Need advice - Is the system worth it

[JonnyVermont]

Hi All,

I hoping you can help me decide if I should go ahead with the SolarCity contract. I am aware that I will not be saving money, but I am willing to pay some extra amount to 1) be a part of the Tesla revolution and support the company, 2) have a backup for power outages (my alternative choice is a whole house generator) 3) generate some of my own energy

My house is in a very wooded area. I am willing to take down some trees (we have a ton of them and I need some firewood). The Tesla rep is proposing a 6.5kw system with an estimated production of 4,129 kWh (i guess that's yearly?) with usage offset of 25%. I may be able to up this with the removal of a few key trees.

The system cost is $37K with two powerwalls. I am getting two because I want to be able to power my house for an extended period of time if the power goes down. We have had a few multi-day outages in my area.

My average utility cost before solar is $231. My average energy cost after color they estimate at $422/mo. Hardly seems worth it. I am paying $200/mo for the system. I also get a $11,100 tax credit.

I could also go with one powerwall bringing down the cost of the system to $31,700. the monthly cost after solar will be $384 with a $9700 tax credit. This is much better, but how will I fair in an extended blackout?

My ultimate goal will be to offset my electricity, power my Model 3 when I can finally get my hot little hands on it, and have power in a blackout.

Does anyone know what I should be trying for with cutting down trees? What would be a good system size? How well will the powerwall be as a generator alternative (with me being in conservation mode during a power outage)? I am hoping I can generate power during the day to run the house at night (weather depending). I am worried that the wall will be empty after a day or so and I will be in trouble.

I am clearly new to all this. I do appreciate any advice you can give me.

 

[D-egg-O]

Based on the information you gave, I estimate the $/Watt for the PV system alone to be $4.05/W. That's pretty high imo. I put in an 11.375kW system with Tesla @ $2.84/Watt. What's your utility's net metering policy? Might be worth going with a larger PV system now, and wait a bit for the Powerwall(s). Definitely shop around and get estimates from local installers. Tesla will price match and beat them. Also, use someone's referral code if you go with Tesla to get an extended 5yr warranty on the PV system.

 

[eml2]

When Tesla proposing 6.5 kW system, I assume it is the PV panels DC output. Do they also give you the solar inverter specs? What is the max output of the inverter? Make sure that the inverter can handle the extra power when you increase the solar output after cutting down trees.

If you only have one PW, you can't do whole house backup. OTOH, do you know if your 6.5 kW system can fully charge 2 PW's in a sunny day?

 

[abasile]

Welcome to the forum!

Yes, I'd certainly assume that the estimated 4129 kWh of production is yearly. That is pretty low for a 6.5 kW system.

It's very interesting to me that Tesla would quote such a system. About a year ago, SolarCity "disqualified" our home because of shading from tall trees, saying that their internal policies prohibit them from installing in non-optimal situations. I'm glad to see that Tesla has apparently relaxed this policy, as it should be up to the customer to make the call as to what they're comfortable paying for. Those who place a high value on generating their own renewable energy may be willing to accept sub-par production for the price paid. In our case, we went with a regional installer that installed 6.48 kW of premium SunPower panels with micro inverters, with an annual production guarantee of about 7100 kWh. As we're currently at about 4760 kWh with four "winter" months to go before the end of our first twelve months, it appears we may fall short of the guaranteed amount by 10-20%, though I trust the installer will make it right and we're happy with the system.

If you're inclined to cut down trees, you might want to target the ones which would most affect your October through February production, likely those trees to the south of the proposed system. I say this because, judging by the chart you shared based on your current tree cover, there's no way a solar plus Powerwall system could keep up with your winter usage in a multi-day outage scenario. No matter what, you'd want to significantly cut your consumption in the event an outage drags on. Is Tesla willing to share the details of their shade analysis?

I think you'll want to stick with Tesla for the Powerwall installation, as I'm not aware of any installers that can beat Tesla's prices. If you're having concerns about the price of the solar PV system, it's probably a good idea to get other bids, as with any sizable project. I went through Pick My Solar and they solicited bids from multiple regional installers. That said, given your need for extra help on shade analysis and tree cutting advice, you might do better to ask around locally and get involved personally with each prospective contractor.

All of that said, I don't think I'd feel too comfortable with a loan or lease on a solar PV system with sub-par production. In the event you need to move, it'd be more of a liability. If you could afford to pay cash and you'd be okay without that money, then that's different. I guess the bottom line is that you'll need to see if you can cut enough trees to make this work without destroying what you love about your home's location in the woods.

 

[Shygar]

You may want to just do powerwalls only, but if you can get some solar, and cutting down trees is an option that provides viable sunlight, then maybe it's worth it.

Also if you are doing a loan, remember that increase in payment is for 10-20 years depending on the loan you got, not forever necessarily. If your panels are warrantied for 25 years and you do a 10 year loan, you are getting 15 years more of production.

I personally have only one powerwall because I can power my entire house (minus AC) for a full day easily without much energy conservation. If I need to go into multiple days with no assumed solar production, then 1 would not be enough. My expectation is my solar with have enough power to at least charge my powerwall plus a little more, but I have great sunlight and only one tree partially blocking my panels.

 

[he1957]

If you look at Mar through Sep there appears to be enough power to recharge one PW-2. This depends on how much power you use each day. With such a system, look at the statistics over a longer period (per year for example). On some days (for possibly several days) you may not get enough Solar to charge the battery however, over a 365 day period, charging the battery and also supplying enough power to run your home (then discharging at night) and possibly having some excess to export may balance things, smoothed over this time span. The cost is what it is worth to you and again over time, - the lifespan of the system should be considered - especially as on-going power prices tend to rise against a fixed cost of such an install.

If you can, increase the solar array to about 8 (or more) kW to cover extended bad weather and unforeseen circumstances, and to allow for lower power in the months not cited.

I would seriously consider micro-inverters because:

1. They are not affected by shading in the same way as other options
2. You can add panels on the fly
3. Panel performance for each panel is very detailed - this allows you to see which panels may be affected by shading. Observing the sun/shade patterns and comparing the statistics will clearly show you which if any trees are targets for firewood
4. Panel failure/shading is limited to single panels and will not affect others
5. Diagnosing/repairing failed panels is very easy
6. In general, power yield is higher

In my installation, 6.5 kW at 42 degrees south, minimal tree obstacles [but a few during winter months], panels not oriented optimally (because of building orientation), we can generate between 40+ kW/hr a day between now (almost summer) and about Mar/Apr going down to about 1kW/hr a day in very bad weather (for a few days) about a month ago.

Having said that, over the last 3 years, my panels have produced about 25.5 MWh which for me was well worth the investment. My initial solar array calculations projected a ROI of some 9-10 years but as things are going it is more like 5-6 years. Adding a PW-2 about 2 months ago extends this back to about 8-9 years but if things go as they seem to be right now this should shorten to a total of 7-8 years and I'm quite happy with that

The UPS feature of the PW-2 is also very important to me so this alone was a very attractive investment since my aged 5 kVA APC UPS died (and to replace it with something similar is actually more expensive).


Cheers,

Harry E.
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[he1957]

I would answer your survey but without knowing your power consumption the answer I'd give is not listed but I'd increase panel count first if possible.