Considering Tesla Solar w/ Powerwalls in North Texas

[jboy210]

bob_p - Our last 12 months bills were about $850. No solar. That's about 9.444 kWh. That's like 1/5 of yours. Can we come live with you?

Just curious if you think these low power rates in Texas are going to last given the winter storms and potential interconnect actions.

We are buying an investment property in the Austin area and looking at all the angles. Homes there seem big and not the best in terms of insulation and other energy-saving features.

 

[Southpasfan]

I don't think research is going to reveal any reason not to go with Tesla if they will install in your area on your roof. The cost differential is simply too big.

I think the easiest way of looking at it is to figure out what the cost per Kwh for the system.

It will be slightly different for everyone, because of location and roof angle. My 16.32 system in SoCal will produce about 25,000 kwh per year, which is also approximately what we use. I would think a system in TX would produce proportionately the same. Although with PV Watts you can dial it in for your house.

I did it for 20 years, because I priced the 20 year loan. The 20 year loan is about 12 cents per kwh with just solar and 16 cents per kwh with three PWs. Other then varying the number of PWs the price per kwh is about the same no matter how big a system one gets.

Since Los Angeles DWP charges between 23 cents per kwh and 27 cents per kwh, that was the end of the analysis for me. Continue to pay at least 23 cents per kwh forever or get a incredibly cool system including back up for 16 cents.

Its not a question of "pay back" ---- its saving money from month one.

Texas seems to have low energy costs compared to CA. Someone up thread said it was 10 cents if I read it right?

Well, to pay 12 cents of 16 cents for something you can get for 10 cents ends up costing you a few cents until the cost of energy from the utility goes up, as it eventually will. The additional cost of the PWs is, of course, harder to calculate exactly because we all can put a different price on the back up feature as compared to a generator.

 

[Feathermerchan]

I live in the DFW area. I can choose my retail electric provider. I pay 9¢/kWh. That's it. No fixed charges. Two year contract about to end. I renew the end of May.
In the city limits of Austin you must buy from Austin's utility (municiality). Around Austin, there are Coops which do not offer choice but if you are in Oncor's territory you have choice. Go to Powertochoose.org and put in your zip code to find out if you can choose retail providers.

 

[ZBB]

We moved to the Houston area last summer.

Our current rate plan is a fixed generation charge of 5.2 cents/kWh (a 100% wind plan...) with a delivery charge from the local utility of $4.39 per month plus 3.3 cents per kWh (although I just received notice that this is going up shortly...). Results in a monthly total cost of around 9.2 to 9.5 cents per kWh (the fixed connection fee drives the variance). That contract expires in June, so I'll need to sign up for a new plan then (and a quick look at Powertochoose.org shows 1 year plans for 100% renewable at about the same rate, perhaps just under 9 cents...).

One of the reasons we're looking at Powerwalls is for backup power, so we're taking that into consideration. If we had a generator put in, we're expecting it to cost ~$11-15k installed, plus the $25/month service fee (our neighbors have a Generac, and theirs was towards the lower end of that range about 2 years ago).

Tesla's design is a 16.3kW system with 4 Powerwalls. Generation estimate is 21,617kWh annually. We don't have a full year in the house, so I don't know total usage, but Tesla's estimate is about 26k/year. We don't have a pool, but charge 2 cars and will have big AC costs for ~6 months of the year, so I think that's going to be fairly accurate. 82% replacement is what Tesla is estimating.

Looking at the loan cost, the Tesla system without Powerwalls is 9.4 cents for 20 years -- so the solar itself is a wash with our current rates. Adding in the 4 Powerwalls takes the cost to 17.5 cents. But I'm taking ~1/3 of that cost out to better compare with other backup power systems -- which means that the system would lock in power generation at about 11.6 cents for the next 20 years. While that's a ~23% increase over ~9.4 cents, its also a constant. Like others have said, Texas power rates are likely to go up significantly with the changes that will happen after the Feb storm and resulting crisis.

That analysis doesn't take into account the opportunity to arbitrage via a free nights plan -- could we shift high demand use (like car charging) to the free TOU period and also top up the Powerwalls. Then generate solar with some Powerwall draw during the charged TOU period and minimize grid draw. That's what I need to see if I can model. But I also want to compare it to the "net" metering plan (I put "net" in quotes since most of the net metering plans we have access to don't give a credit for the delivery charge, only the retail generation charge -- so you would buy power at ~10 cents and sell back at ~6.7 cents.

 

[bob_p]

We're coming up on renewal for our Free Nights plan - which is currently charging us around $.20/KWh for electricity from 9AM to 9PM and completely free between 9PM to 9AM.

Yesterday, Direct Energy sent us a renewal notice - and because we used 77% of our energy during the Free Nights period during our current agreement, they are recommending we renew the Free Nights plan. They are offering us a 2 year term - and reducing the daytime cost to $.18/KWh.

Because we expect electricity costs to go up in the next few months after the effects of the winter storm start impacting electricity rates - plus the legislature is likely going to mandate winterization of all power plants and the grid, which likely will increase electric rates in the short term - we quickly hit the RENEW button.

Before the Free Nights plan, we were on a fixed rate plan with cost under $.10/KWh.

Because we can use our solar panels and PowerWalls to generate power for use during the daytime, with only 23% of our electricity being charged at $.20/KWh, our overall costs are effectively $.046/KWh - much better than any fixed rate plan.

At some point, we're expecting the utility companies to exclude homes with energy storage from the Free Nights plans, because we're able to drive our daytime usage so low, they must be losing money on our contract...

But, at least for another two years we'll have the Free Nights plan - and under the new rate, we'll even lower our effective energy cost to $.041/KWh!

For those planning systems - another factor to take into account when projecting how long it will take to pay off the system. Electric rates will increase in the long term. When we were planning our system, we assumed an average increase of 3% per year (which is likely to be higher in Texas later this year). With the solar panels & PowerWalls, you're basically locking in the generation cost for solar energy, while the grid power it is replacing will continue to increase over time. And after a few years, the difference starts becoming significant...

The other factor to consider when planning a system is how you using electricity today. We discovered our pool pumps were using 30% of our electricity - and were able to reduce that considerably by using variable speed pumps, lowering the speed & reducing the scheduled time to only what was needed. We also fine tuned the schedule for our 3 HVAC systems, which use a lot of power in the summer heat to cool the house. And for the lights we have on most frequently, we replaced those with LEDs. And when we went to the Free Nights plan, we shifted as much of the pool pumps and EV charging as we could into the Free Nights period. And, by doing that, we reduced our daytime electric usage last year to 10% of our total usage prior to solar panels. And compared to before solar panels, we reduced our daytime usage from 29MWh in 2019 to 4.3Mwh in 2020!

 

[ZBB]

Thanks for the update @bob_p !!!

I was modeling our usage for the first 8 months in the house (with a guesstimate for the other 4 months) to see what a free nights plan would look like... Currently, about 63% of our usage is during peak (9p-9a), and the range has been 61-66% during the 8 months (a bit lower in Aug-Sept, higher in winter) -- although since we are not on a TOU plan, we haven't paid attention to high draw use, such as charging the cars, which has been mostly during the day. I estimate our annual usage to be ~25MWh, and Tesla is estimating ~21MWh of annual generation.

The model shows that we'd be able to shift nearly all of our grid draw over to the free period (I assumed solar only generated during peak, although there would be a little generation in the mornings before peak starts). Solar should generate enough to cover the on-peak use, plus a surplus in nearly all months (only August would have a grid draw during peak -- a total of ~12kWh for the month!). Looks like our electric bills would be under $17/month -- mostly for the fixed fees. I did a sensitivity to see what it would be if we still drew 10% of peak use from the grid, and bills would average ~$42/month (with summer peak of $57).

So -- I really like the idea of the free nights plan. Should model better than net metering plans since we will still draw ~4MWh annually. And this model doesn't assume that we'd shift most EV charging to night time (we had a TOU plan in Arizona and very rarely charged during the day -- was easy enough to plan charges out; the only difference now is that we have 2 EVs instead of 1, and only a single wall charger -- but we should be able to rotate charging nights easily enough).

A couple other questions:
1) How do you set your PowerWalls in the Tesla app? I assume Time-based using the Cost Savings setting? What do you set for backup power reserve (I'm thinking we set it at 30% unless expecting a storm...)
2) Do you pay for CenterPoint delivery charges during the free nights window (the EFL labels vary -- some say yes, others say no...),
3) Do you mind sharing which free nights plan you are on? Looks like there are currently 4 plans avail for those of us in CenterPoint delivery area, but have different windows for "night" (I will need to model the plans since they have different fixed costs and rates)... I'm guessing you are with Direct based on the free window...

• Direct "Twelve Hour Power" - 9p-9a free (which is what I modeled for billing). EFL says no delivery charges during free period
• New Power Texas "Free Power Nights" 8p-6a free. EFL includes delivery charges during free period
• Reliant "Truly Free Nights" 8p-6a free
• TXU "Free Nights & Solar Days" 8p-5a

 

[bob_p]

We're on the Direct Energy Twelve Hour Power 12 plan right now and will transition to the 24 plan in June at the end of the current plan, so we'll have Free Nights for at least two more years, and at a slightly lower rate!

1. Using Cost Savings with 9AM-9PM as the peak period and 9PM-9AM as the off-peak with backup reserve typically set between 25-35% to provide at least a few hours of power during unplanned outages.
2. There are no delivery charges during the free period [which is why I expect they'll eventually exclude homes with battery storage, since they must be losing money on us!]
3. Direct Energy Twelve Hour Power 12 plan now and will transition to the 24 plan in June at the end of the current plan, so we'll have Free Nights for at least two more years, and at a slightly lower rate!

One small hiccup on Free Nights...

If a hurricane or winter storm is approaching, Tesla will trigger Storm Watch, which causes the PowerWalls to immediately charge from the grid - if this happens during the day, the charging is done during the daytime period when we are paying around $.20/KWh for electricity (which could cost $7-8). When this happens, I've started disabling Storm Watch temporarily and then re-enable it after 9PM that night, so the charging is done during the free period. When the storm has passed and I don't believe there is much risk left for a power outage, I also have disabled Storm Watch during the daytime - so the PowerWalls will be used during the day for power and reduce the daytime grid costs.

Our installers had recommended we sign up for one of the net metering plans (there aren't many yet in Texas) - they didn't mention anything about the Free Nights plans. Since our system is designed to provide most or all of our electricity, the Free Nights plan is much less expensive than using a net metering plan.

 

[ZBB]

Thanks @bob_p !

I was also trying to think of how to handle Storm Watch. I guess another way to handle it would be to disable it, then slide the backup % up after 9pm when a storm is on the way manually. The other thought is to just not care too much about it -- let the system handle that automatically. Part of the reason we're doing this is for backup power -- and paying an extra $7-8 a few times a year really isn't a big deal...

 

[bob_p]

$7-8 isn't that much - though we've reduced our monthly electric bills from $400 (average) to $65 - so $7-8 to charge is more noticeable.

 

[miimura]

Looking at the loan cost, the Tesla system without Powerwalls is 9.4 cents for 20 years -- so the solar itself is a wash with our current rates. Adding in the 4 Powerwalls takes the cost to 17.5 cents. But I'm taking ~1/3 of that cost out to better compare with other backup power systems -- which means that the system would lock in power generation at about 11.6 cents for the next 20 years. While that's a ~23% increase over ~9.4 cents, its also a constant. Like others have said, Texas power rates are likely to go up significantly with the changes that will happen after the Feb storm and resulting crisis.

That analysis doesn't take into account the opportunity to arbitrage via a free nights plan -- could we shift high demand use (like car charging) to the free TOU period and also top up the Powerwalls. Then generate solar with some Powerwall draw during the charged TOU period and minimize grid draw. That's what I need to see if I can model. But I also want to compare it to the "net" metering plan (I put "net" in quotes since most of the net metering plans we have access to don't give a credit for the delivery charge, only the retail generation charge -- so you would buy power at ~10 cents and sell back at ~6.7 cents.

Tesla does not allow grid charging Powerwalls when paired with solar in the USA. You can shift as much usage as you like to the Free Nights period, but you cannot routinely add energy to the Powerwall batteries like that. Grid charging is only available during Storm Watch events.

 

[mully]

Thanks for the update @bob_p !!!

I was modeling our usage for the first 8 months in the house (with a guesstimate for the other 4 months) to see what a free nights plan would look like... Currently, about 63% of our usage is during peak (9p-9a), and the range has been 61-66% during the 8 months (a bit lower in Aug-Sept, higher in winter) -- although since we are not on a TOU plan, we haven't paid attention to high draw use, such as charging the cars, which has been mostly during the day. I estimate our annual usage to be ~25MWh, and Tesla is estimating ~21MWh of annual generation.

The model shows that we'd be able to shift nearly all of our grid draw over to the free period (I assumed solar only generated during peak, although there would be a little generation in the mornings before peak starts). Solar should generate enough to cover the on-peak use, plus a surplus in nearly all months (only August would have a grid draw during peak -- a total of ~12kWh for the month!). Looks like our electric bills would be under $17/month -- mostly for the fixed fees. I did a sensitivity to see what it would be if we still drew 10% of peak use from the grid, and bills would average ~$42/month (with summer peak of $57).

So -- I really like the idea of the free nights plan. Should model better than net metering plans since we will still draw ~4MWh annually. And this model doesn't assume that we'd shift most EV charging to night time (we had a TOU plan in Arizona and very rarely charged during the day -- was easy enough to plan charges out; the only difference now is that we have 2 EVs instead of 1, and only a single wall charger -- but we should be able to rotate charging nights easily enough).

A couple other questions:
1) How do you set your PowerWalls in the Tesla app? I assume Time-based using the Cost Savings setting? What do you set for backup power reserve (I'm thinking we set it at 30% unless expecting a storm...)
2) Do you pay for CenterPoint delivery charges during the free nights window (the EFL labels vary -- some say yes, others say no...),
3) Do you mind sharing which free nights plan you are on? Looks like there are currently 4 plans avail for those of us in CenterPoint delivery area, but have different windows for "night" (I will need to model the plans since they have different fixed costs and rates)... I'm guessing you are with Direct based on the free window...

• Direct "Twelve Hour Power" - 9p-9a free (which is what I modeled for billing). EFL says no delivery charges during free period
• New Power Texas "Free Power Nights" 8p-6a free. EFL includes delivery charges during free period
• Reliant "Truly Free Nights" 8p-6a free
• TXU "Free Nights & Solar Days" 8p-5a

Gexa also has free nights from 8p-8a, but their daytime rates are a bit higher than Direct Energy.

 

[bob_p]

We used a Gexa fixed price plan prior to the PowerWalls - they typically have some of the lowest rates.

They're Free Nights plan is more expensive. They're daytime charge is currently $.235/KWh (free from 8PM to 8AM). Direct Energy is charging $.206/KWh (free from 9PM to 9AM).

 

[garrett5688]

I’m using GMEC free nights. I like that it starts at 8pm instead of 9. We use more energy at night than in the morning, so 6am peak doesn’t affect us much. They also have no monthly flat fee, so that was also attractive.

 

[ZBB]

I’m using GMEC free nights. I like that it starts at 8pm instead of 9. We use more energy at night than in the morning, so 6am peak doesn’t affect us much. They also have no monthly flat fee, so that was also attractive.

Thanks for pointing this one out. It models better than the Direct "Twelve Hour Power" for our usage profile... Plus, its 100% renewable...

 

[darrelld]

JayKay80,

Welcome to the TMC. Enjoy your stay.

An advantage to micro-inverters are the benefits of higher production during partial shading and the 25 year warranty. The warranty is covered by the manufacturer. A disadvantage is that roof access is required to replace a faulty micro-inverter.

The Enphase micro-inverters rely on the Enphase IQ Envoy installed in the Enphase IQ combiner for monitoring, command and control. Unfortunately, this is a single point of failure the other installers will forget to mention. Tesla's inverters carry the manufacturer's 10 year warranty. In both cases, they are typically installed on ground level and can be easily accessed and replaced as needed.

IMHO, the cost difference between Tesla and the 3rd party installers alone is worth the consideration. Yes, Tesla's customer service can be a hit or miss and they use "standard equipment"; but their "standard prices" prices are great. If you need total customization, (potentially) better service, at a higher price, go with a well regarded 3rd party installer.

As a side note, a less green, more cost effective solution for backup only would be the installation of a natural gas generator. Depending on local energy rates, the cost of Powerwalls may be recouped by time-of-use rate arbitrage. Rely on solar and battery power duing peak rates.

If you want to save some money (and if they meet your needs) you can downsize to two Powerwalls.

I had problems with my natural gas generator during the big Texas freeze. Gas pressure dropped due to high utilization, did a test run just to see if it would start and it did. Fortunately I had Tesla solar and powerwalls for my main source of power.

 

[ZBB]

Just a quick update…. It took a while to get through a design change and HOA approval, but our install is scheduled for tomorrow and Thursday. Our rate plan also expired a couple days ago and we went ahead and switched to the Green Mountain free nights plan. I looked at going with another plan with no cancellation fee, but figured we could shift enough demand before solar was installed to end up about the same average rate. Over the first 4 days on the new plan, the average cost is under 10 cents per kWh, so that is working so far.

Hopefully the install goes well and inspection/utility approval is quick…

 

[bob_p]

We planned our solar panels & PowerWalls to provide us about 50% of our average annual energy.

Through a combination of the solar panels/PowerWalls and energy conservation (LED lights, more efficient pool pump, less EV charging due to COVID, ...), we've reduced our electricity from the grid by 80%.

This year, under a free nights (9PM-9AM) plan, we've reduced our electricity bill by over 90%.

For those installing systems with PW (that won't provide 100% of home power) - if a free nights plan is available, strongly recommend considering that as an alternative to a "buy back" plan, because with energy storage, you should be able to reduce your daytime usage (and shift EV charging overnight when it's free) enough to save more money than buy back plans.

At least until the utilities decide to exclude homes with energy storage for plans with free energy periods.

 

[scdald21]

bob_p: What setting do you use in the tesla app to draw power at night to fill up the PW's?

 

[loan-potato]

bob_p: What setting do you use in the tesla app to draw power at night to fill up the PW's?

I have my system setup similar to bob_p. In the power wall settings in the Tesla app, I set it to time base control. Then entered my plan. At night I run from the grid, and durning the day solar+power wall.

However it only charges the powerwall from the grid when in an active storm watch alert. The rest of the time it will only charge from solar.

 

[Feathermerchan]

I'm a solar newby. Only a month or so in. No battery.
Your power supplier is as important as your Solar system. One I checked said they did an audit every Jan and if you were a net generator over the past 9 months you could not receive more solar credits until your contract renewed. Some solar credits expire. Some have no cash value. One I called said they could tell me their policies but could not send me anything in writing.
In addition, my system was designed to supply as many kWh as I use annually and it was implied that my bill would be $0. Well my provider rate has 3 parts. A customer charge $12.37 per month ($148.44 per year) and two energy charges. One energy charge is for the retail provider $0.09691/kWh and is also the credit for excess generation then $0.03891/kWh for the wires utility. So I need to make an excess of about 1530 kWh/yr to cover the customer charges and then more to cover the wires utility per kWh charge. So my 16 panel system should be about 19 or 20 panels to 0 out my bill.