Sun hours

[bcroe]

Bruce, I know you have 2.0 DC/AC ratio. How do you keep from over
current situations? Do your Fronius inverters just ignore over current?

Or did you just increase string size and up voltage to keep current within specs?

If so those transformer machines are much more robust than I thought.

Remember the effort to keep a flat output curve over a sunny day. Panels facing away from
the sun are only delivering like 10% output. So essentially they are derated to 10% capacity
as far as the inverter is concerned, my EFFECTIVE instantaneous DC/AC ratio is not based
on full panel rating.

With 720 cells in a string, they run 360VDC in summer, 420 in winter, pretty much centered in
the inverter range. An inverter just draws less current to keep power limited, letting panel voltage
rise. My earlier thoughts were to create a readout indicating what the effective number is at any
time, based probably on panel temp and operating voltage. This might be used for fine tuning
the tilt of array sections (arranged by string). Since I tend towards clipping most of the day, I
can't just note the power level. Other crises around here in some of my other hobbies have
prevented any actual development. After last nights zoning meeting, came home and worked
on rebuilding brakes, the antenna preamp was taken out by lightning, etc, etc.

I did think about momentarily shutting down part of the array so that peak power could be read
directly at a level below clipping. If each orientation had 2 strings, perhaps shut down one. A
way to do this gracefully might be short one panel, then another, perhaps 3 total to take a string
out. I hope not to need to resort to this method.

So although my Fronius inverters may in fact be running within spec, I am still beating them
pretty hard with 8 straight hours of clipping on many a day. They have managed 5 years of this,
but just in case I have spares. Bruce Roe

[DanS26]

Bruce, I know you have 2.0 DC/AC ratio. How do you keep from over current situations? Do your Fronius inverters just ignore over current?

Or did you just increase string size and up voltage to keep current within specs?

If so those transformer machines are much more robust than I thought.

[DanS26]

Certainly a 2 sided array will be the cheapest. But I don't see a way to make seasonable tilt changes,
and it requires twice as large an unshadowed area. To minimize snow clearing efforts, and trying to
avoid a lot more tree cutting, I am moving toward single orientation arrays facing varied directions
across a common clearing, and easy tilt changes. Bruce Roe

My original design included the ability to make seasonable tilt changes......but I decided against it......fixed tilt is less parts, less cost and less labor.

In my life I need a lot less reminders to do things every so often.


ps....Fronius published that technical paper in 2012 and revised it in Aug 2013.

[bcroe]

Here is a Fronius technical paper that discusses concepts involved. Although
not exact match to what I am doing, it does discuss the shoulder array concept.

Looks like Fronius has figured out what I did in 2013. They say the E-W system is actually cheaper, I
figured it might be 5% more expensive per KWH. I don't see an attempt to get a flat as possible curve
over the day, or discussion of reduction in the resulting peak power (compared to the simple total of
the panel ratings) versus the inverter over paneling rating.

What they don't mention, is the benefits under clouds. That was the starting point here, more panels
under clouds make more power. Having concluded that, the issue then is what about when there are
minimal clouds? That brought the E-W orientation, to avoid simply throwing away the available energy
on clipping under minimal clouding. I think the argument for E-W gets stronger with more clouds or
overcast, but it is hard to put numbers on this.

Certainly a 2 sided array will be the cheapest. But I don't see a way to make seasonable tilt changes,
and it requires twice as large an unshadowed area. To minimize snow clearing efforts, and trying to
avoid a lot more tree cutting, I am moving toward single orientation arrays facing varied directions
across a common clearing, and easy tilt changes. Bruce Roe

[DanS26]

Here is a Fronius technical paper that discusses concepts involved. Although not exact match to what I am doing, it does discuss the shoulder array concept.

SE_TA_Efficient_East_West_orientated_PV_systems_with_one_MPP_Tracker_EN (2).pdf

[DanS26]

Dan: Why are you mounting panels in an E-W orientation ? I missed class the day you explained it.

Thanx.

J.P.M.

Well I never really explained it but Bruce has a few times. The concept is to expand the productive capacity of the DC side of the system without having to expand the AC side of things. Since I already clip a few days of the year at mid-day it is better to increase production in the mornings and evenings without aggravating the mid-day clipping too much by using an East/West oriented array.

It just so happens that my Fronius string inverters will accept a fourth string without exceeding the max current limitation. The Fronius units are sturdy with an active cooling system.

Finally I'm on a net billing system which allows me to sell all my excess at wholesale rates, currently around $0.075 per kWh. So by doing the work myself and getting an especially good deal on Trina 245's my ROI is relatively short.

[J.P.M.]

Hung the under structure today and the array is starting to take shape......

IMG-2585.JPGIMG-2586.JPGIMG-2587.JPGIMG-2588.JPG

Dan: Why are you mounting panels in an E-W orientation ? I missed class the day you explained it.

Thanx.

J.P.M.

[DanS26]

Hung the under structure today and the array is starting to take shape......

IMG-2585.JPGIMG-2586.JPGIMG-2587.JPGIMG-2588.JPG

[DanS26]

Here's a link to a GSES Technical Paper indicating a DC/AC oversizing ratio of 150% will maximize benefits. Hope they're right.

https://www.gses.com.au/wp-content/u...Oversizing.pdf

If you look closely at the middle pic....the close up of the 3" top cap.... you will see an object in the background below. Kudos to anyone who can identify the device. It is a hydraulic ram jet used to pump water without electricity. The power of water running down hill in a larger pipe was used to pump water uphill in a smaller pipe. Very popular in the farming community before electrification.

The device belonged to my spouse's grandfather. It pumped water from a spring a hundred yards from the house to a holding tank in the attic of their home. They had running water when all their neighbors were still using outhouses and hand powered sink pumps.

[DanS26]

Here are pics of the under-structure of the shoulder array......

IMG-2574 (1).JPGIMG-2575.JPGIMG-2576.JPG

I built this under-structure in my workshop this winter. First off that is 2" x 2" x 3/16" aluminum angle 6061-T6. All bolts, taps and washers are stainless steel.

If you look at the middle pic you will see an IronRidge 3" Top Cap.......that was the basis of the design idea. Maybe IronRidge would be interested in my re-purposing their Top Caps?

It will all come clear to everyone once I mount the structure. The bracing is amazingly simple, which I will show later.

[DanS26]

We get tornadoes, but residential stuff isn't intended to withstand a direct hit. If that happened, the
panels (a quarter of the investment) might be damaged, but likely ground supports and underground
would still be intact. In a video of a seriously damaged area, I noted a car lift identical to mine (bolted
to concrete) standing intact.

Lets see the hardware to mount a 2 sided array. Likely the wind effects are about the same as single.
Bruce Roe

Bruce I think you will appreciate my design for a two sided array on a single post. Detail pics coming.......

[bcroe]

We get tornadoes, but residential stuff isn't intended to withstand a direct hit. If that happened, the
panels (a quarter of the investment) might be damaged, but likely ground supports and underground
would still be intact. In a video of a seriously damaged area, I noted a car lift identical to mine (bolted
to concrete) standing intact.

Lets see the hardware to mount a 2 sided array. Likely the wind effects are about the same as single.
Bruce Roe

[DanS26]

All five posts are now set and waiting for concrete to cure....used 25 80lb bags of Sackrete...no water mixing required....just poured the dry mix in the hole then added 3 1/2 quarts of water on top of each bag.....then tamp...then repeat. Very quick and easy.

Shoulder Array #2.JPG

Posts are 3" Schedule 40 galvanized pipe set 48" deep in 12" holes with rebar. Weight capacity should be no problem. Only serious threat to the array complex would be a tornado.

[TAZ427]

Setting posts.....my method. Five to six bags of Sackrete per hole dry then just add water.

Rebar inserted through pipe about 20" from bottom of hole which is 48" deep.

Post Set.JPG

Will use a laser level to align the remaining four posts.

My back aches just thinking about that. I think I would have ordered 3 yards of concrete and been done with it (yeah it probably only needs 2.5 yards based on the 5-6 backs of sackrete per hole and looks like 20 pylons from the picture.) About the same cost.

[J.P.M.]

Setting posts.....my method. Five to six bags of Sackrete per hole dry then just add water.

Rebar inserted through pipe about 20" from bottom of hole which is 48" deep.

Post Set.JPG

Will use a laser level to align the remaining four posts.

Dan:

Any attention to external loadings with respect to design ?

Don't forget to dome the concrete to help avoid ponding and freeze resulting freeze/spalling damage.