Building Reserve and Using KWH

May arrives, one month into a Net Metering year. Many typical April
clouds, but did manage 151KWH the last day from the 15KW inverter
plant. Kept them flat out over 10 hours, literature says 4 sun hours are
about right for this area.

After 8 years of inverter abuse, thoughts on failures were that the most likely
failure mode might be, caps filtering the switching currents gradually lose
their ability. Then the transistor switches are caused to fail. The thought is,
a scope on the cap waveform might be able to detect the degradation before
anything blows up. Replace the critical caps (like oil changes) and avoid a
more serious failure.

There are a pair of identical spare inverters here, one shelved, the other
mounted next to those operational. Just move the DC input wires, close a
breaker, and the spare could take over. What might be done, is examine
critical power circuitry, and measure filtered noise on an 8 year inverter,
switch power over to the spare, and see how they compare. If operational
cap noise starts to creep up on annual check, time to switch to standby
and replace caps?

One thing that might be built, is the CLIPPING METER. The idea is to put
a panel out there with no load to provide an open circuit voltage reference.
A quick measurement should reveal the MPPT voltage as the inverters
are approaching (but not reaching) clipping. Will need to divide that voltage
down by the number in my strings (12), to compare to a single panel. The
difference between open circuit and inverter input voltage should be a good
indication of clipping, a fairly straight line transfer function I hope. Not sure
where that display should reside, or the type of display. Bar graphs are popular
here.

Major pushes in past years have left a lot of lower priority stuff neglected,
this may be a mostly catch up year. Planning will continue, I will need to get
some of the new design in place before the time the (experimental) wood
supported array falls down. Bruce Roe

3 months into this Net Metering year, my annual KWH reserve (building up for winter
heating) matches my best year ever, which I credit to an efficiency boost from the bigger
buried cable. I was actually at record levels, but recent weather has not favored solar.
And I have seen so many days running below clipping, that smoke drifting over from the
left coast seems to lose a lot more energy than similar appearing vapor.

New equipment to convert water heating to heat pump has not become available, that
problem does not yet have a favored solution. The CLIPPING METER remains an
on paper exercise. Efforts here are shifting to all the projects that were lower priority
than PV solar upgrades.

One thing I concluded after last years exercise. Underground cable additions will be
direct burial, conduit is too much trouble. And I always wondered, what happens if
water got into the conduit and froze?

Working on a future 2 sided version of my last array project. Bruce Roe

After a good start, it has been a lackluster solar summer here in northern IL.
The clouds are dominating, though they hardly bring us any rain. Many a day
we were reminded of the west coast forest fires by the smoke drifting through.

Despite all that, KWH reserve for winter is at least average for this date, that
high DC:AC ratio and the rest are doing their job.

Now the half century old shingle house roof is being replaced with new steel. I
read solar installations use clips that clamp onto those ridges, no holes drilled.
Is anyone able to steer me to sources of those clips? No there will not be any
panels on this house. But stuff like antennas, cable management, and safety
handles need to be on this rather slippery roof. thanks, Bruce Roe

Bruce:

Without care as to what the application looks like, I'd be skeptical of clips and in any case, I'd sure want to know about the what the wind profile and wind resulting wind loading would do to a roof even if a clip would hold.
No penetrations are nice, but wind loads are variable and non regular, and things like antennas etc, can likely present much larger resultant wind loadings to an attachment, and so to the roof than a solar array.
If the wind load transferred to the roof from the clip is large enough to cause some deflection of the steel roofing material, even a little bit, the cyclic bending could, even after a short period of time, cause metal fatigue and soon you'll be saying good bye to a no penetration roof attachment.

Just sayin'.

Look at racking manufacturers sites or Google "standing seam roof clamps".

The initial fastening of the standing seam roof may have to be modified to accommodate any future uplift loads in areas that might have additional loads. You would know what those areas are and what the loads would be based on your antenna needs.

And in your best engineering judgement what areas may that be and what types of additional loads might you have in mind ? Your advice is so general that it's useless.
At least it's probably not dangerous.

I answered Bruce's question about sourcing clamps and offered some insight which others have discovered about attaching panels to seamless roofs. I think Bruce probably has enough engineering skill and knowledge about the size and location of his antennas that he can take take that conceptual information and translate it into a plan.

Thanks for the input, the clamps found so far are in the $5 -$10 range. That is enough
to have me round up some stainless and make my own. There is quite a range of styles,
need to match mine.

Noting strain, the actual antenna IS mounted with thru holes, but there are cables (coax,
ant rotator, etc) that need to not just be left lying on the roof. They run off the roof and
down to my ground rods for lightning mitigation, before entering the house. With enough
clamps, these should not be a problem. thanks, Bruce Roe

Another clean up, need to get the backup gen set ready. 25 years old, less than
10 hours running, never at this location. My problem is the PoCo breaker is in the
house, the solar inverters in the shed, which must both be shut off. Then go to
the car repair garage and push the gen set out the motor home sized door. I have
a 6 gauge extension cord.

My old suicide cord gets replaced with this unit, which has a big switch to be closed
after every thing is shut off, cords plugged in, and the gen set started.

GenSCord.JPG

To monitor both lines and even the frequency, I can insert my dual meter unit near the gen set.
I used to have the old 3 wire stove cord stuff, but have now upgraded most everything to
the 50A 4 wire setup, separate neutral and ground. Bruce Roe

4W50ADVM2.JPG

Once again in Nov the net metering winter energy reserve has peaked near14,000KWH, and
is trending back down with short days and 20 F temps.Energy collected for a year is at the
same 30,000KWH as in the past with this solar 15KW AC array. Energy use is up a bit with
conditioning the shop building, which is only done for very hot or cold months, and the winter
use ventless clothes dryer. But PV system efficiency is up with the lower loss AC wiring.

The first 3 mini split Heat Pumps here are starting their 4th winter, the next 2 their 3rd winter,
and the last one its second. This technology teamed up with PV is quite a game changer.
Besides being far superior in every operational respect to the old fixed speed compressor
HPs, they are just much more pleasant to be around. It is cold enough I sometimes spot a
defrost cycle. I just cleaned their air filters the first time using the powerful central vacuum.
Of course they are supposed to be cleaned every year, the filters were dirty.

I just got word from NYLE that the residential hot water model e8 air-source heat pump will
become available in April. Of course they said that a year earlier. I can connect it to my
existing water heater, if it works out I would change that heater from propane to electric. Not
sure I want to use it in mid winter, since it absorbs inside heat that my other HPs bring in.
Maybe best would be the ability to change water heat sources a couple times a year.

From another source I read, some of those electronic KWH meters like the PoCo uses for
net metering, use a battery. No battery needed in my ancient but reliable spinning disc
meter. Bruce Roe

Tis the season to watch Wonderful Life, where a fantasy hero is played by a real
life hero, Major General Stewart. Even the dry days are pretty overcast and
cloudy, PV solar is way down. However PV still usually collects at least 25% of
optimum condition harvest, instead of dropping to more like 10%, thanks to the
extreme DC:AC panel ratio. Net metering accumulated reserve should carry the
property carbon free thru March, when average solar output once again usually
exceeds consumption.

One of the subjects of energy conservation here is drying clothes. No problem
in the summer, the sun does the job directly out on the line. Not so in winter, that
clothes dryer blowing all the inefficiently heated air outside was a matter of extreme
irritation until replaced by a heat pump, UNVENTED dryer in 2019. Moisture is
directed down a drain.

UVdryer.JPG

HOWEVER in practice it has been found, anything (not only clothes) can be quite
quickly dried by hanging near the output of one of my mini-split Heat Pumps. This
I believe not only saves a bit of energy, but helps boost the quite low winter indoor
humidity. Although I have gotten by with 3 HPs in the house, for more even temps
and plenty of reserve in case of -20F weather or an HP failure, the number has been
boosted to 5. They are located near the 4 corners, and one at the exposed end of the
basement. 2 are doing regular drying service, the thought is to put hardware in place
to extradite the practice for most of them.

MiSpIn8.JPG

I suspect when the weather does hit -20F, the Coefficient Of Performance of my HP
setup may drop to around 1, the same as the old resistive heating scheme used here
half a century ago. But that temp is only temporary, and as it soon rises, so does my
COP. It appear I am at about the practical cold weather limit of the current air to air
heat pump technology, probably could not carry thru the entire year at a lot higher
than my 42 deg latitude. The original 70s HP was COMPLETELY and TOTALLY
outclassed by my current units.

Still clinging to the old technology is my very reliable, easily repaired, electric stove.
At the beginning of my PV Net Metering, it actually did a lot more than heat food, and
there were a few days when every incandescent light in the house was left turned on
24/7. No need for that anymore. Most seasons my 240V KWH meters show the stove
only uses about 0.4 KWh a day, not even 1% of my energy budget. It, with some
standby drain, is an acceptable tradeoff.

240KWM2.JPG
Bruce Roe

Did you build that 240V power meter yourself?

The readouts are DROK 80-300V 100A Voltage/Current/Power Factor/Frequency/Electric Energy Monitor
I picked up for $21 from Amaz. I use a pair because sometimes the load may be unsymetric, so then one for
each 120V line. The rest is just a box for a 4 wire 50A plug feeding a same socket, the hot 120V wires passing
thru the meters current transformers. Each has a pair of voltage wires, one of each meter is connected to that
wire. The neutral volt wires are connected together, and switched to the big neutral for 2 meters. The switch
can connect that node to a 120V line instead, then one meter monitors a single 240v load and the other is off.
Bruce Roe

4W50ADVM1.JPG

I used the same Drok device and it worked well. I my case it was to monitor current and voltage while parallel top balancing a LFP pack.

Here I use my DROKs to monitor my EV circuit..........

EV Circuit Monitor-001.jpg