20 cents per here in VT.
But I have a question.
A fellow I know recently put in a rather large solar array on his roof and also put in a pair of the Tesla uninterruptible battery power units. He says the Tesla units will power his home "normally" for one full day. More if he controls his water well pump.
The solar panel puts out three times the his consumption during peak hours of sunlight. Which I am advised is sold back to the power company at discount, and rectified over the annual billing.
BUT...
He can not use the Tesla panels to power his home when the main service is NOT interrupted! This just seems illogical.
The battery packs were paid for, the solar panels were paid for, but he is NOT PERMITTED to use the excess energy produced by the panels to cover the less productive hours of each day.
Seems like a plan to keep money flowing one way to me.
I have never heard of a power company regulating solar or battery use behind the meter for home use. Do you know who his power provider is?
I have seen commercial power contracts that did regulate time of load use, max size, power factor, and a variety of other arcane things, but never a battery use.
From the power utility perspective, they can't tell if today's solar power export is lower due battery charging, overcast, dust on the solar panels, someone is running the AC,... it is just a load.
Powerwalls are just big AC batteries. If he is producing more solar power than he is consuming, either in the house or charging the Powerwall(s), then his meter is going backwards, and he is only using power from solar directly. If he is using more than the solar produces, his Powerwalls can power some or all of the deficit (depends on his Powerwall settings, how big his load is, how many Powerwalls he has, and how much is left in the batteries). So, he could set his Powerwall reserve to be 100%, and they would never power his house except in outage. I know only a small number of folks who have theirs set that way, and most live in areas where there is little or no payment for power exports.
Powerwalls are installed with a control unit for for every 10 Powerwalls. That control unit is, amongst other things an automatic transfer switch that will switch the backed up loads to the Powerwall(s) in the event of an outage. The control unit can also shift the frequency to throttle the solar output if needed, when the house and battery load is smaller than the solar output. Not everyone has their whole house backed up, so during an outage, some loads may not be powered for some Powerwall owners.
Call me skeptical, but but I would love to learn more.
We have our Powerwalls set up to absorb excess solar during the low cost power portion of the day, and to export the solar during mid and high priced (peak) times of day, with the Powerwalls powering 100% of our usage during peak cost power. Depending on the time of year, we may be net exporters of power, or net importers, but in both cases, the solar plus the Powerwalls keep us from importing power during the peak times.
And best of all, the Powerwalls keep us running when the grid dies, which happens not infrequently here.
All the best,
Peter