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Tesla Solar / Powerwall question - New roof, panel

Pilot1226

Member
Dec 20, 2019
355
157
USA
Hi all,

My wife and I looked into installing solar panels earlier in the year but ultimately decided not to because of the pandemic. Now that things are starting to get under control here (NJ / NYC metro area) we are looking to start the process again and considering Tesla.

We don’t want the solar roof tile product, just traditional panels.

Have some questions and would appreciate some advice:

We have a roof that is nearing the end of its useful life. We would want to replace it before we put panels on it as we are trying to avoid having to do this again with the panels on top. It’s a typical asphalt shingle roof.

In summer months where we are running air conditioning we are typically between 30 and 45 kWh of use daily depending on temperature (July was the 45 average daily use). In winter we have gas heat (steam boiler) so electrical usage is lower, typically around 20 kWh.

I had a non Tesla solar company draw our plan out earlier this year and they were suggesting we go with an array of 20 LG or Panasonic 350W panels. This would have been a 7 kW system and I’ve attached a picture of the layout - they are basically taking up my entire south facing roof and not using the north one because of bad efficiency as I understand it.

9F5ADB68-4817-429D-826D-B12D9C1D8C14.jpeg

Anyway, this project also included an electrical upgrade from 100A to 200A and a new panel to go from my maxed out box to a new one with room for several new ones in the future.

It also installed a 14-50 outlet on the side of my house.

I am wondering if I have to do the roof and panel and circuit installations before they come do solar or if they can do it all. I’m also wondering how Solar Credits and tax credits work here.

I am guessing that the install wouldn’t happen until 2021, so I’d like to know the tax credit for that year. And, I’d like to know how solar credits work - NJ now has a system where you get credits for production:

60% of SREC rate per 1 MW generated for 12 years after turn on.

The SREC rates typically are around $200. So if this brings in $120 every 1 MW, I would think I could generate around 8-9 MW per year. That would bring in around $1800*60% or $1080 per year for 12 years and help offset the cost.

I’m trying to figure out how the SREC fulfillment is done. If Tesla does this automatically or if I can do it.

Also wondering about powerwall cost. I think I want one for efficiency but we do not have time of use payment. So I would essentially be using it as a battery backup if we lost power at home.
 

bkp_duke

Well-Known Member
May 15, 2016
5,189
16,968
San Diego, CA
Federal ITC for:
2020 - 26% of all solar+battery related costs
2021 - 22% of all solar+battery related costs

I would get the panel upgrade done WITH the solar, since you could make a legitimate argument that it was required for the solar, and would be eligible for the ITC. It's a harder argument, but still plausible, if you do it separately.

Get a quote from Tesla. Even if you don't go with them, use their quote to drive down the quotes from local installers.



Also, double-check the companies giving you quotes for the size of the system. Best way to do this is:
1) go add up the power used on all your power bills for the last 3 years, then divide by 3 to get your average annual consumption
2) take consumption, go to pvwatts.nrel.gov and plug in your address and see what size system is recommended there. There are a lot of variables you can play with there, but the defaults are pretty good
3) add 10% to the number you get above, if you have the roof space, to protect you against future usage changes (i.e. people always run the AC more when they have solar b/c they have invested in their own power and it's cheaper)
4) add more than 10% to the system if you will be installing things that will increase power consumption in the future (i.e. 1st, 2nd, etc. EV; a pool, sauna, etc.).
 

Pilot1226

Member
Dec 20, 2019
355
157
USA
Yes I hope to add an EV. I’ve had my eye on a Model Y and am leasing right now. But I am hoping that around this time next year I will place an order for the Y. It gives them time to get any first run quality issues under control and then I don’t have to break the lease early and pay any penalties.

The south roof is maxed out completely per my first site survey. The north roof as I understand doesn’t make nearly the same amount of solar energy so it seems wasteful for me to put panels on the north.

I will dig out the electric bills for past usage. I believe it’s been pretty comparable for the last 2-3 years as we have installed central air about 3 years ago. Seems like we use about 10 MW per year.

Don’t have a lot of land here so a pool is out of the question. Hot tub... maybe... but most likely not. We just redid our yard and considered it and decided not to. Appliance wise the only thing I think we would consider is the EV, otherwise everything is pretty much set as is.
 

bkp_duke

Well-Known Member
May 15, 2016
5,189
16,968
San Diego, CA
To determine your electricity needs for the EV, a ball park calculation would be to take the number of miles you drive each year, and multiply that by the Wh/mile efficiency of the car you would purchase. A lot of this depends also on the terrain you drive (hilly vs. flat) and your driving style (chill vs. road rage).

Example:
10,000 miles, Model Y, chill would be something like:
10,000 x 250 x 1 = 2,500,000 watts = 2,500 kwh needed in home charging needs



Regarding your roof (N vs. S). This would be one of those instances that if you can install a secondary South facing ground mount system (after filling up the S roof), you might be better off than if you had lots of extra N-facing panels. Solar panels LOVE direct light, but don't like indirect, and given you are in the northern hemisphere, north facing panels could produce half or less as their south facing counterparts.

Also, a consideration, if you cannot add ground mount, is to go with as efficient panels as possible. For example, if you can fit 20 panels on your South facing roof, and that is all, then panels that are 22% efficient will produce 15% more power over the course of a year than panels that are 19% efficient. (i.e. 22 / 19 = 1.15). The downside is that these are considered "premium" panels and you will pay a disproportionately higher cost for them compared to the industry average (which is about 18-19%).
 

Pilot1226

Member
Dec 20, 2019
355
157
USA
Thanks. To clarify I am not looking to completely eliminate my need for the grid electricity - at least in summer months. I’m looking to reduce the bill substantially while also generating some long term savings and having the side effect of a better carbon footprint and climate awareness.

My typical commute would only add around 4-5 kWh of use assuming a 250 watts per mile efficiency. Even if this is closer to 333, I’d still be using around 6-8 kWh per day.

I won’t do the ground mounts you described. I will fit what I can on the roof - which looks like that 8.16 kW system Tesla offers - and that will be that.
 
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