Placed order for 16.32kW + 4 Power Walls system downgraded to 14.28 kW

[coney27]

Hi All,

I found this forum last week and I have been reading over the ton of information that is discussed inside. I just placed an order for 16.32kW + 4 powerwalls last night on 7/11/20 and had a reply today from Tesla with the solar design.

To my dismay it appears as though my roof isn't large enough to fit the 16.32kW system and has been downgraded to 14.28 kW, still with 4 powerwalls.

My concern is the 14.28kW system might not be large enough to fully cover my entire household needs. Any tips or tricks to really gage if the 14.28kW system will actually cover my needs. This past month, with 5 people home and central air running 24/7 my utility bill read 50kMh as a average DAILY usage over 32 days and 1588 kWh for the entire 32 days. I reside in the north east of the US and obviously use alot morr energy during the summer months compared to the fall and winter ones. Based upon my rough estimates at probably a maximum 1588 kWh the 14.28kWh system will only cover roughly 7.5 months. I am apprehensive ( due to lack of knowledge) believing that the solar system might not be large enough.

Any input or guidance is appreciated. Thanks.

 

[gpez]

Hi @coney27, welcome!

What are your goals with installing solar + Powerwalls? Sounds like maybe energy independence but if your utility does TOU/net metering or you live in an area that there are frequent outages there may be other considerations.

 

[coney27]

Hi @coney27, welcome!

What are your goals with installing solar + Powerwalls? Sounds like maybe energy independence but if your utility does TOU/net metering or you live in an area that there are frequent outages there may be other considerations.

Mainly energy independence. And my utility provider, Eversource, does in fact do net metering. Outages vary depending on storms but normally 2 to 3 per year which can be a few hours to a few days, hence the 4 powerwalls lol.

 

[Ampster]

@gpez makes a good point. I am in California and regularly consume more than I produce, but because of load shifting I can leverage TOU rates. Powerwalls are a tool to do that.
I notice you have WSW and ENE orientations which while not as optimum as pure South facing arrays may generate more revenue in the afternoon. It is not an easy question to answer without modeling your production and comparing that to monthly consumption.

 

[garrett5688]

Are there any kids over 18 you could encourage to move out to lower your monthly usage?

 

[coney27]

@gpez makes a good point. I am in California and regularly consume more than I produce, but because of load shifting I can leverage TOU rates. Powerwalls are a tool to do that.
I notice you have WSW and ENE orientations which while not as optimum as pure South facing arrays may generate more revenue in the afternoon. It is not an easy question to answer without modeling your production and comparing that to monthly consumption.

Sorry for my naivety but what is TOU? And yes unfortunately my house does not face south but I can say we get plenty of sunshine being on a mountain. I wish i could estimate how much this system would actually push out but I guess thats where this entire solar panel venture is somewhat of a gamble.

Are there any kids over 18 you could encourage to move out to lower your monthly usage?

Hahaha I wish. All are babies.

 

[DrSmile]

Your system estimate is on your quote, it is 11,382 KWh for the year, or 948 KWh per month on average. If you have net metering you just need to set your settlement date correctly, in the northeast probably around March 1, so you build up an excess to cover your high use Summer months. The estimates tend to be on the low side so they don't over-promise and underdeliver. 11,382 KWh is very low for a 14KW system even with East/West facing panels, I'm wondering how undersize your inverter is? As a comparison I have 100% South facing panels here in Northern NJ, and my 13.2KW system produced 17,482KWh in a year (11.4 KW inverter).My solar installer estimated less than 16KWh for the year.

You can look at your meter readings for the last year and find out exactly how much energy you used. Here in NJ there is a 100% limit on solar, meaning you can only have enough solar to cover 100% of your annual needs.

 

[DoyleS]

I just ordered Powerwalls, my system is small. 7.5KW. It's 105F today here in Northern California and AC is running all day. I did just recently swap out the old 10 SEER 5 Ton AC unit for an 18 SEER unit which should cut the electrical use by about 40%. I am on a grandfathered TOU Rate and so during Summer Peak I can sell excess back to PGE at $0.40/KWH. That rate goes away at the end of 2022.

 

[garrett5688]

PVWatts Calculator

Good resource. There’s a few others out there - googles project solar being one of them.

 

[DrSmile]

I forgot to add that solar production obviously isn't the same every month, I produced less than 500KWh in December and more than 2000 KWh in May and June, the highest production months.

The PVWatts estimator is quite accurate in my experience, my production was within one percent of the estimate from that site.

 

[Big Dog]

Hi All,

I found this forum last week and I have been reading over the ton of information that is discussed inside. I just placed an order for 16.32kW + 4 powerwalls last night on 7/11/20 and had a reply today from Tesla with the solar design.

To my dismay it appears as though my roof isn't large enough to fit the 16.32kW system and has been downgraded to 14.28 kW, still with 4 powerwalls.

My concern is the 14.28kW system might not be large enough to fully cover my entire household needs. Any tips or tricks to really gage if the 14.28kW system will actually cover my needs. This past month, with 5 people home and central air running 24/7 my utility bill read 50kMh as a average DAILY usage over 32 days and 1588 kWh for the entire 32 days. I reside in the north east of the US and obviously use alot morr energy during the summer months compared to the fall and winter ones. Based upon my rough estimates at probably a maximum 1588 kWh the 14.28kWh system will only cover roughly 7.5 months. I am apprehensive ( due to lack of knowledge) believing that the solar system might not be large enough.

Any input or guidance is appreciated. Thanks.

Add a couple of bedrooms for the babies, so you'll have more roof space?

 

[coney27]

Your system estimate is on your quote, it is 11,382 KWh for the year, or 948 KWh per month on average. If you have net metering you just need to set your settlement date correctly, in the northeast probably around March 1, so you build up an excess to cover your high use Summer months. The estimates tend to be on the low side so they don't over-promise and underdeliver. 11,382 KWh is very low for a 14KW system even with East/West facing panels, I'm wondering how undersize your inverter is? As a comparison I have 100% South facing panels here in Northern NJ, and my 13.2KW system produced 17,482KWh in a year (11.4 KW inverter).My solar installer estimated less than 16KWh for the year.

You can look at your meter readings for the last year and find out exactly how much energy you used. Here in NJ there is a 100% limit on solar, meaning you can only have enough solar to cover 100% of your annual needs.

So based upon my meter reads from last year I average 1229 kWh per month. And its nice to know that they underestimate the power of the system. I will also go ahead and try out the PVWatt estimator and report back.

As for the inverter this is what tesla sent to me. To be honest this is all very new to me and means nothing. I am very appreciative for your help though.

 

[DrSmile]

Those are SolarEdge inverters, the maximum single inverter configuration is 11.4KW like mine, I would assume they would go with two inverters for you (but maybe not I'm not familiar with how you'd string East/West panels), so maybe two 6KW inverters is what they are thinking of using? You'd definitely want to know which inverter and how many.

The inverter controls the maximum output to the grid. An 11.4KW inverter will only deliver 11.4KW max, no matter how much more your panels produce. This is called clipping. Most systems are overpaneled by design as you are unlikely to produce nameplate capacity for any significant time period. A 1.15 to 1.2 multiplier is pretty standard, with East/West panels maybe higher would work.

 

[pdx_m3s]

Perhaps try investing in tech to reduce your usage? If you’re maxed out on roof space, and you want to be net-zero, then this is really your only option.

 

[coney27]

PVWatts said i would have an output of 18,221 kWH / per year



I went off the "generation service charge" listed on my bill @ .09414 . If thats correct. Sorry for being clueless.

 

[coney27]

Perhaps try investing in tech to reduce your usage? If you’re maxed out on roof space, and you want to be net-zero, then this is really your only option.

I have a in home energy assessment scheduled for next week hoping I can see if there are any real energy issues with the house.

 

[DrSmile]

PVWatts said i would have an output of 18,221 kWH / per year

What did you put down for azimuth for your system? For the East/West configuration you'd have to use the drawing mode in PVWatts to get an accurate result. Actually I don't know how you'd get an accurate result for multiple panel azimuth locations, my guess is you'd have to do each azimuth separately?

 

[pdx_m3s]

I have a in home energy assessment scheduled for next week hoping I can see if there are any real energy issues with the house.

That’s great. There’s always a way to improve.

 

[Southpasfan]

That PVWatts estimator is exactly on track with the performance of my neighbors system. He was nice enough to share it as I was researching our system.

I don’t know his specific orientation. But the estimate was right on for July

 

[coney27]

Those are SolarEdge inverters, the maximum single inverter configuration is 11.4KW like mine, I would assume they would go with two inverters for you (but maybe not I'm not familiar with how you'd string East/West panels), so maybe two 6KW inverters is what they are thinking of using? You'd definitely want to know which inverter and how many.

The inverter controls the maximum output to the grid. An 11.4KW inverter will only deliver 11.4KW max, no matter how much more your panels produce. This is called clipping. Most systems are overpaneled by design as you are unlikely to produce nameplate capacity for any significant time period. A 1.15 to 1.2 multiplier is pretty standard, with East/West panels maybe higher would work.

Is there a "better" inverter I should be looking for or asking for?

What did you put down for azimuth for your system? For the East/West configuration you'd have to use the drawing mode in PVWatts to get an accurate result. Actually I don't know how you'd get an accurate result for multiple panel azimuth locations, my guess is you'd have to do each azimuth separately?

I used what the website applied on its own. I guess I have to redo it and see what it spits out this time.