A number of Peoplenomics subscribers (and a few others) have made a personal investment in auxiliary solar systems for their home. Although, it makes the power industry a bit crazy: Home solar’s contribution to the grid is an algorithmic demand management nightmare.
Take our place, for example: With an existing 3.5 kw of power from the existing arrays we can either be a) selling 3 kw into the grid, consuming 10-12 kw (and more, depending on projects). And somehow, the grid operators have to make all this “play nicely.” It’s not a trivial load management problem.
Our next 2kw of panels – which are being installed as time permits – are used panels that nameplate says should do 265 watts each. However, being used (on another site for five-years) they are likely down to 230 watts each. Solar degrades over its lifespan.
One thing of interest I’ve found – having torn apart and rebuilt an almost 20-year old panel last week – is that the decrease in panel output is not attributable to only the cells.
The (at least equal) degradation is from the odd behavior of copper wire. Over time, the junction between bare copper corrodes. And, in the case of this old 30-watt panel, what I found was that it wasn’t just the copper wiring that age hadn’t been kind to: It was the panel junction wiring box.
Turns out the wiring where the panels came in – to tie into the longer wires to the array – had evolved enough corrosion in 20-years to reduce panel output effectively to zero,
What I suspect is that some of the “recycled panels” hit the market because it’s faster to just slap in new (tax-advantaged, purchased by the container lot-size, underwritten by taxpayers) than it is to replace all the wiring from the panel leads on out to the charge controller. At least rewiring to ensure good dielectric grease, clean connectors, and so forth.
The panels going in now will end up being on their own charging system. You see, the existing panels are already split (1.5 kw on one array and 1.7 kw on the other) using a pair of Outback Power Systems Flex-60 charge controllers. Amazon has ’em for $380 a pop (OutBack Power FM60-150VDC FLEXMax 60 Charge Controller).
Were I ordering today, I would have gone for the higher-capacity Flex-80 controllers.
As wired presently, the array runs at panel voltage (37-40 V in bright sunlight) but I may series-parallel them to run at 74-80V from the arrays to the power center, effectively halving my wire-loss for the in-ground cable run.
Occult solar info:
The wire losses of any circuit (DC) are largely determined by the cross-sectional area of the wire. S0 for a wire than will handle 10 amps of current, that would be only 50 Watts of work being done at USB charger voltages. Or, if you’re plugged into 220V, the same wire will handle 2,200 Watts of work. (The relationship is very close to linear, which is why a 48V wiring system is favored for whole-home off-grid systems. The savings on wire-size can be significant!
The run from the new panels is a pair of #4 for each five panels. With a run of 125-feet, the wire loss is acceptable. Normally, you’d use a 3% wire loss table, but remember, values are usual 2X understated: One for the incoming energy and the other for the return…
The primary system has been (with the invert issues from lightning strikes, as to be expected) a real joy and very stable. We got 11-years of good service from our rack of Interstate deep-cycle batteries, too.
The system – as it sat prior to the new panels – was well-balanced. There was plenty of charging, good supply of solar, and the grid-tie chores were handled by a pair of Outback 24-volt GT-FX (grid-tie) inverters.
The design choice came down to: Do I put in a single Flex 80 controller (series paralleling the panels to run 80 Volts on the wiring), or do I put in two smaller (and much cheaper) 40 Amp MPPT (maximum power-point tracking) “Chineseum” units?
I opted for the latter. Wiring this way, one entire charging system will be completely independent of the balance of system.
New panels will be set to drive the battery bank to 28-volts in winter and 27-volts in summer.
Since the grid-connected portion is set to begin selling into the grid at 26-volts, the system should in winter, sell a kilowatt (or two) when our palatial office is on (electric heating and cooling). Of course, that may not “make it off the property” depending on whether the big a/c unit for the house (5-tons worth) is on at the time, or not.
Our summer power bills for 2,400 square feet run about $190-$230, but that’s for almost 3,000 SF under air since the shop went from evaporative cooling to hard a/c this past year.
The design objective is not to make money on any of this. It’s to reduce operating costs to zero. We don’t want to “draw attention to ourselves” by being a “big source” should we ever get into “sketchy grid” conditions.
Workflow of Installation
Honestly, a little sore this morning. Got the rest of the T-posts pounded in with the help of this lash-up:
This will punch in holes 24-inches deep. With a minute, or two, of filing on the bit’s face, it went through some rotting roots OK.
The design of the panel racks couldn’t be simpler: T-post and 5/8-inch rebar. Here’s an array that has been producing power for 18-years:
I’ve highlighted some of the welding points – but as you can see, not much to it.
Those white hunks of PVC are used 6-months out of the year when the Sun is high in the sky. With the top attachment point of the panels hinged, we have both summer setting *(between equinoxes) and winter (when the PVC pipe is out, like now).
With the T-posts laid out (two lines and on 5-foot centers for 40-feet (to joints of pipe worth) the next step was putting in the panel angles:
Panel angles aren’t critical. If you know the Sun drops 23.5-degrees below the equator in the winter, and that far about in the summer, there’s no really hard math to it. An 18″ digital protractor and clamp plus a piece of edge trim helps.
Palestine, Texas is about 31°45?29?N 95°38?19?W, which I round off to simple 32-degrees North out of sheer laziness. Best winter angle (solstice) for summer is 32 (minus) 23.5 – so 8.5 degrees (*which is measured and the PVC pipe cut for). Best winter angle is 32 (plus) 23.5 or 55.5-degrees.
Except! Those are your extremes.
So the total angular spread is (23.5 X 2) 47-degrees. If I wasn’t including two set points for summer and winter, we’d just use our latitude (32-degrees) and go drink beer.
However, since we DO have two set points, we have two angles – so 1/3rd of 47 is the magic design number: So like 24-degrees for the summer part and 40-degrees for the winter. EXCEPT there is more solar path loss (due to depth of atmosphere at lower winter angles, so I use 44-degrees. I also use 18 in the summer setting because, well, that’s when loads are highest so we don’t use a simple 1/3rd.
Soon as the chow’s done, back to work on where I stopped last night:
You can see the cut-offs from Mr. Grinder going through. You can cut down about 2 T-posts for each 1/16th inch cut-off wheel on a 4 1/2 inch grinder. Which is why we buy ’em in 50-packs!
Today, I’ll be lugging the welder up, burnishing up the rebar for clean welds, and then getting the rails and cross-pieces installed.
The Work Crew Mindset
When you have a complex project like this, one of the hints to “tapping in to the right personal energy” is to imagine yourself as being on a work crew that specializes in doing just one particular thing. Then dress appropriately. That includes THE RIGHT HAT.
Today, the welding skull cap goes on. And once that’s down, I will put on a laborer’s hat to trench in the wire that needs to be buried.
A whole article on the importance around here of proper [ritual] work headgear is found in “Coping: Hats as a “Secret Energy Source.”
We’ll see how it goes, but with the right hat comes the right attitude.
When my “welder persona” came by yesterday, first thing he demanded was welders chalk be on hand for marking up the metal. Where to cut, where to burnish, and so forth.
Yeah…there really is such a thing. If you work on metal, it’s a “gotta have it.” It’s not “chalk:” as revealed in the formal part name: Welding Soapstone Refills, Brazing, Machining, Marking Metal Surfaces, 127 (5.0”) x 12.7 (1/2”) x 4.8 mm (3/16”), 36 Pieces, Tech Team $10-bucks on the Zon.
Unless you do metal fab for a living, this may be a lifetime supply – has been for me, lol.
3D Printing Adventures
Learning continues on this front this week, as well.
Here, one of the parts for the time machine (being printed in color-change PLA filament) teaches the lesson that if you want 6 mm lasers to fit in the holes, make them 6.4 mm on the TinkerCAD drawing. The width of a print line needs to be added.
Ah! And over here?
Those connected round tubes teach us that when you put a fresh bed cover on the 2D printer, wipe it down with denatured alcohol. Otherwise, the residual parting compound makes the bed so slippery that when the print gets too tall, it will slide out from under the print head, resulting in a ball of PLA and a holder for zip ties that didn’t make it to planned height.
Well, off to another day of working it… The reason you want to work hard when you’re young is so you can hire all this shit out when you’re 71.
Well, almost 72…one month to that marker.
What Does This Mean?
Quake south of the Bay Area overnight (4.2) has our passing attention.
But seriously, it was where, USGS?
“11.5 km (7.1 mi) NNE of Prunedale, California”
AYFKM Prunedale? ISYN, lol…
Write when you make something,