 dogmaXYZ
Premium Member
join:2002-08-15
Boulder City, NV |
to Jack_in_VA
Re: I've gone and done it ... solar installsaid by Jack_in_VA:Dogma do you have solar panels? Just asking....
Why yes. Yes we do. When we moved from L.A. a few years back out here to the Nevada desert, the house we purchased was a foreclosure (like the 200,000 other foreclosures around here at the time) and it happened to have Solar panels already installed by a previous owner. I knew there was some Solar on the roof, but was fairly ignorant of it all until this smart meter debacle last year. Up to that moment, I just thought the electricity rates out here were dirt cheap and that because the home was fairly new (9 years old), the insulation was well above average. I didn't do a good job of reviewing our NVEnergy bill. But I learned a lot about Solar due to that event. We think that it's a 3 or 4 Kw system as there isn't much documentation. It pays/generates for about 60% of our overall yearly power. Moreover, we will probably Double Down on Solar in the very near future by removing the existing panels and replacing them with a system that generates close to 8kW said by Jack_in_VA:I agree nunya and what dogma doesn't account for the $17000 in tax money he got as an individual is not "Free Power" in any stretch of pushing the pencil.
If you're referring to the offset via tax dollars, again this is an issue better suited to another topic that takes into account ALL tax subsidies. said by cowboyro:The assumptions are wrong.
Perhaps. This is why I show my work for peer review!  I was running these numbers basically in my head, but Lets look again and include a little more detail (hopefully ke4pym  can provide his current Total Annual KWhr Demand) From the best I can figure, Duke Energy in North Carolina charges For the first 350 kWh used per month: 9.2899¢ per kWh (excluding taxes which probably kicks it up to around 11¢ per kWh) The OP's 23 245W panels should generate 25 annual average Kilowatt hours/day including a 12% DC-AC conversion loss. (4655DC-4096AC) @ *6.03 Hours a Day of Irradiance x 365 (per year) = 2,200 Hours a Year of Irradiance per year From that I'm getting about 9011.2 Annual Production (KWhrs) from his proposed system. (4.096 x 2200 annual hours) 9011.2 x 11¢ (kWh) = $991.23/year or $82.60/Month 13 years to break even and a 7.7% IRR... main assumptions here include: 1.) his existing electricity rate never goes up over that time period. If it does, which I think we can all agree that it will, his IRR increases. 2.) his new panels produce at least 90% of their effective rating over that time and any defects are covered under warranty. 3.) he actually gets those Hours a Year of usable Irradiance 7.7% annual IRR is still great. Again, can anyone present a better low-risk investment? |
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said by dogma:If you're referring to the offset via tax dollars, again this is an issue better suited to another topic that takes into account ALL tax subsidies. said by cowboyro:The assumptions are wrong.
Perhaps. This is why I show my work for peer review! I was running these numbers basically in my head, but Lets look again and include a little more detail (hopefully ke4pym can provide his current Total Annual KWhr Demand) From the best I can figure, Duke Energy in North Carolina charges For the first 350 kWh used per month: 9.2899¢ per kWh (excluding taxes which probably kicks it up to around 11¢ per kWh) The OP's 23 245W panels should generate 25 annual average Kilowatt hours/day including a 12% DC-AC conversion loss. (4655DC-4096AC) @ *6.03 Hours a Day of Irradiance x 365 (per year) = 2,200 Hours a Year of Irradiance per year From that I'm getting about 9011.2 Annual Production (KWhrs) from his proposed system. (4.096 x 2200 annual hours) 9011.2 x 11¢ (kWh) = $991.23/year or $82.60/Month 13 years to break even and a 7.7% IRR... main assumptions here include: 1.) his existing electricity rate never goes up over that time period. If it does, which I think we can all agree that it will, his IRR increases. 2.) his new panels produce at least 90% of their effective rating over that time and any defects are covered under warranty. 3.) he actually gets those Hours a Year of usable Irradiance 7.7% annual IRR is still great. Again, can anyone present a better low-risk investment? You are manipulating the data of what the OP has posted to fit your numbers. OP states: It is estimated that I will produce about 7,047 kWh/year on my system that is sized at 5.635kW.
Derate factor is 0.78 making the system AC size 4.4kW. This is what the OP says he's installing 7047 / 360 = 19.30 kWh max with max sunlight. All the variables have been figured in his estimate. Since the OP uses approx. 43.3 kWh/day there is a big shortfall from the solar panels. This is exactly what I ran into when I checked into solar. >$30K for solar panels that would generate less than 1/2 of my annual demand. |
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dogmaXYZ
Premium Member
join:2002-08-15
Boulder City, NV |
dogma
Premium Member
2012-Oct-2 6:54 pm
I see what you're saying, but 43kWh/day x 30.4 (days in a Month) = 1308 kWh Month right?
@ 11¢ per kWh = $143/Month. So that would be offsetting about $80/Month against his expense. It's still saving him $80/Month - or whatever it is - anyway you look at it, it's a viable investment. |
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ke4pym
Premium Member
join:2004-07-24
Charlotte, NC |
ke4pym
Premium Member
2012-Oct-2 6:59 pm
said by dogma:I see what you're saying, but 43kWh/day x 30.4 (days in a Month) = 1308 kWh Month right?
@ 11¢ per kWh = $143/Month. So that would be offsetting about $80/Month against his expense. It's still saving him $80/Month - or whatever it is - anyway you look at it, it's a viable investment.
Averaging across the entire year, this usage is pretty close. Last month, in 29 days, I used 1500 kWh. I think my low is somewhere in the neighborhood of 600kWh in Dec and Jan and the high this year was like, 2500 kWh in June when it was 100 billion degrees out. BUT the panels won't be producing as much energy then due to the sun being lower on the horizon and not being up as long. Eventually, the a/c is getting replaced. And that'll be a high efficency system. So, the potential for the energy usage to go down is pretty good. |
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to dogma
said by dogma:I see what you're saying, but 43kWh/day x 30.4 (days in a Month) = 1308 kWh Month right?
@ 11¢ per kWh = $143/Month. So that would be offsetting about $80/Month against his expense. It's still saving him $80/Month - or whatever it is - anyway you look at it, it's a viable investment.
You're still too high on your savings. A 7000 kWh/year system is going to yield 583 kWh/mo @ 0.11/kWh = $64 less 43.33/mo for his initial #13,000 investment equals around $21/mo savings. So he has 143 - 64 = 79 (Duke Power). 79 + 43 = 122/mo. 143 - 122 = 21/mo actual savings. |
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dogmaXYZ
Premium Member
join:2002-08-15
Boulder City, NV |
dogma
Premium Member
2012-Oct-2 7:36 pm
I think this is our issue and how each of us arrives at the final savings amount. I'm getting more power from his system (9011kWh) based on my experience and the number of panels and production. However, using the 7000kWh is 23% less production, which should equate to $82.60 x .77 = $$ he would otherwise have to pay the utility = $63.60/Month in savings = $63.60/Mo. in his pocket (IRR). I am not seeing how you get $21/Mo. If he shells out $13K upfront, he gets $63.60/Mo. Where does the $43 come from? ke4pym , did your Solar company give you a detailed breakdown of cost vs. current expenses? |
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said by dogma:I think this is our issue and how each of us arrives at the final savings amount. I'm getting more power from his system (9011kWh) based on my experience and the number of panels and production. However, using the 7000kWh is 23% less production, which should equate to $82.60 x .77 = $$ he would otherwise have to pay the utility = $63.60/Month in savings = $63.60/Mo. in his pocket (IRR). I am not seeing how you get $21/Mo. If he shells out $13K upfront, he gets $63.60/Mo. Where does the $43 come from? ke4pym , did your Solar company give you a detailed breakdown of cost vs. current expenses? From your earlier post: quote:
OP correct me if I am wrong) has a electricity cost of about $144/Month on average, your model [$13,000 / 300 = $43.33 per month in cost]
Spread out like you posted it would be $43/mo. Upfront it would just take that long for the ROI on initial investment. Assuming his rates stay the same it will take him 300 months to start realizing the full $63.60 reduction of his $143/mo Duke Power bill. |
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ke4pym
Premium Member
join:2004-07-24
Charlotte, NC |
to dogma
said by dogma:ke4pym , did your Solar company give you a detailed breakdown of cost vs. current expenses?
Indeed they did. There are several charts and graphs and such. This is all based off of 2011 actual usage I provided to them. Current Consumption: kWh - 17,600 Cost - $1,848 Annual Solar Production kWh - 7,047 Value - $775 Annual Electric Bill Offset kWh - 40% Cost - 42% |
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banner
Premium Member
join:2003-11-07
Long Beach, CA |
to ke4pym
said by ke4pym:Eventually, the a/c is getting replaced. And that'll be a high efficency system. So, the potential for the energy usage to go down is pretty good.
So the solar install is going to save more on an annual basis than a higher efficiency a/c? |
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dogmaXYZ
Premium Member
join:2002-08-15
Boulder City, NV |
to Jack_in_VA
said by Jack_in_VA:Spread out like you posted it would be $43/mo. Upfront it would just take that long for the ROI on initial investment. Assuming his rates stay the same it will take him 300 months to start realizing the full $63.60 reduction of his $143/mo Duke Power bill.
I see. Okay, take the ROI one of two ways, but not both. A.) ke4pym makes the up front $13K investment. Since the panels have a 25 year (300 Months) lifespan, it would take him the $43/Month to recoup the initial investment over that period. The investment itself performs. However, the asset also depreciates down to zero over 25 years. So his principle investment of $13K goes to $0 over 25 years. A performing asset that depreciates. If it produces $64/Month, it pays for itself in ($13,000/$64) 203 Months or 16.9 years. The balance of the 25 years is 97 Months x $64 = $6,208.00. Of course if it's expressed your way, it's $6.2K profit/300 = $21 per Month. You are indeed correct in that respect. [caution, the following is me thinking aloud/rambling] This is very interesting however in that a "cash" investment depreciates over time as well due to inflation. But never down to zero. I would first need to determine what a fair discount rate (rate is the return that could be earned on an investment in the financial markets with similar risk) is. The discount would be equivalent to a 10-year CD earning a 2.3% yield. IOW, if ke4pym took his $13K and put it into this CD. In 10 years, the CD would be worth $16,358. $3,358 in earned interest - or $28/Month. So if ke4pym put his $13K into this CD, and in 10 years he cashes out, takes the profit as an offset for his previous 10 years electricity cost, and comes out $9/Month ahead for an extra sum of $1080. And he still has his entire principal balance, whereas his Solar system would have depreciated down to about $8,000. But that CD just keeps up with inflation (2.7% over the past 10 years), as $16.3K in 2022 would buy exactly what $13K does today. Conversely, if we apply an inflationary rate to energy based on the previous 10 years, that rate has gone up 44%! (see: » metricmash.com/inflation ··· ode=SEHF ) B.) This means in 10 years, assuming present trends, ke4pym 's electric rate will be .1584¢/kWh and the new calculation would be: 7,000 x 16¢ (kWh) = $1120/year or $93.33/Month - not $63.00/Month - which in turn accelerates his ROI. It's late and I can't do the calculus for this ongoing rate increase model over the 25 life of the system. But off hand I'd say somewhere around the 8 year mark would pay off the initial $13K, and the remaining 17 years could be close to $15,000 in overall savings vs. the ROI on a 10 year CD. I will try to find or build a calculator that takes all of this into consideration. |
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quote:
A.) ke4pym See Profile makes the up front $13K investment. Since the panels have a 25 year (300 Months) lifespan, it would take him the $43/Month to recoup the initial investment over that period. The investment itself performs. However, the
You should leave the depreciation scam out of it. After 25 years, the panels will not magically stop working. Nor will they automatically be replaced, and also will have some (albeit small) value left. They may be worth $0 in the "accounting sense" but in the real world they wills till have some value. |
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cowboyro
Premium Member
2012-Oct-3 9:08 am
said by itguy05:quote:
A.) ke4pym See Profile makes the up front $13K investment. Since the panels have a 25 year (300 Months) lifespan, it would take him the $43/Month to recoup the initial investment over that period. The investment itself performs. However, the
You should leave the depreciation scam out of it. After 25 years, the panels will not magically stop working. Nor will they automatically be replaced, and also will have some (albeit small) value left. They may be worth $0 in the "accounting sense" but in the real world they wills till have some value. However things will fail. Panels will have to be replaced, inverters will have to be replaced. The warranty is worth nothing if the company is out of business. Realistically, how many electronic devices have you seen to last 25 years in harsh environments? |
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ke4pym
Premium Member
join:2004-07-24
Charlotte, NC |
ke4pym
Premium Member
2012-Oct-3 10:17 am
said by cowboyro:However things will fail. Panels will have to be replaced, inverters will have to be replaced. The warranty is worth nothing if the company is out of business. Realistically, how many electronic devices have you seen to last 25 years in harsh environments?
I'll get back to you in 24 years, 6 months. |
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said by ke4pym:said by cowboyro:However things will fail. Panels will have to be replaced, inverters will have to be replaced. The warranty is worth nothing if the company is out of business. Realistically, how many electronic devices have you seen to last 25 years in harsh environments?
I'll get back to you in 24 years, 6 months. It will be sooner than that. Your roof will need replacing before then and the panels will have to be removed. 25 years is a stretch for a shingled roof. |
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ke4pym
Premium Member
join:2004-07-24
Charlotte, NC |
ke4pym
Premium Member
2012-Oct-3 10:57 am
said by Jack_in_VA:It will be sooner than that. Your roof will need replacing before then and the panels will have to be removed. 25 years is a stretch for a shingled roof.
Just put a brand new, 30 year roof on last Tuesday. See you in 24 years, 6 months The shingles under the panels outta last a WHOLE lot longer since the sun will never shine on them. |
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said by ke4pym:said by Jack_in_VA:It will be sooner than that. Your roof will need replacing before then and the panels will have to be removed. 25 years is a stretch for a shingled roof.
Just put a brand new, 30 year roof on last Tuesday. See you in 24 years, 6 months The shingles under the panels outta last a WHOLE lot longer since the sun will never shine on them. It's the ones around the cells you will have to address. Are you planning on just replacing those and leaving the shingles under the cells? Even if it is touted as being a 30 year roof we all know how that works out. |
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ke4pym
Premium Member
join:2004-07-24
Charlotte, NC |
ke4pym
Premium Member
2012-Oct-3 12:48 pm
said by Jack_in_VA:It's the ones around the cells you will have to address. Are you planning on just replacing those and leaving the shingles under the cells? Even if it is touted as being a 30 year roof we all know how that works out.
On the main back roof of the house, no shingles will be (should be) exposed. The garage/bonus room, well, that's another story. The north facing roof will have no panels on it. If money were no object, I'd put them there, though. Just to honk off my HOA - cause they can't do anything about it and stuff. |
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 pike
Premium Member
join:2001-02-01
Washington, DC |
to cowboyro
said by cowboyro:Realistically, how many electronic devices have you seen to last 25 years in harsh environments? Would you consider civil aircraft and urban transit vehicles harsh environments? I do, and I've personally seen a significant number of 25+ year old electronic assemblies perform flawlessly and continue to operate at their original specification. A better question would be, is anything built in the last 10-15 years realistically going to last that long? Ha! |
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ncbill
Premium Member
join:2007-01-23
Winston Salem, NC |
to dogma
The only tax on my Duke bill is a 3% state sales tax. Which gets us nowhere near 11 cents/kWh. So both the simple payback & IRR calculations are even worse than everyone's already calculated. All of which also ignore maintenance & repair costs - IIRC, somebody's going to have to get up on the roof to swap out a failed micro-inverter. said by dogma:From the best I can figure, Duke Energy in North Carolina charges
For the first 350 kWh used per month: 9.2899¢ per kWh (excluding taxes which probably kicks it up to around 11¢ per kWh) |
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said by ncbill:The only tax on my Duke bill is a 3% state sales tax.
Which gets us nowhere near 11 cents/kWh.
So both the simple payback & IRR calculations are even worse than everyone's already calculated.
All of which also ignore maintenance & repair costs - IIRC, somebody's going to have to get up on the roof to swap out a failed micro-inverter. said by dogma:From the best I can figure, Duke Energy in North Carolina charges
For the first 350 kWh used per month: 9.2899� per kWh (excluding taxes which probably kicks it up to around 11� per kWh) I don't need charts, graphs estimates. I go by what's on my bill. 8/14 to 9/13 880 kWh, cost including all taxes and fees $101.53. Cost per kWh $0.115. That's the bottom line. Two figures, kWh used and total cost. |
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