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Solar panels
Old 03-12-2008, 06:43 AM   #1
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Solar panels

The thread about the US energy policy got me thinking about solar energy. Many electric companies offer incentives to home owners to switch to solar and most will buy the excess electricity generated. How big of an array is needed to run a typical household?
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Old 03-12-2008, 11:04 PM   #2
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How big of an array is needed to run a typical household?
That's a tough question to answer because it's a function of your particular KWHr consumption (from your monthly electric bill) and the number of hours of "good" sunlight you can expect on your roof.

You could try this calculator: PV Watt Solar Energy Calculator PVWatts
It might be more optimistic than realistic but they're less biased than a solar contractor. Other calculators might be available from a local utility or solar contractors, and you'd want to compare their results with a sense of skepticism. For example our power generation varies about 25% between January & July, both as a function of hours of daylight and the sun's elevation (your latitude may make a bigger difference). We also get a lot more clouds & rain in the winter (hopefully you don't get snow). If you don't have a south-facing surface (in the Northern hemisphere) then you'll be penalized even further.

Your best bet would be to find a solar geek near you with a similar home. You'd have much more to compare between you and you could base your design on theirs. Those names might be available from the local utility's net-metering or grid-tied permit list or could be found through something like the Sierra Club or research organizations or local newspapers.

Like LBYM, it's always easier/cheaper to reduce your consumption than to raise your production. You'll want to bring in CFLs, high-efficiency heating/cooling systems, setback thermostats, insulation, tinted windows, EnergyStar appliances, and a host of other options before you go solar. You might even want to add passive solar features to your home, convert to a wood-burning stove, or add solar-water heating systems. The investment on our EnergyStar dishwasher and our solar-water panels was far cheaper (and pays back far more quickly) than photovoltaics.

A final issue is pricing points. Much of the price of a PV installation is labor, and another big chunk is the inverter. Inverters tend to come in capacities of 3-6 KW. Most residential systems are built to about 3 KW and most utilities limit their net-metering agreements to 10-KW systems. You might get a quote of $25K-$30K for a 3 KW system, and not too many homeowners are willing to go for 6-10 KW systems. So unless you're willing to design from scratch and do a lot of your own installation, you'll find the best price points at a 3 KW installed by an experienced contractor with all the fancy speed tools and rail-mounted systems. Most PV systems pay for themselves in 15-20 years, but if you live in a state with huge subsidies then you may be able to accelerate that to 10-12 years.

Before we started our PV installation in 2004 we were using an average of 500 KWHr/month. Our last 12 months of PV production averaged 270 KWHr/month (ranged from 218-303 KWHr) and our consumption averaged 108 KWHr/month (ranged from 3-157 KWHr). That implies our monthly energy use has dropped to 378 KWHr/month, a reduction of almost 25%.

We've only had our EnergyStar dishwasher for a couple months, and we just boosted our generating power by another 10% to 3370 watts (on a 3000-watt inverter). So 2008 promises to be even better, and I think we're just about done tinkering with consumption/production.

Our February electric bill was $22.51, an all-time low for that month. I suspect that we may actually generate more than we consume in July-August. While I know we could find cheap solar panels, we're pretty much out of roof space and a 4-5 KW inverter would cost a lot more than it would benefit. We'll just have to keep looking for ways to eliminate night lights, the aquarium, Fridgezilla, the toaster oven, the conventional oven the remaining big power-suckers.
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Old 03-13-2008, 12:39 AM   #3
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Our February electric bill was $22.51, an all-time low for that month. I suspect that we may actually generate more than we consume in July-August. While I know we could find cheap solar panels, we're pretty much out of roof space and a 4-5 KW inverter would cost a lot more than it would benefit. We'll just have to keep looking for ways to eliminate night lights, the aquarium, Fridgezilla, the toaster oven, the conventional oven the remaining big power-suckers.


Now you are talking.
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Old 03-13-2008, 08:36 AM   #4
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Now you are talking.
Don't forget, Nords has a number of things that make solar more cost effective than they would be for the average US homeowner. IIRC from his earlier threads...

1) Hawaii electric rates are much higher than the national average since they need to boat in the fuel to run the generators (can't they tap that volcano for power?).

2) IIRC, Hawaii provides some pretty big subsidies to homeowners for solar.

3) Nords scrounged around ebay/Caraigslist for deals, including used panels.

4) Nords did much of the labor himself. Maybe even removing panels he bought?

5) Hawaii is ~ 20 degrees latitude (offset by some cloud cover in areas?).

So this works for someone like Nords, with high energy prices, lots of sun, and the motivation and knowledge and skills to pursue deals and put in sweat equity. While I think there is a lot of promise for solar, it will either take much higher $/KW prices, or much lower installed cost of solar before the average Joe starts buying these in any significant amount.

Sometimes I wonder if neighborhood installations don't make more sense. Concentrate that installation in one area rather than climbing on a hundred rooftops. And there is always this option:

Personal Nukes: Toshiba Builds Personal-Sized Micro Nuclear Reactor? Huh?


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Measuring 20 feet wide by 6 feet long, it cranks out 200kW ...

They're saying that Toshiba will be installing the first one in Japan next year, with working reactors coming to Europe and America by 2009.



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Old 03-13-2008, 09:12 AM   #5
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Actually the reason I was asking is my long term plan is to purchase a larger tract of land, about 20 acres, and was thinking of clearing a portion, so any solar panels would not be threatened by falling trees or in the shade. I was just curious if this option would be at all feasible.There isn't any snow in the area I live, but hurricane's do have a habit of hitting us, so the tree thing was important and I am not too thrilled about mounting them on my roof top because of the storms. Currently tracts of land that size in the country aren't too much more expensive than a city lot in a good area.
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Old 03-13-2008, 12:34 PM   #6
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Actually the reason I was asking is my long term plan is to purchase a larger tract of land, about 20 acres, and was thinking of clearing a portion, so any solar panels would not be threatened by falling trees or in the shade. I was just curious if this option would be at all feasible.There isn't any snow in the area I live, but hurricane's do have a habit of hitting us, so the tree thing was important and I am not too thrilled about mounting them on my roof top because of the storms. Currently tracts of land that size in the country aren't too much more expensive than a city lot in a good area.
I'm so jealous. I've been forbidden to shade our grass with PV panels but all it does is sit there and grow... a city building on the lot next to ours has thousands of square feet of roofspace but I can't get away with it...

It's easily feasible but a conservative payback would be 15-20 years, depending on prices, rates, & credits.

There are three ways to look at PV costs. First, there's the "dividend" rate on your electric bill savings. If you spend $30K on a PV system and it reduces your monthly bill by $50 then you're getting a 2% dividend. It's financially better to buy a blue-chip dividend fund, but solar sales guys love to use this math because people love to use it to justify the purchase. They'll also point out that utilities raise their electric rates, so your "dividend rate" will increase over the next 20 years-- but probably not as fast as Phillip Morris or Exxon.

The second way is the payback. A $50/month savings will add up to $30K in 50 years. PV systems are widely quoted on a 25-year lifetime but systems from the 1970s are still pumping out electrons so 50 years is hypothetically achievable. However most investors are unwilling to wait around that long, even though that monthly savings will climb as utility rates climb.

The third, and most conservative, is opportunity cost. If you plunk that $30K in a decent small-cap value fund appreciating 6%/year after taxes then it's going to take a very long time for a $50/month contribution (starting from zero) to compound above it. Even despite rising electric rates.

Despite the investment, PV systems have no value for home buyers. If you try to sell your property you will not recoup the price of the PV installation.

Installation prices are anyone's guess. Research is promising and the media loves to trumpet "The next big solar breakthrough!" but commercially there haven't been any great leaps forward. Most of the price drops have been due to volume production, but Germany & Japan have created so much demand for PV panels that prices have been rising again while production ramps up. In general, though, I believe panels will be cheaper in 3-5 years. Last-generation technology (panels that are 5-10 years old) is already on sale at half-price-- as are cosmetically blemished new panels. Panel racks and inverters are much better as the materials & technology improve, but the big advantage goes to the installer who can take advantage of faster installation times. They'll want to install certain racks or inverters because they have the special tools & training and can do it faster (more profit margin) than some other system you may prefer.

But wait, there's more to add to the spreadsheet. Your $30K investment may get an installation credit from a local utility, a locality & state tax credit, and a federal tax credit. Some of those credits may expire in 2008, so don't wait until October to make a decision or you'll be paying a premium for an installer's time. Just to make things more interesting, our Hawaii credits are only good to the extent of our actual taxes owed (no refunds) so we have to carry them forward 4-5 years to use them up. You may be in a similar situation.

Because most credits are capped at an annual amount or a percentage of the spending, very few owners buy it all at once. Most buy a cheap 1 KW system with an oversized inverter, take the credits that year, expand the system with another 1-2 KW of panels the next year, take more credits, and expand the system to capacity in the third year. That maximizes credits (which tend to accumulate faster than monthly electric-bill savings) but it stretches out the installation.

Then your utility adds their own rules. Hawaii used to credit net-metering agreements monthly. If you made more than you used that month, your usage went to zero and your excess production wasn't carried over. Now that we have a digital meter the net metering is a rolling 12-month account. However it still makes no sense to produce more than we'll use in a year, especially if we drop our consumption via other energy-savings appliances (or by having our kid move out). Most utilities credit net metering at the residential retail rate (your electric bill) but if you're producing "too much" (as determined by them) then you may be reclassified as a power producer and only reimbursed at the wholesale rate. Bad deal.

Finally there's the "hobby" or "green lifestyle" issues. I thoroughly enjoyed the hunt, the design, the installation, the expansion, and the tracking. (The payback is an unexpected bonus.) It's a hobby that keeps on giving, too-- we're buying a Prius in a few months that I hope to convert to a plug-in, which could justify the acquisition of a second 3KW PV array to recharge its batteries. But I have a lot of math to do on that spreadsheet.

You can go two ways. If you want to do your own installation labor and you understand electrical code/safety, then have an electrical contractor install a small PV array with a huge inverter. You'll want an exterior-grade inverter (or a weather-resistant shed/bunker) and panel racks rated for whatever weather you're going to have to endure. They'll need to understand that you want plenty of room for expansion, which implies an inverter that can handle five or six inputs of up to 600 VDC each. Then over the coming years you can buy more panels (eBay, Craigslist, discount outlets, wherever), build your own racks, connect them electrically, and enjoy the process.

If you want the benefits without having to labor, you could find a local installer who's willing to take on a 3-4 year project while you maximize your tax credits. You'd want someone with volume discounts on panels (and inverters) and who was willing to be flexible on their labor rates if you're flexible on schedule.

If you're not dealing with snow (and especially if the temps stay above freezing) then you may want to consider a solar water-heating system before you go PV. Non-freezing solar-water systems typically have a 5-8 year payback compared to PV.

With a submariner's experience at maintaining grid voltage and dealing with lead-acid storage batteries, I wouldn't recommend going off the grid unless you have to. Maybe someday when NiMH or Li+ batteries are easy to recharge at high rates, but even modern lead-acid batteries are no fun to maintain.
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Old 03-13-2008, 03:06 PM   #7
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I was just curious if this option would be at all feasible.
I saw a guy near my old house that had (I think) 8 panels in a 4x2 arrangement (nearly square)...I wanna say the whole thing was about a 12'x12' array. It was mounted on top of a motorized pivot and seemed to move with the sun to keep an optimal lock on it. At least every time I drove by it was pointed or tilted differently and there was a big motor in view.

Looked like this:



I guess its called a 'solar tracker'. Some detect and optimally direct the array, some simple ones work on a basic 24 hour timer and you change the tilt yourself throughout the year.

Seems like if a roof mount isnt necessary, such an arrangement might allow for a smaller array, cheaper install, and more power all day long from fewer panels.

It WAS however, butt ugly. Worse than a BUD.
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Old 03-13-2008, 03:29 PM   #8
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Nords - thanks so much for that summary - I am enamored of going 'off the grid', especially since I hope to have a little homestead in AZ, however, your points are well taken - the ROI isn't there yet and there are small things one can do, like the solar water heater, as well as limit consumption that can be better short to mid-term decisions.
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Old 03-13-2008, 03:49 PM   #9
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I did a fair amount of research on this last year, but in my case the payoff didn't really seem worth it to me. If I recall correctly, the key factors were a lack of state tax credits (Idaho), very cheap electricity rates (I pay around 5.2 cents / KWH), and lousy sunlight (I'm at ~43 degrees North latitude).

It was fun to do the investigation. Maybe I'll update the spreadsheet and see if anything has changed to make it worth it now.

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Old 03-13-2008, 06:22 PM   #10
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I did a fair amount of research on this last year, but in my case the payoff didn't really seem worth it to me. If I recall correctly, the key factors were a lack of state tax credits (Idaho), very cheap electricity rates (I pay around 5.2 cents / KWH), and lousy sunlight (I'm at ~43 degrees North latitude).
It was fun to do the investigation. Maybe I'll update the spreadsheet and see if anything has changed to make it worth it now.
For you, 2Cor, if things change you can get the word (and much cheaper shipping than me) from these guys. I was drooling over their catalogs in the 1980s:
Backwoods Solar Electric Systems
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Old 03-13-2008, 11:41 PM   #11
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Nords,

Thanks for the link. I'll add it to my spreadsheet.

I pulled up my spreadsheet and found the following numbers:

Sizing:

kWh per day 16.86 module watt rating 130 module size (sq inches) 1959.3 module weight (lbs) 34.2 module cost $599 peak sun hours 5.4 wire losses 0.98 batterry efficiency 1 inverter efficiency 0.9 power per module 619.16 modules needed 28 PV array size (square feet) 381 PV array weight (lbs) 957.6 PV array cost $16,772

Price per watt $4.61

Assumptions
kWh used per day 20 cost per kWh ($) $ 0.050562 inflation rate in kWh costs 6% marginal state tax rate 8.10% discount rate 8%
Decision Measures:
NPV ($10,748) IRR -13.6% MIRR -2.5% Payback 29.60
Opinions welcome. I know the cost per kwh has gone up some since I built my spreadsheet, and I was looking at new 130 watt panels from kyocera at affordable-solar.com. Probably spendier than the panels you acquired?

2Cor521
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Old 03-14-2008, 09:49 AM   #12
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Price per watt $4.61

Assumptions
kWh used per day 20 cost per kWh ($) $ 0.050562 inflation rate in kWh costs 6% marginal state tax rate 8.10% discount rate 8%
Decision Measures:
NPV ( $10,748 ) IRR -13.6% MIRR -2.5% Payback 29.60
2Cor521
When I found these guys:

Nanosolar - Articles

talking about trying to get panel prices down to $1/Watt, I did some calcs with our current $0.10/KW rates, and Northern Illinois solarization. Even $1/Watt for the panels, while good, did not strike me as a 'no-brainer' to go solar (inverter and installation costs add to the number). But, if these guys can do $1/Watt solar, it at least caps my electricity costs at some level. I'm sure that $.20/KW electricity costs would drive it to the no-brainer category. That's nice to know, but I'm not holding my breath until I can actually buy these for $1/Watt.

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Old 03-14-2008, 10:57 AM   #13
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We're in the 14-15c range and I still couldnt make the numbers work right. We were looking at a 10-12 year payback if the array produced fairly optimal numbers in theory vs what we'd actually get in practice.

Solar also seems to work just like a pool in resale. Some people want it, some people dont. It may make the home easier to sell but doesnt seem to boost the price much.

I do keep hearing about these major leaps in the technology expected to show up in just a few years that'll make the efficiency/size a lot better. That they're mimicking roofing materials also helps. Maybe in 5-7 years they'll have some stuff that looks good and is efficient enough at a good enough price that everyone will want to do it.

Our water treatment plant up the street has a 900kw array set up. Maybe I'll just run over to Home Depot and see how many extension cords they've got.
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Old 03-14-2008, 02:37 PM   #14
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Nords,
Thanks for the link. I'll add it to my spreadsheet.
I pulled up my spreadsheet and found the following numbers:
Sizing:
kWh per day 16.86 module watt rating 130 module size (sq inches) 1959.3 module weight (lbs) 34.2 module cost $599 peak sun hours 5.4 wire losses 0.98 batterry efficiency 1 inverter efficiency 0.9 power per module 619.16 modules needed 28 PV array size (square feet) 381 PV array weight (lbs) 957.6 PV array cost $16,772
Price per watt $4.61
Assumptions
kWh used per day 20 cost per kWh ($) $ 0.050562 inflation rate in kWh costs 6% marginal state tax rate 8.10% discount rate 8%
Decision Measures:
NPV ($10,748) IRR -13.6% MIRR -2.5% Payback 29.60
Opinions welcome. I know the cost per kwh has gone up some since I built my spreadsheet, and I was looking at new 130 watt panels from kyocera at affordable-solar.com. Probably spendier than the panels you acquired?
2Cor521
Uhm, yeah, we got our first 1100 watts for $2.25/watt and the rest for just under $4/watt. All used from the local classifieds, eBay, and Craigslist. Compare that to current panel prices of $6-8/watt and (installed) rates of $8-10/watt.

If you're building an array of 28x130w panels for 3540 watts, your 16.86 KWHr/day might be overly optimistic. With our decade-old panels of just over 3000 watts I was averaging 12-13 KWHr/day for a south-facing roof at 22 degrees latitude, and probably at least five good full-sun hours per day (12 hours per day of power production). Winter averages were more like 8-9 KWHr/day. Your performance will also be affected by clouds, rain, and haze.

The best thing to do for your calculations is to find someone in your area with their own performance numbers. The contractor I worked with put the Kailua public library's PV array's inverter data online so that you could monitor it real-time through his website. He was bought out last year and his site appears to have been taken down, but you might be able to find a similar project closer to your location.

And one of these days I'm going to connect our inverter to our PC to log the data. Yup, I'm all over it.
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