Building Reserve and Using KWH

[SunEagle]

Good question, hope I have a good answer. First, there was already a 4 gauge feed from the
shed to the house, which would be run at 75% of capacity with the inverters in the shed. If
I had put the inverters at the house near the PoCo meter, I would have needed to trench the DC
wires all the way to the house, doing this same trench in 2013 (when I had less experience). So
I would still have had to dig the trench. Later I saw that my AC transmission efficiency was poor,
and the very high line voltage (well above the legal limit) was going to cause alarms.

The DC wiring is still trenched from the array 230 feet to the shed, through a less difficult area. I
was just as happy to have total control of this 2020 wire upgrade, as opposed to letting an installer
do it. As usual, with the needed tools on hand, DIY reduces the cost to parts wholesale, I think less
than $1K. Maybe I should add a few hundred for a replacement trencher belt, this one survived the
rock but is pretty beat. The other thing is, I want the solar stuff completely separate from the house.
For example there are spare inverters in the shed. Bruce Roe

Wow. I just spent about $1600 to DIY a 100amp U/G feed to a remote panel about 160 feet from my main one. One of the big costs was the wire at $800. The next was about $500 for the Sh 80 PVC pipe and fittings, about $200 for the trencher and $100 for the panel and 100A CB. I know I saved some money with DIY but staying withing code still cost me.

[bcroe]

Why did you not mount those Fronius string inverters next or close to the service and run high voltage DC to the inverters? Seems like you could have avoided a lot of time, expense and aggravation.

Good question, hope I have a good answer. First, there was already a 4 gauge feed from the
shed to the house, which would be run at 75% of capacity with the inverters in the shed. If
I had put the inverters at the house near the PoCo meter, I would have needed to trench the DC
wires all the way to the house, doing this same trench in 2013 (when I had less experience). So
I would still have had to dig the trench. Later I saw that my AC transmission efficiency was poor,
and the very high line voltage (well above the legal limit) was going to cause alarms.

The DC wiring is still trenched from the array 230 feet to the shed, through a less difficult area. I
was just as happy to have total control of this 2020 wire upgrade, as opposed to letting an installer
do it. As usual, with the needed tools on hand, DIY reduces the cost to parts wholesale, I think less
than $1K. Maybe I should add a few hundred for a replacement trencher belt, this one survived the
rock but is pretty beat. The other thing is, I want the solar stuff completely separate from the house.
For example there are spare inverters in the shed. Bruce Roe

[DanS26]

Why did you not mount those Fronius string inverters next or close to the service and run high voltage DC to the inverters? Seems like you could have avoided a lot of time, expense and aggravation.

[bcroe]

FWIW, there is a mini-split brand by the name of "Mr Cool" that is aimed at DIYers. Unit comes precharged with special fittings so that you just plumb the lines together, then open the internal valves in the fittings and you are done. No HVAC serviceman required. Very simple to install. Limited to 25 feet between units though.

I saw that, wonder if it was primarily for DIYers, or installation ease for all? Now
wait to see if it becomes universal. I could not consider that for my units, the
paramount consideration was their ability to operate at outside temps far below
0 deg F. Bruce Roe

[solarix]

FWIW, there is a mini-split brand by the name of "Mr Cool" that is aimed at DIYers. Unit comes precharged with special fittings so that you just plumb the lines together, then open the internal valves in the fittings and you are done. No HVAC serviceman required. Very simple to install. Limited to 25 feet between units though.

[bcroe]

Meanwhile, the weather is improving, and the project to trench 4/0 aluminum wire
out to the inverters may start soon. Conduit coming out to a trench is near
complete, and some dirt has already been moved. Bruce Roe

Perhaps the second biggest disadvantage of a ground mount array (after cost) is the
distances power must be conducted to the destination. The trade off between cost
of large enough conductors and efficiency becomes significant.

At startup in 2013, the 600 foot (mostly buried) loop of 4 gauge wire connecting my shed
with my solar inverters to my electric meter, was burning up too much power. It was causing
unacceptable high voltage at my converters, and running a higher risk of failure with daily
heating up and cooling down. In 2018 the section running half the length of my house
section was replaced with 1/0 wire. Last year I started planning to bury a new feed of 4/0
aluminum wire for the rest. 2/0 copper would accomplish the same but would cost $2600
instead of aluminum for $600.

When the weather was finally favorable, I started a 235 foot trench 2 feet deep for the direct
burial 4/0, 4/0, 2/0 triplex wire. This can be difficult here because of all the rocks, here by the
Rock River. After the better part of a month I finally got the trench ready, frequent rain did not
help. Here is the biggest rock dug out, one of many removed or broken up with my hammer
drill. My rock pile grows with every project.


BigRock.JPG

7 July I got the (really big) wire hooked up to the house, and by 14 July had the shed
hooked up and running. Also in the trench is a ground wire, something the 70s installation
did not have.

Use of 200A dist boxes at both ends as sub panels really simplified the termination of the
big wires. The terminations worked out at the sub panel level for 4/0 aluminum (2/0 neutral)
looked like this going operational.


2ndBox11Jly3.JPGShedBoxAL2.JPG


The new wiring reduces AC loop resistance approximately from an original 0.15 ohms, to
0.045 ohms. At max inverter output of 15.2KW, power lost in the loop drops from about
560 W to about 170 W. While inverter output does not change, the rate of reserve registered
at the PoCo meter goes up by nearly 400W any sunny day. My estimate is its a few KWH a
day, over 1000 a year. My spinning disc reserve meter speeds up from 32 rpm to 33 rpm.
No more warm wiring at the end of a sunny day.

BiDirMtr.JPG

Here are a few pics of the operation in progress. Remaining is to get the last of the dirt
back in place. I put another (spare) internet cable near the surface of the trench, from
my tower dish. The old furnace blower made 95 F temps more tolerable. No propulsion
on this bottom end trencher, a boat winch pulls it along even better.

Trn4Jly.JPG
2ndBox7Jly3.JPG


Bruce Roe

[bcroe]

The PoCo bill came, I looked over the first 2 months of this net metering period. 2 years ago I was not
running the 5 mini split heat pumps. By subtracting reserve built up from inverter generation, I have a
pretty good idea of my KWH consumption. Going back 2 years, the consumption for April-May was
about 46.3 KWH a day. The past 2 months consumption was about 31.6 KWH a day. I am going to
credit this 32% reduction in use to the increased efficiency of the mini-split heat pumps, over the other
heaters. It would be even more, except an additional building is now being temp controlled.

Had a brief issue 29 May, both inverters went off and were having trouble getting back in service. Half
an hour later things were normal again, doing about 50% of capacity under some clouds. I guess there
must have been some kind of line fault, later I noted it was about 120/240VAC even with the inverters
pushing, think that has dropped a bit.

Meanwhile the new AC feed trenching is inching along. With all the rocks, that
term may be too optimistic. Millimeters? Bruce Roe

[bcroe]

Generally by 9am this time of year, a visit to the inverter shed reveals the twin 7.5KW
solar systems are both saturated at full power. That even if a slight bit of cloud is
present, with this arrangement. But a couple days ago one system was down some
hundreds of watts from the other. I decided to wait a day for better sun, got the same result.

OK, a quick walk around with the clamp on DC ammeter revealed, String 9 was putting
out ZERO current. I actually had been a bit suspect of somewhat reduced output from
S9 before winter, but tests had not revealed any fault. I went to the combiner and pulled
the S9 fuse, S9 was delivering zero volts.

At the array, some test points I had left in place revealed substantial S9 output available.
Apparently the string was not connected to the combiner. More checking revealed this
failed MC4 connection of the string return connection.

String9rtn2.JPG


Why is that a 3 way connection? This 2 sided array has strings facing East and strings
facing West. To save wire an E and a W string share a common return, since they could
not both deliver peak output at the same time. Even if they had, the return wire would
not be overloaded. I decided to wait for dark for a simpler and safer repair job, an
outdoor outlet on the end of this array would power a light.

So what was to be learned from the 7 years of experience with several hundred MC4s?
First my ability to compare the 2 systems at a glance had immediately demonstrated this
serious fault.

2nd the output difference between the saturated system and the faulted system showed
that the total number of panels facing E (in this case) was about right. A properly
operating system generated enough power to saturate the inverter, but not enough to
mask the loss of any section.

3rd my past warnings about MC4s were not excessive. Perhaps this one got a bit
of weather exposure, and/or perhaps the seals were not moisture tight, and the
heating/corroding daily cycle finally escalated and destroyed it. In the future all
MC4s here will receive a dab of anti-oxidant compound as insurance.

4th this will probably not be my last MC4 failure.

Meanwhile, the weather is improving, and the project to trench 4/0 aluminum wire
out to the inverters may start soon. Conduit coming out to a trench is near
complete, and some dirt has already been moved. Bruce Roe

[bcroe]

Wow, that's just awesome Bruce, Thanks for all your documentation and information.

It is not as awesome as being off grid, but I am way too lazy for that. Bruce

[Mike90250]

Wow, that's just awesome Bruce, Thanks for all your documentation and information.

[bcroe]

With net metering resetting my reserve KWH to zero at the end of March, the challenge is
to get through April generating more KWH than used, so I do not need to buy any. To add
more challenge, this is my first April with 5 heat pumps on line keeping 2 buildings comfy.

Sat and Sun each generated 149 KWH, amazing in these parts. That requires the 15 KW
plant to run flat out saturated some 9 hours and 48 minutes each day. That is only 8 KWH
short of my best June day record. Not to worry, I am not only breaking even, but my
spinning disc reserve meter shows more than 800 KWH reserve already built up. Those
heat pumps are just so efficient. Bruce Roe

[bcroe]

Another solar year, the PoCo reset date was reached 30 March. I gave them my surplus of 4,240 KWH.
That is a surplus of around 18% over usage. No propane heat was used in keeping 2 buildings in a
very comfy temp range. The winter might be summarized as having relatively cold fall and spring, but
relatively warmer winter. No resistive or propane backup heat was used, the heat pumps did it all. It is
easy to imagine a much more severe winter using up all my energy reserve and more.

The heat pumps have reduced to a NEW LOW, my labors and attention to managing energy. Things
pretty much run themselves, with some snow removal required by me, just a part of the cleanup of drives
and walkways here. Sort of like those Medallion Homes after the war, but I have even more stuff and do
not pay for energy. A few problems not originally anticipated have been solved, some using technology
not originally anticipated.

Future improvements anticipated include recovering close to 800 KWH annually lost in transmission
between buildings, by burying much larger aluminum wire. The prep work is in place at both
ends, on site are the 24 inch deep trencher, and the 300 lb of wire on this cart to avoid much manhandling.

RelCrt1Ma20.JPG

Also possibly install an electric water heater, with a propane unit remaining as power outage
backup. 5 rooms are prewired to get ceiling fans, or at least high efficiency overheat lighting.

I am waiting to see if a certain tree is dead, before making a final revision of best array placement.
Foundations can be worked on half the year, above ground stuff longer. This is not high priority,
but each section completed will give an incremental decrease in snow removal efforts and some
additional energy. In one case I just drove the snow blower by the newest array with
blown snow hitting the top, and the little snow just fell off without manual effort.

I am thinking of no longer making daily performance log entries, perhaps
just record about the time of the monthly meter reading by the PoCo.

Bruce Roe

[Ampster]

Thanks for the updates and demonstrating that we can all have different goals. The important issue is to have a well though out process to accomplish our goals.

[bcroe]

First time this winter the temp got down to minus 10F. The 4 heat pumps managed to keep
the house in the 70s without any action from me. The out building (1 big heat pump) also
managed to stay 55 degrees warmer than outside. The next big test is - 20F. Bruce Roe

[bcroe]

Overnight was a serious test of the car shop heat pump. With an output of up to 24,000 btu
it has been set for 60F in the 1080 sq ft, modestly insulated building. This had been
maintained in warmer weather. With 3F this morning the interior was 53F, so a 50F differential
may be maintainable. It may do less well if we see Neg 25F outside, the pump effective
limit, but any of these are way better than no heat. A propane furnace stands by to make
up the difference if ever needed, but has not been used this winter. Bruce Roe