Sun hours

[bcroe]

I see no mention above of how an array might be optimized for frequent
clouds, not to mention smoke in wildfire seasons. Certainly building
twice as large a system could double energy collected under any
situation. Fine for a clean sheet build, not an option here. I would need
twice as many inverters. The hundreds of feet of 8 gauge wire carrying
inverter output to the house and meter ran 75% of capacity, would have
to be replaced for a larger system. Then the 200A house box might be
at capacity (some belt and suspenders people think I am way over) so
convert to 400A box plus more hundreds of feet of wire to the pole trans,
which would also need to be changed. Besides, the net metering
contract limits the AC output to 15kW.

Instead of all that, I just increased the cheapest part of the system, the
panels. Orienting them E-W kept them from over driving the inverters,
added many hours to high level output per day, and at least doubled
output under clouds. Even the expensive panel ground mounts are
greatly reduced, since panels are on both sides. I think in this situation
this is the cheapest way to get to the desired energy collection level.

I do not understand adjusting to maximize winter production. Here we
have gone up to 29 December days in a row without seeing the sun.
In spite of that, and shorter days, this system manages about 1/3 the
summer month production. With Net Metering what matters, is the
yearly total. I just take whatever little the winter will give me.

Let's mention, the sun is weaker at the fringe hours than at noon. The
Idea here it to get into clipping at soon as there is no shading. The E-W
panels to do that leave a bit of a drop near noon, but that is compensated
for by enough S facing panels.

A tracker was mentioned, but besides all that complication, it does not
compensate for intensity variation over the day. But it is totally unable
to deal with the clouds, as mine does.

As it is, my annual production exceeds a straight S facing system in
the SW desert. Unless, it had even more over paneling than mine, with
even more panel mounts, which might blow the inverter at noon.

There is a lot more than the solar array going on at these 5 acres. Solar
has fallen into a mostly minimum maintenance mode. The spinning disc
in the basement notes which way power is flowing, roughly how much, and
the scale keeps track of my annual net metering reserve. I could fine tune
some things better, but with all the energy I need, why bother? Meanwhile
there are other science projects to play with. Bruce Roe

[J.P.M.]

I keep detailed records of my solar production both predicted by PVWatts and actual production. As I mentioned earlier I use 0.7% degradation factor for my Kyocera panels. In the 13.5 years, actual production of my plant was 309.9 mWh compared to PVWatts pridiction of 310.5 mWh. So my plant produced 99.8% of prediction so I think that was pretty good. I got the 0.7% degradation factor directly from the Kyocera engineers way back in 2011.

Now I was also interested in how much my shoulder array would decrease my plant efficiency. Efficiency being defined as Average Daily Production divided by DC plant size in kW. My plant size before erecting the shoulder array was 17.28 kW and after it was 23.16 kW. Efficiency was 3.64 before and 3.106 after. So it is very apparent that the shoulder array reduced production from having a standard south facing array. These are long term numbers so I'm confident in my statement.

Dan:
Thank You.

From what you write, it sounds like you and I kept similar types of information and records.

I kept daily and more often records of array and inverter (at 5 minute intervals ) performance and weather records (at 1 minute intervals) continuously between system startup (10/13/2013 at solar noon) and about 3 years ago when Sunpower when belly up and when I passed the 3/4 century mark, and decided to spend less time on my roof including less time in the 12"-14" or so clearance between the bottom of my array and the roof deck measuring panel temps. with an IR thermometer which, on a hot day seemed like being stuck in tight toaster inclined at 19.75 degrees to the horizontal.
I've written epistles on those efforts in these archives over the years with all the gory and probably boring details, but I, like you probably, had a lot of fun and learned a lot doing it all.

One item I looked into was my array's average annual performance degradation. The Sunpower spec sheet for my panels said to expect up to a 5 % burn in loss the 1st year and 0.4%/yr. performance loss of STC performance thereafter. By my measurements and calculations, my array lost 2.9% of STC power the 1st year (burn in) and, as best as I can measure and calc, about 0.4%/yr. thereafter, +/- about 0.02% or so
FWIW, if it doesn't rain my array's performance seems to roll off at a rate of very approximately 1% of clean performance/week somewhat linearly and, if not hosed down with tap water about every 4 weeks, seems to stop experiencing further performance loss at somewhere between 12 and 14 weeks or so incurring about a 12% performance loss stop fouling. I'm still trying to figure that one out. Interesting subject but not very amenable to analysis.

One thing you wrote above confused me - the 3.64 and 3.106 numbers. if you produced 309.9 mWh over 13.5 years, not accounting for the output of the shoulder array, that averages out to 309.9mWh/13.5 yrs = 22.96 mWh/yr., or (22.96mWh/yr.)/(17.28 STC kW) = (1,329 kWh/yr.)/(installed STC kW), again, not accounting for the shoulder array, which seems to make rough sense.
But, I don't understand what the 3.64 and 3.106 numbers represent.
Can you enlighten my ignorance ?

[DanS26]

I keep detailed records of my solar production both predicted by PVWatts and actual production. As I mentioned earlier I use 0.7% degradation factor for my Kyocera panels. In the 13.5 years, actual production of my plant was 309.9 mWh compared to PVWatts pridiction of 310.5 mWh. So my plant produced 99.8% of prediction so I think that was pretty good. I got the 0.7% degradation factor directly from the Kyocera engineers way back in 2011.

Now I was also interested in how much my shoulder array would decrease my plant efficiency. Efficiency being defined as Average Daily Production divided by DC plant size in kW. My plant size before erecting the shoulder array was 17.28 kW and after it was 23.16 kW. Efficiency was 3.64 before and 3.106 after. So it is very apparent that the shoulder array reduced production from having a standard south facing array. These are long term numbers so I'm confident in my statement.

[J.P.M.]

Hi All,

I'm not scared of inverters clipping either Bruce, I'm sure JPM must realize if you want max production in the winter months you put as many panels on the inverter as you can or are allowed too. As always thanks for the update Bruce.

Some may have noticed that we have a link to the solarreviews.com (our site sponsors) calculator again, we had it on a few years ago but they took it off when google started to not like forums as a source of info, I think they are just trying an experiment to see if that's still the case. If things haver changed, I hope they have as we will get some IT department time to spend on SPT to fix up or improve a few things, cheers

Pete:

Respectfully, I don't know any such thing.
But I think I do know or would at least suggest that maximum production, as a concept must be defined by the user/owner/operator as (duty required).
For example, one definition might be to have a string inverter operating at or close to its maximum rating for the maximum number of daylight hours over a certain period.
Or, have a string inverter operate as close to its rated output at certain times such as at times of high T.O.U. rates.

Or, as seems to be the case for Bruce and Dan, If one wants to prioritize max. production out of a string inverter as a design goal over the course of a winter day for some reason(s), orienting the array for max. clear sky winter production would be a good start (which Bruce has not done), and then sizing the inverters such as to cause inverter clipping under an hourly average winter irradiance level until the inverter clips for as long as (or when) you want to ensure it will clip while in the end meeting some goals, whatever they may me.
NOMB or concern, but I've never seen the logic behind such actions as being the most financially sound way of proceeding.

All that said, I'm aware of, or at least I can conjure up lots of applications that require more generation at certain times than others and that such situations may and probably will require array orientations and other design decisions and actions that will result in less than maximum available panel output and/or increased per kWh production costs. But, like putting the cart before the horse, sizing the inverters before the arrays without careful analysis of alternatives seems backwards to me.

I'm also aware that some applications are inverter size limited by POCO or AHJ requirements.
In such cases, the COST of complying with those requirements can sometimes be minimized optimizing array orientation(s) to the greatest extent possible and (unfortunately) also perhaps biting the bullet and realizing that to get what you want under the imposed constraints may cost more than you're willing to spend. See the "I want what I want" logic below.

I say (write) that because I'm also aware of something called solar process economics where one (usually) common goal is achieving all the other project goals in the most cost-effective manner as possible as defined by the person or organization paying the bills. I have yet to come across anyone or any organization that does not want the most bang for their buck to achieve the stated and defined project goals or requirements whatever they may be including whatever the imposed constraints on the project may be (while still keeping in mind that "costs and logic be damned, I want what I want" can also be a project goal.
I've seen that thinking 1X/awhile and usually manage to avoid being involved in such projects as a matter of policy. Somebody always gets it in the shorts on such projects.

Anyway, if I want maximum production and maximum cost effectiveness from a system (and not just the maximum duty cycle out of a string inverter) during winter months, or perhaps over the course of a defined "winter", I'd first define my production requirements and schedule and other goals by hour, time of day, day, week, month or season as required and then size and orientate the array(s) to meet that duty cycle using a design model or models, and then size the inverter(s) with an output (AC) rating to meet about 90% or so of the STC rating of the array(s). Iterate the design a few times to convergence and get some preliminary cost estimates. I suppose the inverters can always be undersized but after sizing the arrays to meet the project goals I don't see the logic in that.

Pete, I'm not afraid of under-sizing inverters, arrays or anything else to meet project goals provided safety concerns are the first priority.
But if good and cost effective design are the goals and I want maximum production out of an array in the winter, or any other time, I'm sure I realize that over-paneling (or maybe better said/written as inverter under-sizing) is not the best use of materials, capital or design capabilities as a first choice and probably not the most cost-effective way to meet a production goal.
IMO only, that's not necessarily good or even safe design.
It's all about good and thoughtful design, defining project goals while keeping within imposed constraints.

Do you want system production at a certain level, or a string inverter that operates at or close to its maximum capacity?
Seems to me one answer might be the one that gets as close to the desired effect in the safest way possible for the least long-term life cycle cost is the way to at least start.
But that's the way I was taught and learned engineering.

As usual, take what you want of the above. Scrap the rest.

[solar pete]

Mike: Bruce is just way over paneled for the inverters he has. He believes it's cost effective to have inverters spend a lot of time in clipping. He and I beat that to death for several years.
He may have the only array(s) that are visible from low earth orbit.

Hi All,

I'm not scared of inverters clipping either Bruce, I'm sure JPM must realize if you want max production in the winter months you put as many panels on the inverter as you can or are allowed too. As always thanks for the update Bruce.

Some may have noticed that we have a link to the solarreviews.com (our site sponsors) calculator again, we had it on a few years ago but they took it off when google started to not like forums as a source of info, I think they are just trying an experiment to see if that's still the case. If things haver changed, I hope they have as we will get some IT department time to spend on SPT to fix up or improve a few things, cheers

[bcroe]

An Analema should be a fun project, about all I have is a sun dial. It gives sun time,
not daylight saving time. I did try to get components for a ground level sun dial
some 20 ft across, but failed. You would stand on the marked spot to cast the
time shadow.

Much agree, one view of the E-W array, is that doubled panels make much better
use of every other part of the system, from the panel supports, and everything else
to the connection to the AC net meter. Even more so for us under frequent clouds.

With a pretty leaky 70s house + water to heat, there is not much left over from
29,000 annual kWh production. Bruce Roe

[DanS26]

When I erected my shoulder array (ie east/west orientation..see profile pic) my objective was not to optimize production since I produce around twice what I consume. My goal was to optimize my plant in relation to my 200 amp electrical service. I was maxed out and did not want to upgrade to 300 or 400 amp service due to expense and hassle that change would entail.

So I opted to maximize production in morning and afternoon to more efficiently use existing plant. But that being said I realize that just adding a standard south facing array would have harvested more power. I think now i just liked the esthetics of the shoulder array and sort of ignored the power dynamics.

This summer I am going to add another piece of art to this project. I'm going to build an Analema with my three grandsons. The gnomon will be 12 feet tall and aligned with the north south axis line of the shoulder array. Solar noon and clock noon on the first day of each month will be identified and staked. Also the equinoxes and solstices will be noted. The Analema shadow points should be around 20 feet in length. It should be a learning experience for everyone.

[J.P.M.]

I think you're metering is broken. 15KW every hour for 10 hours. Unless you have trackers on all the panels.

Mike: Bruce is just way over paneled for the inverters he has. He believes it's cost effective to have inverters spend a lot of time in clipping. He and I beat that to death for several years.
He may have the only array(s) that are visible from low earth orbit.

[bcroe]

I actually have a pair of 7.5 kW systems, like DanS26. I doubt they are both
broken, they tend to agree very closely. You may have seen my past graph
showing the inverters in clipping for over 8 straight hours, my record is
157 kWh in a day. After 12 years, I conclude clipping does not shorten the
inverter life. They are capable of 277V operation, so my 240Vs gives them
margin against voltage. Bruce Roe

[DanS26]

I got 121.6 kwh on Monday from the same size 15 kW inverter plant. A few clouds around but my DC to AC ratio is only 1.54. Lots of clipping mid day.

Over 13.5 years of production now stands at 309.9 mWh with zero downtime for both panels and inverters. Those two Fronius transformer based 7.5's just keep chucking along....knock on wood. The Kyocera 235 and 245 panels look like brand new but they are degrading ~0.7% per year as expected.

[Mike 134]

Memorial Day was sunny and long, how about 155 kWh produced by my
15kW inverter plant in a day? Bruce Roe

I think you're metering is broken. 15KW every hour for 10 hours. Unless you have trackers on all the panels.

[bcroe]

Memorial Day was sunny and long, how about 155 kWh produced by my
15kW inverter plant in a day? Bruce Roe

[organic farmer]

When I was making the cables to fit between the batteries of my bank. I considered the wattage rating of the cables. Some of them needed to be bent into weird shapes. But it was all done during summer weather. and those cables will never be bent to a different shape ever again. What are you doing with wire that requires it to be bendy flexible in negative temps?

[jflorey2]

A lot of wire insulation loses too much of its flexibility at -20F to be reliable. Finding an insulation with the right combination of sunlight resistance and flexibility could be interesting

I got a spool of 10ga wire labeled "locomotive cable" years back that had insulation that was supposedly flexible down to very low temperatures, sunlight and oil resistant and good to 600 volts. It's hard to find though.

[bcroe]

So it was 17 F below zero this morning, a tour revealed the 6 heat pumps
were keeping up and performing as intended in 2 buildings. I believe
heating capacity at best is about 9 tons, that is degraded quite a bit at
this temp. The "just right sizing" people would say I have way too much,
but I say this allows a couple things. First I never need to switch to
auxiliary heating, although it still exists here. Second no single failure
(like a furnace blower motor) can cause a desperate situation, spare
capacity will carry me through till I get around to repairs in summer.
Cost was quite minimal when bought on the internet and DIY installed.

Well into the 11th winter things are quite stable, system repairs amount
to 3 burned out electrical connections and one panel hit by a tree. And
I did have to scrape sap off some panels till that tree was removed. So
it may be the coldest day of the year, but the spinning disc shows with
sun the cold panels are collecting more energy than I am using. I see
about 4200 kWh energy still in reserve, but days will soon be here when
I can make as much as I uses again.

One thing the extra energy has made possible, is running the big
electronic air filter nearly a third of every hour. Looking at the particles
(or rather the lack of them) in a beam of sunlight shows a drastic
reduction in solid stuff floating int the air. Of course the particle charging
method used works no matter how small the particle, not just the ones
bigger than a mechanical screen. And maintenance ia way less as well.
Wish I had done this much earlier in life.

I am realizing the E-W array design has more advantages than I first
planned. It takes an absolutely minimum of snow cleaning effort, often
none while I am clearing the S facing panels. It basically operates all
year with no need to worry about changing tilt. I can collect a better
ratio of energy to unshaded space. And the cost of material for my
6061 aluminum ground mounts has increased so much (way more
than the panels mounted), it makes economic sense to mount twice
as many panels, facing opposite directions. The original objectives
were to maximize energy collected with a 15KW peak limit, and double
output under clouds.
Bruce Roe