[tibberous]

Solar systems are rated (ie: 7kw) : http://www.ebay.com/itm/7-KW-Comple...014?pt=LH_DefaultDomain_0&hash=item19d8416dd6

So, I'm guessing that means it will make 7kw/hour in full sun? Or does it mean that it could make 7kw/hour in southern texas, but won't make close to that where I'm at?

 

[Missouri Bound]

The systems are rated for the maximum capacity under ideal conditions....IE: they won't exceed the rating.:yes:

 

[mpoulton]

A kilowatt is a measure of power, which is energy per unit time. So "kilowatts per hour" is a meaningless term (or actually it has a really obscure meaning that's not relevant here). A 7kW system produces 7kW in full standard sun. Standard sun is usually defined as 1000W of sunlight per square meter. You will not likely get that in your location, unless you live on the equator. If you need to know how much energy you will get from the system during a day, you will need to do a solar survey (or at least look up some charts for your region) and calculate what the irradiance at your location is. You can then calculate what output you can expect from a given system. In other words, if your location gets the equivalent of 4 hours of standard sun per day, then you will get 28kWh per day out of a 7kW array.

 

[micromind]

Also, even under ideal conditions, solar panels will lose about 2% of their capacity each year.

I've installed about a dozen of them over the last 10 years, I doubt if any of them has performed at 100% of rated capacity. Close, but not completely there.

Rob

 

[DanS26]

Try PVWatts web site. The app in that site will tell you how many kWh you will produce in a year based on size of system, location and insolation. My experience is that it is very accurate.

 

[tibberous]

Try PVWatts web site. The app in that site will tell you how many kWh you will produce in a year based on size of system, location and insolation. My experience is that it is very accurate.

REALLY ****ty where I'm at - $25,000 would save me about $150 a month. Least now I know :thumbup:

 

[DanS26]

REALLY ****ty where I'm at - $25,000 would save me about $150 a month. Least now I know :thumbup:

Most solar panels, if good quality, are guaranteed to produce for 25 years, but they do degrade about 2% a year. But lets just say for simplicity that you are able to save $150 a month for 25 years. That's $45,000 return on a $25,000 investment. My IRR calculator indicates that's an annual return of 7.2%. Of course the return on investment changes dramatically if you have to borrow money or lease the equipment.

So if you have $25 grand laying around in a CD or savings account, making maybe 1 or 2% if your lucky, it may be something to look into.

Oh, there is a 30% tax credit, but I assumed your $25k was after taking the credit into consideration. Credit good until 2016.

 

[mpoulton]

Most solar panels, if good quality, are guaranteed to produce for 25 years, but they do degrade about 2% a year. But lets just say for simplicity that you are able to save $150 a month for 25 years. That's $45,000 return on a $25,000 investment. My IRR calculator indicates that's an annual return of 7.2%. Of course the return on investment changes dramatically if you have to borrow money or lease the equipment.

So if you have $25 grand laying around in a CD or savings account, making maybe 1 or 2% if your lucky, it may be something to look into.

Oh, there is a 30% tax credit, but I assumed your $25k was after taking the credit into consideration. Credit good until 2016.

It's only a 7.2% ROI if your capital is preserved. Since the solar panels depreciate to zero after 25 years, you have to figure in the depreciation. That's $1000 per year. So you save $1800 per year at a cost of $1000 per year in depreciation. The net savings is $800 per year on a $25k investment, so it's a 3.2% ROI. This also doesn't take into account that the energy production (and thus the utility savings) decreases over time so the revenue is actually lower.

 

[DanS26]

It's only a 7.2% ROI if your capital is preserved. Since the solar panels depreciate to zero after 25 years, you have to figure in the depreciation. That's $1000 per year. So you save $1800 per year at a cost of $1000 per year in depreciation. The net savings is $800 per year on a $25k investment, so it's a 3.2% ROI. This also doesn't take into account that the energy production (and thus the utility savings) decreases over time so the revenue is actually lower.

Agree, thanks for pointing that out.
If you really want to fine tune the analysis then things like salvage value, tax benefits on depreciation (if a business), annual maintenance costs, and change in the retail cost of electricity should also be considered.

 

[Oso954]

The other question would be "do you plan on being in that home 25 years from now ?"

You move out and it throws a monkey wrench in any calculation you made.

 

[tibberous]

change in the retail cost of electricity should also be considered.

This one probably being the most important - I can see electricity more than doubling in 30 years.

So, while it might not be a bad investment, I'm not sure it's a good one either.

 

[DanS26]

This one probably being the most important - I can see electricity more than doubling in 30 years.

So, while it might not be a bad investment, I'm not sure it's a good one either.

Well, one more thing you might want to consider is to calculate your cost of production by kWh. To do that, take the total cost of the project and divide by the total kWh production from PVWatts over the 25 year life of the system. Don't forget to derate the system production 2% per year.

Now we know that a gallon of gasoline is equal to 33.4 kWh in energy equivalent. Let's say you can produce at $.10 per kWh or $3.34 equivalent cost per gallon. But if you are a true DIY person, and I assume you are since you are a frequent poster on a DIY site, you could avoid outside labor on installing a solar system and thus produce power at $.065 per kWh. Equivalent cost of gas is now $2.17 and is locked in for the next 25 years. What do you think the price of gas will do in the next 2.5 decades?

 

[DanS26]

I'd like to resurrect this tread for you true DIY'ers. Solar PV is doable and is profitable. The cost of solar panels and the necessary accessory parts is competitive with the retail cost of electricity. Solar parity. But only if you do it yourself. If you have to pay someone to do it for you, then forget it for now, maybe later when power is much higher.

If you are a true DIY'er, then jump in. If you are not intimidated by the NEC code book, then study it. It is not rocket science, but it does take your effort to understand and apply the safety standards.