Sun hours

[bcroe]

Finished the first full month (May) with the new array, which doubles the panels facing the rising sun to around
80% of inverter capacity. Doing the same for the setting sun remains for another year, that is now the weakest
performing section.

After years of wondering how many weeks before the PoCo bill would come, or come at all, the new smart meter
seems to have solved the problem. There is a remote reading a couple days before the end of the month, and
the bill (with the latest figures) arrives in the mail about the 1st. This will help keeping track of energy reserve as
winter ends, though I now have my own private bidirectional meter as well.

Any good mid day sun keeps these inverters at capacity, the difficulty being operation near day extremes.
Comparison to earlier years suggests the earlier increased production is an increase of about 8% overall for May.
This is accomplished by longer running at max, the peak power does not change. There is also a contribution from
bumping up the reduced production under clouds, don't have a way to break these apart.

Anyway, something it couldn't do before, every sunny day produced a number of KWH more than 10 times the
inverter KW capacity (MAOF). So, 154 KWH from 15KW of inverters. Cloudy days do relatively better too. Soon,
I will try for another plot of power vs sun time with that nice flat top, no bell curves here. Then, estimate end of day
power as the mirror image of rising sun, to approximate what rebuilding the west facing section might do.
Bruce Roe

[bcroe]

Its still April, under a clear sky today, the solar brought in a new record of 151KWH. The peak power is
always the 15KW inverter rating, but the new panels facing the rising sun extended the day and brought in
more energy. And of course performance under clouds is respectable, its difficult to apply hard numbers.
A MAOF of 10.07, equivalent of the inverters running at max for more than 10 hours.

Only a couple weeks, but the latest arrangement seems to verify what the test panels indicated. If this
continues, next year will find panels currently facing south, being moved to face the setting sun, mirroring
the new array. The remaining S panels may get taken down, then set up again with new mounts on the old
(rather irregular) foundation to take on the characteristics of the newest array.

All this while I was fixing another leaking pipe. And the PoCo emailed me an ad suggesting that if I had
some space on my roof, money could be saved by installing solar. Wonder what the latest is? Bruce Roe

[DanS26]

Bruce...I'm with J.P.M. on this....don't complicate the definition of standard terms.

Next on your cleanup list should be the "Efficiency" calculation on the PVOutput site.

[J.P.M.]

I for one welcome our new MAOF overlord cheers

As you wish. Not that anyone need care, but I regard Bruce as a valued resource around here. Hell (and with apologies for talking about you in the 3d person Bruce), he's probably the only one more eccentric about this stuff than I am, but in different ways.

Now help find a practical and useful application for the concept and the term MAOF.

Since the units of the parameter MAOF seem to be kWh/day - or just as well any time period - per kW of inverter size, regardless its seems, of array size, then perhaps some use could be made of the ratio MAOF/(array output per day/installed S.T.C. kW of panels). That would give array S.T.C. size /inverter capacity , so the ratio might be considered dimensionless, and that ratio may be useful as some parameter to use as some possible tool to help choosing and sizing single or multiple inverters for an installation.

Just trying to improve communication and maybe reduce confusion a bit along the way.

J.P.M.

[solar pete]

I for one welcome our new MAOF overlord cheers

[bcroe]

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.

Hey, I already said I would try not to use bad language any more. Bruce

[J.P.M.]

Ha Ha, do not want to interfere with established convention, with the slang term. INETDOG suggested
Multiple Array Orientation Factor (MAOF), maybe it is time to start using it. Not really up to me to name it.

Did an MAOF of 9.93 Friday, hoping during longer days to see 10. Bruce Roe

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.

[bcroe]

How would you define a solar array that" tracks" the sun from morning to night? That may fall into the
"10 hour sun day" category.

From what I have seen, a tracking array will come in second. First, it uses the same panels all day for
collection. There will still be a bell curve of less extreme variation.

You need MORE panels near sunrise or sunset, to keep inverters at the same level. The curves
measured here of actual sun take that into consideration, and the panels are set up accordingly to
try and approximate a flat energy curve.

And of course, a tracking array cannot do anything about clouds. Adding panels for cloudy operation
was the starting point of this project, getting the energy broadened when there are no clouds (almost
never here) is the second step.

We should hear what some trackers have actually done here at 42 deg Latitude. But I don't see them
as practical for homeowners. Perhaps the MAOF idea could be applied to them. Bruce Roe

[SunEagle]

Ha Ha, do not want to interfere with established convention, with the slang term. INETDOG suggested
Multiple Array Orientation Factor (MAOF), maybe it is time to start using it. Not really up to me to name it.

Did an MAOF of 9.93 Friday, hoping during longer days to see 10. Bruce Roe

How would you define a solar array that" tracks" the sun from morning to night? That may fall into the "10 hour sun day" category.

[bcroe]

Since the more common and for several reasons unfortunate definition, IMO anyway, of 1 "sun-hour" = 1kWh/m^ per day of irradiance, usually but not always referenced to the horizontal plane, I'm just trying to avoid more confusion in my own mind over the term.

Looks like your definition has units of kWh of system production/day per kW if inverter capacity. Following the S.I. naming convention for many other derived units, maybe we should name such a unit a "Roe" to perhaps avoid more confusion over the term "sun-hours".

Respectfully,

Ha Ha, do not want to interfere with established convention, with the slang term. INETDOG suggested
Multiple Array Orientation Factor (MAOF), maybe it is time to start using it. Not really up to me to name it.

Did an MAOF of 9.93 Friday, hoping during longer days to see 10. Bruce Roe

[J.P.M.]

This not officially recognized term, here is the AC production for the day, divided by the inverter capacity.
So 150KWH divided by 15KW plant would be 10 hours. Only 9.93 yesterday. Bruce Roe

Since the more common and for several reasons unfortunate definition, IMO anyway, of 1 "sun-hour" = 1kWh/m^ per day of irradiance, usually but not always referenced to the horizontal plane, I'm just trying to avoid more confusion in my own mind over the term.

Looks like your definition has units of kWh of system production/day per kW if inverter capacity. Following the S.I. naming convention for many other derived units, maybe we should name such a unit a "Roe" to perhaps avoid more confusion over the term "sun-hours".

Respectfully,

[bcroe]

This not officially recognized term, here is the AC production for the day, divided by the inverter capacity.
So 150KWH divided by 15KW plant would be 10 hours. Only 9.93 yesterday. Bruce Roe

[J.P.M.]

145KWH yesterday was pretty good. But today did 149KWH, a match for my best day ever, and not in
June this time. With 150, looks like that elusive 10 sun hour day might happen this summer. Bruce Roe

How do you define a 10 hour sun day ?

[bcroe]

145KWH yesterday was pretty good. But today did 149KWH, a match for my best day ever, and not in
June this time. With 150, looks like that elusive 10 sun hour day might happen this summer. Bruce Roe

[bcroe]

Can the new array tilt to the west for afternoon summer production?

No, that would be efficient in an open field. But here it would just be looking straight at the west neighbors
trees. So the plan is, I have a big clearing, and all panels are at an edge looking across the clearing. To
cover the other direction (setting sun), panels need to be on the opposite side of the clearing facing west.
Give me another year. This is not actually wasteful (by my definition), because I needed this many panels
to keep production up under various levels of clouds, my starting point.

But it was a pretty sunny day, collected 145 KWH. The only time I made those numbers before, was
around June. But this is April, the new array is doing what those test panel curves said, getting power
going pretty early in the morning. If this continues to check out, I expect to move some of the south
facing panels around to face west. Not planning to add any more. Bruce Roe
PVm17Jn16.jpg