~100kwh for 24/7 off grid home

iamrich

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I am about to build a new house that will be all electric, so it will be interesting to see how much the usage changes. The house will be slightly smaller (2400 vs 2800) and single story vs two (current). Hopefully the build quality being better and more energy efficient will offset moving from gas oven/range, water heater, force air heating, but I get the feeling I am going to end up with a solar farm on my roof :p I think I have room for about 18kw of panels if I plan it correctly.
 

Scph9002

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I am about to build a new house that will be all electric, so it will be interesting to see how much the usage changes. The house will be slightly smaller (2400 vs 2800) and single story vs two (current). Hopefully the build quality being better and more energy efficient will offset moving from gas oven/range, water heater, force air heating, but I get the feeling I am going to end up with a solar farm on my roof :p I think I have room for about 18kw of panels if I plan it correctly.
Have you looked into "passive house" designs? Basically super insulated houses where air intake for aircirculation is being cooled or heated underground before it enters your home.

I have read claims of houses in freezing regions being able to stay warm with just waste heat from normal appliances
 

iamrich

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Have you looked into "passive house" designs? Basically super insulated houses where air intake for aircirculation is being cooled or heated underground before it enters your home.

I have read claims of houses in freezing regions being able to stay warm with just waste heat from normal appliances
I have not. I live in Central Texas and cold is generally not a concern except maybe a couple of months (Jan-Feb) or a freak snowmeggegon like this year. We live on AC most of the year.
 

serene_badlands

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We're building a SIP house, 10" walls, 12" roof.
I'm a solar installer up here in Maine. I highly recommend installing a common standing seam metal roof. You will be able to easily install safety, if you're using it, and feet for the rails go up quickly. If you use SIPS with an asphalt roof, you'll have to screw into the SIPS itself with something like zillarac. They are good, but they are heavy, expensive, harder to install, and...more. I also recommend Ironridge rails and UFO fasteners. Just some unsolicited advice!
 

tanoshimini

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I'm a solar installer up here in Maine. I highly recommend installing a common standing seam metal roof. You will be able to easily install safety, if you're using it, and feet for the rails go up quickly. If you use SIPS with an asphalt roof, you'll have to screw into the SIPS itself with something like zillarac. They are good, but they are heavy, expensive, harder to install, and...more. I also recommend Ironridge rails and UFO fasteners. Just some unsolicited advice!
awesome advice! we just received our standing seam roof (24ga) yesterday, and it's due to be installed next week. what would you recommend for fastening the rail to the roof seam?
 

serene_badlands

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I would go with S-5. They have like 50 options, and you can use the same brackets for a snow catch. We use S-5 clamps with an Ironridge L-foot to hold the rail. You'll need a foot every 4' or less and stagger the feet for each rail. Center the array on your roof, unless you plan to expand at a later date.

For Example:
footfootfootfootfootfoot
footfootfootfootfootfoot
footfootfootfootfootfoot
footfootfootfootfootfoot
 

curiouscarbon

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never heard of PHIUS until now. these are some maybe related links for others interested
 

djnorth

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Regarding passive houses, one issue to be mindful with their super sealed construction is indoor air quality and carbon dioxide build up, for which there are solutions.
 

upnorthandpersonal

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Regarding passive houses, one issue to be mindful with their super sealed construction is indoor air quality and carbon dioxide build up, for which there are solutions.

Mechanical ventilation with energy/heat recovery. These things have been standard here in Finland for decades.
 

curiouscarbon

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Regarding passive houses, one issue to be mindful with their super sealed construction is indoor air quality and carbon dioxide build up, for which there are solutions.
agree important aware

sealed house two BIG things

LOWER fresh air supply in absence of forced ventilation

LOWER power consumption possibility due to insulation
 

Mike 604

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Last year we completed our first mandated BC Step Code #4 home (2800 Sq ft) which is getting
close to "passive haus" for our clients.
Here in BC we had an extremely dry and warm summer. We had heat dome that we endured for close to a month.
Typically our daytime summers are in the mid 20s to low 30s and night time going to the teens.
The heat dome that we had in the Pacific Northwest brought temp up to 49C = 120F and night temps in the mid 30s.
Spoke to the client in Sept this year to see how the home was performing.
"We turned on the AC for the first time in July for 2 days. Extremely comfortable beyond our expectations."
Their combined utility bills over a 16 month average is $30 CDN for Natural Gas and Electricity.

The home has flat roof, we installed 7 solar tubes , 2 skylights and two motorized opening skylights on the high side of the mono pitch roof.
His combined utility bills for a 15 month average is $30 CDN.

So after this build I conclude , insulate inside, insulate the exterior of the building, inverted roof, no thermal bridges, make house airtight test to confirm, wet glazing in all double or triple glazed windows.

The retirement cabin that we have been building for 7 years has applied the same fundamentals just more so on the insulation.
 

Mike 604

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awesome advice! we just received our standing seam roof (24ga) yesterday, and it's due to be installed next week. what would you recommend for fastening the rail to the roof seam?
If it's not to late see if they can install a layer of Enka mat or something similiar between the metal and your membrane.
This will help cut a lot of the noise when it rains hard. and allows for air to circulate and cuts down on condensation on the underside
of the metal roof.
 

iamrich

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I just want to offer that for the OP, adding more layers may not be cost effective or desirable.
I bet there is a lot of variance depending on the region you are in as well. What works in Texas, may or may not work in Alaska. I don't even know how people live with a frost line that goes down 4-6 feet or more or where you have to worry about snow load on your roof.
 

KauaiMolokai

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Awesome thread! Thank you. I need to reroof my Kauai place asap. Any links or suggestions on where to research best ideas for doing it right would be most welcome. I did half the roof a few years ago. Replaced all damaged 1 x 6 T and G boards, put on 3/4 inch marine ply, put on rolls of sticky vapor barrier, then topped it off with standing seam galvalume. Has worked great. The other half is the difficult half.
 

Mike 604

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It is true that regional weather can affect design but actually, using an external vapor barrier and putting all the insulation on the outside of the structure will work in any region in the world. The system was developed by Neal Hutcheon and Gus Handegord in the 50s and it can't be beat. Danged Canadians really knew their stuff when it came to building science and building enclosures.
Here in BC, Canada on the coastal areas it rains lots. We had close to 12 inches in 24 hrs on the weekend and close to 41 inches since Oct 1st.
The main reason I suggested enka mat for my clients is because of rain noise. First time I used metal for a roof was in 2000.
Once the the big rains start it get it's a little too noisy. On all my builds since then we have used either Delta drain mat or the Enka mat for noise reduction.
If the metal is painted and the underside gets scratched during installation it could rust.
Most prefabricated metal not all but most that are made with some sort of die for the extrusion. The wider the panels get the more oil canning will happen. Therefore the 14 to 24 wide panels are not typically flat but have a form that is extruded to provide some strenght. This does allow for some air to be underneath. Not a lot of air but still air.
When the sun beats down on the roof some vapour droplets will form and where does it go.

FWC an architectrual company had to oversee a waterfront project to completion after the original Architect was let go.
The zinc roof was installed with no breather layer, before the house was completed it had to be replaced with a second new zinc roof
at the roofers expense. There were signs of corrosion visiable upon an inspection. Zinc requires a breather board and is part of the zinc manufacturers spec. Rheinzink was the manufacturer.

Since then I have always had sheet metal roofing complanies install a breather board first and foremost for noise, and to allow any vapour to escape.
 

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alvirtuoso

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Yes it did. I like to see the thought process behind these calculations as it gives me (and hopefully others) food for thought. I have 6kw and I am into it for about $150/kw, so it is good to see less expensive options.

Last month was my lowest bill ever at 12.61kw per day. My house is a two story 2800sqft, but I will be downsizing to a single story 1500ish house soon. Hoping I can reduce that number by a lot. I really didn't pay much attention until late last year when I got into solar. I routinely pull 45-50kw a day in summer here in Texas with the heat, so it will be a challenge even in the smaller house, but I am hoping to mitigate that a bit with as much solar as I can squeeze into 2 acres. :p
My Arizona summer energy peak usage was 71kwh in a day. Hoping to lower my bill substantially with solar project in the horizon. Keeping track of your progress.
 

tanoshimini

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If it's not to late see if they can install a layer of Enka mat or something similiar between the metal and your membrane.
This will help cut a lot of the noise when it rains hard. and allows for air to circulate and cuts down on condensation on the underside
of the metal roof.
The SIP panels that make up our roof are 12-1/4" thick. The EPS foam that cores the panels makes for some pretty good noise insulation. Our roofing goes up this coming Tuesday, but we've had some hard rain in the week since the panels have gone up. I went out to listen to the noise, and TBH, it's pretty negligible as-is.

I'll be interested to see what it works out to in the end.
 
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