At $3500, you can put in two and be entirely off grid. Solar panels are cheap enough you only need batteries to last one night, as you can size the array to operate your loads even on cloudy days.
4kW inverters seem to be around the $1000 mark… but they don't seem to increase linearly (10kW inverter $4000 for example).
Of course you could go totally off-grid, but the cost isn't going to be just $7k… it's likely to be at least $15-20k by the time you get everything you need and installed. At that price, you could've bought a larger capacity deep-cycle storage solution already readily available on the market with batteries that will last 20+ years.
I'm assuming you'd minimize your loads, it is silly to size your solar system for a business-as-usual set of loads.
Actual power storage is a reasonably small cost (probably < 20%) in even the solar, power equipment (inverter, switches, controllers, etc), power-storage equation anyway if you want to go completely off-grid. So why does this product make anyone more likely to switch than the existing options?
You seemed to be suggesting you could just buy 2x $3500 batteries and go completely off the grid.
To quote from the original post:
"Solar panels are cheap enough you only need batteries to last one night, as you can size the array to operate your loads even on cloudy days."
Citation? Deep cycle lead acid batteries have a maximum life expectancy of 5-8 years, even if aggressively managed.
http://ironedison.com/iron-edison-usa-series-nickel-iron-nif...
Just did some load tests yesterday.
Tesla's product requires none of that to be done.
Suggesting running an electric oven on solar is crazy talk.
Larger solar ovens (usually known as “solar furnaces”) can reach 4000°, adequate not just for cooking or even cremation but also for firing terra-cotta, blowing glass, calcining lime, firing earthenware, making glass, firing porcelain, calcining portland cement, making borosilicate glass, casting aluminum, melting porcelain, purifying metals by zone melting, casting iron, smelting iron, casting steel, melting lime refractory, making quartz glass, casting basalt, boiling aluminum, vaporizing steel, vaporizing quartz, vaporizing lime refractory, melting tungsten, and sublimating graphite. Although people have been doing most of these with solar ovens for a while, especially the famous solar furnace at Odeillo, you can’t do all of these with Iron Age materials; apparently if you want to do anything useful with melted tungsten, you have to use Ta₄HfC₅ or similar.
Of course none of this works when it’s cloudy or dark, although molten-salt heat storage might be a usable solution to that even at a household scale.
Lithium clearly exists in nature. Elemental lithium might not, but they don't make the batteries from that either.
Molten salt also explodes on contact with water.
A charge controller is unnecessary. It's just a cheap way to improve efficiency. The bucket of salt would have a similar controller.
Also since price isn't a part of the equation for whether it's exotic, feel free to mentally replace the lithium ion battery with a lead acid one, made out of utterly boring materials and full of water.
However, I don't think it's true that the charge controller is just a cheap way to improve efficiency; it's actually necessary to keep the battery from exploding like a firebomb when you try to charge it.
The bucket of molten salt has a much higher energy density for cooking purposes, although you're right that this only becomes an overwhelming factor if you consider joules per dollar instead of joules per kilogram. Lead-acid batteries are 0.17 MJ/kg; the particular molten saltpeter mix commonly used for energy storage is 0.16 MJ/kg just from the melting, plus another 0.3 or 0.4 MJ/kg from melting, depending on the temperature range. The practicality difference is that saltpeter costs US$1/kg, while lead-acid batteries cost about US$6/kg.
You only need to worry about it when you're riding near the edge of what the batteries can handle. If your solar array outputs 4 volts and needs a minimum of 6 hours to mostly-charge the batteries, and your batteries are in a nice cool basement, I'm pretty sure you can just hook them all together. It wouldn't be ideal but I don't think you'd have any real fire hazard.
However, I replaced my electric with gas last year.
4kW is enough to power an entire home continuously, without thinking about energy use, even a large one with a home office with several people working in it + washing machine + oven + electrical stove at the same time. I have the data to prove it, too - 10 second interval power consumption logs for the last 4 months for my house/office, and I never had a load of more than 3.5kW. To be fair, this is all with modern, top of the line appliances, so yes that 199$ no-brand Chinese oven will probably draw a lot more power, but still.
Worst case, you'd need a second 'peak power' supply, which could provide e.g. 6 or 8 kw for 10 mins max, maybe using some sort of XXL capacitor. I don't know about the EE side of this, or whether such a thing exists already, just saying - 4kW is perfectly feasible and even heavy users would maybe need just a little bit more.
(of course this also assumes you have a better quality house than the standard American cardboard 'house' in which you need A/C running 24/7 just to not die in summer).
Different issues over the pond, my kettle can draw 3kW :)
Since so many of my countryfolk have something similar, this actually causes our energy production quite severe issues when popular TV shows finish. Often a 200-400 MW spike but at the end of the 1990 world cup semi final penalty shootout against Germany, there was a spike of 2.8GW.
An interesting example of some of the problems that could be solved at least to a large degree by local batteries.
http://en.wikipedia.org/wiki/TV_pickup
I wonder if this will move more from ones in the home to ones placed by the national grid. While every house on my road might have one, and it's not enough to cover the load from a kettle, one for the whole street could cover it just fine as long as we don't boil them at an identical time (the worst case there is basically equivalent to the normal case for individual batteries).
Well depending on which pond you're talking about, we're actually on the same side :)
" my kettle can draw 3kW :)"
True, you have some special circumstances in your country. You'd still be better off with a boiling water tap, the cost of which (even when amortized over only a few years) is the same as using a kettle (when accounting for all costs - lost energy, water, installation costs etc). So for somebody implementing this in the UK, they'd have to budget for an additional 1500 pound up front cost - which has the potential to turn into a cost saver after 5-10 years (probably closer to 5, depending on how fast energy costs will rise - which I think is fair to expect will be at a higher-than-linear rate).
Pretty awesome for when you want that coffee ready in like 30 seconds flat, huh?
But you're probably not, and that was my whole point - my stove top is rated at 10kW, too, yet even when using alongside all other appliances in my house I have never gone above 4kW actual use. Actual need != summing all the nominal maximum rated loads of all appliances. In other words, it's not because your AC is rated 12kW, that you'd need 3 of these battery packs just for the AC. You might need 2, or maybe 3, I'm not saying that 2 (or 4) kW is enough always, everywhere for everybody - but there is no 'normal' (middle to upper middle class) home anywhere that would need 5 or 10 of these units, as is suggested at various places in this thread.
(Probably some jackass is going to downvote me because they think this violates conservation of energy, but no — those 12kW coming out of the heat exchanger include the 5kW of electrical energy that went in, plus another 7kW of heat that’s being extracted from the air being conditioned; and if you were to try to run a heat engine off that 7kW of heat difference, you wouldn't be able to recover the original 5kW. All perfectly thermodynamically copacetic.)