[throwaway90446]

I'm still trying to figure out why everyone, including Deutsche Bank, seems to think the Tesla Battery is such a great deal at $3500 for 7kwh.

I can buy 18 35Ah 12v AGM batteries, plus 0 AGW conductors, for about $1350. That's 7.5kwh for $1350.

What exactly defines the "good deal" argument I keep seeing?

[manicdee]

Are you going to fully discharge that 7560kWh lead-acid system every day?

No, you are not. You are actually going to buy five times as many batteries and work in the 20% of the storage range which is suitable for continual cycling. So that's 90 batteries off the bat, or about $6750, almost double the cost of the Powerwall, not including the ancillary equipment you haven't budgeted for to bring your batteries into the same league as the Powerwall.

You still need the battery room to install them in, and the fire protection system to put out electrical or chemical fires when things go wrong.

The Powerwall includes thermal and fire containment (the batteries are swimming in gel), the Powerwall also takes care of the "battery room" issue by storing the battery in a container on the wall.

For those with greater power requirements, there are rack mounted power cells, again with thermal and combustion mitigation already in place.

The integration and packaging is why everyone is excited about these batteries at this price.

[lotsofmangos]

Those AGM batteries have at best around a tenth of the life expectancy in equivalent charging cycles.

[IkmoIkmo]

Lead acid batteries don't last as long, and suffer much more from large depth of charges, meaning you need to replace them 2-3x more often. This doesn't just have a cost to it financially, but also environmentally.

It also means that if you want your batteries to last, you can reduce your depth of charge by purchasing excessive capacity. This way instead of discharging 100% of X capacity, you can discharge 50% of 2X capacity, and this lower discharge depth makes the battery last longer. Which means you tend to have to buy a lot more capacity than li-ion.

Beyond that, look at it like any system. e.g. do you want 4 small fridges that give you x liters of volume, or one large fridge that gives you 4x liters of volume for a slightly higher price? Do you want 10 harddrives that give you 100gb each for $250, or would you buy a $300 1 TB drive?

There are non-financial reasons to go for simplicity, something that works out the box, plug and play. Especially for consumer grade equipment. Beyond that, Tesla's solutions offers some integrated solutions e.g. concerning fire hazards that you'd need to do yourself otherwise. And lastly, it appears batteries benefit from economies of scale. Their battery is already for sale today, and considering the factory they're building, it's quite exciting to see how cheap batteries will get by 2025, but that's a different story.

[ghshephard]

Your AGM batteries are Lead Acid. Tesla Powerwall is a LiOn Battery System, designed for 10 years. Implies somewhat more than 10 kWh "actual" in order to deliver 10 kWh, day-in, day-out for 10 years, and avoid deep discharge. The value is greater efficiency, great life span.

The price for the 10 kWh model is basically 50% of what everyone was expecting, which is what has everyone excited. You don't often see a 50% drop in price in systems that are this closely followed.

[albemuth]

this one just works?