44 Panel Sunpower 345w Installation

[Freakyguy666]

No solar city is not cost-effective.

[Markinphoenix]

You know you could always look into SolarCity panels. They have a new manufacturing plant in Washington State and they're claiming a three to 6% efficiency increase approaching 26% efficiency. Plus it's owned by Elon Musk who also owns Tesla so maybe you could get a 3-fer! You could get Tesla batteries, Tesla panels, and a Tesla car. A 3-fer! giddy up!
And now ladies and gentleman, back to our regular schedule program.

[sensij]

Well said in the last two posts.

I'll reiterate what was spoken a few posts back about length of ownership. Given this is intends a multi-generational home, all the value over time calculations will be tremendously different in comparing a 10 year payback vs. a 40 year term. Much easier to justify going with the largest size system possible at that point, which with limited space being the bottleneck, SP may be the best option for him.

Though I'd spend money in home efficiencies first/concurrently to reduce size needed or makeup for lack of southern roof face.

I'd really be cautious about basing a decision on a 40 year calculation. Discount rates can be used to help account for risk... even a 4% rate means any benefit 20 years from now is only worth 46% in today's dollars. Any projections of benefit past 20 years can not use net metering as it exists today; we don't know what the tariff will look like, but 1:1 retail credit for every kWh produced seems unlikely. One approach would just consider the benefit of self-consumption at that point... accounting only for the reduction in energy being purchased during the day because it is being generated by the PV system.

Of course, a lot of things can go wrong in 20 years, and even if I intend to be alive and living in the same residence, I would prefer to have a system that has been of benefit to me much sooner than that. When I've looked at it before, the time required for a Sunpower system to be more cost effective than a smaller non-Sunpower system was 12-15 years, but the latest LG panels are much better and I would guess the calculation is approaching 20 years now.

[cebury]

Well said in the last two posts.

I'll reiterate what was spoken a few posts back about length of ownership. Given this is intends a multi-generational home, all the value ove time calculations will be tremendously different in comparing a 10 year payback vs. a 40 year term. Much easier to justify going with the largest size system possible at that point, which with limited space being the bottleneck, SP may be the best option for him.

Though I'd spend money in home efficiencies first/concurrently to reduce size needed or makeup for lack of southern roof face.

[sensij]

Yes, that is the point I had hoped to make. With respect to degradation rates, these panels have not been on the market long and it is hard to know what the actual differences will be. LG certifies 98% after 1 year and 0.6% loss per year thereafter, with no less than 83.6% after 25 years. Sunpower currently states 95% after 5 years, 0.4% loss per year thereafter. Using those values for modeling the output over time would be justifiable.

Warranty is a tough one to value... panels have proven to be reliable, and the warranties are written in ways that make it hard to prove and hard to know how much value they will really have 5, 10, or more years from now. You could ignore the warranty altogether, or assign it some value if you think it deserves some.

Probably the biggest variables are future power company rates and rate structures. Even grandfathered net metering customers could eventually face charges that change the equation. The most sure way to reduce the rate risk is to reduce consumption. If you want to go with the maximum offset that Sunpower provides because of rate uncertainty, so be it... I don't know the future, and can't say whether it will prove to be right or wrong. However, by taking a guess or two, and modeling it out, more confidence in the relative cost effectiveness of any plan can be developed without relying on the opinion of someone like me, who might have different assumptions or priorities.

[Freakyguy666]

With 31,000kWh usage, what better can you get besides SP 345Watts panels? 44 panels need lots spacing even with a 6000 sq ft home. With multi roofs installation I'm sure they aren't true South and he will be getting less output. He will be really lucky to get around 25,000kWh annual and that is about 80% of his usage. If he only get 22000kWh, then that is about 71% of usage.

Now, if anyone plan their solar base on TOU plan today, that is a risky decision especially the high users. With high electricity users, the bigger solar yield better cost effectiveness.

I think SENSIJ is making the point that although you may produce more power with the SP system, the delta in output is more than offset by the premium. In other words, had you kept the additional cash in your pocket, it would pay for the production shortfall (LG 320 vs SP 345) for 20+ years so you would never realize the savings.

Now whether or not this is true requires a bit of math....$/watt, annual savings delta between the 2 systems, & number of years of usage....plus the delta between the 2 brands in efficiency degradation going forward, as well as the differences in warranty. Not sure I'm familiar enough with the latter 2 items, so I would appreciate any light that could be shed on them (pun intended!).

[silversaver]

OP is not looking for feedback on "max sizing solar arrays". The questions have all been about cost-effectiveness. The Sunpower proposal might be cost effective, it might not be. There are other choices.

With 31,000kWh usage, what better can you get besides SP 345Watts panels? 44 panels need lots spacing even with a 6000 sq ft home. With multi roofs installation I'm sure they aren't true South and he will be getting less output. He will be really lucky to get around 25,000kWh annual and that is about 80% of his usage. If he only get 22000kWh, then that is about 71% of usage.

Now, if anyone plan their solar base on TOU plan today, that is a risky decision especially the high users. With high electricity users, the bigger solar yield better cost effectiveness.

[sensij]

What is absolutely no true? If he is looking for max sizing solar arrays with limited roof spacing, what other can you suggest?

OP is not looking for feedback on "max sizing solar arrays". The questions have all been about cost-effectiveness. The Sunpower proposal might be cost effective, it might not be. There are other choices.

[silversaver]

This is absolutely not true. The goal, for most, is to minimize the cost of electricity. In many cases, the lowest cost comes by paying for a less expensive system up front, and paying a little bit more each month to the Poco because the offset is less. With EV(s) as a significant portion of demand, consideration of TOU plans is another important part of this.

What is absolutely no true? If he is looking for max sizing solar arrays with limited roof spacing, what other can you suggest? Even LG 60 cells are max at 320Watts per panel which no where to be found at moment. Yes, you can argue using TOU plan for a small size solar but he said he is looking for another EV. 31,000kWh is a very high usage for single family home which I believe he will be intended to using even more after solar installed like many others.

In real life, any family that can use up to 31,000kWh per year on the single family home does not looking for budget life style.

That is my friend's 20kW system.

20kW.jpg

[sensij]

Then you have no other choice but SP. You probably getting about 23,000 to 25,000kWh output on your SP on multiple roofs

This is absolutely not true. The goal, for most, is to minimize the cost of electricity. In many cases, the lowest cost comes by paying for a less expensive system up front, and paying a little bit more each month to the Poco because the offset is less. With EV(s) as a significant portion of demand, consideration of TOU plans is another important part of this.

[cebury]

You may be correct but you could also be wrong. It depends on if the installer figured them. If they were not familiar with SE then they very well may have left them out.

Sheesh that's like arguing some of those quotes COULD be wrong if the salesman made typos or reversed numbers, or what was actually implied "they may not have known what they were doing".

[silversaver]

As mentioned, roof space is limited relative to the usage.

Then you have no other choice but SP. You probably getting about 23,000 to 25,000kWh output on your SP on multiple roofs

[sensij]

Thank you. I've only found data thru January on that site. Is there another way to get more recent data?

Data through January will give a very good idea of what to expect. Prices move and equipment changes over time, but missing 6 weeks of data isn't going to change the story much. You might want to include LG300's and LG305's in the filter, which represented their top of the line many months ago.

[Freakyguy666]

When you choose the most expensive setup of solar panels, the cost effective issue will only be limited roof spacing. If you have more roof apace to accommodating more panels, then why pick SP?

As mentioned, roof space is limited relative to the usage.

[Freakyguy666]

I'm not sure "cost effective" is very applicable here. Setting aside the Powerwall for the moment... have you compared the lifecycle costs of an LG315 system to that of your planned sunpower system?

I'd second the question on your usage... It sounds very high, especially for a dwelling with a small roof. Have you had an energy audit performed to explain what is responsible for the consumption?

Since many are asking, annual usage is ~31,000kWh per annum. And it may rise once we add a 2nd Tesla auto next year. The plan is to keep the property for multiple generations.