is my project economically viable ?

[J.P.M.]

I don't think that at all. Being honest is, at best, neutral - and at worst, leads to the loss of the sale to someone who is less honest and promises more.

But my responsibility as a seller (of anything, not just houses) is to be honest about the details. When I sold our last house, I told the buyers that the solar power system I had generated about 16kwhr a day. I also told them we had recently replaced both bathrooms, had re-insulated the attic and replaced the kitchen floor.

Now, the buyer might hear that and think "wow, that means I can run an A/C all the time and never pay a power bill ever again!" Or they might think "new insulation! Heck, I won't have to run the A/C at all!" That's his fault, not mine. All I can do is give him the facts. As you mention, it is his responsibility to educate himself, so he does not make foolish assumptions. But if he does not, that's on him - not me.

It seems . . . . less relative to me. If you are honest with them and they get all pissed off, it's on them. If I tell them how much the system generates and they don't understand the units - AND they don't ask - that's also on them. If I lie to them, it's on me. All I can do is be honest about what I am selling. I cannot educate an arbitrarily foolish person, nor would I try unless they ask me to.

I go in assuming they are going to be honest. Then I verify the more important items (i.e. with a good inspection, a title search etc.) If it turns out they weren't honest - I walk away, even if it's a great deal otherwise. I'd expect other people to do the same with me.

Understood. Thank you.

I see the difference as you trusting more than me, but verify and then act accordingly. Being basically cynical about human nature, I trust less than you (and probably less than most) but look for reasons to correct my opinion and act accordingly. So looks to me like we start from different sides but work toward the same goal.

The last word is yours.

[jflorey2]

But to say, or imply as you seem to be doing that honestly always leads to a sale is, and I mean this to you respectfully, naïve.

I don't think that at all. Being honest is, at best, neutral - and at worst, leads to the loss of the sale to someone who is less honest and promises more.

But my responsibility as a seller (of anything, not just houses) is to be honest about the details. When I sold our last house, I told the buyers that the solar power system I had generated about 16kwhr a day. I also told them we had recently replaced both bathrooms, had re-insulated the attic and replaced the kitchen floor.

Now, the buyer might hear that and think "wow, that means I can run an A/C all the time and never pay a power bill ever again!" Or they might think "new insulation! Heck, I won't have to run the A/C at all!" That's his fault, not mine. All I can do is give him the facts. As you mention, it is his responsibility to educate himself, so he does not make foolish assumptions. But if he does not, that's on him - not me.

Now, when they get surprised and all pissed off and feeling screwed when they see bills that will probably be >> $10/month, who's to blame ? Me ? Them ? Their ignorance ? When/Where does my responsibility to inform them stop ? Where does their responsibility to be informed start ? It seems pretty relative to me.

It seems . . . . less relative to me. If you are honest with them and they get all pissed off, it's on them. If I tell them how much the system generates and they don't understand the units - AND they don't ask - that's also on them. If I lie to them, it's on me. All I can do is be honest about what I am selling. I cannot educate an arbitrarily foolish person, nor would I try unless they ask me to.

I'd also be kind of stupid to believe or assume someone with skin in the game that I probably don't know will be honest with me if there is $$ involved.

I go in assuming they are going to be honest. Then I verify the more important items (i.e. with a good inspection, a title search etc.) If it turns out they weren't honest - I walk away, even if it's a great deal otherwise. I'd expect other people to do the same with me.

[J.P.M.]

?? So you would think it was deception if a seller talked up the pool? I disagree. They are sellers; of course they are going to talk up the pool (or the granite countertops, or the solar installation, or the new insulation.) As long as they are honest about the facts behind it, then they're going to try to sell their house. I have done the same thing; I am sure you do too.

All this is off topic, but since you ask and since IMO, you're one of the more informed and critical thinkers around here:

I'm referring to the idea or proposition that potential buyers wind up getting screwed by their own ignorance at least as much or more than by sellers/peddlers deceptively taking advantage of that ignorance. That is, most of the origin of the screwing starts with buyer ignorance.

A well informed buyer is hard(er) to screw.

Example: How many folks who bought a residence at least partly on the on the premise of no electric bills and then discover at closing that they will still probably get a bill from high, profligate, self inflicted and ignorant usage, but also are committed to something like 15 years remaining on a lease for a system that doesn't cover their entire bill as they, in their largely self inflicted ignorance, were led to believe.

Or, the PV system is oversized for their usage and so they were sucked into perhaps paying more than they would if the system were sized for their needs sort of like buying a home with a grossly oversized A/C unit and told it's a money saver because it won't run as long and so save electricity/$$ while keeping the house cooler. As I'm pretty sure you know, both of those statements sound logical, but are false and in my book are deceptive. Compounding the ignorance, the person making such statements may actually believe them.

Buyer ignorance, to the degree it exists is still the culprit in most scenarios. The seller, or seller's agent is no more than an opportunistic tool used to turn the buyer's ignorance against that buyer with the goal of separating the buyer from more of their assets than would occur if the buyer was more informed. Is the real estate slug a scum bag ? Sure. But also not much more than an opportunist taking advantage of buyer ignorance and emotions.

I was a commission sales rep for ~ 10 yrs. peddling industrial process equipment of the type I later engineered before switching to engineering (and taking a pretty substantial pay cut, BTW, in the process). If I didn't sell anything, I didn't get paid. I appreciate the ethical dilemmas when dealing with customers who can be obvious and easy marks based on their ignorance. Sometimes it was hard not to take buyers to the cleaners. Most everyone I know who has ever sold things for a living understands that. In some ways, it's one of the hardest parts of the job.

Of course I talked up the advantages of my product(s). As long as I'm honest about the facts behind my products, I might be successful.

But to say, or imply as you seem to be doing that honestly always leads to a sale is, and I mean this to you respectfully, naïve.

As for honesty, truthful disclosure and personal integrity, the reality is most of that is a moving target subject to interpretation with a lot of the need for the any honest interpretation and self evaluation stemming from what I believe is a deeper need in most folks or at least most peddlers anyway, to be able to get out of bed in the morning, look in the mirror and like what they see. Sometimes, more often than I at least was comfortable with, it came down to a matter of situational ethics and interpretation. IMO, depending on their moral compass, honest peddlers deal with that most every day. To the degree they do may say something about how easy it is to B.S. people who are often so uninformed and eager to part with their assets it seems like they have targets painted on their faces.

Look, the best defense against getting screwed is for the buyer to take responsibility for being informed, not relying on the honesty of whoever is on the other side of the table. I don't like it much but that's how I saw and still see the game being run.

To repeat, it's hard(er) to screw a well informed person. And the more informed they are, the harder it is.

As for your surmise about what I've done and will do if/when I sell a residence, I've always been straight w/buyers (or sellers for that matter), and made sure residences I've owned and sold were, IMO, in good repair, or I know it'll cost me when I disclose defects that I couldn't or chose not to correct. My choice, my penalty. Potential buyers' opinions about my honesty in a business dealing such as that may be different from mine and relative. I intend to do the same when I sell this residence. Example: I will, among other documentation, provide hard copies of electric bills that prove $120/yr. I also intend to disclose that a good portion of that low annual bill is due to the fact that in spite of the array on my roof and the solar thermal water heater next to it, I only use ~ half what the average residence uses. My guess is folks will ignore that and see the 10 bucks/month for their potential bill and not hear, much less understand that unless they can keep their usage below ~ 9,000 kWh/yr., the PV system on the roof will likely not offset 100 % of their future bills if they buy my home.

Hell, if they're as informed as more than a few posters around here and also most of my neighbors and friends, they won't even have a clue what a kWh is much less what their usage is. So much for being informed.

Now, when they get surprised and all pissed off and feeling screwed when they see bills that will probably be >> $10/month, who's to blame ? Me ? Them ? Their ignorance ? When/Where does my responsibility to inform them stop ? Where does their responsibility to be informed start ? It seems pretty relative to me.

So, to your question, do I think it's deception ? For one thing, and for me only, until I verify for myself the veracity of what I'm being told, Yup. Sure do. But that's just me. But while I believe there's enough blame to go around, I honestly believe the deception starts with self deception. If I get screwed by my own ignorance that comes about due to a lack of due diligence to be informed, shame on me. If I don't take time and make the effort to be informed, that's my bad, no someone else's.

I'd also be kind of stupid to believe or assume someone with skin in the game that I probably don't know will be honest with me if there is $$ involved.

Respectfully,

[RShackleford]

You appear headed in the right direction but, IMO, you need background material and knowledge

Good luck.

Well, I decided to just go ahead and pull the trigger. I'll do the installation as inexpensively (hopefully not cheaply) as possible, with lots of sweat equity, and good deals like the $0.36/kW Talesun panels.

I can always employ the chainsaw, if I don't like the results.

[jflorey2]

Agreed, but that doesn't make the problem go away or the deception any more ethical.

?? So you would think it was deception if a seller talked up the pool? I disagree. They are sellers; of course they are going to talk up the pool (or the granite countertops, or the solar installation, or the new insulation.) As long as they are honest about the facts behind it, then they're going to try to sell their house. I have done the same thing; I am sure you do too.

[J.P.M.]

Perhaps. But that's true of any feature of a house that doesn't keep the rain off your head, like granite countertops, pools, insulation, efficient lighting, instantaneous hot water heaters, sheds, nic views, proximity to water etc etc.

Agreed, but that doesn't make the problem go away or the deception any more ethical.

[bcroe]

So I guess you still have to manually add up all those half-hour numbers for each month ?

I would use it more as a guide, as to where my chain saw would do the most good. For numbers
you might note the sun rise clearing shade times for 6 months, and also times for sun going down.
Compare those dozen times to official sun rise/sun set to see how much time you are losing. But
for the typically south facing array, poor angle production in those intervals is quite small anyway.
It is more important if you have arrays directly facing the rising/setting sun as here. Bruce Roe

[jflorey2]

Or, as I've seen more often on a local level, and similar to a lot of the posters I see around here, residential PV may add perceived value if the buyer is uneducated enough to let others with skin in the game oversell the benefits and swallow the hype - a lot of it from friends and neighbors who are equally ignorant, and/or from sources such as the green wash media shills of the solar peddlers.

Perhaps. But that's true of any feature of a house that doesn't keep the rain off your head, like granite countertops, pools, insulation, efficient lighting, instantaneous hot water heaters, sheds, nic views, proximity to water etc etc.

[J.P.M.]

So perhaps I'm going to get more irradiance on my panels that a simple shading model (like the one I did) would indicate ?
So maybe in the winter (trees without leaves) my 50% transmission is pretty reasonable. But in the summer, I should allow more than zero when the sun is below the treeline, perhaps 3/4 of 20%, or 15%. But only when it's something like 15 degrees below the treeline. When I make those adjustments, I'm down to 3600 kwh/yr (less, because formerly I didn't have the 15 degrees-below-treeline restriction on my winter 50% transmittance thru the trees.

It's very hard to estimate. That's on big reason why most of the methods are as empirical as they are. To have a detailed discussion is beyond the scope of this venue. That's why I suggested you read up on beam/diffuse irradiance and related concepts. If you do, you'll still not get a simple answer, but you may well understand a bit more of why you won't get a simple answer and learn a bit along the way - if you're curious.

You appear headed in the right direction but, IMO, you need background material and knowledge

Good luck.

[RShackleford]

This PATHFINDER is one method of checking shade for all season in a single measurement.

So I guess you still have to manually add up all those half-hour numbers for each month ?

[RShackleford]

Is this still accurate - "I calculate a return of about $368 per year"

For $30 clams per month forgettaboutit,

Actually, the way my net metering is done makes computing the savings pretty simple. All my generation zeroes out first my peak kwh's, then the off-peak;, and I'll always generate more than my peak usage. This works even if the generation during peak hours is less than the peak usage. This all boils down to a savings of about $300/year. However, right now I am making a voluntary "green power" contribution of $16/month on my electric bill (this somehow funds "blocks" of renewable energy generation); I would stop doing that, so now the savings is about $500.

If I build my system on the cheap, use the $0.36/watt Talesun panels, and no optimizers, I think I can get it up for about $6000, or $4000 after federal credit. So 8 year payoff.

[RShackleford]

Precise: Under a "clear" sky, diffuse irradiance makes up ~ 20 % of the total irradiance reaching the ground. Of that 20 %, and depending on the method used to allocate beam/diffuse irradiance, very roughly, about 2/3 - 3/4 of the diffuse will be incident on a shaded surface such a shaded array if the shading object is solid.

So perhaps I'm going to get more irradiance on my panels that a simple shading model (like the one I did) would indicate ?
So maybe in the winter (trees without leaves) my 50% transmission is pretty reasonable. But in the summer, I should allow more than zero when the sun is below the treeline, perhaps 3/4 of 20%, or 15%. But only when it's something like 15 degrees below the treeline. When I make those adjustments, I'm down to 3600 kwh/yr (less, because formerly I didn't have the 15 degrees-below-treeline restriction on my winter 50% transmittance thru the trees.

[J.P.M.]

I decided to get more serious about figuring out my shading losses. One simplifying thing: I can model my shading as though my panels will sit at the bottom of a bowl with a very irregular lip, in other words, for any given azimuth the sun is blocked up to a certain elevation angle, and then it's clear above that. So I built this little gizmo (photo below) which I can aim in a certain direction, giving me an azimuth within a degree or so, and then aim the tube at the top of the treeline, giving me an elevation within a couple of degrees. I aimed it for every 10 degrees of azimuth from 120 to 240 (no chance I'm gonna get any yield from directions outside that range), and measured the elevation angle of the top of the treeline.

Then, in the pvwatts_hourly file that PVWatts generates (with shading loss set to zero), I added columns in which I compute the azimuth and elevation of the sun for every hour of every day. I put my measurements into a little lookup table. Indexing into that table for each sun azimuth position to grab the treeline elevation, I compared the sun's elevation to see if I'd be shaded. I also added a column for the degree of sun transmittance if the sun angle was below the trees; for now, I set that to 0 for all days except Dec 1 through March 15, for which I set it to 50% (optimistic perhaps). Finally, I computed a column for the overall percentage of transmittance (complement of shading) I'd see for each hour of each day: 1 if the sun's elevation is above the treeline, 0 if it's below the treeline for any days except Dec1-Mar15, and 0.5 if it's below the treeline and it's one of those winter days.

Finally I did a dot-product (Excel SUMPRODUCT function) of the "AC system output" column with this "percentage of transmittance" column, and came up with a kwh/year figure adjusted for my measured shading. Pretty grim result: just a little over 50% of the PVWatts number (which already has all the system losses except shading incorporated). Specifically, PVWatts gave 7315 kwh/yr with 0% shading (but all the other system losses). PVWattts gives 5107 kwh/yr with the 30% shading number the installer used for their guaranteed-production quote. And with my modeling of shade I get 3757 kwh/yr.


IMG_20191109_172619430.jpg

That's a pretty serious attempt and, if I understand what you are writing correctly, it appears, to me anyway, well thought out. FWIW, nice work so far.

I've done things similar to what you describe.

A comment meant as constructive criticism: If you want to perhaps improve on your method, read up on solar irradiance, particularly the direct and diffuse components. It's not complicated, but a bit messy to understand because a lot of the information is either semi- or entirely empirical.

Precise: Under a "clear" sky, diffuse irradiance makes up ~ 20 % of the total irradiance reaching the ground. Of that 20 %, and depending on the method used to allocate beam/diffuse irradiance, very roughly, about 2/3 - 3/4 of the diffuse will be incident on a shaded surface such a shaded array if the shading object is solid. And of course, that solid shading will be changing constantly.

Because no two are alike, and making things more complicated, shade from trees or semi transparent objects is nearly impossible to model. That's most of the reason all this is so empirical. Then there is also the idea of how an array works under partial shade.

The shade modeling I did back in the day (and back east) was slightly before the solar pathfinder got to market. When available, I borrowed one from my last alma mater to compare results with what I'd done. I was also under the yoke of a hand held irradiance meter which was OK, but probably less than fit for purpose. What I found was that the solar pathfinder gave results that were about in line with what I had done in terms of shading penalties. However, and perhaps different to what you write of here, irradiance measurements were a bit higher than the what the solar pathfinder would lead me to believe if I'd discounted the contribution of the diffuse component. The two got closer, but still off a fair amount when I adjusted (and still a big SWAG) the P.O.A. irradiance to account for some of the diffuse portion of the irradiance hitting a surface that is in shade.

All that was pre-spreadsheet days so I was working in Fortran IV and later in BASIC. Looking back, all that seems, and probably is archaic compared to current tools.

While whole heartedly encouraging you to continue your investigations, I'd respectfully suggest you consider looking into either acquiring or renting a solar pathfinder of the type Bruce has pictured. Most folks need it one time and renting is probably a more cost effective way to go. Not a plug, but I believe the solar pathfinder can give reasonably reliable shading estimates. For most applications, that's more than sufficient with results that are about as accurate as necessary with not too much effort.

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

[bcroe]

I can model my shading as though my panels will sit at the bottom of a bowl with a very irregular
lip, in other words, for any given azimuth the sun is blocked up to a certain elevation angle, and then it's clear above that.

Pretty grim result: just a little over 50% of the PVWatts number

I see my open area as a bowl as well surrounded by shading trees. To minimize shading, the
array facing east is placed at the west edge of the bowl, looking over the maximum length of
clear space. Facing south are at the north edge, etc.

This PATHFINDER is one method of checking shade for all season in a single measurement.
Yes that is rather grim, would call for a chain saw here. Bruce Roe

PathFd1.jpgPathf2.jpg

[hardwired]

Is this still accurate - "I calculate a return of about $368 per year"

For $30 clams per month forgettaboutit,