Sun hours

[DanS26]

Bruce....since the nameplate capacity for our two Fronius 7.5 inverters is the same it is interesting to make comparisons.

One measure I have used is Capacity Factor of the installed plant. The actual calc is explained here.....

https://en.wikipedia.org/wiki/Capacity_factor

I have calculated my plant at ~20% capacity and using data you posted on PVOutput.org your plant runs at ~22% capacity. Your greater plant capacity is most likely due to DC/AC ratio and panel orientation.

[J.P.M.]

J. P. M.,
There was quite a list of constraints trying to get this all together. First was timing. I had a decent handle on energy,
especially electrical. The long reduction of KWHwaste at the new property was concluding, and the heating levels
were established. The gas company was about to serve my country block, and I was quite familiar with their billing
escalations entirely outstripping my attempts to conserve. The solar technology was becoming competitive with
other energy, along with regulations and rebates, and I had space.

So spring 2013 I contracted to build a solar system in line with HVAC and electric consumption here. The largest
15KW option seemed about right if the house insulation was improved some. This was already larger than the base
consumer level, and as I recall approaching the largest the PoCo could accommodate with the existing 200A service.
It was also the largest I could handle using the existing buried 600 foot loop of 4 gauge AC wire. This wire was
marginally efficient with over 3% loss, and the 9V boost over the already high line voltage was on the edge. The
PoCo contract specified inverters down to the serial numbers.

Very soon discovered, was that the perpetual clouds of varying density, would severely reduce energy collection. I
often got to watch all my equipment sitting there doing very little. Increasing the system peak rating was out of the
question because of all the above constraints. And a bigger plant would have had me
watching EVEN MORE equipment doing very little.

Anyway, I did not need a bigger plant, I NEEDED to keep the existing plant busy. I just needed more panels to
increase output under clouds. Panels were only a quarter of the system cost. Pointing more panels S would exceed
the inverter rating, but phasing them E and W would solve that problem while also extending useful hours when the
sun did shine. If this had not worked, I would have needed to electronically phase in as many panels as the inverters
could handle, a dynamic and dangerous method with clouds constantly moving. That was not necessary.

The E-W array was very cheap and efficient, a mount could handle twice as many panels, and I believe the wind
loading was not increased. A south only mount would require about twice the support structure.

Later array modifications had minor energy improvements, they were mostly a traded off of convenience (snow
handling) vs first cost. The house insulation upgrade is still largely in the future, but I found other ways to compensate.
With the additional costs per KWH of these approaches, it could be concluded that this system is too expensive. My
own estimates are that ANY solar system attempting to operate under these clouds is not very much more effective,
and that that is just part of the cost of avoiding all the problems of living near the oceans. Bruce Roe

Bruce:

Thank you for the information. I would have done it differently, but you would have probably done my stuff differently as well. Either and any way, it doesn't matter much now.

Respectfully,

[bcroe]

J. P. M.,
There was quite a list of constraints trying to get this all together. First was timing. I had a decent handle on energy,
especially electrical. The long reduction of KWHwaste at the new property was concluding, and the heating levels
were established. The gas company was about to serve my country block, and I was quite familiar with their billing
escalations entirely outstripping my attempts to conserve. The solar technology was becoming competitive with
other energy, along with regulations and rebates, and I had space.

So spring 2013 I contracted to build a solar system in line with HVAC and electric consumption here. The largest
15KW option seemed about right if the house insulation was improved some. This was already larger than the base
consumer level, and as I recall approaching the largest the PoCo could accommodate with the existing 200A service.
It was also the largest I could handle using the existing buried 600 foot loop of 4 gauge AC wire. This wire was
marginally efficient with over 3% loss, and the 9V boost over the already high line voltage was on the edge. The
PoCo contract specified inverters down to the serial numbers.

Very soon discovered, was that the perpetual clouds of varying density, would severely reduce energy collection. I
often got to watch all my equipment sitting there doing very little. Increasing the system peak rating was out of the
question because of all the above constraints. And a bigger plant would have had me
watching EVEN MORE equipment doing very little.

Anyway, I did not need a bigger plant, I NEEDED to keep the existing plant busy. I just needed more panels to
increase output under clouds. Panels were only a quarter of the system cost. Pointing more panels S would exceed
the inverter rating, but phasing them E and W would solve that problem while also extending useful hours when the
sun did shine. If this had not worked, I would have needed to electronically phase in as many panels as the inverters
could handle, a dynamic and dangerous method with clouds constantly moving. That was not necessary.

The E-W array was very cheap and efficient, a mount could handle twice as many panels, and I believe the wind
loading was not increased. A south only mount would require about twice the support structure.

Later array modifications had minor energy improvements, they were mostly a traded off of convenience (snow
handling) vs first cost. The house insulation upgrade is still largely in the future, but I found other ways to compensate.
With the additional costs per KWH of these approaches, it could be concluded that this system is too expensive. My
own estimates are that ANY solar system attempting to operate under these clouds is not very much more effective,
and that that is just part of the cost of avoiding all the problems of living near the oceans. Bruce Roe

[J.P.M.]

Let me try to cover that. The inverters have an AC output rating of 15KW, at an efficiency of 96%
they can take in 15.6KW DC. My odd collection of 7 year old panels (when new) had a Standard
Test Condition rating 2.244 times that, though I have doubts some the no-names really made it.
Bruce

Thank you.
Another question/2 please: Are you inverter limited by the POCO or other reasons to a max. inverter size/capacity ? If so, what is it ?

Respectfully,

[bcroe]

Bruce:

Thank you. I found it.

A question if I might: How many STC watts did it take to produce that 157 kWh ?

Let me try to cover that. The inverters have an AC output rating of 15KW, at an efficiency of 96%
they can take in 15.6KW DC. My odd collection of 7 year old panels (when new) had a Standard
Test Condition rating 2.244 times that, though I have doubts some the no-names really made it.
Bruce

[J.P.M.]

Here is the post I was trying to use for guidance. Bruce

Bruce:

Thank you. I found it.

A question if I might: How many STC watts did it take to produce that 157 kWh ?

[bcroe]

Well Bruce, seems to me the term "sun hour" causes enough unnecessary and easily avoidable confusion already among neophytes and newcomers as evidenced, for example, by those who think because the sun is above the horizon for, say 8 hrs., that means there was 8 sun-hours that day. Or, they are told that their location gets, say, 4 sun-hours/day on average, not knowing that the common units of a sun-hour are kWh/m^2 per hour insolation with no mention of that energy being on a horizontal surface or that a tilted surface may very well see more (or less) insolation over the course of a day simply by virtue of orientation. The way I see it, it's a B.S. term that invites errors and causes needless confusion, wastes time and so can easily cause errors, plain and simple. I see it here and elsewhere all the time.

The confusion is easily overcome by simply using the term "Global Horizontal Insolation per time period" instead of "sun-hours", with the time period being anywhere from a second to a year or longer as appropriate, with abbreviations such as "GHI/day", or GHI/hr., or GHI/year, etc. Units are Wh/m^2 per time period, etc., or, for example, kWh/m^2 per day instead of "sun-hours". As a matter of reality, that usage ("GHI/time period") is pretty much common in the rational and working solar community and has been accepted for longer than I've been around alternate energy. The term "sun-hours is an anachronism made so by the confusion it causes.

Now, you come along with a different and somewhat parochial definition of sun-hours that seems to be useful to you, and I don't doubt that it is (useful for you), but is so specialized and cryptic that not only does it do nothing to clarify an already confusing and less than helpful characterization of insolation by use of the term "sun-hours", but seems pretty much useless for system analysis as well.

Here is the post I was trying to use for guidance. Bruce

[J.P.M.]

Here in So Indiana the last three years the solar insolation has been 4 to 5% below PVWatts predictions so my production has suffered. But I'd rather have the clouds and rain over drought.

Good luck with your projects.

FWIW, data of POA (irradiance) taken here at ~ 20 minutes past solar noon (the time within 30seconds of daily min. incidence angle on my array) for dates between ~ 03/20 and 06/01 for the 6 years 2015 through 2020 inclusive and only on days when the sky was cloudless and with a clearness index > 0.72 have not shown any significant variation I can detect for 2020 vs. the 5 prior years.

While the data is a snapshot, and not from the midwest, I'd suggest that because of its nature, the stuff I've collected may have some use or value or comment to your query about how the covid business has impacted irradiance values.

Aggregate mean POA (irradiance) for years 2015 through 2019 = 1011 W/m^2, std. dev. 16.0 W/m^2. Sample size for that period (2015 through 2019) for each year varied from 26 to 34. Total n for 2015 through 2019 = 149.
Data for 2020: mean POA = 1014 W/m^2, std. dev. = 15.3 W/m^2, n = 35.

Irradiance and other weather variables data taken at 1 minute intervals using a Davis Instruments Pro II Plus. Pyranometer replaced every 2 years with calibration tracing.
The pyranometer is a silicon device and beyond that, its response is not wavelength sensitive. However, the response curve is quite similar to other silicon devices such as PV panels.

GHI to POA irradiance conversion via HDKR algorithm.

As for array output for the same periods (03/20 through 06/01) and the same 6 years, 2020 actual array output has been 99.7 % of what PVWatts models. The prior 5 years for the same calendar period for each year varies from 89.0% to 109.7 of what PVWatts models. SAM shows about the same variation as do the models I wrote. I believe most of my variation is weather related with not much of the variation due to changes in the atmosphere's clearness index.

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

Bruce: Seeing as how this is your thread, I'll delete this post if you wish.

[J.P.M.]

That was taken from your post 21 April 2018, but if you changed your mind I can go back to
SUN HOURS. Bruce Roe

Maybe it's because you are using imprecise sentence construction - that is, my confusion about just what is the antecedent to your first word "That" ?

I sure as hell don't think I ever wrote the definition of "Sun Hours" the way you have defined it.

I may have written and still agree that what I believe is the vague, imprecise and confusing term "Sun Hours" has the units of kWh/(m^2*day) and that the term "Sun Hours" is often the (IMO unfortunate) term used for Global Horizontal Insolation.

I can't get at that post. If you can get to it and somehow repost it, I'll be happy and eager to discuss it.

The way the terms "Sun Hours" or GHI are defined and used in the literature and by everyone except you it seems, it's simply not possible to have GHI - that is, Global Horizontal Insolation - that high. Not only that, but the way you define and use the term, and as I pointed out, the units are nonsense.

GHI (Global Horizontal Insolation) with units of kWh/(m^2*day) is often called "Sun Hours", and I disagree with the use of that term for reasons I've described, but what you call "Sun Hours" and how you describe it is never something I wrote, nor has most anyone else who knows anything about the subject.

[bcroe]

. As long as I'm having my name taken in vain:

That was taken from your post 21 April 2018, but if you changed your mind I can go back to
SUN HOURS.

Yea the Fronius pair are holding up very well. My DC/AC exceeds 2, but I try to keep the panels
arranged so that, that much power never hits the inverters all at once. Keep in mind, the REASON
for all the panels, is to keep the inverters busy even under the (perpetual) clouds. Having done that,
I need to make the panels useful but not destructive when there are no clouds.

The gauge for clipping project is still in the background, but not forgotten. And I did blow a 40A
breaker early on, maybe it was a counterfeit. Bruce Roe

[DanS26]

My best is a GHI of 8.96 . My DC/AC ratio is 1.54.....I believe your DC/AC ratio is much higher......maybe closer to 2.0?

All I can say is that those older Fronius 7.5 transformer inverters are robust to take the kind of abuse we put them through on these sunny days. I check my 40 amp breakers with a temp tool and I'm running a high of 58* C on a 40* C rated GE breakers......hot to the touch but no trips in eight years......knock on wood.

[J.P.M.]

Sunny skies, yes have seen a few of them lately. A month before the longest day, on 31 May the 15KW system
matched my record production of 157KWH. That is a Global Horizontal Insolation/day of 10.7
(J. P. M. frowns on SUN HOURS).

As long as I'm having my name taken in vain:

I don't like term Sun Hours" because it's confusing and can easily mislead folks as has been shown here many times, as in:" The sun is above the horizon 10 hours today, so that's 10 sun hours, right ?".

Even the misleading term "Sun Hours" as it's commonly used - with units of kWh/time period of insolation incident per m^2 of horizontal surface is different than you appear to be implying its use.

I appreciate that the term "Sun Hours" has become more/less embedded in the vulgate of solar energy, but it's still a confusing term that can easily lead to confusion that doesn't need to happen.

Global Horizontal Insolation (GHI) is the term used to describe global insolation that strikes a horizontal surface over a period of time, often a 24 hour period by those trying to convey insolation availability at a location over a certain period of time.

It appears to me, and please correct me if I'm wrong, that you are dividing a daily system production (157 kWh/day) by that system's STC rating (15 STC kW) and calling that Global Horizontal Insolation/day, and/or implying/applying the term "Sun Hours" to it. Not that it matters much, but additionally that would give your definition units of kWh/(STC kW-day).

What you call that quantity as you define it is your business, but that's not what the rest of the world is talking about when they say or use the terms "Sun Hours" or kWh/(m^2-day). Your use of the term makes an already confusing and imprecise term ("Sun Hours") even more confusing to those trying to make sense of the terminology.

Respectfully,

[bcroe]

Bruce...you live in the Midwest (IL I think)...have you noticed that the skies are clearer and cleaner? My eight year old solar system is making record production many days this spring even with the degradation of older panels. This is welcomed relief here in So. IN.

Talk about "Sun hours".............

Sunny skies, yes have seen a few of them lately. A month before the longest day, on 31 May the 15KW system
matched my record production of 157KWH. That is a Global Horizontal Insolation/day of 10.47
(J. P. M. frowns on SUN HOURS).

Something I have long noticed, the array may keep the inverters in clipping for over 8 hours in March, but that
time does not increase much with the lengthening days. I credit that to the sun rising and setting more toward
the north, causing a couple effects. One is the arrays are set to near straight E or W, so the angle of incidence
at day extremes is poorer. I anticipated that, but a more northern alignment would start to severely impact
winter production, so they are aligned about midway.

The other effect is that the arrays are backed up against trees, which start to block the sun at summer day
extremes. If the entire array gets rebuild to match my latest mount design, the tree issue will be much reduced.

There is no plan to increase the number of panels. But the south facing panels will become a more minor
part of the total. Once these are moved away from trees and tilt mounted, they will be straight up for the
snow months to increase production and reduce snow removal efforts. For summer the experiment will be
to tilt them back to facing straight up. This will not be very efficient mid day, but should be enough. In that
position they will be better able to respond to sun to the north on the beginning and end of summer days.
Bruce Roe

[DanS26]

Bruce...you live in the Midwest (IL I think)...have you noticed that the skies are clearer and cleaner? My eight year old solar system is making record production many days this spring even with the degradation of older panels. This is welcomed relief here in So. IN.

Talk about "Sun hours".............

[DanS26]

Here in So Indiana the last three years the solar insolation has been 4 to 5% below PVWatts predictions so my production has suffered. But I'd rather have the clouds and rain over drought.

Good luck with your projects.