Tesla Energy • Hacker News Board

Re: Tesla Energy

#401

Post by jessriedel » Fri, May 01, 2015, 3:23 PM UTC

krschultz wrote: post #355

andrewtbham wrote: post #320

Earlier quoted context omitted.

I wonder if technology becomes prevalent if we will see appliances change to run on DC.

I would take a wall plug standard for low current DC. If I have a giant battery pack in my garage full of DC, why do I need to convert it back to AC to run 15 feet into my house where it then gets turned back into DC to charge my phone & laptop? I had a boat with both AC & DC sockets, but we had the normal socket for both and the label plates showed you which was which. I don't think that solution is acceptable for t…

From an efficiency standpoint, the only thing that matters is how you handle the high drain equipment. It doesn't make sense to worry about inefficiencies in your 5V phone charger because its power draw is trivial anyways.

Re: Tesla Energy

#402

Post by msandford » Fri, May 01, 2015, 3:27 PM UTC

roel_v wrote: post #391

msandford wrote: post #287

Earlier quoted context omitted.

> only 2kW? 2kW is enough to power any residential, single-family house for 95-98% of the time You obviously don't live where it's hot. I live in Houston, TX and while I rarely run the A/C right now, in another month it's going to run on average 15 minutes per hour, every hour, for 3-4 months straight. Highs in the low 90s to high 100s and lows in the 80s (F). I have 2.5 tons of A/C which is pretty moderate. The cond…

I guess that my phrasing of "any residential house" is a bit unfortunate, and that 'the majority of all residential houses' would have been better, but that doesn't take away from the fact that with one extra of these units + 10k Wp of solar panels, you could power your AC's with power to spare to be stored in the battery pack, which you can then use to power the AC at night. Many people use AC's as a counterpoint to…

> How much is your power bill in summer? Must be $300+, going on 500 during the hottest months? At that rate, you'll make back the $20k + $10k that 10k Wp + 2 of these batteries would cost you in what, 5 to 7 years?

No, here in Houston we've got "deregulated" power in a completely reasonable way. One company owns the lines and handles recording the meters. They charge about $0.015/kWh for this. Then there are about 100 companies that offer electricity in a multitude of different ways. I'm paying $0.08/kWh delivered to my "door" so my worst months are only $150 or so.

Your idea is a nice one, except that I would need more panels and at least 2x the batteries/inverters. If I need 3kW CONSTANT to run the AC then 3kW PEAK doesn't do me any good.

> but that doesn't take away from the fact that with one extra of these units + 10k Wp of solar panels, you could power your AC's with power to spare to be stored in the battery pack

Not really. Look I know Tesla is awesome, and solar is awesome. I'm interested in both. But the economics really aren't here yet in Houston because of how cheap power is, because there's not a state owned utility screwing us bigtime. Houston has a lot of problems to be sure but power prices aren't one of them.

tl;dr Houston isn't California.

Re: Tesla Energy

#403

Post by danielweber » Fri, May 01, 2015, 3:27 PM UTC

IanCal wrote: post #204

hackerboos wrote: post #176

Earlier quoted context omitted.

Economy 7 power is significantly cheaper in the UK than peak power. Charging overnight in the E7 period could save money long term depending on the lifetime of the battery.

I did a quick bit of calculation on this. Assuming you use 10KWh per day and a perfect battery: Economy 7 KWh cost : 8.4p (Best deal I saw was 9.4 for me, but this was a figure on MSE) Standard tariff KWh cost : 14.5p (Best deal I saw was ~12 for me, but this was a figure on MSE) That'd be a £306/year cost on economy 7 and £530 on a standard, taking some more extreme figures. A $3500 (~£2300) battery would then have…

You are planning to charge the thing overnight and use it exclusively during the day, nearly exhausting it each time?

The battery is going to wear out well before 10 years. If you oversize your battery so you are only pulling out half the charge in the battery[1], you can probably get 1500 cycles out of it[2]. That's still less than 5 years.

(This is a common pattern if you are trying to price-compare an electric car to a gas car. For the electric car, the electricity cost is a rounding error compared to the capital cost of the battery, so you can just about assume electricity is free, and worry instead about how long the battery will last.)

You will get a much bigger bang-for-the-buck by demand-shifting: if the biggest load is cooling your building in the heat of the day, run the A/C overnight to superchill a heat sink that can be accessed during the day. No battery installation needed.

[1] Toyota did this with the Prius. They purposefully did not use the full range of the battery because they wanted the battery to last 7+ years.

[2] http://batteryuniversity.com/learn/article/how_to_prolong_li...

Re: Tesla Energy

#404

Post by hyperpape » Fri, May 01, 2015, 3:28 PM UTC

fancyketchup wrote: post #400

krschultz wrote: post #377

Earlier quoted context omitted.

I agree in the long term (50 years) that is true, but in the medium term (15 years) solar + storage might be moving faster than utility companies want. If you built a power plant with a 40 year lifespan in the year 2000, you would not be happy if peak demand is lower than expected in 2025. I would not expect the utility companies to be allies in this transition period to clean energy. It requires major capital outlay…

That doesn't really make sense. Electric utilities require capital investment proportional to peak usage, but only earn returns on average usage. This will only increase the ROIC of an electric utility by reducing the peak:average ratio. Additionally, electric utilities are in a constant cycle of capacity upgrades to keep up with increasing demand. Customers adding distributed storage allows utilities to delay capita…

I think they're saying that the investment in peak capacity may be already made, whereas the returns on use are ongoing, so creating incentives to save electricity may not be valuable to the companies.

Don't know if that's their actual cost-structure, but it's plausible in the abstract.

Re: Tesla Energy

#405

Post by billiam » Fri, May 01, 2015, 3:29 PM UTC

I am just going to cut and paste my previous comment on Musk.

The Musk M.O: 1. Identify industry with big inefficiencies that depends on huge government subsidies. That's cars, commercial space vehicles, mass transit and now: colonizing another planet with the 0.1%. 2. Convince the media and envious government officials you are Tom Swift, boy inventor. Have these governments fight over how many billions to give you to build your space car factory. 2. Use these taxpayer dollars and gigantic tax breaks to create iconic products and services for the elite class, effectively transferring huge dollars from the poor to the rich. 3. Rinse and repeat.

I see no evidence at all that Musk cares any more about technologies to enable several billion of us to live together without slaughtering each other than he does about money.

Add the utility business to the growing list of government supported industries Musk wants to "disrupt" by which I mean establish a publicly funded, government subsidized mechanism to siphon off dollars for himself, just like Tony Stark in fact. The electricity generating and distribution system is one of the most provably useful "common goods" in the history of the human race-- why not convince people to spend more than 10 grand to power their house for 24 hours?

His reasons:

Load Shifting - residences generally have NO economic incentive to ride the demand curve, only businesses do in some cases. It is one of the most important things about the electrical system--these huge monopolies manage that curve collectively for us. Sure, transmission is inefficient, but so is decentralizing that task, while adding the risks of keeping your battery from breaking/catching fire.

Increasing self consumption- a battery does not stimulate this at all - the grid needs your power most when the sun is shining. Solar power and an inverter provides that incentive today.

Backup - One day of power in the event of a true natural disaster for $10,000 is expensive and not sufficient.

I am not a Luddite and I am a libertarian, and certainly our society needs technology visionaries right now, but I find Musk's increasingly cynical ploys and the adulation they receive pretty annoying. They seem designed to distract from the overall failure of his businesses, even if he continues to generate ideas and hype.

Re: Tesla Energy

#406

Post by uberdog » Fri, May 01, 2015, 3:29 PM UTC

sfrigon wrote: post #312

je_bailey wrote: post #298

Earlier quoted context omitted.

You missed an additional subset of users. I live in an old neighborhood that experiences power outages and fluctuations once or twice a year. This is fantastic and something I will be installing as soon as I can. So older neighborhoods, rural areas with inconsistent power supply. All of these potentially benefit from this.

Living in a region with cold weather, this is the kind of situation I would like to solve too. The problem is that a generator still has benefits over a battery, it can be refilled (i.e. when you lose electricity for a longer period).

Having lived through Hurricane Sandy in NYC: don't assume you can get gas to fill your generator in a disaster situation. Solar panels paired with a battery aren't dependent on a supply chain (that itself needs energy).

Re: Tesla Energy

#407

Post by technofiend » Fri, May 01, 2015, 3:31 PM UTC

freshyill wrote: post #209

ChuckMcM wrote: post #138

Nice, that came in lower than I was expecting. I was thinking $5K for the 7kWh unit. Of course that is the "installers" price so who knows what those folks will consider the 'retail' price. My wife still has her solar installer certification so we could presumably get one that way. It also makes for a really interesting opportunity for grid tied solar inverters. Now you want the inverter to power the house first, the…

How about stuck to the side of your house? From further down the comments, this is a rebranding of a battery already offered to SolarCity customers. http://www.solarcity.com/residential/backup-power-supply The image on SolarCity has been updated to show Tesla branding.

That was my thought took until I remembered people already steal copper wiring whether or not it's carrying load. That would be a tempting target for theft. I think I'd stick it in my garage instead, but that's just me being paranoid.

Re: Tesla Energy

#408

Post by donpdonp » Fri, May 01, 2015, 3:35 PM UTC

balabaster wrote: post #399

wiremine wrote: post #310

What I'd love to see is a ROI calculator that: * uses my zip code to figure out what my non-peak costs might be. * allows me to optionally calculate solar energy capture (so I can see what impact having solar would be, given the average sunny days in my area) * takes into account the wear and tear average cold weather would have on the lifetime of the batter and the payback period. For example, I live in Michigan, an…

What I'd like to see is an ability for me to provide a list of appliances that I tend to use in my house (makes/models) along with a "typical" use pattern like "washer, dryer, dishwasher, fridge, freezer, stove, 50" TV, 200W sound system and blu-ray player or cable box frequently get used at the same time" With a usage pattern like that, which of the two batteries would be most useful? would I need multiples wired in…

There are easy to use meters such as the Kill-A-Watt for 120V appliances to measure usage directly.

Re: Tesla Energy

#409

Post by chadgeidel » Fri, May 01, 2015, 3:40 PM UTC

willholloway wrote: post #286

Animats wrote: post #195

The wall mount surprised me, but 10KWh at the same density as the Model S battery should be only 155lb. That's not too bad, although you need a solid connection to the building structure. Having it above floor level is a good thing, since it won't be shorted out by minor flooding. If you get a new solar installation, installing one of these seems an obvious win. The solar installation already includes the inverters a…

As I've learned more about heat pumps I've been wondering why we all use air-source cooling for central A/C. We are cooling our condensers with hot summer time air when the temperature is much lower just four feet under the yard. The energy requirements would drop way down by cooling the condenser with a water ground loop. Ground loops are seen as expensive for installation, but I don't understand why. It's just plas…

I'm just spitballing here, but one has to be concerned about how much heat soaking the ground loop can take before its effectiveness goes down significantly. Dirt is a pretty good insulator. How much will the "ambient dirt temp" increase after X hours of running AC? How long does it take for the heat to dissipate?

Re: Tesla Energy

#410

Post by Tuna-Fish » Fri, May 01, 2015, 3:43 PM UTC

nine_k wrote: post #379

ams6110 wrote: post #345

Earlier quoted context omitted.

I would guess for most people it would show an ROI number that is not conducive to sales. Also, what is the environmental impact of the manufacture of LI batteries at this scale? Lithium mining, processing, assembly, delivery... we can't just ignore that.

Lithium mining has relatively little environmental impact: it's mostly evaporation of lithium-rich brines. But lithium is still not cheap. I suppose that a different battery technology, with lower energy density per unit of weight, could be much cheaper with comparable efficiency. But Tesla only has expertise in lithium batteries, so some other manufacturer could use the momentum with a lower-cost offer.

> But lithium is still not cheap.

Lithium is extremely cheap. The cost of the Lithium has practically no impact on the cost of the batteries. Most of the cost of batteries is work.

This venture makes sense because as lithium batteries are used, they lose capacity, and thus their specific energy gets worse. At this point, they are no longer very useful for cars, yet still can be used for other things. As Tesla recovers the used batteries from their cars, they can resell them as home batteries.