What is the solar potential of your roof

August 14, 2008 7:22 AM

Have you ever thought about putting solar panels on your roof? Would you like to know how much power you can generate and what it would cost. RoofRay is a fun site that will calculate it for you and then let you know how much it would cost and how many years you'd need to recoup your investment. You enter an address into a version of Google Maps, and then draw where you want to put the array on your preferably southern facing roof.
posted by willnot (47 comments total)

Finally!

It was like 3 years ago that I made a gmaps app that would calculate real energy captured from an area the user demarcated. And now they made my (yes, MY!) idea useful.
posted by DU at 7:30 AM on August 14, 2008 [1 favorite]

Wow, it even includes state rebates. This site is awesome. (On my west-facing, northern-climate house and with a more-or-less random monthly bill of $200, I can break even in 26 years. I can also tweak it down to 14 years by just getting a 1kW system. ohmanilovethissite)
posted by DU at 7:34 AM on August 14, 2008

Fun. Except: it doesn't work for Canada (they don't have climate data for outside the US, it appears, so while you can draw your panel and get a rough estimate, the site cannot generate performance curves or create a financial analysis). Also, their presentation of roof tilt angle is surprisingly blase - it can make a tremendous difference in the generation of power season to season. (Essentially, the panel tilt should be roughly equal to your location's latitude, higher still if you want to generate energy during winter).
posted by Bora Horza Gobuchul at 7:38 AM on August 14, 2008

According to this site, installing a solar array on my forehead would produce 9.92 watts DC peak power output.
posted by XMLicious at 7:38 AM on August 14, 2008

their presentation of roof tilt angle is surprisingly blase

The map makes you pick an azimuth and they give a slider for elevation. What else do you want?
posted by DU at 7:40 AM on August 14, 2008 [1 favorite]

Zoinks. Sez it will take 20 yrs to break even.
posted by Mister_A at 7:42 AM on August 14, 2008

Net cost: $23,839
Years to breakeven: 18
This disregards opportunity loss for the time value of money.
posted by Daddy-O at 7:42 AM on August 14, 2008

The "performance" seems to be broken. Pressing "recalculate" creates new empty grids. It may be because I didn't "save" the grid I did, since that required registering an account (lame).

There is a good chance that the price of Solar could drop significantly soon. For years, most solar panels were made from scrap silicon from microprocessor creation, the stuff is 99.9999999% pure (nine nines), but you only need six nines for making solar panels (if I'm remembering this stuff correctly, I'm not sure if I am). Other people are working on making solar panels out of even lower quality silicon (called metallurgical grade). As solar panels become more popular more silicon processing plants will come online.

If you go back a hundred years or so, Aluminum was worth almost as much as gold.

Then there are companies working on much cheaper thin-film solar panels that, if their systems can scale up could be much cheaper as well.

(Again, this is just stuff I've read lately, so I'm not sure exactly how correct it is)
posted by delmoi at 7:44 AM on August 14, 2008

24 years to break-even for me. I guess I won't be implementing solar anytime soon. Anyone got a link for a wind calculator? What about a bunch of hamster wheels spinning in parallel?
posted by fusinski at 7:45 AM on August 14, 2008

This disregards opportunity loss for the time value of money.

and also resale value of the array, so it's a wash.

I'm VERY interested in picking up a place in a sunny clime and PVing the hell out of it, since sunny places like LV are very nice when it's not hot and livable given sufficient AC, and a PV-driven AC unit seems like a perfectly reasonable solution.

According to this, a 7KW roof installation has a 16yr breakeven point; $50K worth of stuff saves $2000/yr.

Hrrm, only a 4% cap return . . . not that economic. Solar is still in its Commodore 64 days; I fully expect what we have now will be total crap compared to 15 years from now, so heavy investment now may be premature.

One interesting market mechanism that the PV industry has exposed to me is the idea that PV is not necessarily priced based on what it costs to make (COGS + gross margin) but rather on how much it is saving the customer; ie. the market will be chasing a 4% cap return regardless of the technology or COGS.

Same thing with all alternative energy. If I had a magic formula that could produce 87-octane equivalent for 20c/gallon, I wouldn't be selling it for 40c, but more like $4.
posted by yort at 7:54 AM on August 14, 2008

nb, the best alternative energy is to find a place with an unmetered water supply and install a microhydroelectric system . . .
posted by yort at 7:55 AM on August 14, 2008

33 years to break even for me, I guess that I'll build that roof deck instead.
posted by octothorpe at 7:58 AM on August 14, 2008

How are people getting worse paybacks then I did, when my roof faces west (i.e. 90 degrees from optimal)?

Hmmm...I reran it and said my roof faces directly south. The power is way higher, the saved money is way higher, presumably the system cost is constant....same payback time. Maybe it's broken.
posted by DU at 7:58 AM on August 14, 2008

Here's a similar site.
posted by Kirth Gerson at 8:01 AM on August 14, 2008 [1 favorite]

Hamster powered nightlight instructions here.

Hamster slavery is not cool. What can you do? Start a blog, distribute a petition, write your congressman. Everyone wants to free Tibet, but no one cares about the hamsters.
posted by Daddy-O at 8:02 AM on August 14, 2008 [1 favorite]

Other people are working on making solar panels out of even lower quality silicon (called metallurgical grade). As solar panels become more popular more silicon processing plants will come online.

there's also various concentrating technologies like mirrors, lenses, and MIT's new edge concentrators.

For my ranch on the south side of Maui, however, I'll be going for solar-driven stirling engines . . .

10 years ago I was talking to a local about land issues and she said development was restricted because of water shortages. I slowly turned around and pointed at THE FUCKING OCEAN and said it wasn't a water shortage but an energy shortage, or more specifically, a startling lack of capital investment in renewable energy, given the geothermal, oceanic thermocline, insolation, AND powerful tradewinds the island has easy access to.
posted by yort at 8:05 AM on August 14, 2008

In addition to the technological advances delmoi mentions, one way they've been doing thin film solar cells is to simply print them on a metallic backing usink inkjet-like technology - I think that's the coolest but there seem to be bazillions of new solar cell technologies developed in the last decade or so. See also quantum dot solar cells.
posted by XMLicious at 8:06 AM on August 14, 2008

Does not seem to work for the UK alas (here in Scotland the sun is a rumoured object only at the moment). Here is a simple calculator for UK people. It lets you work out your likely load and array size for our climate.
posted by rongorongo at 8:07 AM on August 14, 2008

DU - I know for me it looked like I wasn't getting any kind of energy buy back for extra capacity. I wasn't sure if that was just my electric company that didn't offer it (seems unlikely in California), or if it was everywhere. I would guess that if there's no buy back factored in, then any generation beyond your annual usage is considered waste and doesn't factor in to they payback calculations. In that case, your monthly electric bill will be a bigger factor in payback time than power generation capacity.
posted by willnot at 8:09 AM on August 14, 2008

I think it's doing the netmetering correctly. Or at least it shows it doing that. But even if it weren't, if all you change is the orientation then it shouldn't matter if there's a bug there.
posted by DU at 8:13 AM on August 14, 2008

My home is powered by snark. It's available in several colors, and is infinitely renewable.
posted by blue_beetle at 8:22 AM on August 14, 2008 [1 favorite]

How are people getting worse paybacks then I did, when my roof faces west (i.e. 90 degrees from optimal)?

Are you in a location warmer than Detroit? (rhetorical)
posted by fusinski at 8:24 AM on August 14, 2008

MIT researchers have also been innovating in the field of solar energy storage.

Of course, when I hear “this is a major discovery with enormous implications for the future prosperity of humankind,” I'm reminded of countless similar statements from solar boosters over the last 20 years. On the other hand, Oregon's growing solar cluster shows that mainstream dollars are going into large-scale manufacturing. We may have (finally) passed the tipping point.
posted by danblaker at 8:33 AM on August 14, 2008

I have a bunch of cats. When it gets cold the cats sit on me, keeping me warm. My co-workers bitch and moan, but then I let the cats crap on their desks.

CAT-POWER!!
posted by Mister_A at 8:36 AM on August 14, 2008 [2 favorites]

Those of you who are getting 25, 30 year break evens, check the size of the system the site is installing on your roof. You don't actually need a 10 or or 20 Kw system (which the app will generate if the the array you drew on your roof is large), especially since with net metering (as we have in California), you will end up giving your excess electricity to The Man*, for free**: a 1 Kw or 1.5 Kw system is plenty. And much cheaper up front.

With net metering, my break even for 1.5 Kw system is 20 years. Which ain't great, but as DU notes, the system should increase the value of my home.


----------------
*This is a perverse disincentive and should be corrected.

**Or, use your excess juice to crack water into hydrogen to power the fuel cell in your car (which hydrogen and fuel cell doubles as a battery on cloudy days).
posted by notyou at 8:38 AM on August 14, 2008

(I did not note that, but thanks for the plug.)

with net metering (as we have in California), you will end up giving your excess electricity to The Man*, for free**

You mean without, right? Net-metering is where you get paid for the excess.
posted by DU at 8:42 AM on August 14, 2008

A question from the resident communist here-- why the hell are we paying PRIVATE COMPANIES for necessary power. Why are people allowed to make a personal profit from utilities, which you MUST purchase. It's not a freaking swimming pool for god's sake, it's warmth in the winter. Why the fuck isn't the goddamned government giving people more than a 10% rebate/tax break on these systems, assuming you #1 own your own home or #2 have the income to install this. And finally, why are individual families expected to solve the energy problem one household at a time?

/rant. have at me.
posted by nax at 8:48 AM on August 14, 2008 [2 favorites]

The map makes you pick an azimuth and they give a slider for elevation. What else do you want?

I do see what you're saying, DU... and it appears that they are working from the assumption that the solar array would be installed parallel with the slope of the roof of one's house. But the Google Maps API has latitude built-in, if I remember correctly - how difficult would it be to set the slider to the latitude of your address to maximise solar gain, with instructions to raise or lower it if you wanted to build the array flat on your roof?

And, of course, a bit of text at the top of the index page saying that Steps 2 and 3 in the process will only work for locations in the United States.
posted by Bora Horza Gobuchul at 8:52 AM on August 14, 2008

We may not have a rate for your location yet. We're working hard to incorporate as many rates as possible. Please bear with us...
posted by An Infinity Of Monkeys at 9:02 AM on August 14, 2008

What's the break-even point for a solar power satellite, and who do I talk to about financing?
posted by blue_beetle at 9:13 AM on August 14, 2008

According to this site, installing a solar array on my forehead would produce 9.92 watts DC peak power output.

Interpolating your results, I'm pretty sure then that Christina Ricci could power a small town.
posted by inigo2 at 9:20 AM on August 14, 2008

Huh. It thinks that zip code 14226 is in San Diego.
posted by ROU_Xenophobe at 9:31 AM on August 14, 2008

This is very cool, even though I apparently suck at figuring out how to use it correctly, and have to guess wildly at some numbers (roof pitch? No idea). We're contemplating getting panels installed on our roof, and this will help. Someone in my house will be better at using this than I am!
posted by rtha at 9:40 AM on August 14, 2008

DU:

Yeah, I took yort's "and also resale value of the array, so it's a wash" rephrased it and gave it to you.

Apologies, yort.

A Net Meter is just a device to measure the flow of electricity to and from the grid. The "Net" is how much the home draws from the utility versus how much it contributes.

In California, consumer-generated electricity shows up as a credit on the monthly Utility Bill. Energy generated in excess of consumption remains a credit in the customer's account and can be used to pay future Utility Bills. The scheme allows the consumer to "store" electricity credits gathered during peak summer production and use them during the winter trough. Credits not used to offset debits for Utility generated electricity are relinquished after 12 months. The net result is that the consumer does not get paid for electricity she produces but does not use.
posted by notyou at 9:41 AM on August 14, 2008

Fun!

One odd thing is that due to the tiered metering I get a much faster payback on a smaller array - say 500-700 Watts. Those pay back in as little as 18 years. Over 1kW the payback goes out to 22 years.
posted by GuyZero at 10:27 AM on August 14, 2008

The numbers I got pretty much match what I cam up with using other sites and some math, a few months ago.

I.e. that I could put up a 600-something kWh array for $40,000 and I'd still be buying power from The Man. Forty grand is a crazy lot of money. Solar has a long way to go, still.
posted by rusty at 10:28 AM on August 14, 2008

why the hell are we paying PRIVATE COMPANIES for necessary power.

Pemex. government arguably doesn't do commercial interfacing with the public that well -- compare the Post Office with UPS & Fedex

Why are people allowed to make a personal profit from utilities, which you MUST purchase.

The profit is regulated and not that great, more or less covering the cost of the capital invested. Eg. for 2007 PG&E reported $1B of net profit on $13B in sales, a 7.6% profit margin.

It's not a freaking swimming pool for god's sake, it's warmth in the winter.

This is why the utilities are regulated, and have been regulated for a century (ignoring that experiment in de-regulation that Gov Pete Wilson foisted on us).

Why the fuck isn't the goddamned government giving people more than a 10% rebate/tax break on these systems, assuming you #1 own your own home or #2 have the income to install this.

The consumer is paying less, but the manufacturers and its retailers are pocketing the rebate in the end. Rebates are subsidies, but don't necessarily result in a more competitive market.

And finally, why are individual families expected to solve the energy problem one household at a time?

Because we voted free market fundamentalists -- "The American Way of Life is Non-Negotiable" -- into power in 2000, and in our Federally-centered system state governments are relatively listless if not powerless at addressing the needs of the people.

Not that the Clinton/Gore team did much with its 8 years of executive power, though he did have this:

"In an effort to spark a sustained solar renaissance and cut U.S. emissions of global warming gases, President Clinton in June of 1997 announced an initiative to put solar energy systems on a million U.S. rooftops by the year 2010."
posted by yort at 10:53 AM on August 14, 2008

I used to be the monkey on the phone if you called Home Depot Solar and wanted to know more [1]. What interests me is that the estimated time to payoff hasn't significantly changed since 2001. I know seven years isn't that long, but still.

[1] Where "know more" == "make an appointment for a pushy salesperson to come to your house"
posted by sotonohito at 11:24 AM on August 14, 2008

This disregards opportunity loss for the time value of money.

and also resale value of the array, so it's a wash.

Not really. Think of it this way, according to this calculator, if I buy a solar array today for $20k, after 20 years I will have saved enough that it was basically free. So, ignoring inflation, I have a solar array worth something less than $20k that I can either sell or continue to use to get cheaper electric bills.

On the other hand, I could have just taken that $20k and put it in the bank or the stock market. The usual stock market guestimate for inflation-adjusted average earnings is about 9% per year, and $20k invested for 20 years at 9% comes out to over $110k. Assuming a more conservative rate of 4% per year, it would be just over $40k. So from an investment perspective it would seem like solar panels might not be a good financial choice.
posted by burnmp3s at 11:50 AM on August 14, 2008

The usual stock market guestimate for inflation-adjusted average earnings is about 9% per year

Real earnings are going to increase 9% for the next 20 years?

That's bunk, and Warren Buffet said as much in a recent 10-Q IIRC.

IMO, even the 4% real return is going to be tough to get going forward for numerous reasons we don't need to get into here now.

But even taking 4% nominal, sure, after 20 years you have a net gain of $24K on your $20K investment, but being an energy producer via the home solar plant also means one is insulated from future price increases (I noticed this site is in fact projecting grid price increases).

For the PV case, going with a $20K capital investment yielding $1000/yr in energy savings I'm seeing a total of ~$42,000 in PV savings (assuming 3% annual cost increase and the same 4% nominal investment return on the annual savings being reinvested).

So by spending $20K on PV now you will have $22K in net income plus whatever the salvage value of a 20yo current-technology PV system is in 2028, vs. the $24K you'd get investing at 4%.

The bigger question though is whether or not it would be wise to wait 3-5 years since PV ~should~ RSN be ramping up like PCs were in the 80s & ops. The systems are very complex -- going into PV installation was something I was looking at career-wise back in 2006.
posted by yort at 1:17 PM on August 14, 2008

This thread is useless without Mutant.
posted by Mister_A at 1:45 PM on August 14, 2008

And then again, Sungevity can already do all this for you. Enter your address on their home page.
posted by mano at 2:59 PM on August 14, 2008

but, but ... I don't have a roof!

compare the Post Office with UPS & Fedex

You mean useful, reliable, and cheap compared to nigh worthless?
posted by mrgrimm at 4:22 PM on August 14, 2008

very well-implemented site!

my wife & I used some of our wedding money to install a small (<2KW) net-metered system on the roof of our garage five years ago. with rebates from our power company in Long Island, and tax rebates, we paid only about $6,000 for a system worth $20,000.

the estimates from the site were fairly close (we're underperforming a bit from their estimate, but we get some shade in the afternoon from a neighboring tree). sure, it'll take us years to recoup the investment, but in the mean time, the value of our home went up (without, by the way, an increase in property taxes), and we feel like we're doing the right thing for the planet (and our kids).
posted by ericbop at 4:58 PM on August 14, 2008

What about the raw throbbing joy of not giving money to those bastards at the electric company?
posted by Lesser Shrew at 6:05 PM on August 14, 2008

We are sorry, but we don't have imagery at this zoom level for this region. Try zooming out for a broader look.
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*click*
It's been years and years, and GMaps for my area still looks like it was hand-drawn by a monkey with astigmatism. Renders many Google mash-ups useless (pun intended). Mostly I use Live Maps and Flash Earth as a result. I guess that's all I can say about it; it's not like there's going to be a protest at the front doors or anything. They must know the traffic/interest for this location, and if that isn't incentive enough, I suppose we're just going to have to live with it use competing products. *sigh*
posted by dhartung at 8:50 PM on August 14, 2008

Real earnings are going to increase 9% for the next 20 years?

That's bunk, and Warren Buffet said as much in a recent 10-Q IIRC.

Yeah, I know, there is no guarantee that future returns will be anywhere near past returns, but like I said that's the usual guesstimate. The point is that Warren Buffet still has money in the stock market, rather than owning a ton of solar arrays, because the stock market is pretty much the investment to beat for long term gains. I obviously can't speak for him but I'm guessing he would suggest an index fund as a good 20 year investment for $20k.

we paid only about $6,000 for a system worth $20,000.
...
sure, it'll take us years to recoup the investment, but in the mean time, the value of our home went up (without, by the way, an increase in property taxes), and we feel like we're doing the right thing for the planet (and our kids).

I think this is more of the point. Solar is a good step in the right direction, and if you can take advantage of tax benefits to be able to afford it, you're doing the right thing for the environment. Even if it ends up not being the best financial decision just going by the bottom line, it's very possible that it's the right decision for you personally.
posted by burnmp3s at 9:29 PM on August 14, 2008