Ground mount vs Roof mount?

[vnatale]

PV equipment for consumers tends toward the most elementary.
Not ground mount, not snow repelant, not variable tilt. Bruce Roe

I assume that you have variable tilt? If so, how often do you adjust it? Done on some sort of seasonal basis?

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

[vnatale]

1.) Thank you. As a preliminary estimate, as a long-term annual average, every unshaded, installed STC kW ground mount of PV can be expected to generate something like 1,300 kWh/yr. of electricity. That's with a 45 degree tilt and a 180 degree array azimuth.
2.) So, once you get a design load in kWh/yr. for the project (not before) divide that design load by 1,300 kWh/yr. for a working estimate of system size in STC kW.
If cost effectiveness is one of the project goals, you'll need a reasonable estimate of the load the system is expected to meet to achieve that goal or balance it with other project/system goals.

In all the reading I've done regarding solar (since about 2016) I think this is the first time I have encountered the term "STC kW". I'm assuming that if I thought I'd needed an output of about 6,500 kWh per year then I divide that by 1,300 then I need a 5 kW system?

You came up with the 1,300 by using my zip code to determine the amount of sun my house would roughly be getting? With the array directly facing south and no shading?

[davidcheok]

I disagree there is an "overwhelming" advantage. Ground will often produce more than roof-mount, but BoS costs are much higher. And I've seen a few examples where PVWatts estimates were lower for ground mount than roof. Roofs, being higher up, get less indirect shading.

Ground mounts will be easier to service/maintain/clean, they can use sun tracking, upgrading will be easier and cheaper and a lot more scaleable assuming you have the space. Yes, if the ground is surrounding by tall buildings/trees/mountains then of course that scenario it wont be suitable but that also applies to roof mounts.

[nerdralph]

Ground always first with overwhelming advantage except for loss of ground space.

I disagree there is an "overwhelming" advantage. Ground will often produce more than roof-mount, but BoS costs are much higher. And I've seen a few examples where PVWatts estimates were lower for ground mount than roof. Roofs, being higher up, get less indirect shading.

[bcroe]

There is plenty of green stuff growing under the array here mounted
high above ground snow (42 inches). But that may not be true if I
get around to building a 2 sided version. Bruce Roe

[DanS26]

Bruce, my wife is a master gardener and grows many shade loving plants under my ground mounts. She has around 10 different types of ferns, some very rare, that love the space. #53

[J.P.M.]

Sorry. That was not the book I'd mentioned above. This is it:

DIY SOLAR POWER FOR BEGINNERS: Your Step-By-Step Guide To Design, Install, And Maintain Your Solar Energy System In Complete Autonomy To Drastically Reduce Your Electricity Bills. Kindle Edition



Amazon.com: DIY SOLAR POWER FOR BEGINNERS: Your Step-By-Step Guide To Design, Install, And Maintain Your Solar Energy System In Complete Autonomy To Drastically Reduce Your Electricity Bills. eBook : Dellinger , Sean : Books

Probably helpful for DIY, but being off grid is a lot of ongoing work and maintenance that's usually more effort than a part time job. It's a different ballgame than grid tied.

[J.P.M.]

I did get the book. Am on page 85. Have not yet found anything that I'd considered dated. Which underscores you saying that its information is timeless. Thanks for persisting in recommending this fine resource.

You're welcome. Keep learing.Your biggest enemy will be your lack of education.

[vnatale]

3.) The Dummies book is a bit dated but most of the information is timeless. It is a free, online PDF and a decent primer of residential PV.
The basics of PV have not changed much.

I did get the book. Am on page 85. Have not yet found anything that I'd considered dated. Which underscores you saying that its information is timeless. Thanks for persisting in recommending this fine resource.

[bcroe]

You are going down the same energy saving trail as me. 100%
solar electric was achieved 9 years ago. Getting numbers on everything
reveals a lot. A meter connected for a month revealed that the 4
decade old electric range was using far less than 1% of my energy.
The microwave was an efficient cooker, but its clock was a vampire
load using more energy in a year than the short time cooking. The
cure was a circuit to electrically disconnect it from the outlet 7 min
after it finished cooking and the door was closed. It stayed at zero
energy until the next time the door was opened.

Finding and replacing older inefficient appliances really helps.
Chasing down vampire loads on some 60 circuits here turned up
half a hundred things that could be improved.

Your 100A service and transformer size are a limit, but possible
with the size equipment you are looking at. My situation is similar,
but the numbers are about 2 X yours at this originally all electric
home built in the 70s.

Sizing my max Solar output at 15KW, was based primarily on the
heat load over a year. I knew how many gallons of propane were
consumed in a year, and a gallon has the energy of 27KWh. But
electric resistance heat is near 100% efficient, and the furnace was
less than that, so I needed to generate about 25KWh from solar
to replace each gallon of propane. PV estimates indicated I would
be a bit short, but the plan was to buy the energy shortfall while
continuing to try and improve the efficiency of the house. My chart
says about 40 KWh have the energy of a gallon of oil, do not know
the efficiency of your furnace. Have you done this calculation?

The efficiency gain was done here several different ways. One was
to use (6) heat pumps to boost heating efficiency to anything from
100% to 400%, depending on how cold it was. There are a few
really cold days when the heat pumps drop to 100%, but overall
there was a big surplus. It was sufficient that I was then able to
maintain a shop well above freezing all year, and a quite comfy
working 65F most months.

The other improvement was to boost solar energy collected. Peak
power was limited to the same above, and also by my net metering
contract and inverter size. What was not limited was how many
hours I could collect solar energy. Normally peak power only lasted
several hours around solar noon. But I replaced a string facing south,
with a pair of strings facing east and west. First the east panels
deliver energy from the morning sun, then the west panels deliver
afternoon energy. With an elevation of near 57 degrees, the power
(limited by the same string inverter) is about the same but for twice
as long.

This scheme gives a big increase in energy collected without an
increase in peak power. It is also quite effecive in increasing output
under clouds of varied density. It reduces the effectivness of the
cheap PV panels, but greatly increases the utilization of all the rest
of the system. Even the ground mounts, which may cost more than
their panels, can be made double sided for considerable economy.

I am finding, my mini heat pumps are excellant for drying clothes
hung in front of them, receivng a lot of use in the winter when outdoor
lines are unusble due to the weather. So much so, I am considering a
couple of short lines to be easily hung near each mini. I do have an
unvented heat pump clothes dryer, but it tends to run too cool for the
job. Its virtue is not sending a lot of heat outside, the heat pump seems
redundant in that all heat remains in the house and and largely in the
machine. For summer of course clothes dry outside. Bruce Roe

[bcroe]

PV equipment for consumers tends toward the most elementary.
Not ground mount, not snow repelant, not variable tilt. Bruce Roe

[vnatale]

Ground always first with overwhelming advantage except for loss of ground space.

Thank you for that. The last solar vendor I talked to today was trying to dissuade me from that direction.

[davidcheok]

Ground always first with overwhelming advantage except for loss of ground space.

[vnatale]

2) Got the book. The other title was mentioned above: "Making the Switch With All Energy Solar"

Sorry. That was not the book I'd mentioned above. This is it:

DIY SOLAR POWER FOR BEGINNERS: Your Step-By-Step Guide To Design, Install, And Maintain Your Solar Energy System In Complete Autonomy To Drastically Reduce Your Electricity Bills. Kindle Edition



Amazon.com: DIY SOLAR POWER FOR BEGINNERS: Your Step-By-Step Guide To Design, Install, And Maintain Your Solar Energy System In Complete Autonomy To Drastically Reduce Your Electricity Bills. eBook : Dellinger , Sean : Books

[vnatale]

1.) Thank you. As a preliminary estimate, as a long-term annual average, every unshaded, installed STC kW ground mount of PV can be expected to generate something like 1,300 kWh/yr. of electricity. That's with a 45 degree tilt and a 180 degree array azimuth.
2.) So, once you get a design load in kWh/yr. for the project (not before) divide that design load by 1,300 kWh/yr. for a working estimate of system size in STC kW.
If cost effectiveness is one of the project goals, you'll need a reasonable estimate of the load the system is expected to meet to achieve that goal or balance it with other project/system goals.
3.) Google is your friend. Try entering "Solar Power Your Home for Dummies + free PDF". Took me 20 sec. and the PDF popped up. But if it's been updated and you have that updated version, you're good to go. What's the other title you mentioned you have ?
4.) A respectful suggestion: Learn more about the strengths and weaknesses of residential PV before you go further. IMO only, vendors will eat you alive if you try to negotiate with them given your current knowledge level.

Partial response. More later

2) Got the book. The other title was mentioned above: "Making the Switch With All Energy Solar"

This morning completed discussions with both my town's Building Inspector and a member of the Zoning Board of Appeals.

I am zone RS-1 (Residential).

The relevant bylaws for a solar ground mount are:

(b) The minimum side yard and rear yard setback from the property line shall be 10 feet

The Building Inspector said I have about 35 feet between my house and my neighbor's property line to the south. That leaves about 25 feet for a ground mount. He also stated that it could not extend beyond my house on the front side.

Zoning District Requirement

RS-1 Special Permit Required if exceeding 150 square
feet of panel surface area

Discussed the possibilities of approval with both the Building Inspector and the member of the Zoning Board of Appeals.

The Building Inspector said he has not yet seen them turn down any appeal.

The member of the Zoning Board of Appeals said that they are quite sympathetic to solar. He also gave me a loophole saying that if I were putting solar on a shed then that would NOT be considered a ground mount. Therefore an alternative is to create a shed large enough to hold the panels which then makes it a roof mount, doing away with the need for an appeal process.

For now I am assuming it will be a traditional ground mount. The member of the Zoning Board of Appeals stated that the more clarity with which I present my appeal then the better my chances of success.

I am asking the solar vendors to assist me in assembling this information to provide to the Zoning Board of Appeals.

He said that the quickest that a successful appeal process can take place is first a two week time period to have an ad in the newspaper with letters going out to adjoining neighbors informing them and inviting them to the appeals meeting. Then the meeting would take place a week later. That means it'd be a minimum of three weeks from when I make my appeal to than, hopefully, getting my special permit.