Grid-tied solar

[farmeratheart]

Dan,

The PVWatts v2 calculator using the airport between Raleigh and Durham as a location, says a 12 KW system would produce 15,556 AC kwh annually. ~50 panels, that's a big residential system. If I plug 12 kw in for my location, the output is 14,517 AC kwh annually, in Colorado Springs, CO the output is 17,931 AC kwh annually.

I suppose your usage, almost four times mine, is driven by AC needs and having kids at home (as I recall) Up north we tend to forget about the cost of AC and focus on heating.

I still think you are hung up on "hidden" costs. Unexpected and hidden are two different things. But I can see your point, it would be roughly a $25K system producing $1,550 worth of power each year. That is 16 years to break even ignoring the cost of money and without any credits/rebates. If you can use the federal 30% credit, your eventual net cost is $17,500, or 11.3 years to break even, ignoring the cost of money. You would have 8.7 years after that worth $10K - $11K at current elec. rates and assuming a 10% drop in system output due to age. It's possible elec. rates would climb at about the same rate output would decline, offsetting each other.

Ten to twelve years is in the ballpark for residential systems after credits that I have looked at. That doesn't seem to change much across residential system sizes because they have very similar costs per watt. The upfront costs are a high hurdle, that seems to be true of most alt. energy even though the lifetime net costs are very low.

Using the Raleigh-Durham example as the closest to me ... 15,556kWh annually for a 12KW system would translate to 518kWh5 annually for my 4 KW system. That's not too far from the 5500 kWh I've seen each year for the 1st two! I really have to agree with what zonta223 says in his post. Think back to 20 years ago. What did a gallon of gas cost? What did a loaf of bread cost? I really don't know what I was paying for electricity per kWh 20 years ago. It was a different utility in a different region. Suffice it to say, I don't think any of us will be paying what we are today 20 years from now.

Frank

 

[meburdick]

There are two additional pieces that I haven't seen anyone comment on, and they have a HUGE bearing on why I won't commit to solar for anything...

1) The lifespan of the panels is warranteed for 20 years. Why would I make an investment into an energy solution that is going to require significant expense for upgrades / repairs right at the point in time when it has finally paid for itself? This effectively means there is NO point in time when it pays for itself.

2) The warranty for the panels is only for 80% output capability of their rated value. Why? Because their ability to provide power over time is diminished. If you're only getting .77 efficiency now, what will your efficiency be in 5 years? 10? 15? Has any of this been factored into the payback model?

I would also fully expect that there are additional costs that need to be added in here as well - homeowner's insurance, for example, will have to go up. Has that been factored into the operating cost for the system?

 

[whirly]

There are two additional pieces that I haven't seen anyone comment on, and they have a HUGE bearing on why I won't commit to solar for anything...

1) The lifespan of the panels is warranteed for 20 years. Why would I make an investment into an energy solution that is going to require significant expense for upgrades / repairs right at the point in time when it has finally paid for itself? This effectively means there is NO point in time when it pays for itself.

2) The warranty for the panels is only for 80% output capability of their rated value. Why? Because their ability to provide power over time is diminished. If you're only getting .77 efficiency now, what will your efficiency be in 5 years? 10? 15? Has any of this been factored into the payback model?

I would also fully expect that there are additional costs that need to be added in here as well - homeowner's insurance, for example, will have to go up. Has that been factored into the operating cost for the system?

Our utility company (HELCO) is approved by the PUC for a 3.3% annual increase every year. That means that at the end of 30 years our utility bill will be 91% higher than it is today. Yours may be different but I will almost guarantee the there will be increases to the base rates across the country. As the cost of generating electricity goes up, i.e. - the cost of fuel, rates will have to rise.

In addition, the price of the panels has continued to drop even in the last year or so while the efficiency of new panels has gone up. The cost of a 5kW system is now less than a 4kW system a year ago. I suspect that will continue for a while. So replacement costs will continue to go down as the demand goes up and more efficient manufacturing processes are implemented. Now may not be the time for some to invest in solar but I'm pretty sure there will be a time in the not too distant future it will make more economic sense to a lot of folks.

On the "hidden" costs of inefficiency. I have seen 30-33% thrown around here often by others, too often to not pipe in.

100-77=23

it has been that way since the universe was first kick-started.

 

[grsthegreat]

I think what may be being missed is the cost of electrical energy. To continue to think the power can be supplied at 5cents or 11 cents a kw for the next 20 years is I think a little short sited. Already in your country in some states power costs 30kw the same price we pay here.
My electricity bill used to be about $450 before we installed solar. Present bill is about $35 to $50. Do we think its a great idea YES. Also means the pressure is off building more power stations and conserving scarce resources (no I am not a greenie fanatic but would like the lpg/natural gas to be used in my car not a power station) . The payback time on the system we have is about 4years. Plus the value of my house went up by about 150% of the price of the solar installation.
So could I suggest that people stop working out payback times on unrealistically low energy costs. The push is on world wide to cut carbon emissions. Makes no difference if you agree with global warming or not carbon taxing is coming and the biggest payers of these taxes will be power companies/cement plants/aluminum plants etc and they will certainly pass on the taxes in the way of price rises.

just my 2c worth

we use hydropower here. 0% carbon footprint. as long as the tree huggers dont demo the dams we will continue with 5 cent /kwh power for a long time.

for the past 16 years its been 5 cents. my bills average about $50/month .. higher in winter of course.

 

[dave1949]

There are two additional pieces that I haven't seen anyone comment on, and they have a HUGE bearing on why I won't commit to solar for anything...

1) The lifespan of the panels is warranteed for 20 years. Why would I make an investment into an energy solution that is going to require significant expense for upgrades / repairs right at the point in time when it has finally paid for itself? This effectively means there is NO point in time when it pays for itself.

2) The warranty for the panels is only for 80% output capability of their rated value. Why? Because their ability to provide power over time is diminished. If you're only getting .77 efficiency now, what will your efficiency be in 5 years? 10? 15? Has any of this been factored into the payback model?

I would also fully expect that there are additional costs that need to be added in here as well - homeowner's insurance, for example, will have to go up. Has that been factored into the operating cost for the system?

My homeowner's policy covers my system at no additional charge. The agent said as long as they are attached to the house, they are considered part of the house. I suppose more expensive systems would push your replacement costs and rates higher.

It's hard to read, but the chart below lists all the derating factors that go into the default .77 efficiency. Age is included, but the default value is 1.00 which means it is
not reflected in the .77 value. (Anything multiplied by 1 is itself) I did mention ~1% per year silicon aging in one of my responses to Dan.

DC-to-AC Derate Factor
The PVWatts calculator multiplies the nameplate DC power rating by an overall DC-to-AC derate factor to determine the AC power rating at STC. The overall DC-to-AC derate factor accounts for losses from the DC nameplate power rating and is the mathematical product of the derate factors for the components of the PV system. The default component derate factors used by the PVWatts calculator and their ranges are listed in the table below.

Derate Factors for AC Power Rating at STC

Component Derate Factors PVWatts Default Range
PV module nameplate DC rating 0.95 0.80–1.05
Inverter and transformer 0.92 0.88–0.98
Mismatch 0.98 0.97–0.995
Diodes and connections 0.995 0.99–0.997
DC wiring 0.98 0.97–0.99
AC wiring 0.99 0.98–0.993
Soiling 0.95 0.30–0.995
System availability 0.98 0.00–0.995
Shading 1.00 0.00–1.00
Sun-tracking 1.00 0.95–1.00
Age 1.00 0.70–1.00
Overall DC-to-AC derate factor 0.77 0.09999–0.96001
The overall DC-to-AC derate factor is calculated by multiplying the component derate factors.

For the PVWATTS default values:

Overall DC to AC derate factor = 0.95 x 0.92 x 0.98 x 0.995 x 0.98 x 0.99 x 0.95 x 0.98 x 1.00 x 1.00 x 1.00 = 0.77

 

[zonta223]

we use hydropower here. 0% carbon footprint. as long as the tree huggers dont demo the dams we will continue with 5 cent /kwh power for a long time.

for the past 16 years its been 5 cents. my bills average about $50/month .. higher in winter of course.

Well I can only say you have been very lucky. Here the eastern states and Tasmania are the hydro power states and what happened. They put long distant feeders in to supply people willing to pay 3 times or more than the locals were. At present Tasmania power generators are looking at putting an undersea feeder to supply power to the mainland states. Why because they get a bigger return than they can get from the locals.
Electricity is relatively cheap to "transport" long distances..yes there are losses involved..they just raise the price to the end user to cover them.

 

[meburdick]

My homeowner's policy covers my system at no additional charge. The agent said as long as they are attached to the house, they are considered part of the house. I suppose more expensive systems would push your replacement costs and rates higher.

Yes, as an attached part of the structure, it will be covered. It may be covered at "no charge" because the policy you have allows for a significant increase over value for replacement cost, but I would be willing to bet you will see a price increase on the next renewal that can ultimately be traced back to this. The fact is that a $20k item is not trivial, and it has a direct bearing on the value and replacement cost of your home. More value = more premium dollars.

 

[dave1949]

Using the Raleigh-Durham example as the closest to me ... 15,556kWh annually for a 12KW system would translate to 518kWh5 annually for my 4 KW system. That's not too far from the 5500 kWh I've seen each year for the 1st two! I really have to agree with what zonta223 says in his post. Think back to 20 years ago. What did a gallon of gas cost? What did a loaf of bread cost? I really don't know what I was paying for electricity per kWh 20 years ago. It was a different utility in a different region. Suffice it to say, I don't think any of us will be paying what we are today 20 years from now.

Frank

5185 kWh vs 5500 kWh, I am surprised it is that close. The model must be reasonable.

I agree totally about the price of power, I just don't have any way of estimating where or how fast it will go. In the near term, 3-6 yrs say, I think the price of natural gas will slow the generation side of prices. The upgrades to create a smart and more robust grid will contribute to increases on the delivery side.

There is a big market for natural gas in China and India, both of which need to reduce their coal use while they can still breathe. US natural gas is expected to supply those markets but that requires building gas compression plants to make it economically ship-able. I think one is under construction now in Texas.

Natural gas has a history of very volatile pricing, time will tell. Two things we know, it will go to the highest bidder anywhere in the world and it won't last 100 years.

 

[JCByrd24]

There are two additional pieces that I haven't seen anyone comment on, and they have a HUGE bearing on why I won't commit to solar for anything...

1) The lifespan of the panels is warranteed for 20 years. Why would I make an investment into an energy solution that is going to require significant expense for upgrades / repairs right at the point in time when it has finally paid for itself? This effectively means there is NO point in time when it pays for itself.

Your logic is flawed. Since when does a warranty expiring mean a system stops working and needs to be replaced. The last two used cars I have bought with no warranty and 4 years later I'm still driving both. More closely related, what type of system do you have in your house that has a 20 year warranty. I don't know if any water heater/boiler/furnace that has a legit 20 year warranty.

So, in Dave's case he has a system that in 20 years (I think it's more like 10) will be providing free energy, even if it is only 80% of it's new rating. What will you be doing in 20 years, buying a new boiler or water heater and paying $0.80/kwh or $8.00/gallon.

Solar is currently the only system that will EVER give you free energy, so to compare "payback" to any other system is flawed in itself.

 

[meburdick]

Your logic is flawed. Since when does a warranty expiring mean a system stops working and needs to be replaced. The last two used cars I have bought with no warranty and 4 years later I'm still driving both. More closely related, what type of system do you have in your house that has a 20 year warranty. I don't know if any water heater/boiler/furnace that has a legit 20 year warranty.

So, in Dave's case he has a system that in 20 years (I think it's more like 10) will be providing free energy, even if it is only 80% of it's new rating. What will you be doing in 20 years, buying a new boiler or water heater and paying $0.80/kwh or $8.00/gallon.

Solar is currently the only system that will EVER give you free energy, so to compare "payback" to any other system is flawed in itself.

The reason that the product is warrantied for 20 years is because after that many years of baking in the sun, it's no longer reliable and/or the power output from it is no longer at a level that makes it useful. PV cells are electrical components, and each heat / cool cycle and "power up" (getting hit with the sun in the morning) cycle causes wear.

When the solar system providers can show me that 90+% of the equipment they installed over 20 years ago is still in use, I'll be at a point where I can consider making the investment.