Solar + storage is OK near the equator, but when you get further north, you get very short days in winter and more or less no usable sun for 2+ months of the year.

+ Even in sunny places you get monsoons etc when you get days of no sun.

I can see that you could get to an 80% solution (solar+storage) at a high but manageable price, but going to 100% would be extortionate.

Thus, you will need the grid or a generator.

The problem then is how do you pay for a grid that people are taking 75% less electricity from.

You will have to keep all the capacity for winter days and expect to pay for it during the summer when you don;t need the grid.

Else, as @DM pointed out, you might use the grid for spikes (Kettle, electric power shower) all year round and main power during the winter.

Setting the rules and costs for this will be a bundle of fun.

Anyone know what they are talking about with the 92% round trip efficiency since no inverter is included?

eci:

Lets see your math then.

@Randy:
Apparently not all of them work, so if you already have an inverter for your solar array you may be out of luck.

Davemart, that is what I say too.

My story concerns my older fridge that the local utility wanted me to replace. In their promotions, flyers with the bill and a feature in the local newspaper etc, I happened to notice that the model depicted was the exact same model that I had. Installed in May '96 and working perfectly ever since I should add. I was therefore motivated to phone the utility and see what their figures were for an 18cu-ft fridge consuming 683Kwh/yr - which I admit is not stellar performance in this class.

Well, this otherwise know-it-all authority could not supply any financial proof of savings or ROI and said I should check with the metal recycler who's 1-800 number was in the promo as it is they who actually run the program. Spokesperson for the recycler said his responsibility was merely to get my address and pick up the fridge - which, incidently, must be in good working order??? Huh, the nerve.

As for Mr Kettle back there. I use a 800W microwave to heat water for instant coffee, and a gas range for an actual kettle when I make tea. But that's just my english heritage. Regarding HVAC, I'm retired so it's safe to leave some windows open with bug screens in place most days. I will allow that there are days when humidity dictates employing the HVAC to dehumidify the house before things become unbearable. In California I think this may not be an option.

A suggestion that Lead Acid batteries working out at $100/Kwh would be a cheaper solution met with disfavor by a friend who had served as a volunteer fireman. Apparently this type of backup solution has been known to have caused call-outs after someone was puttering about in the basement, while smoking and in the vicinity of cells which happened to be gassing at the time.

TESLA's competence in thermal management of lithium ion energy storage enables safe in-home installations that will hopefully promote changes in the HVAC industry. Why not DC current compressor feeds ? Then there's the problem of 110vac LEDs, why not change to 24Vdc lighting circuits at the breaker/fuse box? Going forwards for the power receptacles, what really needs to be operating on 110Vac that now requires upwards of 50 receptacles in the average house ?

'Powerwall comes in 10 kWh weekly cycle and 7 kWh daily cycle models. Both are guaranteed for ten years and are sufficient to power most homes during peak evening hours. Multiple batteries can be installed together for homes with greater energy needs.'

http://bit.ly/1Pcgc82

Which is a flaming lie, unless most US homes don't have anything drawing more than 2kwh more than briefly.

BTW, since the weights are given as the same for both the 7kwh and 10kwh versions, they have clearly used the same cells in both, and have simply given 3kwh more slack to enable daily cycling.

I agree that 2kW continuous and 3.3kW peak is rather low. I think these first-generation units will supplement grid power, not replace them. Its the Tesla Roadster of home battery packs (you buy one to have another car, not to replace your daily driver).

If your house is pulling 4kW, then you'll get 2kW from the grid and 2kW from the battery. If you want more then buy more and daisy chain them, but I doubt it'll be economical at anything less than grid-scale applications with industrial inverters that get 95%+ efficiencies.

Davemart,
you bring up some great points. Would you please compare this Tesla pack to those home H2 units we're all waiting to buy for our HFCV? LOL
:)

Hi T2:
I simply used the figures someone else did without adverse comment or correction on another blog.
Since I do not live in the US I have found it difficult on other occasions to work out what typical US spec equipment is.

Two questions:
Are the differences you suggest enough to make a very material change to the requirements suggested?
That back up generators have often been uprated in the latest models from 20kw to 25kw suggests not, in relation to a source which can only provide 2kw continuous.

What specs would you suggest are appropriate to a reasonably modern although perhaps not state of the art air con installation?

Here in the UK heating systems are very different, and air con in the home very rare, although I happen to have it in an air source heat pump, which though runs on different principles.

Davemart,

Oh come on! You're doing it again. You're picking apart every little detail and say that this would never be sufficient to supply a home with 2kW with 3.3kW peak...yada yada yada. Then turn around and tell us about a .7kW H2 generator? LOL

You think that half the homes in the US don't use gas to heat their water and/or their home heating? LOL

You question the 92% efficiency and then ignore that you lose efficiency in converting the NG to H2 and then lose another 50% efficiency on the fuel cell itself?

If you're going to keep claiming your open to "multiple alternate technologies" then you've got to stop being so blatantly hard on batteries/EVs while picking them apart at ever opportunity and then not only giving a pass to fuel cells...but making excuses for their every shortcoming.

You bring up very valid points...but do it fairly on BOTH sides.

:)

Here is a link to Musk's presentation of the Tesla power systems. One commentator called it the best tech keynote presentation by any CEO ever in history even better than Steve Jobs presentations of the iPhones. I agree. It is really good. Musk have you convinced that Tesla has a product you can order now that you can afford and that can make a real difference for a better future for all of us. Now homeowners in the Northern hemisphere will have an option to become pollution free during summer and spring using Tesla Powerwalls, solar cells, a geothermal heat pump and battery electric cars.

http://www.theverge.com/2015/5/1/8527543/elon-musk-tesla-battery-feels

I noted that musk during the presentation said Tesla was in talk with a utility to deliver a 250MW backup system based on the Powerpack! So it is truly scalable. Also good to see that Tesla can deliver 10kwh for only 3500 USD at the pack level. That is the lowest price 350 USD per kWh I have ever seen for such a battery backup system. The powerwall weights 100 kg so 100wh/kg which is not much. For that reason and also because the cycle life of the Model S batteries is not high enough to support a 10 year warranty on a battery that will see daily deep cycles for ten years I am convinced Tesla uses another battery cell for those Powerwalls and Powerpacks than they for the Model S. May still be a 18650 cell though.

I think people have this the wrong way round.
This is not designed to take you off grid, it is to enable you to spread your Solar energy across the whole day and reduce, but not eliminate, the amount of power you take from the grid.

Thus, if you have a 5kw solar and one or two of these, you will need very little power during summer, spring and autumn,excepting peaks (power shower, kettle+freezer etc.)

During winter, you could use it to shift low rate night power to day time use, while taking 90% of your power from the grid.

Thus, they are NOT a solution for going off grid, they ARE a solution for reducing the amount of power you take from the grid.