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Old 10-16-16, 08:02 AM   #31
Roostre
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It may be obvious from the pictures; the entire front of our roof faces south. You can also see our shop in the backyard has a nice south facing area that might be used for panels, but I'm not sure how far apart they can be.

You can also see the service going into the left corner of the garage; it hooks into a 200 amp panel there.

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Old 10-16-16, 08:57 AM   #32
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That looks like it will work.
What direction is the roof facing?
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Old 10-16-16, 09:19 AM   #33
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Roostre,

First, you can get years of back monthly data (for years) from the electric utility. You just have to ask for it. You need monthly kWhr, monthly $ and the various rate plans. I like to get five years of data and get an average looking for odd months that are not consistent with other years.

Let's assume your yearly historic total kWhr consumption is 20,000 kWhr (1,666 kWhrs/month). This is not unusual.

Since you have yearly net metering, you "bank" excess kWhrs in the summer for winter use. Sweet - not many people have that. So we plan for a system that will deliver, for this example, 20,000 kWhrs.

I can help you with PVWATTS. This will tell you the amount of sunshine hours per month over the year. What is you local zip code?

From this, we get the number of panels. Let's assume a 40 panel, 265 W system. The panel dimensions are ~ 40 inches by 66 inches. Can you do four rows of ten on your roof? You will need to go up there and measure the roof carefully.

The least expensive way to mount panels is in the portrait configuration with mounting rails going perpendicular to that.

It looks like you have a 3-tab shingle roof (is that correct)? I really like the IronRidge "Flashfoot" attachment (on the Renvu site in the IronRidge section).

You can go to the Renvu site and they have very nice design software that will guide you to the type of rail strength, interval between roof attachments, etc, all dependent on your location (snow load, wind, etc).

But first steps first - get utility data, send us (me) zip code), measure roof and try out Renvu software on a simple trial system.

I am going to assume you have natural gas heat and conventional compressor type AC?

Assume you have put in LED bubs everywhere? That is actually the first step!

Get 'er done . . . . .


Steve







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Old 10-16-16, 10:26 AM   #34
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Quote:
Originally Posted by oil pan 4 View Post
That looks like it will work.
What direction is the roof facing?
The whole house faces south.
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Old 10-16-16, 10:28 AM   #35
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Quote:
Originally Posted by stevehull View Post
Roostre,

First, you can get years of back monthly data (for years) from the electric utility. You just have to ask for it. You need monthly kWhr, monthly $ and the various rate plans. I like to get five years of data and get an average looking for odd months that are not consistent with other years.
I called and they will not give me previous owners usage information; it may be worth calling again to see if the policy varies dependent on the person you talk to like so many things in life.
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Old 10-16-16, 10:29 AM   #36
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Quote:
Originally Posted by stevehull View Post
Roostre,

What is you local zip code?
xxxx is the zip.

Last edited by Roostre; 11-10-16 at 04:06 AM.. Reason: zip
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Old 10-16-16, 10:34 AM   #37
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Quote:
Originally Posted by stevehull View Post
Roostre,



But first steps first - get utility data, send us (me) zip code), measure roof and try out Renvu software on a simple trial system.

I am going to assume you have natural gas heat and conventional compressor type AC?

Assume you have put in LED bubs everywhere? That is actually the first step!

Get 'er done . . . . .


Steve
LEDs was the first thing done. Gift cards from real estate agent were put to good use immediately.

Natural gas heater and conventional A/C system is correct.

I spent a few hours on Renvu, but I was mostly exploring their kit pricing not *really* understanding what I need per snow/wind, etc. I even tried to call my local building department with no luck.

Storm rolling in right now, but I will try and make some angle and dimensional measurements this afternoon. Thanks for all your enlightening help and support!!
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Old 10-16-16, 12:27 PM   #38
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Quote:
Originally Posted by MN Renovator View Post
It wouldn't be 1.5x the return.
I considered this when I bought my solar system and mine doesn't beat the stock market.
If I consider a conservative average annual return for the total US stock market to be about 7%, that means the value would double every 10 years.
If I figure a lower cost solar system is $10,000(mine was slightly more) after the tax credit, ignore the delay in getting the tax credit money back, and consider the idea that the money put into the solar system is sunk until it comes back out, this is what my math looked like based on my own expected payback.

Solar installed(figuring 8 year payback, but mine is actually over 10) -$10,000
$-8750 Year 1
$-7500
$-6250
$-5000
$-3750
$-2500
$-1250
$0 Year 8
$1250
$2500 Year 10
$8750 Year 15
$10000 Year 16 (Took 16 years to double)
$15000 Year 20
$27500 Year 30

Of course, this isn't accounting for changes in electricity cost or net metering factors specific to your region or electric provider.

Stock market starting with $10,000 with 7% annual return
$10,700 Year 1
$14,025 5
$19,671 10
$27590 15
$38696 20
$76122 30

Compounding returns is powerful. You could take the returns you get from the solar system and invest those in the stock market, but even if you do that, you still need to consider that the price paid for the system is not going to be in the stock market and you've lost the opportunity cost for that initial potential principal. The idea that the original poster is about to otherwise lose the cash and is willing to DIY the install, I'd say that it's still a good move to do.

For what it's worth, the financial component of solar was a factor but I still wanted the solar and I figured it was better than spending the money on a couch, a car, or some other depreciating asset. It is fun for me to look my eGauge power graphs and see the power the system is generating and what the house is using.
The problem with your example is that you're starting off with -$10000 in the PV panel comparison. In either situation, you would start out with a +$10000 investment. In one, you put that money into the PV panels, and the another, you put it into the market.

You could deduct that amount you spent on panels at some EOL (although they should still have some residual value/generating capacity), but starting at -$10k is assuming you're spending $10k on the panels and another $10k on something else like installation. With that said, you should still invest your annual savings from the panels in the S&P, or some other broad index.

In your 25 year example, with PV panels at a real 9+% and the S&P 500 at a real 6+%, you should have a $10k initial investment in both scenarios. Granted, the $10k PV panel investment will depreciate, while the all S&P investment will do whatever the market does, but there's no -$10k starting point in the PV panel example unless those panels run you $20k.

At 25 years, in the PV panel scenario, you'll have the value ($2000?) of your depreciated PV system, plus your 9% earnings/savings, plus the amount that your 9% in annual earnings (savings from PV system) made in the S&P, less repair costs ($2000 for inverter replacement is the only thing I can think of), and less taxes on your S&P earnings. That should be about $22500(9% annual returns from the PV panels, so $75/month) +$28300(6% earnings on reinvested PV panel savings) - $10000 (initial investment) + $2000 (marginal value of PV panels) - $2000 (inverter replacement) - $28300*your_tax_rate($4200 at 15%), so about $36500-$40800.

The straight S&P 500 example will be the value of your initial investment ($10k) plus after tax earnings on the compounded 6% rate of return. That's $32,900(6% of the initial $10000, or $50/month) - $32,900*your_tax_rate + $10,000(initial investment). That would probably be ~$38,000 to $42,900 assuming your capital gains rate is 0-15%.

You're going to see a much larger difference in the next 25 years though (~$80k more from the PV panel scenario, less taxes), since the first 25 years of higher earnings in the PV panel scenario are offset by the depreciation of the panels.

Like you said, energy rates could drop a lot, but I wouldn't bet on it b/c the costs of the utility, transmission, and distribution are in my experience much greater than the costs of generation, and if people continue to install PV panels and/or disconnect from the grid, it's likely going to be more expensive for whoever isn't self-generating and/or off the grid.

On the flip side, it's possible that you could enter the market at a low point and decide to cash out at a high point, which would put the all S&P investment solidly ahead of PV panels at 25 years. At the same time, you could also enter the market at a high point, and be far behind the PV panels at 25 years.

My sense is the returns will be similar in the near term (first 25 years), and diverge in the long term (50+ years), with the PV scenario having a lot of depreciation (I'm guessing it's 40% once installed, even if it's brand new), but ultimately providing greater returns with less volatility in the long run b/c the PV panels are, at least at the moment, going to return 3% more in untaxed earnings/savings than the market.

Edited b/c I forgot about capital gains on S&P earnings in the PV scenario.

Last edited by roflwaffle; 10-16-16 at 06:48 PM..
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Old 10-16-16, 01:32 PM   #39
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Roostre,

I assumed you have a roof pitch of 14 degrees (3/12 pitch). At least it looks like that from the photos.

Here is the solar radiation data for your specific area using the SLC airport (PVWATTS) using units of kWhr/M**2/day.

This unit is also called a "solar hour" as it represent the average amount of 100% sunshine hours you would get on an average monthly day hitting a panel at 14 degrees facing 180 degrees south.

For January, this means, on the average January day, you have about 2.55 hours of 100% sunshine "hitting" a PV panel at 18 degree pitch facing due south. This PVWATTS summary includes rain/clouds, etc so is a conservative number to start with. For the month, you multiply by the number of days in that month to get the total monthly solar "sunshine hours".

Note the July data where you get almost 8 total hours per day. In summer, you "store away" kWhrs for winter use and then it all gets wiped out in March where you pay some - or loose those banked kWhrs. The key is not to overproduce in the summer so you don't loose too much every March.

For estimates a 10kW system (40 panels producing 250 watts max) would give you about 17,000 kWhrs a year. If history plus your EV use shows a yearly use of 20,000 kWhrs, you would reduce your kWhr consumption by some 85%.

Your EV cars consume 25 kWhrs per day and that accounts for some 9000 kWhrs yearly (25 x 365). This may be a bit high as I counted every day, but on a M-F basis this is still some 6500 kWhrs. For an average call your EV consumption 7500 kWhrs per year. This needs to be added to the historical utility data (as I did above).

But 250 Watt panels in reality only put out 90% of that in real world conditions. That is why I couple 265 W panels with the M215 (that actually puts out 225-230 watts maximum. 90% of 265 = 239 W which is a perfect match for the Enphase M215.


Jan 2.55
Feb 3.65
Mar 4.65
Apr 5.64
May 7.03
Jun 7.34
Jul 7.60
Aug 7.14
Sep 5.95
Oct 4.63
Nov 3.05
Dec 2.10

average of 5.11

Now, we just need an estimate of those monthly kWhrs. If you could even get the YEARLY total, that would be a huge help. We don't want to put up more solar panels than necessary.


Steve
ps I have always gotten this data by asking for a supervisor if need be.
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Last edited by stevehull; 10-16-16 at 02:42 PM.. Reason: typos
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Old 10-16-16, 03:20 PM   #40
Roostre
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Quote:
Originally Posted by stevehull View Post
Roostre,

I assumed you have a roof pitch of 14 degrees (3/12 pitch). At least it looks like that from the photos.

Here is the solar radiation data for your specific area using the SLC airport (PVWATTS) using units of kWhr/M**2/day.

This unit is also called a "solar hour" as it represent the average amount of 100% sunshine hours you would get on an average monthly day hitting a panel at 14 degrees facing 180 degrees south.

For January, this means, on the average January day, you have about 2.55 hours of 100% sunshine "hitting" a PV panel at 18 degree pitch facing due south. This PVWATTS summary includes rain/clouds, etc so is a conservative number to start with. For the month, you multiply by the number of days in that month to get the total monthly solar "sunshine hours".

Note the July data where you get almost 8 total hours per day. In summer, you "store away" kWhrs for winter use and then it all gets wiped out in March where you pay some - or loose those banked kWhrs. The key is not to overproduce in the summer so you don't loose too much every March.

For estimates a 10kW system (40 panels producing 250 watts max) would give you about 17,000 kWhrs a year. If history plus your EV use shows a yearly use of 20,000 kWhrs, you would reduce your kWhr consumption by some 85%.

Your EV cars consume 25 kWhrs per day and that accounts for some 9000 kWhrs yearly (25 x 365). This may be a bit high as I counted every day, but on a M-F basis this is still some 6500 kWhrs. For an average call your EV consumption 7500 kWhrs per year. This needs to be added to the historical utility data (as I did above).

But 250 Watt panels in reality only put out 90% of that in real world conditions. That is why I couple 265 W panels with the M215 (that actually puts out 225-230 watts maximum. 90% of 265 = 239 W which is a perfect match for the Enphase M215.


Jan 2.55
Feb 3.65
Mar 4.65
Apr 5.64
May 7.03
Jun 7.34
Jul 7.60
Aug 7.14
Sep 5.95
Oct 4.63
Nov 3.05
Dec 2.10

average of 5.11

Now, we just need an estimate of those monthly kWhrs. If you could even get the YEARLY total, that would be a huge help. We don't want to put up more solar panels than necessary.


Steve
ps I have always gotten this data by asking for a supervisor if need be.
Ok, called the power company and got a much nicer operator. Although they cannot divulge previous persons info she was able to give me the following:

May2015-May2016 total KWhrs 14,761
Average bill: $153
High bill: $273
Low bill: $88

Keep in mind that we have 2 EVs added to this. It's funny that our highest bill this summer was still lower than the POs... the LEDs must be working.


Measured the roof using a downloaded pitch gauge app. It read 3.9 on both the house and back shop. I'm going to guess it was built as 4/12 and the phone or app is a little off.







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