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solar panels in the Land of the Sun
Old 07-13-2013, 08:49 AM   #1
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solar panels in the Land of the Sun

A recent thread in MexConnect on solar panels in Mexico:

MexConnect.com Forums: General: Living, Working, Retiring: solar panels

The economics are different but very real.
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Old 07-13-2013, 11:25 AM   #2
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Interesting, but I don't think that guys calcs are right. He talks about aiming the panels to the north May-July at a 20N lattitude, and relates this to a 40% V delta.

First, his power calcs are wrong (but the correct formula would increase the difference):

wrong>>
Quote:
For fixed resistance, 20% higher voltage = 20% more power... etc
correct>> P=V^2 / R


So a 20% increase in voltage would be 1.2 * 1.2 = 1.44, a 44% increase in power. A 20% drop in voltage would be .8 * .8 = .64 ; a 36% drop in power.

But how can a few degrees change voltage by 40% as he claims (an 84% drop in power!)? That makes no sense. Even the full 23 degree change at the tropic of cancer at each Solstice would be only something like an 8% drop in solar energy at the panel (assuming I can still do High School Trig, but that's a big assumption even with the help of the web). I guess 'solar noon' affects this a bit, but I doubt it is much.

Think of the panel as the hypotenuse, set perpendicular to the sun, the angle would be zero and the hyp equals the adj (it's just a line). Hold the hyp equal to one, now rotate it 23 degrees, and the surface it presents to the Sun is now equal to the adjacent side of the triangle.

cos(23 degrees) ~ .92

cos(c)= adj/hyp

adj = cos(c) * hyp so we lose ~ 8% of effective surface area.

Interesting notes about the effect of dust and bird droppings. I've seen that on my little solar lights along the driveway. Of course, they are small relative to a panel, so a single bird drop covers a lot %-wise. But with those cells in series, it does not take much to lower output of the entire array.

-ERD50
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Old 07-13-2013, 11:31 AM   #3
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More and more houses in New Orleans have solar panels these days. Our question (here), is what happens to them during a hurricane? I have no idea because I have not yet looked into them sufficiently to know. But anyway, if they could be removed somehow and taken inside with minimal effort, solar panels could be wonderful here. If they remain on the roof, it seems to us that surely they would be blown off and become dangerous projectiles.

Imagine how great it would be to have power after a hurricane, though, when normally it takes a little time to get normal power sources back online.

You are so right - - the economics can be very different in different locations. Here, electricity is relatively inexpensive so the main objective for me would be to provide electricity after hurricanes.
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Old 07-13-2013, 12:09 PM   #4
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I've been fascinated with the concept of solar energy for many years so I am NOT anti-solar by any stretch. Still, I have never seen good figures suggesting that (without heavy gummint subsidies) solar electric makes much sense (even in Hawaii where electric rates are around $.30/kwh and the sun shines much of the time.) BUT in places where there is consistent sun (think sun belt and Hawaii) solar hot water heaters DO pay for themselves without subsidies. So, why our gummint doesn't push these and (at least for now) down play solar electric a bit, I do not know. I hope for a time when solar is cheap, easily buffered and strictly non-centralized. I think that day is a ways off. Throwing money (we don't have) at it when suddenly natural gas could be cheap makes no sense to my pea sized brain. I'm sure many disagree with me, but I've yet to see the figures (and an actual plan to make it all work). Again, I'm anxiously waiting for that day. YMMV
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Old 07-13-2013, 12:22 PM   #5
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...

Imagine how great it would be to have power after a hurricane, though, when normally it takes a little time to get normal power sources back online.

... main objective for me would be to provide electricity after hurricanes.
It is normally a big job to take the panels down and re-install. I suppose something could be done to make this easier, some quick-clamp system, but you are still talking about getting large things up/down from a roof.

The typical solar PV install will not provide power during an outage, even when the sun shines. The inverters rely on the grid power to provide a 60-cycle sync and as a buffer. There are alternatives, more expensive bi-directional inverters, but that also requires batteries, and it all gets rather expensive and limited.

Do they have Natural Gas supplies to homes in NOLA? A small NG generator can be convenient, no gasoline storage, and NG is typically available throughout a storm.

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Old 07-13-2013, 12:25 PM   #6
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... BUT in places where there is consistent sun (think sun belt and Hawaii) solar hot water heaters DO pay for themselves without subsidies. So, why our gummint doesn't push these and (at least for now) down play solar electric a bit, I do not know. ...
I suspect because solar hot water is just not as 'sexy' as generating electricity. It's more about the sizzle than the substance.

I also agree with the rest of your post.

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Old 07-13-2013, 01:12 PM   #7
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Maybe it's because solar water heaters look like something the Borg would install on the roof of their vacation cube:




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Old 07-13-2013, 05:49 PM   #8
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I've been fascinated with the concept of solar energy for many years so I am NOT anti-solar by any stretch. Still, I have never seen good figures suggesting that (without heavy gummint subsidies) solar electric makes much sense (even in Hawaii where electric rates are around $.30/kwh and the sun shines much of the time.) BUT in places where there is consistent sun (think sun belt and Hawaii) solar hot water heaters DO pay for themselves without subsidies. So, why our gummint doesn't push these and (at least for now) down play solar electric a bit, I do not know. I hope for a time when solar is cheap, easily buffered and strictly non-centralized. I think that day is a ways off. Throwing money (we don't have) at it when suddenly natural gas could be cheap makes no sense to my pea sized brain. I'm sure many disagree with me, but I've yet to see the figures (and an actual plan to make it all work). Again, I'm anxiously waiting for that day. YMMV
I posted the math in the Tesla thread. but for the non DIY type (i.e. not Nords) in Hawaii the payback period is 8-10% for those of us with $200/month bill and probably 10-12% for those with $400/electricity bill, without subsidies. Price per KWH goes down with bigger systems. It certainly makes sense here if you plan on staying in your house for 10+ years. One of the interesting things is when selling a house can you convince the new owners instead of $3-4K house payments and then spending $300-400 on electricity you have a $17 bill. There for you should increase the value of the house by say $10 -25K.

The problem with solar is they are just really labor intensive. I had a super easy installation on a metal roof (not drilling required) so the 4 men team did the job in 8 hours. But there were also 2 electrician. However you also have to add in the salesman time, including the other salesman who didn't get the job. The designers time to design the system, the electrician planning time. The time for the city inspectors to issue permits, come to the inspection, plus the 2-3 trips by the electric company. My friend is the VP sales of one the largest solar companies on the island and he tells me that labor cost is roughly 25% and moving to 30% as equipment costs drop. So even if panels, inverters etc. drop labor cost will remain pretty much fixed.

My guess is there is less money to be made selling solar water heaters <$2k + installation vs 20-50k for a PV system.
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Old 07-14-2013, 11:31 AM   #9
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When we lived in FL many years ago, I remember seeing the city of Tampa dismantling roof-top solar water heaters from public housing. Seemed like a dumb move to me.
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Old 07-14-2013, 11:36 AM   #10
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I have loved the idea of PV, ever since I was kid. If it is practical anywhere today, it should be in Mexico.
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Old 07-14-2013, 11:39 AM   #11
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I have loved the idea of PV, ever since I was kid. If it is practical anywhere today, it should be in Mexico.
I recall traveling in Mexico years ago and every house seemed to have a black painted water tank on the roof. What a concept!
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Old 07-14-2013, 11:43 AM   #12
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......Here, electricity is relatively inexpensive so the main objective for me would be to provide electricity after hurricanes.
Solar panels don't make much sense as an emergency backup, unless you have a big battery bank. The grid tied systems shut down when there is no grid power detected. So, a small generator would make more sense for an emergency backup, though it would be cool if you could use PV system in an emergency.
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Old 07-14-2013, 03:09 PM   #13
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It is feasible to have an off-grid system that can sustain one through power outage periods. It is not too different from a PV system for a motorhome, just scaled larger for a home.

A typical $3K system would have as major components:

1) Ten large panels of 210W each
2) Twelve golf-cart batteries for storage
3) One charge controller
4) One 2.4kW inverter

The price above does not include mounting component costs (racks, wires, conduits, breakers, etc...), nor labor. It would run a refrigerator, the lighting and appliances like TV for a typical home through the night if one watches usage. Cooking is possible using a microwave and a portable induction cooktop, definitely not the normal residential range/oven. Definitely no central AC, but during the day, I think a small window AC consuming only 500W would be permissible, or perhaps even through the night if one carefully watches the battery state.

The problem is the additional cost for installation, and the high chance the panels would be blown away by a hurricane. Hail is less of a problem than people think, unless it's Texas hail size of an orange.
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Old 07-17-2013, 11:50 AM   #14
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I have a correction to make. The cost of the above components is $4K, not $3K. I was looking at an actual price quote, but failed to see that they did not include the batteries.

I still think the above price is quite good, and that is possible only after the recent drop in price due to saturation of the panel market. However, adding in installation cost and other miscellaneous parts, and it may get up to $8-10K.

Not exactly cheap, nor maintenance free due to the required care for the batteries. It may not be worthwhile as an emergency power source, but for longer-term off-grid applications, it is an excellent solution relative to noisy generators.
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Old 07-17-2013, 08:19 PM   #15
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When I was living in Mazatlan, Mexico, I had a good friend that seriously looked into this. His main high cost usage was Air Conditioning during the hot season and it was blazing hot and sunny that time of year.

But the economics still did not work out. He ended up investing in much more efficient air conditioning units. The return on capital was much better.
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Old 07-17-2013, 08:36 PM   #16
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Compared to power consummed by air conditioning, solar panel outputs are puny.

I have been following the blog of a guy who has been trying to build his own travel trailer of perhaps 8'X20'. His goal is to be able to keep it cool using a small windows AC type, using the power from 2kW worth of panels. He found out that he needed a lot more insulation that what was typically put in the commercial RV.

There, the economics are not the same as for a home with grid power, and highly favor solar panels vs. fees for nice RV parks, or self-contained generators that run non-stop in the boondocks. Even so, it's tough.
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Old 07-17-2013, 09:20 PM   #17
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I recall traveling in Mexico years ago and every house seemed to have a black painted water tank on the roof. What a concept!
When in Haifa, a high-tech town in Israel, I saw many simple solar tanks on roof tops. The difference there was that many homes had a terrace or a patio as the flat rooftop, hence the tanks were not visible from the ground level. I was on a hill looking down.

An Israeli engineer explained that when a home applied for a construction or renovation permit, the city would not issue it unless a solar tank was included in the project. Such simple solar tanks would work well in areas not susceptible to freezing, such as part of Mexico or Israel.

In Phoenix, during the solar boom of the energy crisis of the late 70s, early 80s, many homes had solar water panels installed. Within 10 years, they were slowly abandoned, bypassed or removed. Reason: Phoenix still has one or two nights of freeze a year. If the anti-freeze sensor failed, the morning you discovered that the anti-freeze system failed to work was also the morning you kissed your cracked panels goodbye.
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Old 07-18-2013, 01:12 AM   #18
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When I last looked into it several years ago, solar water heating made pretty good economic sense if it was displacing electric water heating, but not so much if it was displacing natural gas water heating. Where I lived at the time almost everyone used a gas water heater, and there were virtually no solar water heaters in use.

There are designs now that pretty well eliminate the issue with solar panels freezing and failing, but no one is really marketing them very hard at this point, and I think a lot of people still remember all the bad experiences with them freezing in the 70's and 80's.
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Old 07-18-2013, 05:28 AM   #19
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I can see the day when solar panels will be integrated into the shingle itself. And it will be tough enough to walk on. I have seen solar panels on sailboats, etc. that are flexible and about 1/8" or so thick in various sizes. They are really neat.

A big part of the problem right now is battery technology. We need better efficiency and storage from batteries. I think we are on the cusp, but not quite there, yet. Solar is being subsidized and not efficient enough right now to stand on it's own...unless you are a hermit in the hills without a mirror, wash tub and shaver.
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Old 07-18-2013, 10:38 AM   #20
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I can see the day when solar panels will be integrated into the shingle itself. And it will be tough enough to walk on. I have seen solar panels on sailboats, etc. that are flexible and about 1/8" or so thick in various sizes. They are really neat......
IIRC that day is here and such a product exists.

We recently had a quote on a solar system that would tie into the grid. While our power bill would be minimal, the initial cost even after federal and state tax subsidies made the investment unattractive to me. Assuming zero opportunity cost of money, the payback was about 15 years, but it stretched out to 25 years if I use the same investment earnings and inflation assumptions that i use for the rest of my financial planning.

We decided not to pursue it because the economics were not particularly attractive and a neighbor's large tree that is close to the property line shades our south facing roof so we couldn't put the array on the roof but would have needed to have a separate standing array that would have taken up some of our yard space.

When I wrote back to the guy I told him that the economics weren't all that attractive and that hopefully the technology would improve and get cheaper and make the economics more attractive. He wrote back and said that I should act now as the economics will be less attractive as the federal and state incentives phase out - which told me that absent government intervention that solar is questionable economically - at least in our area.
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