DIY Grid Tie Planning - Requesting Advice

[svetz]

.... An argument is a discussion....

A discussion is an exchange of information and ideas. An argument is proving oneself right. Subtle, but they're different. You don't know anything about me, what I know, or what I've done and commenting on it as a way of proving a point is inappropriate. But apology accepted.

To be clear, I have not used SAM's shading algorithms so it may be junk. I know it uses math rather than the voodoo satellite imagery you mentioned and I have a lot of faith in the programming skill of the folks from NREL. It's also an active project, so if someone points out a flaw they'll fix it. Even so, it'll have some margin of error and the trees will grow anyway.

I have no "argument" your gizmo allows you to map shade locations at different points of the year. I'm dubious it will easily show you shade that hasn't hit the roof from a nearby building and only hits in one season when you're measuring 6 months away (where operator skill undoubtedly comes into play). I'm disappointed it can't tell you about reflective light as well as shade. I suspect it cannot tell you what the annual power will be based on those seasons, based on the length of shadow traversal/shape/panel-tilt/spacing like a 3D simulation can provide. Which, assuming there is no 100% shadow-free roof space, seems like it would be better at finding the optimal panel locations. I think you agree with this too, as I believe you mentioned you've programs that do this. So, for a DIYer, I think SAM is good enough. If someone needs to be more accurate, or has extreme shading, they should probably hire a professional.

 

[kernel]

A discussion is an exchange of information and ideas. An argument is proving oneself right. Subtle, but they're different. You don't know anything about me, what I know, or what I've done and commenting on it as a way of proving a point is inappropriate. But apology accepted.

To be clear, I have not used SAM's shading algorithms so it may be junk. I know it uses math rather than the voodoo satellite imagery you mentioned and I have a lot of faith in the programming skill of the folks from NREL. It's also an active project, so if someone points out a flaw they'll fix it. Even so, it'll have some margin of error and the trees will grow anyway.

I have no "argument" your gizmo allows you to map shade locations at different points of the year. I'm dubious it will easily show you shade that hasn't hit the roof from a nearby building and only hits in one season when you're measuring 6 months away (where operator skill undoubtedly comes into play). I'm disappointed it can't tell you about reflective light as well as shade. I suspect it cannot tell you what the annual power will be based on those seasons, based on the length of shadow traversal/shape/panel-tilt/spacing like a 3D simulation can provide. Which, assuming there is no 100% shadow-free roof space, seems like it would be better at finding the optimal panel locations. I think you agree with this too, as I believe you mentioned you've programs that do this. So, for a DIYer, I think SAM is good enough. If someone needs to be more accurate, or has extreme shading, they should probably hire a professional.

Did you look at the display graphic on the optic. This gizmo is one of the most common ways it has been done for 20 or more years now. It absolutely does show all shade obstructions and their movements over the day and any time in the year with high accuracy.

 

[kernel]

A meter is used for light levels if you like. If a diy is not using shade analysis, why would they be dissapointed in a shade instrument which does not measure light reflectivity or flux on a location. Now that is a nit!

 

[kernel]

Ill just remember to not give advice on here..... only comments, like; sounds good.

 

[svetz]

Ill just remember to not give advice on here..... only comments, like; sounds good.

That would, IMHO, be a waste. You seem very knowledgeable.

Did you look at the display graphic on the optic. This gizmo is one of the most common ways it has been done for 20 or more years now. It absolutely does show all shade obstructions and their movements over the day and any time in the year with high accuracy.

Yes, I even agreed the device did that in the post above yours:

...I have no "argument" your gizmo allows you to map shade locations at different points of the year....

I suspect you might have been addressing the 2nd part of that:

... I'm dubious it will easily show you shade that hasn't hit the roof from a nearby building and only hits in one season when you're measuring 6 months away (where operator skill undoubtedly comes into play).

Although I'm not sure what was objectionable there as it says there are cases where it might be hard to do, not impossible. For example, a shadow currently on the ground is at a different elevation than the roof, so that's bound to make it more difficult to figure out.

Just to be clear, my stance is that for a DIYer SAM is a great tool and was summed up above as:

So, for a DIYer, I think SAM is good enough. If someone needs to be more accurate, or has extreme shading, they should probably hire a professional.

 

[svetz]

Found a video on SAM's 3D shading system. Perhaps they'll talk about it's level of accuracy... if so I'll follow up with updates.

It's sort of cool, you can put an aerial photo in as a backdrop to get things like tree/building position/diameter. Not sure how you'd get heights of objects. Perhaps a side photo and comparison to known heights (e.g., roof) and distances? Or angles would work.

Update 1: At ~6:30 it talks about inputting data from a solar pathfinder (aka, the gizmo)
Update 2: At ~7:56 they say it's better for large commercial rather than residential (but can still be used)
Update 3: At ~10:30 they say more accurate shade calculations is the most requested and they're funded for it (video was in 2014, so should be done)
Update 4: At ~16:10 they state they use linear shading, so may under-predict systems with string inverters.
Update 5: At ~17:00 Tool doesn't consider leaf drop in winter, adding to uncertainty.
Update 6: At ~41:47 they say it's a rough estimate, but better than nothing.

 

[kernel]

I think the best available site survey incorporates both computer modeling and optic measurement of shade obstructions. It has always been this way except we used to find the heights amd plot the sun angles with a bunch of string and sighting tools amd measuring tape.

Way easier to find angles with a graphed out gazing ball gizmo!

Dude, again sorry about the scuffle, i did mean all good will, just sounded like my method was being marginalized, ill have to let those go on forums. We get to pound the table on these topics at work!

As far as leaf fall i guess we are at a loss

 

[svetz]

Two cents worth on the other questions:

What should I be considering when choosing panels?

I think you have the right idea, see Comparing Solar Panels. You're right that a 355W panel might produce more power that a 360W for your location being different from STC based on its parameters (e.g., pMax). BTW, as SAM has most panels built in, it's easy to swap different panels in/out and run a 30 year analysis.

Is there a reasonable way to include factors besides rated wattage when doing energy estimates?

You can use a watt meter. Just make sure you leave it plugged in long enough to catch things like the freezer's defrost cycle. Probably easier is to look at your power bill to get an idea as to what you're consuming (generally each month will be different due to AC or heat)

Are used panels something that should be considered?

Panels can last a long time, but they do degrade (beyond the PV, things like insulation getting brittle, contacts corroding, diodes wearing out). I'd rather get new with a warranty, but that's just so I don't have to futz with it.

Are high quality panels worth it?

From a home resale value I think the answer is yes; but beyond that it's tougher to answer. Typically higher quality panels have less energy loss over time. There's an analysis in Comparing Solar Panels that shows over 30 years the Panasonic HITs are less expensive than QCells, but that's very price dependent and was done with prices from AltE. I was going to go Panasonic HIT, but then got a great price on LGs and went that that way (LG's were nearly as good IMHO, and they have a more mainstream lower panel voltage).

ROI seems to be better the larger I go with the system

If you're counting on net-metering in that, keep in mind some states that had it did away with it. As you're thinking DIY and Enphase, you have the flexibility to put a toe in the water to see what it's like with a small system in the first year...then if it pans out go bigger. Do it all in the same year 6 months apart, use the final install date and I think you can get the full 26% federal tax credit - hopefully someone more knowledgeable (kernel?) can confirm/deny.

 

[aaknitt]

Well for some reason I stopped getting email updates for this post so I'm playing catch up now. Thanks for all of the input!

As for shading, I did use the 3D shade modeling tool in SAM and it does seem to show shading from the adjacent roof section. Whether I'm entering everything in correctly enough to trust the results is a different question, but at some level it seems to be working. It seems to be confirming that my primary section of roof gets little to no shade from trees and that the secondary roof section does get some shading from the taller roof, but the impact doesn't seem to be as bad as I had anticipated, particularly during the summer when the sun is higher.

I think the best available site survey incorporates both computer modeling and optic measurement of shade obstructions.

So dumb question since I'm new at all of this...wouldn't I need to take optic measurements at different times of the year and times of day to get enough data to make good predictions? Or use the measurements from one day to compare to something like SAM and make adjustments in the simulation so that it closely approximates the measurements?

You can use a watt meter. Just make sure you leave it plugged in long enough to catch things like the freezer's defrost cycle. Probably easier is to look at your power bill to get an idea as to what you're consuming (generally each month will be different due to AC or heat)

Sorry I should have been more clear. I was asking more about how to quantify the difference in lifetime output of a solar panel other than by it's wattage. I'm struggling with what the benefit is of a panel that costs $1.00/watt vs. one that's only $.70/watt, because without any additional information besides wattage, the lower $/watt always looks better on paper. I think SAM should help with that, but I haven't yet been able to tease out that type of information from the results yet...still learning.

If you're counting on net-metering in that, keep in mind some states that had it did away with it.

Yes, I'm counting on net-metering at the residential rate, with credits for overproduction good for one year. Once a year any excess credit is payed out at the wholesale rate, so my goal would be to not have excess credit (keep annual solar production just under annual usage). Are you saying that some states have done away with all residential-rate net metering? If that's a real risk, then the whole thing may not be worth it, as net metering at the wholesale rate isn't worth it.

Thanks,

Andy

 

[svetz]

... I was asking more about how to quantify the difference in lifetime output of a solar panel other than by it's wattage. I'm struggling with what the benefit is of a panel that costs $1.00/watt vs. one that's only $.70/watt, because without any additional information besides wattage, the lower $/watt always looks better on paper. I think SAM should help with that, but I haven't yet been able to tease out that type of information from the results yet...still learning.

On the "lifetime" tab you can enter the panel's yearly degradation rate. Then when you look at the numbers over 30 years you can get a better feel for the lifetime total watts/$

...Yes, I'm counting on net-metering at the residential rate, with credits for overproduction good for one year. Once a year any excess credit is payed out at the wholesale rate, so my goal would be to not have excess credit (keep annual solar production just under annual usage). Are you saying that some states have done away with all residential-rate net metering? If that's a real risk, then the whole thing may not be worth it, as net metering at the wholesale rate isn't worth it.

Probably depends on where you live and how quickly solar is being adopted. The gist of thread The shocking cost of Electricity, is that energy prices are continuing to rise. Solar is already cheaper than any fuel source, but battery prices haven't decreased to where they can enter the mainstream. As battery prices fall and more and more people switch over then governments will need to do something to subsidize the public utility as they lose their economy of scale - the PUs won't be allowed to fail because they're critical to everyone that hasn't converted and like it or not solar users will need to support some of the brunt of that. Because of all sorts of agendas and interests, it will probably take a long time for PUs to change their nature. But eventually, it should all level out.

Click image to get to source....

 

[kernel]

Well for some reason I stopped getting email updates for this post so I'm playing catch up now. Thanks for all of the input!

As for shading, I did use the 3D shade modeling tool in SAM and it does seem to show shading from the adjacent roof section. Whether I'm entering everything in correctly enough to trust the results is a different question, but at some level it seems to be working. It seems to be confirming that my primary section of roof gets little to no shade from trees and that the secondary roof section does get some shading from the taller roof, but the impact doesn't seem to be as bad as I had anticipated, particularly during the summer when the sun is higher.



So dumb question since I'm new at all of this...wouldn't I need to take optic measurements at different times of the year and times of day to get enough data to make good predictions? Or use the measurements from one day to compare to something like SAM and make adjustments

Andy

Its not dumb to ask a question. The tool will plot the shade fall for anything in sight on the horizon. It will do this and be a reference for that spot any time of day for any month of the year.

Only large arrays need more than 3 sightings many times one or two spot checks for setback do it.

There is a number line for total days radiation. If you subtract the shade segments you have a total percentage to feed to the simulator for that area.

There is a disc with the tool that will take you digital photo and simulate leaves on or off the trees and make better sense of the data for some.

If you dont have shade issues, id skip it. I use it mainly to backset rows or columns of modules from obstructions including other array portions, trees, poles, power and com lines, roof vents, adjacent roof lines, etc.

Makes it a quick accurate and easy thing to do. If you installation is a bean counter (investment only) system, shade analysis is required (even if the photos only confirm no shade) for asset protection and investment analysis.

Some (half of) utilities near us require shade analysis for an intertie agreement.....

 

[Danny]

I would do the DIY install. The break even is too long otherwise. Here is a video on panel size.

. In most cases it is best to use large panels to minimize racking and labor. Iq7a and large panels like Hanwa 385w cost are the correct way to go. $500 for wiring is a bit on the low side. See my project play list to get an idea of all the details and we can talk if you like https://www.youtube.com/playlist?list=PLCal7Co3mAHSR5tg48M8NGKBcjBso8Wle

 

[aaknitt]

I would do the DIY install. The break even is too long otherwise. Here is a video on panel size.

. In most cases it is best to use large panels to minimize racking and labor. Iq7a and large panels like Hanwa 385w cost are the correct way to go. $500 for wiring is a bit on the low side. See my project play list to get an idea of all the details and we can talk if you like https://www.youtube.com/playlist?list=PLCal7Co3mAHSR5tg48M8NGKBcjBso8Wle

Thanks. I agree the higher wattage panels make sense. Unfortunately I can't quite fit the larger 365/380 watt panels on the roof sections I have to work with and still meet the 3' open space requirements at the peak and for eave to peak. I think I'm going to constrained to 350 watt panels. If they're longer than 70 inches I can only fit one row rather than two. Similar issue if I orient them horizontally...sizing just doesn't quite work out and I end up with fewer panels.

 

[ronnie263]

Its not dumb to ask a question. The tool will plot the shade fall for anything in sight on the horizon. It will do this and be a reference for that spot any time of day for any month of the year.

Only large arrays need more than 3 sightings many times one or two spot checks for setback do it.

There is a number line for total days radiation. If you subtract the shade segments you have a total percentage to feed to the simulator for that area.

There is a disc with the tool that will take you digital photo and simulate leaves on or off the trees and make better sense of the data for some.

If you dont have shade issues, id skip it. I use it mainly to backset rows or columns of modules from obstructions including other array portions, trees, poles, power and com lines, roof vents, adjacent roof lines, etc.

Makes it a quick accurate and easy thing to do. If you installation is a bean counter (investment only) system, shade analysis is required (even if the photos only confirm no shade) for asset protection and investment analysis.

Some (half of) utilities near us require shade analysis for an intertie agreement.....

Sorry, which gizimo is this. Is it the 'Sun Pathfinder'?

 

[kernel]

Sorry, which gizimo is this. Is it the 'Sun Pathfinder'?

Yes, worth every penny if you need one or if someone else does. I site greenhouses amd gardens with it, all kinds of stuff.

 

[ronnie263]

ohh yes,, I definitely need it. Where can I get the best deal for this gizimo

 

[kernel]

Not sure. About 180 without tripod. I bought mine in 2006 or 2008. Altestore may have them.

 

[ronnie263]

Thank you

 

[aaknitt]

WI net metering provides credit for excess generation at the retail rate over a one year interval. At the end of that interval, any surplus is paid back at the wholesale rate. Therefore, a system that goes beyond net zero doesn’t make a lot of financial sense.

Just for the benefit of anyone that comes across this, it turns out that's old information. The current net metering arrangement for my utility is not nearly as good. Net metering is done on a per-month basis with any excess for a given month paid back at a much lower rate (about 1/3 of retail). As a result, I'm looking at a smaller ~5kW system to reduce overproduction during summer months and keep a decent rate of return.

Even a battery system wouldn't help much with this arrangement...storing energy from summer to use in winter isn't really practical with current technology.

 

[Surferdudemi]

Just for the benefit of anyone that comes across this, it turns out that's old information. The current net metering arrangement for my utility is not nearly as good. Net metering is done on a per-month basis with any excess for a given month paid back at a much lower rate (about 1/3 of retail). As a result, I'm looking at a smaller ~5kW system to reduce overproduction during summer months and keep a decent rate of return.

Even a battery system wouldn't help much with this arrangement...storing energy from summer to use in winter isn't really practical with current technology.

The utility here has a 10 year period where you get the higher rate, and mine just dropped off the cliff. If I understand it correctly (have not gotten a bill with the new rates yet), they deduct the distribution charge, which is about $0.06/kWH (I'm in MI, next door, LoL). I looked at the ToD rates they offer, though, thinking I could save money by shifting my loads to cheaper times (like programming my EV to charge from 11 pm - 7 am). Turns out, one of the ToD rates allows net metering! (The other doesn't, and they actually CHARGE YOU for power exported to the grid.) So not only can I save money by shifting loads, I also get a slightly higher rate for the power fed back to the grid, so I just switched to that.

My system has been running for 10 years, so here are a couple of things to consider:
First, look at any trees and add 10-20 feet and think about whether or not they will start blocking your array(s). I'm looking at cutting down a mulberry tree ...
Second, the panels will lose some efficiency over time. The panel mfr should give you the numbers.
Third, in one of the comments, there was mention of voltage difference in summer. Yes, the voltage changes with temperature and if you're using a string inverter, you need to figure out the max open-circuit voltage (at the coldest temp) and make sure your inverter can handle it. However, don't confuse voltage with power. I have not checked what happens to output current with temp. It may be that voltage goes down in summer, but current goes up. Your inverter MPPT will find the best combination at each temp. You may be able to find the power curves by temp on the panel spec sheets.
Fourth, do you plan to clear the panels in winter? I've found that it's only worth clearing them a couple of times. And if you do, don't worry about completely clearing them: the sun will generate enough internal heat that the snow will melt and slide off. I've considered putting in a small heat tape to avoid dragging out the ladder and climbing up two stories in the snow at 0 deg. Make sure there's nothing below that will get smashed ... like plastic covers over window wells ... Oh, and as sure as it will rain after you wash your car, it will snow 8 in after you clear your panels.