Ground mount vs Roof mount?

[vnatale]

From the Dummies index, see p. 264 of the 2d. ed., 1st para., 1st word.

Also, see any solar panel data sheet for details and parameters of std. test conditions. I specify STC as identifying the panel power rating as different from other ways of rating a panel which do little more than muddy the water and confuse people and are therefore B.S. The STC method keeps everyone on the same page and is the standard by which all panels are rated and their output measured.

From my version in the book .. nothing in the index:

standalone photovoltaic system, 249
stand-off mount photovoltaic system, 255
static lighting, 129, 354
stationary water, 233
stationary windows, 39
stock portfolio, 10
storm windows, 40, 57
string DC-to-AC inverter, 257–258

First sentence of first paragraph on page 264 is: "The most important consideration is the wire size, and you need to consult
tables in the NEC (National Electrical Code) to determine which sizes work optimally for your application."

I did twice search the PDF for both STC and Standard Test Conditions and came up with nothing for either.

But most importantly ... I do understand your point. Basically want to be to do the proverbial "apples to apples comparison" and not be comparing apples to oranges.

[Mike 134]

From here: What does BOS stand for? — Page #4 (abbreviations.com)

It seems like it could mean close to a 100 different things! Good thing I asked.

I thought it meant Balance of System
Search (portalced.com)

[vnatale]

The microwave oven was one exercise in cutting down my
electrical vampire loads, which were some 100 devices and
300W, or 2,630 KWh per year. A KILL-A WATT meter will easily
make measurements of plug in stuff. I did design a small circuit
added to the microwave, others might go the replacement Energy
Star route. Things like the furnace, central vac, seurity devices,
doorbell, chargers, wireless phone, computer devices, smoke
detectors, door openers, TV remote monitor and distribution
system, and more have small transformers running 24/7, burning
several watts each. I trimed around 80% of that over time.

The 100A upgrade makes your solar possible. 200A would be
more comfortable, but would would involve the feed wiring and
possibly the PoCo pole transformer, besides the box.

That appears to be a very energy efficient house. Say you use
200 gallons of oil a year, 200 gallons X 0.85 eff X 40 KWh per
gallon = 6800 KWh. If you change to electric resistance heat
with 100% efficiency, you would need that production plus
your electric energy use, from your solar. Heat pumps with
efficiency from 100 to 300 % efficiency will reduce your need.
A mini split heat pump for your 75 F room will be more efficient
than a simple space heater. This if your net metering contract
allows energy collected in the summer to be used one for one
in the winter.

Doing all of what I discussed would be very difficult on a roof
mount. Double sided is for an east-west arrangement. Can work
on a roof, but optimum elevation is likely a lot steeper than your
roof.

The reasons for a 2 sided array here are to get near twice as many
productive hours out if a solar day, and to double the output under
clouds. It sacrifices individual panel efficiency, while maximizing
use of your mounts, electrical equipment, and net metering contract.
It works here by wiring an east facing string in parallel with a west
facing string (individual fuses). Since they do not produce peak
power at the same time, the inverter sees them as just a single string.

Here is a pic of my first 2 sided array, and a graph of more optimized
dual string output, 8 hours of peak production. Bruce Roe

3Direction.JPGNScurJn17.jpg

Again. A lot of different points to respond to here.

1) You are motivating me to finally do something with the microwave. First put a meter on it for several days just to see what its light is drawing. Then make myself remember to turn the strip off after each use.

2) I am looking at a Kill-A-Watt meter on my table that I've had for a number of years. I had bought another one but loaned it to a neighbor and never saw it again. I have bought three of these:

Poniie PN2000 Plug-in Kilowatt Electricity Usage Monitor Electrical Power Consumption Watt Meter Tester w/Extension Cord - - Amazon.com

They came highly recommended on Amazon and were cheaper than Kill-A-Watt. Seems to do just as good a job. Plus it comes with a short cord to plug the device you are measuring into and then the cord into the meter. Makes it easier to plug in some devices rather than going straight into the meter.

3) I have a lot of things that run all the time in. But nowhere close to the devices that you have that have transformers that are constantly running.

Several years ago, though, I did put all my many, many pieces of living room equipment, e.g., TV, amplifiers, that were on "instant on" on a strip that gets shut off when they are not in use. I was shocked how much electricity that saved. Maybe a 20% reduction in total electricity used?

4) All six vendors who quoted me last year gave me a passing grade for the 100 amp service.

5) My house was built somewhere between 1945 and 1955. Several months after I bought it in 1982 I had it insulated - blown in insulation in the walls and the attic. I recently had the inches in the attic raised from 9 to 15.

6) Three weeks ago I had a 6,000 BTU Mini Split installed in each of the two bedrooms and an 18,000 BTU Mini Split installed in the living room to cover the rest of the house. Each of are on their own separate heat pump.

One of the reason that the Mini Split appealed to me was how little electricity they used in comparison to space heaters. I just looked at the old style space heater I have in my bathroom. Top setting 1,500 watts! I had assumed Mini-splits would use even more electricity so was quite surprised when I saw a 6,000 BTU one was in about the 400 watt area?

And, yes, the net metering contract allows excess summer buildup to be used during the following winter.

7) Now that you have shown a picture I am remembering to ask .... how does one put a picture in a post? Once I am able to do that you will see what limited space I do have on the south side of my house. Would not be permitted on the west side of my house since that is the front of my house. The east side would not work because my house would shade it once it reaches a certain time each day.

You have WAY more available space on your property than do I. My total property is 0.38 acres, I think.

[bcroe]

How much more complicated / expensive is adding variable tilt to a ground mount?

Tracking is quite a project. My E-W arrangement accomplishes about
the same without the complications. And E-W performs far better under
clouds, tracking can do nothing. Bruce Roe

[vnatale]

Here is a pic of my first 2 sided array, and a graph of more optimized
dual string output, 8 hours of peak production. Bruce Roe

3Direction.JPGNScurJn17.jpg

I finally determined how to insert an image into a post. Here is my property:

Capture2.JPG

The outlined blue area is roughly my 0.38 acres. My street is basically south on top and north on the right. My roofs are east on the left side and west on the north side. The outlined black area is the south side and where the ground mount can go. It cannot extend to the west to be in front of my house. It has to be 10 feet away from the property line to the south. It's about 35 feet from my house to the property line, leaving 25 feet for a ground mount. I have circled in red a tree across the street from me on a neighbor's property. It's an extremely fast growing tree. Starting the summer of 2021 late in the day and late in the summer it casts a shadow nearly completely covering all the area I have on my south side. Is that a concern for a south facing ground mount?

[vnatale]

Tracking is quite a project. My E-W arrangement accomplishes about
the same without the complications. And E-W performs far better under
clouds, tracking can do nothing. Bruce Roe

Now that I have just provided a picture of my property I think you will agree that on my property your fine east / west solution would not work on the limited space that i have available?

[vnatale]

I have been asked if I know what my annual electricity load is. The following is what I am using to help me determine that.

First is a table I've maintained since 1998. It shows the average kWh's used each month for each year. To the far right is a column for the average used for that year and the final column is total used for the year.

electricity.JPG

I don't have any of major changes in my house documented as to when they occurred so I'm making guesses when they did occur as reflected in the above.

From 1998 to 2008 my average used per day was between 19.0 and 26.1 Then it took a permanent downturn to 16.7 in 2009 and then even further down to 13.7 in 2010. The two major changes I made was putting all my living room TV & audio equipment on an electrical switch that got shut off when they were not being used. Was quite surprised that that resulted in such a drop in my electric usage.

The next was instead of having two computers always on every second of the day ... I would turn them off at the end of the day and when I'd leave my house to go to my office. In other words they were now only on when I was home and awake.

I'm seeing a large permanent increase starting in May 2020. This must have been when the fan died in my electric hot water heater heat pump. Once the fan stopped working the hot water heater was working at its most energy inefficient mode - strictly electric resistance.

Stating in June 2021 my electric usage dropped dramatically from the prior year and stayed that way. I attributed this to finally replacing my 30 year old refrigerator. Obviously something i should have done years ago.

Starting in July 2022 and continuing through August 2022 my electric usage was up considerably. This was after I'd started using an old dehumidifier in my basement. I finally put a meter on it and I was shocked to see that while it was only running from about 7 AM to 11 PM it was still using as much electricity - 8 kWh during that time - as the whole rest of my house was using - the same 8 kWh.

A few days later in late August I replaced it with a brand new Energy Star dehumidifier, which uses only about 25% to 30% as the older unit was using and with the new one running 24 hours a day. Mid-September I had the fan replaced in my hot water heater so it was again working as a heat pump. That led to it using 25% to 30% of the electricity it had been using prior to being repaired.

You can see the drastic reductions in kWh per day for October to December compared to July and August.

If I had stopped here it would have been easy to determine what my annual load would be.

But then three weeks ago I had three mini-splits each with their own heat pumps installed.

It's only been since last Tuesday that I've been able to get good readings on each circuit to see what each of those mini-splits are using. Here is what I am seeing so far:

G.JPG

My overall daily usage is about 24 kWh per day. The three mini-splits are using about 16 kWh per day of that total.

However, it's been an incredibly mild January winter so far. The last week's 8 AM temperatures in my garage have been around 37 degrees. Far higher than the zero degrees that we have had for the same time period in other years.

Additionally, I've kept the temperature of the 18,000 BTU one in the living room at 61 degrees and the 6,000 BTU one in the other bedroom also at 61 degrees. In this bedroom I've had it anywhere between 65 and 72 degrees.

Once the weather gets colder those mini-splits are going to use a lot more electricity. How much? I do not know. Also, if I increase the temperature settings on any of them it's also going to increase their electric consumption.

Therefore in attempting to answer that question -- do you know your annual load -- these mini-splits have injected a major, major unknown into the equation. I've been asking the solar companies how late in the process I can give them my final size of my system. The more time I have to monitor the electricity usage of this mini-splits the better position I will be in to most accurately size what solar installation I need.

[J.P.M.]

Now that I have just provided a picture of my property I think you will agree that on my property your fine east / west solution would not work on the limited space that i have available?

Bruce has the only residential PV array that can be seen from outer space.

[vnatale]

From the Dummies index, see p. 264 of the 2d. ed., 1st para., 1st word.

Also, see any solar panel data sheet for details and parameters of std. test conditions. I specify STC as identifying the panel power rating as different from other ways of rating a panel which do little more than muddy the water and confuse people and are therefore B.S. The STC method keeps everyone on the same page and is the standard by which all panels are rated and their output measured.

BREAKING NEWS!

I have finally made it to the PVWatts Calculator web site.

Under the first item it clearly states: "The DC system size is the DC (direct current) power rating of the photovoltaic array in kilowatts (kW) at standard test conditions (STC)."

!!!

Thanks for your patience regarding this.

It's definitely a concept i have fully learned and will not forget.

[J.P.M.]

Vinny:

You mentioned oil for heating until you got the mini-splits. Do I have that right or did you use natural gas for space heating ?
Whatever the fuel is (was), do you have any historical information on how much of that prior fuel has been used for heating ?
Reason for the questions: With usage for the prior fuel and some assumptions about burner efficiencies, duct losses, etc., and the mini-splits' C.O.P's, it will be possible to get a 1st approx. of how much electricity those mini-splits will use.

[vnatale]

Bruce has the only residential PV array that can be seen from outer space.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[J.P.M.]

BREAKING NEWS!

I have finally made it to the PVWatts Calculator web site.

Under the first item it clearly states: "The DC system size is the DC (direct current) power rating of the photovoltaic array in kilowatts (kW) at standard test conditions (STC)."

!!!

Thanks for your patience regarding this.

It's definitely a concept i have fully learned and will not forget.

No thanks needed. Just keep learning.
and know that just like the rated horsepower on an internal combustion engine ("ICE") powered vehicle will rarely be achieved , STC conditions and panel output will rarely be achieved with a PV panel under working/in situ conditions.

Also, a respectful suggestion on the PVWatts model:
For shade free applications many users have found that using a system loss factor of 10 % rather than the 14% the model defaults to often results in a long term average model output that comes closer to actual model output.
Play with the model after reading all the help screens a couple of times. Do a few runs to get comfortable with the model and come back here with any questions/comments your education creates. It's user friendly as long as you know the model's limitations.
Lots of regulars here are knowledgeable users and will probably be more than willing to answer questions.
Just keep in mind that opinions vary and there is not common agreement on all points.

Good Luck.

[vnatale]

Vinny:

You mentioned oil for heating until you got the mini-splits. Do I have that right or did you use natural gas for space heating ?
Whatever the fuel is (was), do you have any historical information on how much of that prior fuel has been used for heating ?
Reason for the questions: With usage for the prior fuel and some assumptions about burner efficiencies, duct losses, etc., and the mini-splits' C.O.P's, it will be possible to get a 1st approx. of how much electricity those mini-splits will use.

Oil.

All used for heating.

In both 2017 and 2010 the furnace had 85% efficiency.

How much prior fuel used for heating?

Capture.JPG

On 11/23/14 started with a full tank. Subsequently purchased a total of 1,071 gallons (including the diesel). That is an average yearly usage of 134 gallons. But following is my usual caveat explanations.

Right after getting that 1/9/20 delivery (a few days after) I was told by oil people that my oil tank needed to be replaced so I should set my thermostat high to use as much oil as possible to reduce the cost of paying them to take it away as hazardous waste. I did not realize at the time they were giving me bad advice on two counts. One: That oil could have been transferred to a new tank. Two: I did not need a new tank. But I did not know that so I had my thermostat all the time at 72 from then on. However, once I got to the next heating season starting around November 2020 I wanted to resolve my whole heating situation.

It took me quite awhile to get to everyone I wanted to interview. Meanwhile I started the season low in the tank and did not want to put any more in it because I was still operating under the false assumption I'd have to pay to have oil in the tank removed. So I stretched that remaining oil by constantly lowering my thermostat until, at the end, I had it down to 42.

After I got my new oil company in March 2021 who corrected all the bad information the prior oil people had given me I left my thermostat at 60.

I came into this year with about 1/4 tank of oil left at the start of the heating season. By mid-November I'd secured someone to install the mini-splits in (late) December. Again I did not want to put any more oil in the tank because I would have had to buy 125 gallons minimum and once I got the mini-splits hopefully that unused oil would never get used. And, worst yet, because my tank is probably as old as the house - probably 70 to 80 years old ... it will probably start leaking at some point and I would have to pay to have the oil removed.

That led me to putting the house thermostat at 52 starting mid-November. For the heating season I only used about 3/32's of a tank of oil (about 25 gallons) as I still have about 5/32's of a tank left (about 40 gallons).

For this bedroom I had been using electric space heaters for supplemental heating in this room to get it to 75 degrees. Since the mini-split has been installed in this bedroom none of those space heaters have been used.

Now my past behavior has been to keep the house thermostat at 60 degrees and I'm effectively still doing that by having both the other bedroom and the living room thermostat at their lowest setting - 61 degrees. But, who knows, some day I may want them all at a higher setting. Plus I have never had air conditioning in this house. I do not intend to use these mini-splits for air conditioning. It's possible I decide that I do want to use them to do that. I do know that it takes ways less electricity for them to air condition than to heat because the temperature differential to cool is far smaller than the temperature differential to heat.

[vnatale]

No thanks needed. Just keep learning.
and know that just like the rated horsepower on an internal combustion engine ("ICE") powered vehicle will rarely be achieved , STC conditions and panel output will rarely be achieved with a PV panel under working/in situ conditions.

Also, a respectful suggestion on the PVWatts model:
For shade free applications many users have found that using a system loss factor of 10 % rather than the 14% the model defaults to often results in a long term average model output that comes closer to actual model output.
Play with the model after reading all the help screens a couple of times. Do a few runs to get comfortable with the model and come back here with any questions/comments your education creates. It's user friendly as long as you know the model's limitations.
Lots of regulars here are knowledgeable users and will probably be more than willing to answer questions.
Just keep in mind that opinions vary and there is not common agreement on all points.

Good Luck.

Several of you have already been quite helpful and you may have noticed that I'm not shy regarding asking questions or requesting information.

I did make a quick look at all the help screens at PVWatts and had already decided to read them slowly two times. That is my usual style for learning.

[littleharbor2]

Another unknown acronym for the uninitiated! "BoS"?

BoS stands for Balance of SYSTEM cost,.ie; all wiring, breakers, nuts and bolts etc.