Powerwalls and Solar how much Offset?

[wbeck]

I am looking into adding a Solar/Powerwall system to my home and curious as to what others have done as far as utility offset.

I am in South Florida, so looking for a basic backup option in the event of a prolonged outtage from a Hurricane (2 ACs, Fridge, Lights, TVs, ETc.) as well as some utility offset for an ROI on the system.

 

[DeanP]

I've been looking as well. Put my $100 down, did all the paperwork and now waiting for approval (credit's bad right now so don't know...). Our power is always getting knocked out. I was looking at 15 kW with 4 powerwalls. With this setup should be good for at least 7 days with no power for whatever reason. Looking forward to getting it.

 

[jrweiss98020]

The ACs are the big load factor. Generally, you have to double their rated power consumption to find their startup demand; that will guide the number of Powerwalls you need, at 5 KW each (peak load). Then the ACs will drain the Powerwalls quickly if you keep them running normally.

You MIGHT get 7 days with that setup... With good sun and reduced use of your ACs, you might be able to survive summer nights and recharge the PWs AND run some AC in the day time continuously...

 

[DrSmile]

A/C is the killer. My two A/C units suck up 9KW if yours is similar I doubt 4 Powerwalls will get you through the night in Florida. Solar starts dropping off in the afternoon by the time darkness comes I have maybe three hours of A/C use before depleting the PWs on a 100+ day.

 

[GenSao]

I'll spit my comment into two; 1) Solar 2) Powerwalls

1) Solar
My goal was to offset 100% of our annual solar use. I initially installed 5.7 kW of solar a year before we had Powerwalls and later added 3.8 kW a year after Powerwalls were installed. Our usage increased quite a bit after we got our Model 3. At a minimum, having solar installed makes sense.

Get a year worth of power bills and add up the annual cost and power usage in kWh. You may be able to do this easily online. Make adjustments accounting for future use such as a EV. Assume 1 kWh for every 3-4 miles of driving. You can use Google Project Sunroof to get a rough idea on what you need and cost. Use PVWatts Calculator for a more advanced calculator. You may need to run a seperate report for each separate solar panel array.

Solar can be installed by a separate company first. Although Tesla may have good pricing with standard sizes (S, M, L, XL, their customer service/support can be a hit-or miss. You may find a separate company for your solar will offer options you many prefer, likely provide decent customer service, but at a (likely) higher price. Get three to five quotes (including Tesla) to see what they recommend and options available.

2) Powerwalls
Installation of battery backup is a nice to have as we have two Powerwalls and it can backup all our loads (including the AC). Due to California's high Time of Use (TOU) cost during peak periods with an EV rate plan, we found it can pay for itself. FOr my case Two Powerwalls is the sweet spot. Just enough to cover our household use and run our 4 ton AC.

How many Powerwalls do you need/want? Check Tesla's website for what can be backed up. The link also provides some AC backup details based on compressor type and LRA rating. Per Tesla support/FAQ, "To ensure reliable operation during power outages, at least one Powerwall is required for each 7.6 kW AC of solar included in the backup circuit." You can get away with less Powerwalls if needed. You may be able to move one of your AC units or any other high loads (pool pump) off the backup circuit.

Powerwalls installed by Tesla are typically a better price than other vendors. You may get a bundled discount when paired with a solar installation. I had mixed experienced with Tesla. Be mindful if you chose to move forward with Tesla directly. Tesla has great prices, with standard sizes, with hit-or-miss customer service/support. As with solar, get other quotes to compare pricing and options.

If moving forward with Tesla, please be sure to use a referral. You'll save $250 on the system. Note, I will not span you with mine, unless requested. =)

 

[bob_p]

We installed a 15.4 KW/4 PowerWall system at the end of last year, partly to reduce grid costs and partly as backup after hurricanes.

In parallel, we also did an assessment on power usage, so we could optimize the system to minimize grid power consumption and be prepared to eliminate non-essential devices during an extended power outage.

Some of our observations:

• We have a separate pump for the waterfall in our pool. It was running 10 hours per day. We measured it was using 2 KW of power - and have now reduced the pump to only running 15 minutes per day and when we want to use the pool. This saved us almost 20 KWh of daily power consumption!
• The main pool pump is a variable speed pump. We were able to get some additional savings by reducing the daily run time by a few hours and reducing the pump speed. The combination of the pool pumps was using about 30% of our electricity, prior to our optimizations.
• We had a towel warmer that was running 24x7. It's using around 130W of power. We connected it to a WeMo switch and now run it only for a few hours in the morning - saving around 2.5 KWh per day.
• We reviewed the lights used most frequently in the house each day and replaced those with LEDs, probably saving us another 3-5 KWh per day.
• We have 2 ton, 4 ton and 5 ton air conditioners - the smaller unit uses about 2 KW of power the larger ones use about 4 KW of power. We can run all three off the PowerWalls during a short outage. For a longer outage, we'll turn off 2 of the units.
• Our electric double oven is a huge power consumer - using 4-5 KW of power each when heating the oven. During a power outage, clearly we'll avoid using those!

Assuming there is sun, we're pretty confident we can run indefinitely without grid power, especially if we reduce running time on the main pool pump, turn off 2 of the 3 air conditioners, and not use the ovens - and may have enough spare power to put a little charge into one of our Tesla vehicles periodically.

 

[mattack4000]

I love how emergency power involves powering 2 AC

 

[jboy210]

I love how emergency power involves powering 2 AC

I read it as one AC running, 2 off. Which 2 more A/C units than we have.