Met with an energy company guy yesterday. I made a spreadsheet where I reverse engineered their model that they use for ROI calculations. I found nothing suspicious or slimy. Moreover, they actually derated the panels by 0.5% per year, which is in accordance with their 20 year warranty standards. That seems fair.
System payback by year 6.5. Annual returns range from 14.5% to 18.58%.
Solar ROI for my house
Solar ROI for my house
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Re: Solar ROI for my house
6.5 years is pretty good. Maybe I should investigate this. I think I would get more energy from the panels in Charlotte but our electricity cost is lower so maybe the payback would be a wash.
Re: Solar ROI for my house
Some items I learned during my reverse engineering process:
- Year 1 electric rate starts at about $0.21/kWh and goes up 3% per year and the consumption itself is assumed to be the same as I have used over the past 12 months
- Energy production decreases by 0.5% per year until year 8 where it decreases by 0.53% until year 25.
- The electricity sell back rate is $0.3125/kWh until year 15
- They multiply my production rate (with the annual derating) by the sell back rate to get to my actual returns, which I guess are called RI FIT payments. This one probably needs the most scrutiny. Thinking about it, I can only sell back electricity when I am A) making it so the sun is out and B) consuming less than I am making. The system is sized to equal my current annual energy production. Which means, during the energy producing parts of the day, I average enough electricity production for the whole day. So over the months and seasons, some days I will produce more than I use and other days I will use more than I produce. What I am currently struggling with is why this assumes I can sell back 100% of what I produce. Maybe this system works differently than I understand. It just seems like I wouldn't be able to sell back unless I was consuming, well, nothing at all during the time the panels were producing. I may need to come back to this.
- After year 15, the special rate goes away and it comes a net metering thing. This I understand - it just decreases my electric bills by the amount I produce. Using the derated panels, and also accounting for the increased cost of electricity (remember, 3% a year is assumed), I can still maintain a fairly strong annual savings of $2300-$2900.
- Year 1 electric rate starts at about $0.21/kWh and goes up 3% per year and the consumption itself is assumed to be the same as I have used over the past 12 months
- Energy production decreases by 0.5% per year until year 8 where it decreases by 0.53% until year 25.
- The electricity sell back rate is $0.3125/kWh until year 15
- They multiply my production rate (with the annual derating) by the sell back rate to get to my actual returns, which I guess are called RI FIT payments. This one probably needs the most scrutiny. Thinking about it, I can only sell back electricity when I am A) making it so the sun is out and B) consuming less than I am making. The system is sized to equal my current annual energy production. Which means, during the energy producing parts of the day, I average enough electricity production for the whole day. So over the months and seasons, some days I will produce more than I use and other days I will use more than I produce. What I am currently struggling with is why this assumes I can sell back 100% of what I produce. Maybe this system works differently than I understand. It just seems like I wouldn't be able to sell back unless I was consuming, well, nothing at all during the time the panels were producing. I may need to come back to this.
- After year 15, the special rate goes away and it comes a net metering thing. This I understand - it just decreases my electric bills by the amount I produce. Using the derated panels, and also accounting for the increased cost of electricity (remember, 3% a year is assumed), I can still maintain a fairly strong annual savings of $2300-$2900.
Re: Solar ROI for my house
Thinking more about it, I noticed it specifies my panel capacity at 5.89 kW. I don't know what they assumed about sun angle, or clouds. But I take it to mean my peak production would be 5.89 kW which is actually a fair amount.
I know that my annual electricity usage is 7817 kWh. That means my average consumption rate is 0.895 kW. Per day that is 21.48 kWh. If I can produce 7789 kWh in the first year, then that averages 21.3 kWh per day. But, those 21.3 kWh are all produced during the day. I can see how I would be able to make more than I am using and sell back. But I still don't understand how I could sell back 100% of what I produce. I will have to inquire about this.
I know that my annual electricity usage is 7817 kWh. That means my average consumption rate is 0.895 kW. Per day that is 21.48 kWh. If I can produce 7789 kWh in the first year, then that averages 21.3 kWh per day. But, those 21.3 kWh are all produced during the day. I can see how I would be able to make more than I am using and sell back. But I still don't understand how I could sell back 100% of what I produce. I will have to inquire about this.
Re: Solar ROI for my house
Logically, the only way to sell back 100% of what I produce would be like if the system wasn't actually connected to my house*. In other words, consider this scenario:
- I continue using electricity from the grid at the rate I have been and pay for that electricity. That's the baseline as I would continue to do that with or without the system.
- Separately and independently, this system makes power and sells all of that power back into the grid. The key to this is if the system got its own meter. I can ask as that would clarify this whole thing. It would have to be wired this way because I don't actually want to use any of the solar electricity - why would I? I can buy it for $0.21/kWh but National Grid pays $0.3125/kWh (for 15 years)! This is where all of the returns come from.
- If that is true, then all of the math I have done and verified, is more or less correct.
* Of course it would still be connected via the big grid and electricity my panels put into it is theoretically available for me (or other people) to use. Kind of a semantic difference.
Let's do another sanity check on the production assumption.
5.89 kW is the capacity of the 19 panel system he specified for me.
His math also said I'd produce 7,789 kWh in the first year.
On average, that assumes 7789/5.89 = 1322 hours of peak production throughout the year. Is this possible? Well...that only amounts to 3.62 hours per day of peak capacity. Given that, I'd say they have probably done a good job accounting for partial sun, as well as the seasons.
So I feel like I am getting closer to understanding this. Though if the system is truly wired the way I said, there would be no way to add a battery and get off grid capability, unless the systems could somehow become coupled when the grid was down (not impossible at all). That is not my main concern right now but I'd like to eventually understand that, as well. Stay tuned.
- I continue using electricity from the grid at the rate I have been and pay for that electricity. That's the baseline as I would continue to do that with or without the system.
- Separately and independently, this system makes power and sells all of that power back into the grid. The key to this is if the system got its own meter. I can ask as that would clarify this whole thing. It would have to be wired this way because I don't actually want to use any of the solar electricity - why would I? I can buy it for $0.21/kWh but National Grid pays $0.3125/kWh (for 15 years)! This is where all of the returns come from.
- If that is true, then all of the math I have done and verified, is more or less correct.
* Of course it would still be connected via the big grid and electricity my panels put into it is theoretically available for me (or other people) to use. Kind of a semantic difference.
Let's do another sanity check on the production assumption.
5.89 kW is the capacity of the 19 panel system he specified for me.
His math also said I'd produce 7,789 kWh in the first year.
On average, that assumes 7789/5.89 = 1322 hours of peak production throughout the year. Is this possible? Well...that only amounts to 3.62 hours per day of peak capacity. Given that, I'd say they have probably done a good job accounting for partial sun, as well as the seasons.
So I feel like I am getting closer to understanding this. Though if the system is truly wired the way I said, there would be no way to add a battery and get off grid capability, unless the systems could somehow become coupled when the grid was down (not impossible at all). That is not my main concern right now but I'd like to eventually understand that, as well. Stay tuned.
Re: Solar ROI for my house
He got back to me already.
Here is a summary of what he said:
- Warranty is actually 25 years. 10 years on workmanship which he seemed to translate to a labor warranty. Ok.
- He stressed that the construction of the system is very simple. 4 bolts hold the panels down, and two plugs for the inverter. Less than an hour to do that. He also reiterated that the entire 19 panel system would install in 2 days and possibly 1 day to get an idea of the labor involved. It's actually not a lot. He also said these systems were designed to be DIY and me or a handyman could handle replacing panels/parts. Fair enough.
- I was right about the dual meter thing. That's exactly how it works.
- They have a promotion where they pay 3 months of my electric bills. That's about $400. The promotion he sent seems to have expired last March so I assume this is somehow extended to me.
So far this has withstood the acid test. I am tempted.
Here is a summary of what he said:
- Warranty is actually 25 years. 10 years on workmanship which he seemed to translate to a labor warranty. Ok.
- He stressed that the construction of the system is very simple. 4 bolts hold the panels down, and two plugs for the inverter. Less than an hour to do that. He also reiterated that the entire 19 panel system would install in 2 days and possibly 1 day to get an idea of the labor involved. It's actually not a lot. He also said these systems were designed to be DIY and me or a handyman could handle replacing panels/parts. Fair enough.
- I was right about the dual meter thing. That's exactly how it works.
- They have a promotion where they pay 3 months of my electric bills. That's about $400. The promotion he sent seems to have expired last March so I assume this is somehow extended to me.
So far this has withstood the acid test. I am tempted.
Re: Solar ROI for my house
The first 15 years of returns do come from what I described. The remaining years come from simply reducing my electric bill. Now technically I'm not reducing my bill - I am using grid electricity and paying for it, but also selling electricity back to the grid. The returns stay at a similar level after year 15 because of the increased cost of electricity in those out years.kevm14 wrote:- Separately and independently, this system makes power and sells all of that power back into the grid. The key to this is if the system got its own meter. I can ask as that would clarify this whole thing. It would have to be wired this way because I don't actually want to use any of the solar electricity - why would I? I can buy it for $0.21/kWh but National Grid pays $0.3125/kWh (for 15 years)! This is where all of the returns come from.
Re: Solar ROI for my house
Another thing I like about the architecture of this system is that each panel has its own inverter. This provides the following benefits:
- Significant efficiency increase in partial shade (i.e. where there is shade on some panels but not others, like from a tree shadow I guess)
- Repair and expansion is super modular
By the way, here are the panels (made in Canada), Silfab SLA 310 M:
https://www.energysage.com/panels/Silfab/SLA-310M/
310-315W
25 year warranty
The output decline says 3% in the first year and then 0.7% from year 2-25. That is different than the RGS model. It would change the numbers a small amount.
https://www.shopoffgrid.com/Silfab-SLA3 ... la310m.htm
$262 each from these guys. It says Silfab has been making panels for 33 years. $262 * 19 = $4,978 in raw panel cost
Data sheet: https://www.shopoffgrid.com/v/datasheet ... LG310M.pdf
Inverters are Enphase IQ6 Plus (not sure where made):
97% efficient: https://enphase.com/en-us/products-and- ... ers/family
25 year warranty
Data sheet: https://enphase.com/en-us/support/enpha ... data-sheet
Other info: https://www.wholesalesolar.com/cms/enph ... 647083.pdf
https://www.wholesalesolar.com/2977245/ ... r-inverter
$152.50 each * 19 = $2,897.50 in raw inverter cost
Remember what I said about the architecture.
https://enphase.com/en-us/products-and- ... g-inverter
Enphase Monitoring:
https://enphase.com/en-us/products-and- ... n-and-apps
It looks like the solution might be Enphase Envoy (a hardware thing that talks to the panels, inverters and my internet router) plus the Enlighten software/app.
One price I got on the Envoy is $495.
So I guess we're looking at $9000 in panels, inverters and the monitoring gateway. Additional costs would be other materials like roof bracketry, wiring, the second meter and that kind of stuff. Add another $1000? Not really sure. So $10,000 in parts? The total cost is $22k though my cost is like $15k. Not sure if I could get that 30% tax credit if I did a DIY install. The particular roof section in question is so steep that I would need to figure out how to actually work on it, because you can't walk on that section. But I guess I look at it as a $10,000 system with a ~$5,000 installation cost when you take into account the tax credit. If the tax credit applied to a DIY install, then it would be 30% off $10,000 meaning $7,000 or about half price if I DIY. Making some assumptions here but I assume these stack up as a back of napkin type calculation.
- Significant efficiency increase in partial shade (i.e. where there is shade on some panels but not others, like from a tree shadow I guess)
- Repair and expansion is super modular
By the way, here are the panels (made in Canada), Silfab SLA 310 M:
https://www.energysage.com/panels/Silfab/SLA-310M/
310-315W
25 year warranty
The output decline says 3% in the first year and then 0.7% from year 2-25. That is different than the RGS model. It would change the numbers a small amount.
https://www.shopoffgrid.com/Silfab-SLA3 ... la310m.htm
$262 each from these guys. It says Silfab has been making panels for 33 years. $262 * 19 = $4,978 in raw panel cost
Data sheet: https://www.shopoffgrid.com/v/datasheet ... LG310M.pdf
Inverters are Enphase IQ6 Plus (not sure where made):
97% efficient: https://enphase.com/en-us/products-and- ... ers/family
25 year warranty
Data sheet: https://enphase.com/en-us/support/enpha ... data-sheet
Other info: https://www.wholesalesolar.com/cms/enph ... 647083.pdf
https://www.wholesalesolar.com/2977245/ ... r-inverter
$152.50 each * 19 = $2,897.50 in raw inverter cost
Remember what I said about the architecture.
https://enphase.com/en-us/products-and- ... g-inverter
This also means that there is no like 600VDC high voltage DC bus up on my roof or going into my basement as would have been the case with previous system architectures.In an Enphase system, there's no single point of failure.
Think of solar panels like bulbs in a string of holiday lights. In conventional inverter systems, when one panel fails, the whole system goes out. Or when one panel’s output drops -- thanks to fallen leaves, a passing cloud, or some other unavoidable factor -- the system’s overall performance drops to match that lowest-performing panel. With microinverters, each panel operates independently -- so no matter what happens to any one panel, the rest of your system keeps shining bright.
Enphase Monitoring:
https://enphase.com/en-us/products-and- ... n-and-apps
It looks like the solution might be Enphase Envoy (a hardware thing that talks to the panels, inverters and my internet router) plus the Enlighten software/app.
One price I got on the Envoy is $495.
So I guess we're looking at $9000 in panels, inverters and the monitoring gateway. Additional costs would be other materials like roof bracketry, wiring, the second meter and that kind of stuff. Add another $1000? Not really sure. So $10,000 in parts? The total cost is $22k though my cost is like $15k. Not sure if I could get that 30% tax credit if I did a DIY install. The particular roof section in question is so steep that I would need to figure out how to actually work on it, because you can't walk on that section. But I guess I look at it as a $10,000 system with a ~$5,000 installation cost when you take into account the tax credit. If the tax credit applied to a DIY install, then it would be 30% off $10,000 meaning $7,000 or about half price if I DIY. Making some assumptions here but I assume these stack up as a back of napkin type calculation.
Re: Solar ROI for my house
Some info on Enphase batteries:
https://enphase.com/en-us/products-and-services/storage
A single unit is 1.2kWh (Lithium Iron Phosphate) and it is fully modular so add as many as you want. They are rated for 100% discharge and have a 96% round trip efficiency which I guess means you only lose 4% to heat as they discharge/charge. So you get 96% of that 1.2kWh.
https://www.wholesalesolar.com/2977255/ ... ry-battery
This says it does not provide AC power when the grid is out. It is made to save on energy costs by using the power you create at a different time, rather than just selling it back to the grid (some scenarios make this more cost effective).
More research needed...
https://www.freecleansolar.com/Enphase- ... attery.htm
$2,250 per 1.2 kWh. Same warning about not providing backup power. Looking into if Enphase provides a solution for backup power. They may not. So then I wouldn't bother with this. My generator is fine...
https://enphase.com/en-us/products-and-services/storage
A single unit is 1.2kWh (Lithium Iron Phosphate) and it is fully modular so add as many as you want. They are rated for 100% discharge and have a 96% round trip efficiency which I guess means you only lose 4% to heat as they discharge/charge. So you get 96% of that 1.2kWh.
https://www.wholesalesolar.com/2977255/ ... ry-battery
This says it does not provide AC power when the grid is out. It is made to save on energy costs by using the power you create at a different time, rather than just selling it back to the grid (some scenarios make this more cost effective).
More research needed...
https://www.freecleansolar.com/Enphase- ... attery.htm
$2,250 per 1.2 kWh. Same warning about not providing backup power. Looking into if Enphase provides a solution for backup power. They may not. So then I wouldn't bother with this. My generator is fine...
Re: Solar ROI for my house
https://enphase.com/sites/default/files ... ystems.pdf
It looks like there is a way, obviously. But they don't seem to be pushing it on their website. It explains in the PDF though.
https://enphase.com/en-us/products-and- ... age/backup
They specifically guide you away from using the battery system as an off-grid backup solution.
I think the cost of the batteries is high and batteries would be required to use the solar off grid, practically speaking. It's just not cost effective.
It looks like there is a way, obviously. But they don't seem to be pushing it on their website. It explains in the PDF though.
https://enphase.com/en-us/products-and- ... age/backup
They specifically guide you away from using the battery system as an off-grid backup solution.
I think the cost of the batteries is high and batteries would be required to use the solar off grid, practically speaking. It's just not cost effective.