Best use of Powerwall in south Florida

[brian954]

So I have two powerwalls that I purchased these to use as backup power for storms and hurricanes down here.

with full net metering is it best to leave my powerwalls set to back up only? Is that healthy for the lifespan of the battery?

I was thinking if I left the battery in backup only it would also save me from the round trip efficiency loses of charging and discharging. Would this be correct?

how do other Florida powerwall owners manage their powerwalls?

 

[morbidz]

I leave my 3 PWs in backup only mode. With full net metering I treat the grid as giant battery that doesn't have ~10% round trip loss.

 

[bob_p]

I'm assuming you have solar panels.

We're in Texas, so our circumstances might be different.

We installed 15.4 KW of solar panels and 4 PowerWalls at the end of last year. Our installers had recommended a solar buyback plan, but after reviewing the terms, we decided instead to go with the lowest price per KWh plan for 6 months, and then based on actual results, re-evaluate our options.

When we configured our system we assumed we would generate about 50% of our energy from solar and buy the rest from the grid, and based on our first month of operation, we appear to have achieved our 50% goal.

The problem with the solar buyback plan is that the 50% of power we would get from the grid would be charged at a higher rate ($.149/KWh) vs. the lower price we could get on a non-buyback plan ($.091/KWh). So using the grid as a virtual battery would have increased our energy bill by over 60%.

So rather than using a solar buyback plan, we're now looking at using a time-of-use plan, where we'll get free electricity from 8PM-8AM or 9PM-9AM - and that should further reduce our energy costs.

In January 2019, we used 3200 KWh. With our solar panels/PowerWalls in January 2020, we used 1550 KWh. But only around 330 KWh was used during the day period. Even if the cost of energy under a free nights plan is 2X (around $.18-.19 /KWh), we could end up reducing our energy bills by another 50% with "free nights" - especially because we have our S and X set to charge overnight and not durign the day.

Even if the net metering plan buys back energy at the same rate the energy is sold to you, if the energy costs per KWh are higher under a buyback plan vs. a normal plan, you may be paying more for the net electricity you are buying from the grid, unless your system is providing all or most of all power you need.

 

[Dan123]

So I have two powerwalls that I purchased these to use as backup power for storms and hurricanes down here.

with full net metering is it best to leave my powerwalls set to back up only? Is that healthy for the lifespan of the battery?

I was thinking if I left the battery in backup only it would also save me from the round trip efficiency loses of charging and discharging. Would this be correct?

how do other Florida powerwall owners manage their powerwalls?

Yes, I use it for backup only. IN the future, if my power usage exceeds solar generation, I might switch to a TOU plan and use it more.

 

[Ulmo]

So I have two powerwalls that I purchased these to use as backup power for storms and hurricanes down here.

with full net metering is it best to leave my powerwalls set to back up only? Is that healthy for the lifespan of the battery?

I was thinking if I left the battery in backup only it would also save me from the round trip efficiency loses of charging and discharging. Would this be correct?

how do other Florida powerwall owners manage their powerwalls?

On days you know you will farm more sun than you will employ, it will help keep the batteries in better condition if you go ahead and store some in the day and use them a little in the evening. Just don't let them discharge too low. I'd say go to 40%, then back to 70%, for the really sunny days, every once in a while, to keep them in good condition. It's good to play with the app on rare occasion just so you're familiar with it. Just don't forget to set the PowerWalls back to backup when you're done with that occasional battery cycling (since you have sensibly decided to use them in a backup capacity for the time being until the rate plans are updated to allow evening battery discharge to be more advantageous).

 

[chrisbailey13]

So, I have 3 power walls set up in self power mode. this time of year they charge (on a sunny day) from about 0800-1230.

They power the house from 1630-0330 (about 3.6 hours per powerwall). which means I am on the grid from 0330-0800 roughly, that still leaves charging back to the grid form 1230-1700.
I expect that to shift as the days get longer and I get more sun of course.

But I am actually considering a 4th power wall to get me further into the night just for this time of year when the days are short. I would only loose about 1.3 hours of net metering but gain 3-4 hours of self power and an even lower or $0 TECO bill.

 

[bob_p]

I've had our reserve set at 40%, and yesterday (as the days start getting a little longer) our 4 PowerWalls were full by mid-afternoon (57 KWh of solar energy).

Looks like it's already time to start reducing the reserve %.

Tesla could help optimize the reserve % if they would add a "dynamic reserve" option, that would automatically increase or decrease the reserve % based on actual and projected solar energy, maximizing the available reserve while also reducing the risk of getting the PowerWalls to 100% (especially for those that aren't on solar buyback plans).

 

[DonD]

... with full net metering is it best to leave my powerwalls set to back up only?

In Florida you must examine your electric bill closely to see how your power company is defining "net metering". When I installed the original PV system on my home in 2008 my power company (SECO) subtracted the KWh my system backfed to the grid from the KWh drawn from the grid; my electric bill was based on the difference. That was "true" net metering.

A few years ago the state of Florida redefined net metering, allowing electric companies to credit your bill based on wholesale rates for the KWh backfed to the grid by home PV systems, while still charging full retail rates for KWh drawn from the grid. This change resulted in approximately $20/month increase in my electric bill.

Given this change in the way Florida defines "net metering" I figure the cost difference between wholesale and retail electric more than offsets the efficiency loss of cycling through the Powerwalls. I allow mine to draw down to a 25% reserve and try to self power my home.