I'm assuming for a moment that Tesla are not complete idiots and aren't allowing the lithium ion 18650 cells in the powerwall to drain to 0%, and that it actually has a low voltage disconnect cutoff around 25%.
Saying all batteries are the same, whether lead acid of li-ion, isn't really accurate... A large pack of 18650s will last 2000 to 5000 cycles if never drained below 25% voltage. That's a lot longer than a set of lead acid batteries will last even if you only cycle them to 40% capacity daily. http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries On Wed, Mar 23, 2016 at 8:51 PM, Chuck McCown <[email protected]> wrote: > It won’t. It has batts. All batts die with cycles and die quicker if > they are deeply cycled. > It is a nice package and much easier for folks to purchase and install. > But it isn’t good for much IMHO. > > *From:* Eric Kuhnke <[email protected]> > *Sent:* Wednesday, March 23, 2016 9:48 PM > *To:* [email protected] > *Subject:* Re: [AFMUG] Tesla 7kWh powerwall as UPS? > > The thing is... Calculating lead acid batteries as 30 or 15 cents per kWh > to purchase doesn't take into account lifecycle cost. If the lead acid > batteries are only good for 800 to 1000 cycles, absolute maximum, and the > competing battery option is twice as expensive but lasts for 4000 or 5000 > cycles, the more expensive option actually costs a great deal less. > > It remains to be seen whether the powerwall will really hold up to > thousands of cycles. > > On Wed, Mar 23, 2016 at 8:45 PM, Chuck McCown <[email protected]> wrote: > >> 7/5=1.4 hours at full load. >> >> Batts are about 30 cents per watt hour for AGM, half that for flooded >> cells. >> Inverters are about 25 cents per watt. >> >> 7kWh battery == $1125 –$2250 >> 5 kW inverter == $1250 >> Put it on your critical loads. Charge the batts with a rectifier that >> is fed from commercial power. >> You can run the inverter all the time, or use a smaller charger and put >> in a transfer switch. >> Transfer switches/contactors are not very expensive. One single relay >> will do the job. >> >> *From:* Eric Kuhnke <[email protected]> >> *Sent:* Wednesday, March 23, 2016 7:45 PM >> *To:* [email protected] >> *Subject:* [AFMUG] Tesla 7kWh powerwall as UPS? >> >> $3000 is not so bad for something that can deliver up to 5kW for multiple >> hours... >> >> >> http://arstechnica.com/business/2015/09/tesla-powerwall-home-installations-are-starting-for-pilot-customers/ >> >> I am interested to see the results of integrating two of these in >> parallel with an off grid solar array. At first glance it appears a great >> deal less expensive than buying a dozen 12V 200Ah lead acid AGM batteries >> to make a string. And should last a lot longer in 60% cycle depth daily >> cyclic use. >> >> >> Interesting they've cancelled the 10kWh model ($3500) which had a much >> shorter lifespan, the 7kW model is rated at 5000 cycles. >> >> >
