On Sun, May 19, 2019 at 3:09 PM andy pugh <bodge...@gmail.com> wrote:
> On Sun, 19 May 2019 at 22:30, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > > You just have to do a calculation, What is the cost per KWH over the > > remaining > > life of the battery. > > > I am not sure that that is the correct calculation. > What really matters is that the battery is big enough for your purposes, > and then cost-per-year is more important that cost / kWh. > What you just wrote almost what I wrote. Except that " big enough" is not a number you can put in a calculator. Cost per "KWh over the lifetime" is a very standard measure to define the value of a battery. I did not make it up. The figure combines three things 1) The size of the battery bank 2) The cost of the battery bank and 3) how long it will last, measured in "cycles" Those three things are what you said, but only with numbers attached Total KWH meant if you have a 10 KHW battery and you chrage and discharge it 200 times then you have 2000 "lifetime" KHW If you can charge the battery 400 times then you have 4000 "lifetime KWH. The second battery as twice as much value. Again I'll say what matters is *lifetime* KWH divided by the cost. "lifetime KWH is the total amount of energy you can get out of a battery before you have to retire the battery. Your formula of "big enough then cost per year" does not result in a number where you and I can compare performance because "big enough" can vary. Look at the Power Wall and try to apply your formula. "big enough" means two units. Cost for the first year is $13,700. Cost for the next 10 years is zero. Is that a good price? How would you compare that to a personwith a smaller house But if you divide by the amount of power used in ten years and it scales to a more universal number that just happens to be the same units as the power company uses on their bills. Makes comparing easy (And, while we are at it, kWh is a horrible unit. What is wrong with MJ? ) > The power company does not bill in MJ. The meter reads KWH and all the batteries and solar pannels are KWH. It's an indury standard. > > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
