bewildered by panel choices for DIY system

[RShackleford]

Soooooooooo! You have 5 acres and it only gets a total of 70% Sun half the day/night that's an 80% loss? Invest in a really good chain-saw. Problem solved.

Not sure where "half the day/night" comes from, but yeah, only 70% if I believe the 30% shading.

I have a good chainsaw. But I have a LOT of trees.

[RShackleford]

If cost is a concern Renvu is selling Talesun panels for $0.36/w.

Yeah, I saw those. Doing ground-mount, I'm not so space-constrained. Nor do I have a rigid idea of how many watts I need.

I've made a spreadsheet to compare a variety of specific panels, configuration (number of panels and landscape/portrait), etc. I assume a $50 optimizer on every panel (Tigo TS4-R-O) and $3500 in add'l costs that are fixed regardless of these other choices (inverter, racking, structure, basically from the OP of this thread). Doing that, a 15 panel system with the Canadian 320watt panels is not much more per watt ($1.54) than the Talesun would be ($1.46), and gives me a good bit more wattage (4800 versus 4050). IOW, those bargain panels don't help me that much because of all the other costs.
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The "panels $" column is a little hinky, because the various panels come from different vendors, all of whom compute shipping separately (flat fee, or some value the shopping cart just computes based on weight or something).

[Paul Land]

That's a very good question, to which I don't know the answer. All I know is that it's an input to PVWatts, and it's the number an installer used in PVWatts to estimate the number of kwh I should generate per year (a number which they are guaranteeing). The installer came up with the number by getting up on my roof with some sort of electronic device.


I am planning ground-mount. One reason being that the location would be a bit sunnier, though not dramatically so, than the roof.

Soooooooooo! You have 5 acres and it only gets a total of 70% Sun half the day/night that's an 80% loss? Invest in a really good chain-saw. Problem solved.

[RShackleford]

Even racking is more important.

What can be got wrong there ? Are you talking about azimuth & elevation, or more subtle issues ?

[nwdiver]

Worth the extra cost and imperfect appearance ?

So what do folks think of these brands, and are there others that might be more attractive to me ?

IMO panel choice is the least important consideration; Even racking is more important. If you want black panels for aesthetics get black panels. If you're space constrained get higher wattage panels; If you're on a budget get the cheapest ones (So long as they're UL) even 'B' grade is fine IMO. I've bought B grade.... it's usually just a cell misalignment that doesn't effect performance and can only be see if you're on the roof inches away from the panel.

If cost is a concern Renvu is selling Talesun panels for $0.36/w.

[scrambler]

So does anyone have answers for the questions in my OP ?

In the "non premium", I like the REC NPEAK, their price-performance- warranty combination seems one of the best. I am curious of how they are going to price their new REC Alpha.
Next I like the price performance warranty of the Qcell QPEAK DUO G5.

Both are Cut Cell panels, so in theory have a slight edge in Shade mitigation.

[sdold]

it's completely shady some of the day, completely sunny other times.

What part(s) of the day would the entire array have direct sun, with no shading?

[azdave]

So what do folks think of these brands, and are there others that might be more attractive to me ?

I'm far from an expert but most people here will tell you that panels are a commodity these days and the brand name you choose is not all that important in a buying decision. I never buy the latest and the greatest model or release when it comes to cars, appliances or solar panels. I also don't buy into the luxury brands that deliver the same thing as others but with a lot of marketing thrown in to make you feel special.

[J.P.M.]

That's why I said it's an input to PVWatts.


Agreed. But the inputs would have to get really complicated to capture what most people (including me) are gonna see - e.g. it's completely shady some of the day, completely sunny other times. Better than nothing though, I guess.

In some opinions, it's worse than nothing.

The more someone knows about the subject the easier it is to understand why.

I believe the way PVWatts calcs. a shade penalty on annual output is probably OK and mostly harmless for small penalties of a few % or so. But much more than that and it's not only pretty useless, but misleading.

One example of many: Suppose you are in the northern hemisphere and your array is shaded by vegetation to the SE such that the insolation on the array is decreased by a total of 30 % until solar noon on Dec. 21. Also assume the array is located at 45 deg. n. latitude with a 45 deg. tilt and an array azimuth of 225 deg. You, wanting to be a bit conservative but also knowing the array is not in shade all the time, plug in 15 % shading (worst shade reduction/2) assuming you want to be somewhat "conservative" but not too conservative. What will happen is that the model will reduce all hourly outputs for every day of the year by 15 %. The reality is that annual production will be reduced by a lot less, probably something like a few % or less. You go merrily on your way and increase the array size by 15 %. Now, oversizing is bad enough. Doing so on bad information only makes a bad situation worse. Oversize if you want, do so knowing what your doing. This would be a case of the model misleading the ignorant.

Point is, shading is a complicated subject and, in spite of what you, I and probably a lot of others might want, there is no easy way to get what's even a ball park estimate.

And, wishing or having an otherwise useful model to provide what looks to be an informed way to get a shade penalty is less than helpful and is misleading - your situation being a good example. If you choose to become more informed on the subject you'll understand where I'm coming from.

Further point is, and for several reasons, simplistic bandaid adjustments to annual output to account for shading such as that used by the PVWatts model can be worse than nothing - not better than nothing.

IMO, it would be better for the model to state that shading is complicated and beyond the scope and intent of the PVWatts model and leave it there.
That way, the probability that folks will be led astray might just be a bit lower.
Or, as appears to have been done with how the PVWatts model handles shading, tell the great unwashed masses what they want to hear.
Better, IMO only, would be to at least inform users of the limits of how the model handles shading as a heads' up. Still not a good option, but as you say, better than nothing.

Take what you want of the above. Scrap the rest.

[RShackleford]

That shading % may be a number the installer used but be sure/clear, (s)he didn't get it from PVWatts.

That's why I said it's an input to PVWatts.

input reduces each month's output and also each of the hourly outputs by very close to the same amount %age wise. That's obviously not a realistic way to do shading.

Agreed. But the inputs would have to get really complicated to capture what most people (including me) are gonna see - e.g. it's completely shady some of the day, completely sunny other times. Better than nothing though, I guess.

[J.P.M.]

That's a very good question, to which I don't know the answer. All I know is that it's an input to PVWatts, and it's the number an installer used in PVWatts to estimate the number of kwh I should generate per year (a number which they are guaranteeing). The installer came up with the number by getting up on my roof with some sort of electronic device.


I am planning ground-mount. One reason being that the location would be a bit sunnier, though not dramatically so, than the roof.

That shading % may be a number the installer used but be sure/clear, (s)he didn't get it from PVWatts. (S)He may have plugged in 30 % shading using the loss calculator under system losses, but PVWatts will not calculate shading. The model takes shading input from the user and reduces the model's output to approx. (1- shading %) of the 0% shade output value with some effects of that approx. accounted for by the fact that some of the irradiance is diffuse and still gets to the array as well as some other minor effects on array temps. that will have a slight effect on modeled cell efficiencies and so output.

As such, and in any case, that input reduces each month's output and also each of the hourly outputs by very close to the same amount %age wise. That's obviously not a realistic way to do shading.

You might see a 30 % reduction in output over the course of a TMY, but that %age will vary as f(time).

PVWatts is a decent model for preliminary design, but handling shading in a realistic way is not one of its strong points, or any point for that matter.

[RShackleford]

So does anyone have answers for the questions in my OP ?

[RShackleford]

Curious as to how the 30% is calculated, and what does it represent? Shading changes daily and will get worse as days get shorter.

That's a very good question, to which I don't know the answer. All I know is that it's an input to PVWatts, and it's the number an installer used in PVWatts to estimate the number of kwh I should generate per year (a number which they are guaranteeing). The installer came up with the number by getting up on my roof with some sort of electronic device.

I have to assume you are referring to a roof mounted array. With 5 acres have you considered a ground mount. You can achieve optimum performance with a ground mount.

I am planning ground-mount. One reason being that the location would be a bit sunnier, though not dramatically so, than the roof.

[littleharbor]

Curious as to how the 30% is calculated, and what does it represent? Shading changes daily and will get worse as days get shorter.
I have to assume you are referring to a roof mounted array. With 5 acres have you considered a ground mount. You can achieve optimum performance with a ground mount.

[RShackleford]

If you're close to being as knowledgeable as Bruce about PV, how it works and the practical side of installation, you might be able to make the economics work. Otherwise, I think you're going to be in for some surprises and rude awakenings.

I don't know who Bruce is or how knowledgable he is. Anyhow, this question of economic viability keeps coming up, so I started a thread dedicated to it: https://www.solarpaneltalk.com/forum...mically-viable

I don't know about the brand specifics, but be aware that panels put out almost no power when shaded.

And yes, I get that the sun needs to be shining on my panels for them to generate electricity. As I state in the other thread, I modeled my system using PVWatts with a figure for shading loss computed by an installer as part of a bid with a production guarantee.