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Joined: Mar 2005
Posts: 1,213
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Tracking has nothing to do with clouds or weather; it increases the efficiency of the solar panels in the early morning and late afternoon when the angle of a fixed panel is poor. Pretend your eye is the sun, stick a post-it-note on a globe, and rotate it. You'll see the aspect ratio change. Then, pretend your hand is a solar tracker and I think you'll see the difference! Even with a solar tracker, you'll still see less power in the morning/evening due to greater atmospheric attentuation (lower sun angle = shining through more atmosphere), but it will be more efficient than a fixed panel. It also helps account for seasonal differences, but these are less of an issue because the cos of the angle between summer and winter is small.

Solar tracking is typically not economical for a-Si solar panels, though. Solar tracking really comes into its own when using parabolic mirrors to concentrate solar energy, as the mirrors must be perfectly aligned to focus the solar energy on the element. So, if you use a parabolic concentrator, you'd need solar tracking. Otherwise, your customers are probably better off just spending that $15k on more panels because they'll see a better return.

Also, why bother with batteries unless they're off-grid? Grid-tie, and save them a lot of cost, complexity and toxic material!

If they're doing this expecting a positive return on their investment... they're not going to see it. Unless there is a HUGE government subsidy, they're going to lose money on this, and lose big. (Even if there is a subsidy, other tax payers take the hit for them- it's still a financial dead-end.) If they want to do it for environmental reasons despite the loss, that's their call, but please make clear to them that they're not going to get any $$$ returns on their investment. Especially in Canada, wow. They may not even make a return on the energy investment of the panels that far north.

Joined: Nov 2005
Posts: 141
C
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Thanks Steve for all your input.

Our client, as you state, "for environmental reasons" is their real motivation. Both he and his wife understand that there will be no return on the investment as far as the grid-tie goes, but it will give a boost to other members of their group to maybe invest a bit more dollars in research towards alternate energy production here in Alberta.

Because we are doing this contract, I think it's important for us to do it so the client can promote this stuff as much as much as he can.

As far as the battery stuff goes, there is the usual stuff going on about the supposed 2 year disposal issue for the deep cycle batteries when the batteries finally give up. (Which in my mind is a bit too short because from my research, they normally can go for 5 years without a significant deterioration.) Our client has made his own arrangements for that with some of his own business folks that he has more contacts than we do regarding battery replacement. From what he has explained to me about that, he is very aware of the requirement to replace the batteries and I checked into his disposal depot, and they are well known for doing it correctly.

In the ultimate end these folks (who are paying for it all) are trying to set an example for others, even though we know that it won't, for the time being, pay back the investment right now and maybe never but that's a decision they have made on their own.

From my point of view, we have work to do. It keeps my guys - even though it's way too cold outside right now and we have a a lot of REALLY good super neatly wired inside stuff, it keeps all of us interested in why we do what we do.

BTW

In the mean time it's minus 25 degrees Calcium and I have put a stop to the outside work for the next little while.

Joined: Mar 2005
Posts: 1,213
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VRLA batteries have a very limited life. Even in UPS applications where deep cycles are exceedingly rare, 3-5 years is typical, and if you lose just one cell, you lose the entire string. Wet-cell lead acid will last longer, but they'll need to go around every month and check electrolyte levels and do other preventative maintenance. And they might not like the idea of all that acid in their basement.

Li-Ion battery has made HUGE progress in the last few years, and may be worth considering. They've developed techniques to stretch the life out of the batteries, too. If I recall, the Chevy Volt only charges it's Li battery from 40-80% capacity, never fully charging it or discharging it. And Chevy is expecting it to last 10 years under normal daily use.

*All* these batteries need to be air conditioned, too. VRLA battery life is cut in half for every 15 degrees above 77F, and others are similar.

Of course, if your client is up on solar as much as it sounds, they probably know *exactly* what they want and all the pros and cons of it and just need you to put their plans into action smile

Joined: Nov 2005
Posts: 141
C
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An update on this installation.

We are now finished (even though the outside temps were around minus 3 bazillion knots below kelvins) with the panels.

As things progressed our client wanted 3 more 93 watt panels and sun trackers installed to increase the capacity even more. It took us two extra days to get that done.

We also installed 10 more lead-acids to handle the charging from the panels. When the whole installation was complete, the whole house was supplied with more than adequate energy to run for at least 2 days without any direct sun. The meter on the outside of the house was running backwards at a rapid rate during the day yesterday when I saw it.

As Steve said, the next move to upgrade the system is likely a move to Li-Ion batteries, or what ever new technology that might show up for energy storage, but so far the system will have to live "on it's own" for the time being.

If we have to do something like this again? I don't know, but we learned a lot about how to get it done, from the AHJ's "opinions" to land zoning issues with the City to the technical aspects. It was a fun "once only" project for now, but I get the feeling that it's going to come up more often these days here in Alberta.

BTW Steve, we put in a couple of 4 inch diameter pipes along with a variable speed coaxial fan in the ducting, running from the outside and over the battery bank and then back outside again with a shroud that contained the air movement over the batteries to keep them as cool as we could. So far, even with minus 30 outside the batteries stayed at a nice cool plus 10C so that seems to be working O.K. Summertime might present some issues when it gets to PLUS 30 however.

We'll be back to deal with that this July, I think. I just hope the batteries don't overheat when the air conditioning system is pulling 30 amps in the house. The system will shut down if the batteries get above 50 degrees C so I'm hoping it's not going to be an issue.

Whether it's worth it or not? My opinion is that the price is just way beyond what the average HO is willing to go for. Our client just spent a little bit over $45,000 to get this all done up. Kudos to them and a brave decision for a proof of concept for them and their friends. I applaud them for their guts at spending funds that will likely never be fully recovered.

Joined: Mar 2005
Posts: 1,213
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What's sad is they'd spend all this money to put this system in Alberta, when, environmentally, they'd have been far better off to have paid to put a grid-tie-only system on the house of a low income family in the arizona desert, which would have provided a MUCH larger offset than the grid power they'd consume in their own house. Probably have gotten 3-4x more energy for their dollar. Would have been even better to have invested in an energy company making an even more efficient commercial-sized solar farm.

Oh well, it's their money.

Joined: Jul 2008
Posts: 98
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Originally Posted by SteveFehr
What's sad is they'd spend all this money to put this system in Alberta, when, environmentally, they'd have been far better off to have paid to put a grid-tie-only system on the house of a low income family in the arizona desert, which would have provided a MUCH larger offset than the grid power they'd consume in their own house. Probably have gotten 3-4x more energy for their dollar. Would have been even better to have invested in an energy company making an even more efficient commercial-sized solar farm.

Oh well, it's their money.


Why do you think that the money would be better spent in Arizona? Both Arizona and Alberta would get roughly the same amount of daylight during the course of the year.

I'm not a meteorologist, but if I remember my high school science correctly, the equator gets 12 hours of daylight and 12 hours of darkness everyday of the year. The north pole gets 24 hours of daylight during the summer and 24 hours of darkness during the winter. The South pole gets 24 hours of daylight during the winter and 24 hours of darkness during the summer. But all 3 average the same amount of daylight during the course of the year. The same is true for all areas in between the poles and the equator.

Or have I forgotten a key lesson from 30 years ago?

Bruce

Joined: Jul 2004
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You missed the part about the attenuation of light in the atmosphere. That is why it is 114f in Phoenix on a day when it might be in the 80s there. There also are not many cloudy days in Phoenix and snow will never cover your collectors.


Greg Fretwell
Joined: Mar 2005
Posts: 1,213
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Exactly. There's temperature derating of a couple percent, too (cold aSi panels are less efficient), but cloud cover, atmospheric attenuation, condensation/frost and snow account for most of it. Sufficed to say, a panel in Arizona will make far more energy over it's life than that identical panel in Alberta.

Joined: Jan 2005
Posts: 5,445
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Cat Servant
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Let's put this "air resistance" issue in perspective.

Assume you start to get a sunburn at sea level in 60 minutes.
In Reno - about 1 mile elevation - you will burn in 30 minutes.
At Lake Tahoe - about 1-1/2 mile elevation - you will burn in 20 minutes.

The same applies for latitude. If a certain panel generates
100 watts at the equator, at 45 degrees latitude it will produce about 70 watts. At the Arctic circle, it will produce perhaps 50 watts ... all because the sunlight has to pass through more air to reach the panels.

Joined: Jul 2007
Posts: 1,335
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Hey Reno, it has been a while for me here. Although the atmosphere thickness does defuse daylight more at northern latitudes, the loss is minimal enough where it does not have any real bearing on the size needed. Panels are deliberatly under rated on their outputs because the panels will degrade over time and many panels come with a 20 year power output warranty. My panels up here when oritentated right exceed there rated wattage when they come out of their box. The only time the output is really affected like at the Artic Circle is in the winter time which the sun is at its lowest and is under the horizion hence zero day light. smile

It would effect the total isolation hours you would get up here but then again so does everything else so the "loss" per say due to atmosphere thickness is minimal since the atmosphere is the thickest at sunrise and sunset and your array is typically not optimally oriented at that time of the day.

Last edited by sparkyinak; 03/04/09 06:44 PM.

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