Anti-solar AHJ's

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
We have one that claims to grant rebates, but to qualify the array has to have an azimuth between 180 and 270 degrees and tilt between 45 and 80 degrees. That's not a typo and they have not confused tilt with elevation. That means that virtually no residences will qualify for rooftop systems; in ten years of designing solar in Texas I have seen roof tilts of 45 degrees only a handful of times and more than 45 degrees exactly never.

These are the same guys that require all PV systems to be interconnected on the line side of the customer's meter. Yes, the meter, not the service disco.
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
Isn't 30 degrees the ideal tilt for a fixed system? If I remember correctly, that's what we were setting them at in North Carolina when I did 1.35 Mwatts worth.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Isn't 30 degrees the ideal tilt for a fixed system? If I remember correctly, that's what we were setting them at in North Carolina when I did 1.35 Mwatts worth.

Yes, but that's not what they are going for. They did some research and found that PV arrays at between 180 and 270 degrees azimuth and between 45 and 80 degrees tilt will produce the most energy between 3PM and 7PM when their demand is the highest.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Yes, but that's not what they are going for. They did some research and found that PV arrays at between 180 and 270 degrees azimuth and between 45 and 80 degrees tilt will produce the most energy between 3PM and 7PM when their demand is the highest.

But that doesn't make any sense. One gets the feeling they've defined tilt for the vertical instead of the horizontal, opposite from everyone else.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Isn't 30 degrees the ideal tilt for a fixed system? If I remember correctly, that's what we were setting them at in North Carolina when I did 1.35 Mwatts worth.

Ideal tilt is basically latitude, perhaps adjusted for weather, but also on whether you want to adjust for economic considerations. For example if you have a rate schedule that pays back higher rates in summer, you'd want a shallower tilt. Or it might be more cost effective to squeeze more panels in the space you have at less than optimum tilt so they don't shade each other. Or if you are off grid you might want to maximize winter production. It all depends.
 
Ideal tilt is basically latitude, perhaps adjusted for weather, but also on whether you want to adjust for economic considerations. For example if you have a rate schedule that pays back higher rates in summer, you'd want a shallower tilt. Or it might be more cost effective to squeeze more panels in the space you have at less than optimum tilt so they don't shade each other. Or if you are off grid you might want to maximize winter production. It all depends.

Actually for the nitpickers among us, ideal theoretical year round tilt is about 6-7 degrees less than latitude for most of the 48.

https://www.solarpaneltilt.com/
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
But that doesn't make any sense. One gets the feeling they've defined tilt for the vertical instead of the horizontal, opposite from everyone else.
That's what I thought initially as well, but we've exchanged several emails with their engineer, and he has stated unequivocally that 45 to 80 degrees off the horizontal is what they mean. The center of their "ideal" time window is 5PM in the summer months, not noon. He sent us demand curves and graphs from NREL to illustrate it. 45 to 80 degrees tilt and 180 to 270 degrees azimuth is what they mean.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
That's what I thought initially as well, but we've exchanged several emails with their engineer, and he has stated unequivocally that 45 to 80 degrees off the horizontal is what they mean. The center of their "ideal" time window is 5PM in the summer months, not noon. He sent us demand curves and graphs from NREL to illustrate it. 45 to 80 degrees tilt and 180 to 270 degrees azimuth is what they mean.

Yeah, but while 80 tilt at 270az might be a reasonable range for that, 80deg at 180az is totally not. So it still makes no sense at all. I think your subject line is more insightful. ;)
 

BillK-AZ

Senior Member
Location
Mesa Arizona
Some calculations of PV system performance

Some calculations of PV system performance

Seems that the real world situation is far from the understanding of the AHJ. A PV system installed at a tilt of 25°, facing South, will provide more output, about 20% more, at 5pm in the summer than if the tilt was 45°. The higher the tilt the larger the difference. Results of calculations assuming Dallas solar data are attached.
 

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Seems that the real world situation is far from the understanding of the AHJ. A PV system installed at a tilt of 25°, facing South, will provide more output, about 20% more, at 5pm in the summer than if the tilt was 45°. The higher the tilt the larger the difference. Results of calculations assuming Dallas solar data are attached.
I know that, you know that, and even they know that. Please note that this azimuth and tilt requirement is for approval of their rebate, not for building PV in general; they are only rebating systems which they believe as much as possible match their demand curve in June - September from 3PM to 7PM. Customers are welcome to build systems with other orientations if they forego the rebate, which they will all do since the losses in production they would incur in building PV that fits the rebate requirements would be more than the rebate itself.

They sent me a graphic from NREL that shows what they are driving at.
 

Zee

Senior Member
Location
CA
Seems that the real world situation is far from the understanding of the AHJ. A PV system installed at a tilt of 25°, facing South, will provide more output, about 20% more, at 5pm in the summer than if the tilt was 45°. The higher the tilt the larger the difference. Results of calculations assuming Dallas solar data are attached.

How bout if its 45 at 270 (and not at 180)? I assume that will produce more than 25 at 180, at the time they want it, which is centered around 5 pm.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
If they set up the criteria that any single system has to match their curve, then possibly the 180 - 80 system does so ... while producing such negligible power as to be of no use meeting the demand. Again, I refer back to the subject line. They have set a goal that is either deliberately or incompetently anti-solar. The goal is definitely not to encourage solar or actually spend the rebate money.
 

beanland

Senior Member
Location
Vancouver, WA
AHJ acting as Utility Manager?

AHJ acting as Utility Manager?

I am a little confused. You mention AHJ. That generally refers to the electrical inspector who enforces the NEC and building codes for the governmental jurisdiction. The utility may have concerns about the time of day when the generation is optimal based on their daily and annual load profiles, but that is not the jurisdiction of the building code enforcement agency. The utility can use rates, rules and regulations as permitted to give price signals to PV installers but the utility generally cannot set a standard for tilt and orientation. This sounds like the code inspector is enforcing a standard that is not in a adopted code. Am I missing something?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I am a little confused. You mention AHJ. That generally refers to the electrical inspector who enforces the NEC and building codes for the governmental jurisdiction. The utility may have concerns about the time of day when the generation is optimal based on their daily and annual load profiles, but that is not the jurisdiction of the building code enforcement agency. The utility can use rates, rules and regulations as permitted to give price signals to PV installers but the utility generally cannot set a standard for tilt and orientation. This sounds like the code inspector is enforcing a standard that is not in a adopted code. Am I missing something?

Ggunn works in a lot of places in Texas where the AHJ and utility are effectively one and the same. Local public power entities that follow same boundaries as code enforcement. In this case I believe he's talking about a policy that would be the utility's if they were separate.
That said, sometimes a entity offering rebates is ultimately the same as the AHJ, i.e. sometimes it comes from a city or county even when the utility is totally different.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Ggunn works in a lot of places in Texas where the AHJ and utility are effectively one and the same. Local public power entities that follow same boundaries as code enforcement. In this case I believe he's talking about a policy that would be the utility's if they were separate.
That said, sometimes a entity offering rebates is ultimately the same as the AHJ, i.e. sometimes it comes from a city or county even when the utility is totally different.

It's simpler that that. The AHJ that is offering the rebate (in this case it's the utility) can set whatever rules they want to regulate that expenditure.
 

Zee

Senior Member
Location
CA
I guess if the requirements are in fact so strict that extremely few systems qualify, then they will relax them. (assuming they have to spend the rebate cash)

They might, over time, offer a proportionally lower rebate based on orientations and tilts that differ from their ideal.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I guess if the requirements are in fact so strict that extremely few systems qualify, then they will relax them. (assuming they have to spend the rebate cash)

They might, over time, offer a proportionally lower rebate based on orientations and tilts that differ from their ideal.

Actually, I'm pretty sure they are perfectly happy not granting any rebates at all.
 
Actually, I'm pretty sure they are perfectly happy not granting any rebates at all.

Lmaooo so true. So here in MA I have run into the scenario with municipalities who run their own power plants. Most of MA is serviced by either National Grid or Eversource, large utility corporations who service many towns across the Commonwealth and also in NH, RI, etc. For customers of these large utilities, the state rebate program is universal and anyone can apply. There are not strict restrictions on azimuth and tilt, and most often the rebate is on a per kWh basis. So it is most beneficial for the south facing, 42 degree tilted arrays who will produce the most amount of energy annually.

However the customers who live in and have a town or city owned municiple electric service, the municipality has it's own incentive program (if any at all). It sounds like this is what is going on for you. For smaller electric providers, the actual time of the day that your solar is feeding into the grid has a much larger impact on the demand curves that the utility has to deal with.

Thus, they will offer a larger incentive, or possible only incentivize, installations which are going to be lowering their demand when it is needed most. Usually this is early AM, but most often late afternoon / early evening when customers return from work and start firing up AC in summer, lights in winter, heat pump(s), etc.

For the utility, they factor in not only lowering instantaneous demand, but the entire demand curve. What is happening in California and states with massive penetration of solar PV is that most of this energy is being produced from 10 AM - 3 PM, when electrical demand is actually lowest (except nighttime). Once customers return home and start consuming more electricity, the East facing solar has pretty much shut off and the south facing solar is starting to drop in production. What the utility faces is a MASSIVE ramp in the electrical demand, and has to fire up expensive peaker plants (Natural Gas usually), to be able to match the ramp required from the electrical demand going up and the solar production dropping for the day.

This phenomenon is why municipalities want to incentivize West facing solar arrays at a higher tilt, as people have alluded to, as it helps the most with the utilities demand response. Late afternoon solar production is the most valuable, and the smaller the utility provider, the larger impact your residential installation will have on their demand curve.

For more reference, google search "Solar Duck Curve, Nessie Curve, utility Demand Response"

Finally, this is also why large scale battery storage of solar and wind energy is going to be EXTREMELY valuable in the coming years as more and more solar and wind gets deployed. We can somewhat predict when the sun will shine and what orientations are most valuable, but no one can predict the wind at a given time. Having methods to store and instantaneously release this energy will allow us to get to 100% renewable energy in our lifetime, despite what the narrow minded Republicans and Drumps have to say about clean coal and fossil fuel energy.

To the future!
 
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