Larger solar panel or power wall?

[gabloo]

Hello Everyone,

I am totally new to Solar and just ordered 4.25kW Tesla solar panel + Powerwall. My monthly electricity bill is around 150 per month and located in Fremont, CA.
While I was doing research, I got a thought. What if I get larger system (10.5kW) without Powerwall instead of my initial order. Both will cost me about the same.
What are the pros and cons of doing so? My thinking is larger system will generate more energy that I need so I will have enough credit to cover my yearly useage.
Am I correct?

Thanks in advance.

 

[Ampster]

My thoughts are that the erosion of benefits favor having a battery to self consume more of your own generated power. This is not the answer you were looking for but if it were me, I would buy 10.5kW of Solar and a powerwall. That would give you a hedge against further erosion of benefits.

 

[jjrandorin]

Hello Everyone,

I am totally new to Solar and just ordered 4.25kW Tesla solar panel + Powerwall. My monthly electricity bill is around 150 per month and located in Fremont, CA.
While I was doing research, I got a thought. What if I get larger system (10.5kW) without Powerwall instead of my initial order. Both will cost me about the same.
What are the pros and cons of doing so? My thinking is larger system will generate more energy that I need so I will have enough credit to cover my yearly useage.
Am I correct?

Thanks in advance.

Its hard to evaluate that without knowing how much you actually use during the year and what your actual goals are. While more solar is good, especially if you dont care about backup / time of use power shifting, you may have issues trying to get solar that size even approved by PGE unless your usage matches up with it.

Getting solar, in CA, with the punitive time of use rates, almost demands being able to shift your electrical use out of that time frame if you are going to bother with getting solar at all.

If it were me, and I was getting solar now, I would ensure I was getting at least 110% of my estimated yearly usage, "as well as" getting enough battery storage to at least shift / not use power from the utility during the 3-10pm time frame. Yes I know TOU right now is 4-9 but I expect those to expand at some point.

 

[SageBrush]

A very large part of any possible answer here depends on OP, meaning how much consumption occurs in the expensive hours and how much time shifting can be done. I'm a fan of time shifting, so I would choose panels over storage.

It is almost certainly true that the utility will continue to make daylight hours cheaper and evening hours more expensive. However, it is also probably true that battery storage will come down in price over time. I would look into making the PV system as 'battery ready' as I could today, with an eye towards adding storage in a few years. Call it a hedge.

 

[arnolddeleon]

TL;DR get the solar

If the considerations are simply saving money the calculus is relatively straight forward in PG&E land. Tesla solar is cheaper than off peak PG&E rates. So you are always ahead even if you are just offsetting off peak usage. Batteries for power arbitrage only allows it roughly break even with current PG&E rates.

Now if you assign some value to being able to have backup power with using a fossil fueled generator then it is a more complicated analysis.

 

[wwu123]

Even in the "old days", say about a decade ago, the highest ROI on your solar investment was usually achieved not by trying to zero out your PG&E bill or usage, but offset about 50-80% of it, by getting out of the more expensive Tier 2-4 electricity rates (Tiered rates were by how much more you consumed per month above an initial baseline). Partly because of solar, the utilities have largely flattened out the Tiers for most users in your usage range; I would almost say the only Tier 2 is summer late afternoon/evening A/C usage, because of TOU rates, as other large loads you can meaningfully move out of peak periods).

Every household's electricity usage is different, but rarely is it the same all months of the year. When you say $150/month, is it truly all year round, or just now in the late fall? Is it higher in the winter, or in summer? If it is $150 in the summer too, are you using less kwh than winter, but paying more per kwh (by comparing summer vs winter bill)?

I have a 4kw (non-Tesla) solar system, and without it I think my bill and usage would be similar to yours around $150/month. But usage patterns may be different; I'm on the western side of SF bay area, I use 2x more electricity in winter (more lighting and furnace blower), least in summer months, (i.e. minimal A/C usage and high solar production). Having a smaller 4kw solar only offsets about 70% of my PG&E usage and bill, but it already paid itself back within 7 years, and will have the highest ROI over the next 20 years.

Anyways, your initial 4.25kw solar will generate and offset a good chunk of your base usage and bill during off-peak periods year round. In Fremont you're likely using and paying more than me in the summer than winter, because of A/C needs, but that's just a guess. Your best ROI is probably to do neither of the additional options. But if you do, if your winter bill is same or higher than summer, you have higher base loads and probably 6 kw more of panels will have better payback. If your summer bill is much higher because of A/C, then that's a much better economic argument for Powerwalls, but really it's still the worst ROI... there's a universal axiom that no one ever regretted getting more solar panels; it's too early to tell if folks will feel same about getting Powerwalls.

 

[sunwarriors]

My install was recently done, but I think the flexibility of at least some minimal energy storage can't be understated and I'd suggest it to everyone, especially in CA. My thinking and everyone agrees the utilities are going to raise rates and after NEM3.0, the credits probably won't be 1:1 for sure. Minimum non-bypassable charges are going up as well most likely.

I think we all know that a very very large number of solar installs have no batteries so the utilities will do things to recoup $$ vs. everyone with only solar and no storage. I'd not want to be in that boat, but that's just me and I see it as $$ not spent on a pool, trip, more expensive car vs. batteries intead. Having power during grid outages is an added plus and you guys in Nor Cal seem to get power cuts so often, it's crazy. A lot of folks also on standard 1:1 net metering, after moving to say 1 or 2 EVs and having to commute back into the office is also going to be in for a rude awakening I think since their systems aren't sized for EV charging which uses a massive amount of energy so having more panels will help with that during the day/night vs. a small system since they are just using so much more energy that they aren't covering their usage anymore.

I oversized my panels as much as I could and put as much on the roof as possible since you can build up credits for the summer months. It also helps on cloudy days where my battery is charged really quickly with only like 3 hours of sun the whole day.

You don't need 4x powerwalls or some insane number, but even 1 or at least ideally, 2 if someone can afford it would be what I'd go for...esp if/when generator technology as well as vehicle to home is more available in a few years so long long cloudy days can be solved.

I didn't use Tesla solar because of concerns with delays/PTO (you can read that daily here), etc...so I'm on Enphase 10 batteries.

Managing a solar project is a headache honestly so a lot of people speak of doing add ons later, but that seems like a lot of work/permits/just overall a hassle to waste time on another upgrade further down the line, but that's just me.

I follow this site about NEM changes:

Blog | Energy Toolbase

Get the latest policy and utility rate updates, industry insights, and solar and storage tips for developers.

www.energytoolbase.com

 

[SMAlset]

We’re in south SFBay area and after one of the PSPS outages, we opted to go solar with PWs. I suspect with drought and red flag gusty wind conditions in our future we will be encountering more PSPS events in our area. If you are okay with losing power to your refrig/freezer, eating cold food, no electricity for electronic devices and maybe no heat or AC or hot water during an undetermined outage then skip the PW. Just realize, some people don’t, that having just solar won’t give you any electricity during outages. The panels can’t export energy to the home then.

If you plan to stay in your home, may get an EV, I would suggest getting as much solar as you qualify for but also add PW/s. At least enough to run basics and not toss your refrig/freezer due to spoilage. During the winter when it gets into the 30s or upper 20s, heat is a nice thing to have. Two PWs all the better.

We have a 3800 sqft house and orig opted for 2 PWs but before install went to 3. Right now with heat on (gas heating btw and a pretty well insulated home) and no major draws from other appliances our 3 PWs are sitting at 27% this morning. Been cloudy yesterday and this morning so far. Two days ago we charged my car for a few hours and drew down our PWs more than we planned and even with good sun in the afternoon yesterday only got to I think 50% SOC. Low evening temps had heat coming on frequently. Reserve on PW was changed from 25% to 20% to avoid pulling from the grid. Even though we have 3 PWs a 4th would have been nice. Our area of the Bay has still seen winter energy production in 30kWh range most days but morning fog has returned and production can be pitiful. Friday only had 9.7kWh solar generated and why we didn’t get much above 50% SOC. Otherwise our sunnier 30-32kWh days seems sufficient to fill our PWs with our level of electrical usage and still send extra to the grid.

If you’re staying put, I’d seriously consider stretching your budget if you can now. It’s gotten harder to add to existing solar/PW systems due to fire code changes and another trip out later, if you can even do it, will mean extra installation fees and additional permitting and any code upgrades that take affect later on top of the cost of the equipment.

 

[SageBrush]

Our area of the Bay has still seen winter energy production in 30kW range most days but morning fog has returned and production can be pitiful. Friday only had 9.7kW solar generated and why we didn’t get much above 50% SOC. Otherwise our sunnier 30-32kW days seems sufficient to fill our PWs with our level of electrical usage.

Are you talking about kWh ?

 

[BGbreeder]

+1 on what @SMAlset and @sunwarriors wrote.
Probably not the answer that you are seeking, but I think that the answer is probably 10.5kW of solar and a Powerwall. The way PG&E is managing (manipulating?) the rates, I suspect that solar production will become less and less valuable with time, with peak rates getting higher and shifted more into the after sunset hours. So, you need solar plus storage. However, adding solar at a future date will be more expensive, more complicated, and likely restricted to the vendor who installed your initial solar, as subsequent installers will want to install completely separate systems. You can get the best deal on the Powerwall if Tesla installs it with solar.

So, yes, go big on solar, and plan to add storage to deal with the necessary load shifting of high peak TOU rates.

YMMV...

All the best,

BG

 

[SMAlset]

Are you talking about kWh ?

Ah yes! Went back and fixed. Thanks.

 

[SageBrush]

Just realize, some people don’t, that having just solar won’t give you any electricity during outages. The panels can’t export energy to the home then.

This is a pretty good rule of thumb but there are exceptions. For one, ground mounts do not have the module level shutoff requirements that often preclude PV -> home when the grid is down. Second, this option can be engineered into a home system that has PV on the roof but it requires extra gadgetry.

 

[NorCalSlrUser]

If you can get on NEM 2.0 and do not have often power outages, you are better off with larger system and no battery, especially if the larger system will cover fully your usage. NEM 2.0 works as a battery that can store energy in the summer and use it in the winter.

 

[SageBrush]

Not mentioned yet, the marginal cost of increasing the number of panels is often dirt cheap.

 

[ptdusn]

We have a 2250sqft home here in AZ and went with Sunrun to do our install as Costco has them as one of their vendors. We have a 9.45Kw system with 2 Powerwall's. We have had to run the A/C in the last week and 1/2 as temps have been higher. This morning when I got home, (work nights), the Powerwall's were at 39% charge. This afternoon, (moderate solar production today 29.6kWh), they were fully charged. Since activation on Nov. 18th, we have had 8 days with 100% self power and no grid draws. SRP, (power company), only pays $.03 per kW and right now charges $.07 off-peak and $.10 on peak. It's summer when they raise the prices. So depending on your home size, I would go with the 10.5kW system and add 2 Powerwall's. I regret not going with 3 Powerwalls.

 

[M3Bayarea]

I am in a somewhat similar boat as OP. Comparing between Tesla 7.65KW system (generating only 9900KWH per year, 6 of 18 panels are facing north) plus 1 PW for $21K net, vs an 8800 KW (13000 KWH per year due to smaller panels => better orientation) system from a local supplier w great reviews/recommendations at the same price, but without PW. I have one concern re PW, I only have one reasonable location for it and it is outside of a bedroom, and I have read that some people complain about a humming noise when attaching directly to exterior wall. I am in Palo Alto, very solid utilities, but it would be great to have a PW for backup if we see outages. We are currently using about 13000KWH per year (incl. M3 and AC). Would really appreciate thoughts/feedback.

 

[jjrandorin]

I am in a somewhat similar boat as OP. Comparing between Tesla 7.65KW system (generating only 9900KWH per year, 6 of 18 panels are facing north) plus 1 PW for $21K net, vs an 8800 KW (13000 KWH per year due to smaller panels => better orientation) system from a local supplier w great reviews/recommendations at the same price, but without PW. I have one concern re PW, I only have one reasonable location for it and it is outside of a bedroom, and I have read that some people complain about a humming noise when attaching directly to exterior wall. I am in Palo Alto, very solid utilities, but it would be great to have a PW for backup if we see outages. We are currently using about 13000KWH per year (incl. M3 and AC). Would really appreciate thoughts/feedback.

In that situation I would probably do the larger PV system and skip the powerwall. Backup sounds like a "nice to have" in your situation. You can always add some sort of storage "later", powerwalls from either tesla or a third party if teslas stance at the time you want to get them is still "only with solar / solar roof".

You can also consider one of the other competitors to powerwalls. What will be MUCH harder to do "later" is, "get more solar" especially if you have a challenging roof line, etc.

 

[holeydonut]

In that situation I would probably do the larger PV system and skip the powerwall. Backup sounds like a "nice to have" in your situation. You can always add some sort of storage "later", powerwalls from either tesla or a third party if teslas stance at the time you want to get them is still "only with solar / solar roof".

You can also consider one of the other competitors to powerwalls. What will be MUCH harder to do "later" is, "get more solar" especially if you have a challenging roof line, etc.

I second the idea that PV is the way to go. @M3Bayarea ... you're in Palo Alto. With your friendly inspector (Rhonda Parkhurst and This Link with 52 comments from irate PA residents!) to contend with, you ain't getting batteries or Powerwalls even if you tried. Most installers just skip doing complex work in PA because of Rhonda.

 

[SageBrush]

6 of 18 panels are facing north)

Uggh

 

[sunwarriors]

I thought the code didn't allow batteries next to bedrooms or was that windows? If you can get into NEM2.0 soon, solar only is probably fine, but I always feel the utilities will make changes to hurt non energy storage people since a large # of installs don't have storage so they will take advantage of that since they can (why we even have ToU already).