I had just done 14 hours straight and I was dead but excited at the same time looking forward to reading these posts.

I'm actually a qualified electrician so even more embarrassed that I stated that

rudebhoy said:

I=V/R Bigger V leads to bigger I . Its not rocket science

It may as well been last night. As you were people

[maffski]

blueacid said:

There's one detail in the spec which might present a problem and that's the maximum power it can supply: around 2.3kw

They've announced that it will now be 5kw output.

http://electrek.co/2015/06/09/tesla-doubles-the-po...

[LordFlathead]

Oh this just gets better

[hab1966]

I think we are going to see a lot more of these 'powerwall' systems.

http://ecomento.com/2015/06/16/nissan-old-electric...

Makes a lot of sense if we can get further use from the batteries once they are deemed unsuitable for use in cars.

[danp]

Interested in this but looks like a long payback time to me, guess it's more attractive in countries with more sun and/or unreliable grids.

7kwh of electricity from the grid is under £1 so that's the max per day it'll save you, and that'll only be from about April to Sept (well maybe March to Oct). So l'd guesstimate £200 p.a. saving on an investment of 3k. Guess you could switch to economy 7 over the winter and fill up your 7kwh battery on the cheap to be used during the day/evening.

Will register my interest and await further details and pricing anyway, doesn't look like will be available for quite a while...

Edit: I suspect a little commuter EV would provide us a better ROI, but that's another story!

Edited by danp on Saturday 27th June 08:49

[LordFlathead]

The secret is not paying £0.15 a unit for it. Then you charge it up on an economy tariff and bank it when you need it. Also most people are at work during the day so you mostly use it when there is no light. The principle is sound; as with any new technology, the early adopters pay the price. In the future the prices will come down.

[rodericb]

hab1966 said:

I think we are going to see a lot more of these 'powerwall' systems.

http://ecomento.com/2015/06/16/nissan-old-electric...

Makes a lot of sense if we can get further use from the batteries once they are deemed unsuitable for use in cars.

GM are starting a recycling program for Volt batteries into static storage. The batteries in Volts (aka Ampera) last a long time as they aren't pushed as hard as those in EV's like the i-miev, leaf etc. MB are also getting into it with that subsidiary they have. IIRC theres is larger scale stuff.

[oop north]

I think Mercedes recently said they were launching something similar

[gangzoom]

High up on the shopping list for the next house is a larger South facing roof - Along with double garage.

The costs might not work well in the short-term, but in the long-run solar generation with local storage HAS to be the future. Why not make use of the most dependable power-source we know (e.g: The Sun), after all, without the Sun there is no life on earth, and even fossil fuels derived from solar energy at the initial stage (when the animal/plant was alive).

I use to think no one has done this before because solar panels are so inefficient at power generation, but as it turns out a moderate sized panel on the roof of our house is enough to power our home with very little need for 'grid' power - car charging excluded:

When Musk showed how little actual land was needed to transition the whole of the US electric generation it was seemed unbelievable the US government hasn't gone down that route already - And it's not only Musk making these predictions - Spend Billions of $$$ on wars in oil rich countries, or use that money to put solar panels in vast bits of empty land.



I suspect that's why the utility companies have gone mad buying up the Tesla power-packs leaving a 12 month long waiting list. From the Energy company point of view, any solution to help reduce their operating costs/meet energy needs cheaper longterm for a initial investment short term has to make sense. For me the most exciting part of solar energy + power wall is the potential for electricity costs to really fall, once a localised system is setup, there is no on-going fuel costs, you cannot put a 'tax' on sun light, even on a rainy day the sunlight still makes it through (otherwise it'll be 'night' all the time) - But I'm sure someone will try...Shell V Power Solar - Power of the Sun in your car brought to you as tested by Ferrari F1 team

Edited by gangzoom on Wednesday 8th July 15:48

[LordFlathead]

Ha! Great post. I've just ordered another 12 panels from bimble.

I've been doing some calcs for work with conventional vs led, and it goes from 17.8kw down to 5.3kw..and that's just the lighting circuit!

I can run everything except air conditioning, induction hob, air compressor and an arc welder from solar. I'm now fitting two distribution boards; one for the electric company and a completely separate system for my pv installation. I'm currently using hugely expensive Sonnenschein batteries hence the reason for the interest in Tesla Power wall. The future is coming and the electric companies cannot see the threat.