New Mexico, Santa Fe

[robbob2112]

Thanks, a very great heads up!


we're not planning on a battery at this point, I've made small lithium batteries for skateboards and e-bikes, I'm slowly building an electric motorbike, and pretty sure I'll get someone with a solid track record to build the battery for that, and same if we ever do get a battery for the house. Seeing videos of bike and skateboard fires looks real bad, I can't imagine having 100s or 1000s of cells letting all that energy out, not good!

House batteries are LiFePO4 chemistry, skate boards and other devices are LiPo. The LiPo batteries supply their own oxygen when they burn and contain many more toxic metals typically. The do have higher energy density but are so much more reactive I wouldn't have them in my house.

For a LiFePO4 battery to be a problem it needs to have damage to individual cells which causes them to vent and off-gas. The primary thing to spew out of it is hydrogen. The others that come out are not nice, but not nearly as bad if you get them on your or in your lungs. That is only going to happen if you be working over it at the time of a vent. The easiest way to damage a cell in a garage or other battery bank is through incorrect assembly or overcharging them.

Once they vent there is no fire since they only reach 300f or so from the chemical reaction. Hydrogen spontaneously combusts at around 650f. So for a battery to burn it needs a spark from something, anything. There are some pretty cool youtube videos where someone sticks a cell with a digging bar and it welds itself into place and the battery catches fire from sparks. They forced the vent from overcharging it.

There are a mountain of ways to make a mistake and cause issues if you DIY a battery. Used to be they were way way cheaper to order everything and bolt it together verse just buying an off-the shelf flavor. These days it is either even or cheaper to buy a pre-assembled unit. That and if you are trying to pass an inspection for grid-tie your battery must be UL listed and certified to work with your inverter. So you don't need to worry about DIY on a battery.

Ideally you will want a battery bank to let you capture all the solar power you can during the day and then run off that all night. Start with a good energy audit and you can "right size" the system so you have zero export and also use zero from the power company. The trick is winter time production from the panels is only 30~40% of summertime.

 

[iampob]

Super helpful, thanks,

my thinking of not getting a battery was that we'd use PNM net metering, so anything goes back to the grid we get a credit on,
I guess I should price up what battery we'd need, and see how that weighs up vs net metering, it seemed that a battery was more relevant if there are lots of outages and not being dependent on the grid, financially it didn't make sense, but will see how it works out.

Finally found where the set back rule is written, it's from the New Mexico Regulation & Licensing Department.
It's better than I thought as it only needs to be on 2 sides of the roof rather than 4.


2021 International Residential Code (IRC)
R324.6.1 Pathways.
Not fewer than two pathways, on separate roof planes from lowest roof edge to ridge and not less than 36 inches (914mm) wide, shall be provided on all buildings. Not fewer than one pathway shall be provided on the street or driveway side of the roof. For each roof plane with a photovoltaic array, a pathway not less than 36 inches wide (914 mm) shall be provided from the lowest roof edge to ridge on the same roof plane as the photovoltaic array, on an adjacent roof plane, or straddling the same and adjacent roof planes. Pathwaysshall be over areas capable of supporting fire fighters accessing the roof. Pathways shall be located in areas with minimal obstructions such as vent pipes, conduit, or mechanical equipment.
2021 International Residential Code (IRC) / CHAPTER 3 / 1. R324.6 / R324.6.1

 

[robbob2112]

Super helpful, thanks,

my thinking of not getting a battery was that we'd use PNM net metering, so anything goes back to the grid we get a credit on,
I guess I should price up what battery we'd need, and see how that weighs up vs net metering, it seemed that a battery was more relevant if there are lots of outages and not being dependent on the grid, financially it didn't make sense, but will see how it works out.

Finally found where the set back rule is written, it's from the New Mexico Regulation & Licensing Department.
It's better than I thought as it only needs to be on 2 sides of the roof rather than 4.


2021 International Residential Code (IRC)
R324.6.1 Pathways.
Not fewer than two pathways, on separate roof planes from lowest roof edge to ridge and not less than 36 inches (914mm) wide, shall be provided on all buildings. Not fewer than one pathway shall be provided on the street or driveway side of the roof. For each roof plane with a photovoltaic array, a pathway not less than 36 inches wide (914 mm) shall be provided from the lowest roof edge to ridge on the same roof plane as the photovoltaic array, on an adjacent roof plane, or straddling the same and adjacent roof planes. Pathwaysshall be over areas capable of supporting fire fighters accessing the roof. Pathways shall be located in areas with minimal obstructions such as vent pipes, conduit, or mechanical equipment.
2021 International Residential Code (IRC) / CHAPTER 3 / 1. R324.6 / R324.6.1

Amend my earlier comment of no fires.

There is a 20 page house burned down thread in the up in smoke section.

Key take-away is the poster had a DIY battery and used an inappropriate type of fuse that provided the spark. Some potentially bad choices in the battery build. These are all avoided with a preassembled battery.

All that said, when we build in Cortez co I'll have a separate structure for utilities that includes a battery room lined with firerock on all sides.


The agreement with the power company is key to the decision. Here the power you buy is at market value. The power you sell is at wholesale prices. My current coop and the coop in Cortez lets you bank the power and then true up once a year with a cap of $500