Went solar

/ Went solar #21  
The whole business of payback on an expenditure is a very tricky area. In the 2006 mindset during the building boom, a 3 year payback was generally accepted as the most people would tolerate. Everyone who was discussing options on what to put in our new house used that figure. I suspect that was driven by how long some thought they would be there, the available funds, and a bizarre self referential feedback that if everyone thought 3 years was the right payback period, and you spent more money and had an 8 year payback period, that no one else would pay for that if you sold. So everyone got into a 3 year payback mindset. I often wonder if people trapped in their home in this market are regretting some of their payback period choices.

The extra costs of spay foam insulation and geothermal heat pumps both had around an 8 year payback. We were cautioned that if we had to sell, we might not get that money back and it might not show up in an appraisal. Other decisions such as 6" walls, better grade windows, generator transfer switch and the like had similar trade off considerations. We even had all the toilets put on their own separate line to avoid "shower shock" when someone flushes. Plumber and trades people said we'd never see that money again yet when you tell people about it they all wish their house had that. So you have a perception in the building trades that it's all about resale and holding value, and cool features (like the toilets) never get a chance because no one will take a risk. Next thing you know we're all living in a Wally World low price is all that matters mentality. We hate the quality but love the price :laughing:.

And now we are seeing a number of payback period trade offs that are at 10 to 20 years. The solar PV arrays are one of them. Our metal seam roof was also in that range, but building/sales/Realtor trades said "you'll get your money back on that". Opting for these long payback periods is risky because no one know what prices will be in 15 years. It's risky because no one knows what would have happened if you cheaped out and invested the extra $$s you put in your house. Contrast that with near zero uncertainty with the 3 year payback, and mild uncertainty with 8 year paybacks.

My point here is that the further out the payback, the more the homeowner is taking some risk. So all attempts to criticize or justify these long term paybacks are generally speaking pretty shaky and not worth getting worked up about. No one can win an argument based on what the world will look like in 15 years.

A final observation: People on this forum tend to lament the decline in quality of things in the world. A lot of young pups I run into are of a mindset where they are willing to pay more for quality and sustainability. They also have a concept of hidden cost or cost down the road that I didn't see a decade or two ago. They know, for example, that in the long run the $250 water heater will be more expensive than the $400 one with good insulation and a smart controller. Many of them would rather have a small living space well done than a large one that's K-Mart Quality. Many of them will try the solar PV panels, better insulation, and a hybrid car as part of this "Pay more, get less, but be better off in the long run" mindset.

I don't want to get into a argument of what's right or wrong on this, but each generation has changing values on what's important. Longer payoff periods are under consideration by many. Paying more for quality is under consideration. The fact that many people are taking a broader view of payback time seems to me to be good. Some will be right, some will be wrong, but we will all win because solutions will be explored that would never see the light of day if they were subjected to simply lowest cost wins analysis.

Pete
 
/ Went solar #22  
With a grid-tied system, payback time depends on your local electricity cost. Here in Northern California PG&E's rates are among the nation's highest, and will only go higher. So will the rates everywhere! My 6 kw system cost $40K after rebates etc, and will pay for itself in 10 years, at TODAY'S rates. I expect it will be working well for another 30 years (guarantee: 20 yrs) will ultimately produce a profit (at today's rates) of about $72,000. My 20 year old domestic hot water system is still going strong and saves about $50 month in propane costs.
 
/ Went solar #23  
We even had all the toilets put on their own separate line to avoid "shower shock" when someone flushes. Plumber and trades people said we'd never see that money again yet when you tell people about it they all wish their house had that. So you have a perception in the building trades that it's all about resale and holding value, and cool features (like the toilets) never get a chance because no one will take a risk. Next thing you know we're all living in a Wally World low price is all that matters mentality. We hate the quality but love the price :laughing:.

It's kinda like a gear head putting $50K into hot rodding his (for example) 1990 Mustang. I really enjoy looking at it, would love to go for a ride in it, do not doubt he spent $50K on it ... but no way in the world would I give him for $50K for it. Maybe ... maybe ... $15K-20K. And probably nobody else will either.
 
/ Went solar
  • Thread Starter
#24  
My papers are at home... It was about an 8 year for payback, at current power rates. One thing that has happened here, is power rates have kept climbing. So, payback will "probably" be more in the 6-7 year range. We bought it for the long haul though; even if it takes a little longer for payback, that is ok.

If not for the 30% Federal credit, it would add about 4 years in our case. And, we would have done this regardless of the credit. Our power supplier also has some rebates.

At least in N. Calif, from what we have studied, they have a pretty good return on investment if selling the house too.

Expectancy is about 25-30 years. But, there are a large percentage of the 25-30 year old systems still working great out there. More so than a failure at 25-30 years, the panels will tend to lose efficency. They have found the numbers at 25-30 years to be pretty good though.

I think the future will see more efficient panels, with a longer life. Also, this is still a ramping technology; I would expect price per Kwh will drop over time.

What do you estimate will be your energy savings payback time? I.E. how long will it take for the system to pay for itself and if there were no tax incentives, how long would it take? Also, what is the life expectancy of the system?
 
/ Went solar #25  
My papers are at home... It was about an 8 year for payback, at current power rates. One thing that has happened here, is power rates have kept climbing. So, payback will "probably" be more in the 6-7 year range. We bought it for the long haul though; even if it takes a little longer for payback, that is ok.

If not for the 30% Federal credit, it would add about 4 years in our case. And, we would have done this regardless of the credit. Our power supplier also has some rebates.

At least in N. Calif, from what we have studied, they have a pretty good return on investment if selling the house too.

Expectancy is about 25-30 years. But, there are a large percentage of the 25-30 year old systems still working great out there. More so than a failure at 25-30 years, the panels will tend to lose efficency. They have found the numbers at 25-30 years to be pretty good though.

I think the future will see more efficient panels, with a longer life. Also, this is still a ramping technology; I would expect price per Kwh will drop over time.

Thanks. :)
 
/ Went solar #26  
I look at those PV panels and can't help but think of hail storms and wind storms. What is the impact on homeowner's insurance? Are the cells rugged enough to take a pounding from really rough weather? When power lines blow down, the utility companies generally have them back up quickly. I just think I'd have to have a good generator backup and probably have it on longer while I rebuilt my solar array. I am NOT enamored with my power company, but like my septic system and well, there is an additional responsibilty that comes with being energy independent.
 
/ Went solar #27  
The reason I am concerned about payback time is this...
My last two years with the wood burner providing winter heat my gas and electric bills combined are averaging about $1500.00 per year.

In 30 years, that will be $45K (at current rates). I don't think I can touch a solar system in this climate that will produce enough electricity to cover all of our needs (that gas and electric currently provide) for anywhere near that. We are in a lousy area for solar, with 293 partly cloudy to cloudy days each year. We also average a tad over 80" of snow per season. We also get 42 days of thunderstorms annually and damaging hail every few years.

I think I would be better off spending the money on super insulating the house for the winters and converting my gas water heater to wood.
 
/ Went solar
  • Thread Starter
#28  
Did not research that too much; we do not get the type of heavy weather you get.

Our system is grid tied. That is how you get the incentives. We still lose power when the grid goes down, even on a sunny afternoon. It is partly the design of the inverter, and how it connects to the house. I believe part of it is to not feed back on the grid; a discussion that has occured a number of times here in regard to generators.

Also regional is the power cost. We have higher power costs out here. And, a lot of sun. So that plays into the factors.

I look at those PV panels and can't help but think of hail storms and wind storms. What is the impact on homeowner's insurance? Are the cells rugged enough to take a pounding from really rough weather? When power lines blow down, the utility companies generally have them back up quickly. I just think I'd have to have a good generator backup and probably have it on longer while I rebuilt my solar array. I am NOT enamored with my power company, but like my septic system and well, there is an additional responsibilty that comes with being energy independent.
 
/ Went solar #29  
The school district I work for out here in the desert looked into solar. After all, what could be better than 330+ cloudless days. We talked to the sales people from several different solar companies and were given glowing reports on how much power we would produce.

We then had our professional engineers evaluate. A different story for us. It turns out that PV panels are most efficient at 59 degrees F. As the temperature climbs the cells produce less and less electricity and at about 110 degrees they about stop performing. Heat within the PV cell itself increases the internal resistance to a point that voltage diminishes to a minimum. Not a consideration for many, but it just didn't fit our environment.

The only other item which they considered a maintenance item was the inverters. They predicted a 7 to 8 year life based upon actual experience.

Currently there are several huge commercial solar power plants in development west of Blythe CA. It's interesting to note that they all will be solar concentrators and not PV.
 
/ Went solar #30  
The school district I work for out here in the desert looked into solar. After all, what could be better than 330+ cloudless days. We talked to the sales people from several different solar companies and were given glowing reports on how much power we would produce.

We then had our professional engineers evaluate. A different story for us. It turns out that PV panels are most efficient at 59 degrees F. As the temperature climbs the cells produce less and less electricity and at about 110 degrees they about stop performing. Heat within the PV cell itself increases the internal resistance to a point that voltage diminishes to a minimum. Not a consideration for many, but it just didn't fit our environment.

The only other item which they considered a maintenance item was the inverters. They predicted a 7 to 8 year life based upon actual experience.

Currently there are several huge commercial solar power plants in development west of Blythe CA. It's interesting to note that they all will be solar concentrators and not PV.


Is that 110F ambient air or the surface of the solar panel? 110F on the pannel would occur on a 90 degree day or so, think about a hot asphault road on a 97F day it will be like 130F.
 
/ Went solar #32  
The school district I work for out here in the desert looked into solar. After all, what could be better than 330+ cloudless days. We talked to the sales people from several different solar companies and were given glowing reports on how much power we would produce.

We then had our professional engineers evaluate. A different story for us. It turns out that PV panels are most efficient at 59 degrees F. As the temperature climbs the cells produce less and less electricity and at about 110 degrees they about stop performing. Heat within the PV cell itself increases the internal resistance to a point that voltage diminishes to a minimum. Not a consideration for many, but it just didn't fit our environment.

The only other item which they considered a maintenance item was the inverters. They predicted a 7 to 8 year life based upon actual experience.

Currently there are several huge commercial solar power plants in development west of Blythe CA. It's interesting to note that they all will be solar concentrators and not PV.

That implies that there's no solar energy to be had when it's 110 outside. Sure seems counterintuitive to me, but I'm no expert.
 
/ Went solar #33  
That implies that there's no solar energy to be had when it's 110 outside. Sure seems counterintuitive to me, but I'm no expert.

We've had plenty of 110 degree days this summer and there was no noticible reduction in power harvested from our array. Daily KWH totals is what I check when I return home from work.

Yes, high temps reduce the power the array will produce (nowhere near the estimate mentioned above) but on those days the sun shines longer to make up for it.

It's those week-long stormy periods that are the only problem I haven't yet figured out a way around, so far the propane bill just rises with the generator use during those times. Adding more panels won't help if there's no sunshine.

Phil
 
/ Went solar #34  
If you're doing long-range planning, here's something I heard from the chief engineer of a pretty-big airport. TVA told him he should expect his cost of electricity to basically double in the next five years. Don't know if that applies to residential customers, as well. But that's where I'm going to be starting my baseline, when I decide whether to switch over.
 
/ Went solar #35  
That implies that there's no solar energy to be had when it's 110 outside. Sure seems counterintuitive to me, but I'm no expert.

Think of an electric resistance heater. The hotter the wire gets the more internal resistance. If you put a clamp meter on a heater and turned it on, the amperage would spike until the wire got hot (a matter of fractions of a second). As the wire heats, it's internal resistance increases until it reaches a balance that is the output of the heater i.e. 1500 watts. That's why wire lowered to cryogenic temperatures has virtually 0 resistance.

The same condition occurs internally in a PV cell.

Maybe what I should have stated is that at high temperatures (and it reaches well into the 120's here), the power produced was less than necessary to achieve the return on investment that we required. This was effectively 0 return on investment, not 0 power.

Sorry for the confusion.
 
/ Went solar #36  
The industry warranties for degradation tend to be 90% of rated value at 10 years, and 80% of rated value at 25 years. My panels (Sharp ND-216U1F) have a 25 year limited warranty. Their rating is 216 Watts with an initial tolerance of +10/-5%.

The data sheet for the panel also has temperature coefficients for the panels. The panels have their ratings at 25 degrees C. The panel I have has a derating of -0.485% per degree C. The data sheet does not state if this temperature is ambient or the surface of the cells. I'll go out tomorrow and measure my ambient vs. cell surface temperature so we can put a number on that.

So at 77 degrees F (25 C), the panel in "full light" makes 216 Watts of power. At other temperatures:
90F makes 208 Watts
100F makes 203 Watts
110F makes 197 Watts
120F makes 191 Watts
448F makes no power (and I suspect the plastic on the back is melting ;))

The temperature derating is linear, and I suspect it's only good for real planet tempuratures not the extrapolated zero power out point :laughing:.

Note also that as the temperature goes down, the output goes up. So:
50F makes 226 Watts
32F makes 242 Watts
0F makes 260 Watts

And again, there is probably a limit on this end too. Temperature has other effects on copper interconnections used. Temperature cycling is probably also a prime means of wear out, even though it takes decades. For here in North Carolina, I'll see an output range between 242 and 200 watts for my 216 watt rated panels. The "110 degree and they stop performing" doesn't make a lot of sense, and I suspect there is other criteria applied to the system performance that makes that temperature a cut off point (as orezok mentions).

ShenandoahJoe's post points out the difficulty of make decade long or more guestimates on payback periods, a point I danced around on a previous post.

BTW, in the last 24 hours I made 86% of the energy my house needed, and made money to boot! Lower temps means lower HVAC use, this is great time of year!

Pete
 
/ Went solar
  • Thread Starter
#38  
Reminds me of dark current noise on image intensified CCD's. The photonic emission microscopes I used to work with had peltier cooling, with liquid cooling of the peltier. Overall affect was -65C on the CCD. When first powering the system, at 25C, noise on the camera was terrible. As the CCD cooled down, the current, and hence noise, minimized. -65C was as cool os we could go without going cryogenic.

We were detecting photonic emissions for failure sites on IC's, while in a dark enclosure. The image intensified CCD could pick up very small photonic emissions, common to a number of leakage types on memory and microprocessor chips.

emmi

The data sheet for the panel also has temperature coefficients for the panels. The panels have their ratings at 25 degrees C. The panel I have has a derating of -0.485% per degree C. The data sheet does not state if this temperature is ambient or the surface of the cells. I'll go out tomorrow and measure my ambient vs. cell surface temperature so we can put a number on that.

So at 77 degrees F (25 C), the panel in "full light" makes 216 Watts of power. At other temperatures:
90F makes 208 Watts
100F makes 203 Watts
110F makes 197 Watts
120F makes 191 Watts
448F makes no power (and I suspect the plastic on the back is melting ;))

The temperature derating is linear, and I suspect it's only good for real planet tempuratures not the extrapolated zero power out point :laughing:.
 
/ Went solar #39  
Yeah, as temp goes up you get more recombination of electron hole pairs at the junction. Noise and leakage current, both temperature dependent, impact the device in a function dependent way. I'm also guess that the junction voltage goes up as the temp goes down, just like any semiconductor junction. That's probably another factor in the thermal derating for the PV panels. The data sheet had thermal derating for power, voltage, and current (I just sited power). They did not have a voltage vs. temp curve, either because most consumers might not know what that's about or because at the end of the day it's just a big honking PN junction.

Cool story , didn't know photonic emissions were a leakage detection mechanism. I had a buddy who back in the days of EEPROMS (like the 2704) spent months working on methods of detecting how many electrons _per year_ leaked out of the floating gate. They tweaked the fab process and got it down into the single digits! I know a few more "you wouldn't believe what someone can measure" stories.

Be it electronics or mechanical stuff, it's amazing how thousands of people have spent decades just quietly understanding and improving stuff. I think a lot of people focus on the big break throughs and don't focus on the effect of lots of little 1 to 2 percent improvements.

Pete
 
/ Went solar #40  
We've had plenty of 110 degree days this summer and there was no noticible reduction in power harvested from our array. Daily KWH totals is what I check when I return home from work.

Yes, high temps reduce the power the array will produce (nowhere near the estimate mentioned above) but on those days the sun shines longer to make up for it.

It's those week-long stormy periods that are the only problem I haven't yet figured out a way around, so far the propane bill just rises with the generator use during those times. Adding more panels won't help if there's no sunshine.

Phil
When you run your generator are you powering the house or charging the batteries, or both?
 

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