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Scott Davis

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Reply with quote  #1 

Depending on how we are using heat, our local utility rates and weather conditions, our payback durations will all be different. That said, we can assume some reasonable averages and calculate the projections as follows:

Let's start with these assumptions:

- The sun provides 300 BTUs of heating per hour per square foot of collector

- The average collector is 50% efficient, returning 150 BTUs per square foot

- The average electricity cost in the US 1n 2009 is 12.05 cents per kilowatt hour (http://www.eia.doe.gov/cneaf/electricity/epm/table5_6_a.html)

- 3.412 BTUs = 1 watt

- The weather conditions average 15 days with 4 hours of sun per month

With those assumptions we can calculate the value of a square foot of collector as follows:

- 720 hours of sun per year X 150 BTUs per hour = 108,000 BTUs per square foot per year

- 108,000 BTUs / 3.412 watt equivalents = 31,653 watt equivalents per square foot per year

- 31,653 / 1000 = 31.65 kilowatts per square foot per year

- 31.65 X 12.05 cents = $3.81 per square foot per year saved.

Based on these calculations and assumptions, simply take your total system cost per square foot and divide it by $3.81. If your cost is $4.00 per square foot, your pay back is just over a year. If your cost is $11.50 per square foot, your system will pay itself back in 3 years.

The short payback financial incentives of investing in solar are already compelling, but add in the total lifetime return on the investment and the case is rock solid. Let's add two more assumptions:

- Your collector will last 35 years

- Energy costs will rise at 6% annually

Based on the assumptions detailed above, the value of the energy generated by your collector is $3.81 per square foot per year based on 2009 energy costs. If energy costs rise 6% next year, the value will be $4.04 and the cumulative total for the two years will be $7.85. Run that same process out 35 years and the cumulative total is $424.57 per square foot!

Based on that value, if you build 100 square feet of collector, your cumulative energy cost reduction over 35 years will be $42,457! Build 200 square feet and you can expect to save $84,914!

Whether you choose to build a big array or a single small panel, every BTU that you generate with solar is one less BTU that you have to buy from your utility company. It's a lot more fun to keep those dollars in your pocket!


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sheilagonzalez

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Reply with quote  #2 
The real questions — the real ways in which going solar affects your finances — is in how much it saves you and how soon or when it starts to save you money.
netttech

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Reply with quote  #3 
Welcome Shelia,

If you asking for a specific dollar amount, I've always said it's pretty hard to have a definitive number.

I'm not trying to talk around answer but explain it, as I see it.

From winter to winter, there are many variables, like price of heating fuel (nat gas, electric, Fuel oil, etc.), how cold each winter is. You would need to calculate the price of fuel, compared to 'degree days' for winter to winter. I guess if you really wanted a definate 'number or percentage' I guess you could do that math.

I don't want to do the math.

This is what I can say is, on a sunny day, my furnace doesn't run from the time I leave for work until I return (8-10 hrs). The coldest my house was 56 degrees when I returned home. I actually turned off my furnace on sunny days to see what would happen. I can also say, my monthly electric-gas bill has never gone beyond $250.00 per month since I started with solar (hot air). Before solar I have had $350.00 bills a month.

Remember I'm not factoring in the variations of the different winters. Last year was a pretty cold winter here.

I've been tinkering with solar for 6 yrs & still redesigning or rebuilding new panels each year. Always trying to get more (nearly free) BTU's, into my house. It's actually been a fun, addictive hobby! I'm currently expanding 1 of my window panels. I've started a new post with pictures in the Projects section.

Plus you are lucky, you found this forum. [smile] It has lots of like-minded people, all working towards the same goal. We are more than willing to help with questions, ideas, etc.

Jeff
Central IL
Solar air & water

sheilagonzalez

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Reply with quote  #4 
Take advantage of your own roof structure room: locate community deals with photo voltaic in your area, eliminate your own power costs, as well as become a member of the photo voltaic trend.
cwwilson721

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Reply with quote  #5 
As far as DIY Solar goes, here's my current take on the various situations:

PV: About all we can DIY is the panel(s) and the mounts for them. Still have to buy the inverters, chargers, possibly batteries, wiring. Not super cost effective, and could be illegal to hook to the grid. Overall, least cost effective for the DIY bunch we have here as far as what you can save and time of payback.

Solar Water: Can pretty much build most EVERYTHING. It ain't real cheap, tho, but you can build your own collector(s), piping, mounts, tanks, even controllers. Pumps/etc will still have to be "off the shelf" (if you use an active system). Overall, though, payback is comparatively short, with significant savings brought on by DIY. The MAJOR advantage is the ability to "store" the heat collected, and use that when there is no sun.

Solar Hot Air: HERE is where you REALLY save. Almost everything, except fans, can be built by the DIY'er real inexpensively. About the only drawback is no cheap, easy, DIY "heat storage" for hot air, so only get the heat in daylight. BUT, as inexpensive as the materials are, payback is almost instant. So many designs, materials, and thoughts are expended on this, the possibilities are almost endless.


gbwillson

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Reply with quote  #6 
Good summary CW-

I doubt PV will ever be cost effective for most people, even the DIY crowd. I'm an experienced DIY'er, but I wouldn't tangle with PV for the simple reason that my electrical needs are not so high as to need it. My house also is oriented the wrong way for rooftop installation. I have, however looked into emergency solar power. I could see myself with a few portable solar panels, and battery to power a few things for a short while.

The average person only lives in their house for a little over 7 years. Even if you are in your retirement home, it might cost tens of thousands for the initial install, and the ROI could be 20+ years. I see PV, and even solar heat and water, really taking off on new construction. Since many new homes are being built much more energy efficient than in the past, the savings are captured and the costs are built into the loan. 

Greg in MN[thumb]
stmbtwle

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Reply with quote  #7 
PV will take off when the local and state gubmints get out of the way. From a DIY perspective it's largely a matter of assembling the components, which are all available and prices are coming down as production ramps up. Yes you can "build" a solar thermal collector, but you didn't make the twinwall, polyiso, pipe, fans, pumps, probably not even the boards. What's the difference?
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gbwillson

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Reply with quote  #8 
I suppose the biggest difference is that you are working with electricity. Yes, our solar heaters have fans, but the level of experience needed with PV is beyond most DIYers. I could assemble all of the components, mount them, but I would never attempt to connect all of the various wiring to my service box, so I would need an electrician, likely for the initial consult of how and where to install the various components and then to connect the final wiring. But a person could save a lot of money by doing a large part of the work themselves.
Greg in MN[wave]
cwwilson721

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Reply with quote  #9 
PV, overall, seems more like "buy and assemble" rather than DIY

Yes, you can build a PV panel, with OK-ish performance. (comparable to a solar heat collector, water or air). BUT, you're probably NOT going to be able to build a inverter, or a charge controller, or batteries. You can wire it in (REAL simple), but basically, you assembled a kit. 

To me, not enough DIY savings.

Solar Heat, on the other hand, you can build almost everything, or get them VERY cheap (like pumps/fans/etc). Seems more in the "spirit" of DIY.

Also, since this is a "How much can I save" thread, the system cost does factor in.

If you're talking 100% savings 'cost' for energy, PV is the way to go. You can disconnect from the electrical grid this way. However, you WILL pay through the nose for this independence. But, no more electric bills.

Solar Heat, however, can replace your fossil fuel bill, and drastically reduce your electrical needs for heating your home and domestic hot water. In a DIY scenario, you save ALOT on system cost, too.

How much can you save? What do you want to save? What is meant by "save"? Is it system cost? Or is it reduction in current utilities, such as oil, gas, or electric? Do you mean "save" by doing everything DIY? Or buy everything and assemble it yourself? Or no DIY?

Big question, many answers.

stmbtwle

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Reply with quote  #10 
We already have "plug-in solar" where you buy the kit (or the components), connect them together (about as complex as your stereo), and plug it in. It's something any homeowner could do, doesn't require an electrician, and is probably safer than your washing machine. From a purist's perspective it may not be "DIY", but I think that's where homeowner solar is headed, once the paperwork and legal issues are dealt with. It's grid tied so storage is not an issue, it runs all year, and it's far more versatile.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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