WHY I DIDN’T INSTALL BACK-UP BATTERIES IN MY NET-ZERO HOUSE

THE HAYFIELD HOUSE was completed in 2019, but I didn’t install back-up batteries then. At that time, my solar company advised me to wait a few years before deciding on whether I wanted to install back-up batteries. Their reasoning was that the upcoming 2nd generation storage batteries would be much better (and maybe cheaper) than the existing batteries. I took their advice and waited. Here is what happened and why I still don’t have batteries.

In 2019, I thought I was being quite smart as I planned ahead for my future batteries. I had left space along my garage wall (near my inverters and electric meter) for my future batteries. In addition, my 400-amp electric service contained two 200-amp panels, one of which could serve as a critical load panel during a power outage. This set-up would minimize additional electrical work needed to accommodate the battery system (or so I thought). Following is what went wrong.

My plan to install batteries along my interior garage wall failed for a variety of reasons.

• What I didn’t realize was the building code in my town prohibits installing batteries on garage walls where a car can potentially hit the battery and start a fire. Instead, the battery needs to be protected from collision. For example, a protective bollard can be installed, but that installation would decrease the useable parking width of that bay of my garage, making that parking bay unusable. — That solution was unacceptable.

• Also unknown to me was that the code also requires that garage walls and ceilings where my batteries would be located needed to be sheet-rocked to reduce fire risk. As my third garage bay was not sheet-rocked, it likely meant that I needed to install more sheetrock.

• I was belatedly told that it isn’t advisable to install batteries in unheated garages in colder climate zones as batteries don’t function well when cold. Therefore, my unheated garage was not an ideal location for batteries.

Instead, I could instead install the batteries in an adjacent, partly heated, utility room, but that’s didn’t work so well either.

• I’d need to relocate my freezer to create enough space in the utility room to accommodate the batteries. This would likely require the installation of a new electrical outlet and/or circuit. Plus, where would I relocate the freezer to?

• Code limits the height that Tesla batteries can be raised above the floor. That limitation precluded installing the batteries on the wall above my freezer.

• Code requires my existing utility room entrance door be upgraded from a 20-minute rated fire door to a 30-minute door. In addition, I’d need to add self-closing hinges to the door.

• Code requires that if I mount batteries in my utility room, I‘d need to install a hardwired smoke detector in that room.

• Finally, additional electrical work would be needed to allow one of my electric panels to function as a critical load panel.

The total installed cost for this system was quoted (in 2024) at approximately $32,000, and that didn’t include adding an additional outlet for the freezer, or upgrading the door to the utility room, or adding a smoke detector.

The installation would have consisted of two Tesla Powerwall 2.0 batteries with 13.5 kWh of total available storage capacity. This is enough capacity to arguably power my critical electric loads for about a day (maybe 2). Granted, if the sun was shining, my solar panels could recharge my batteries. Maybe this set-up would allow me to limp along during an extended power outage. But most extended outages in New England happen during snowstorms in the winter when the sun isn’t shining, and your solar panels are likely covered with snow. This probably would mean that I couldn’t recharge my batteries when I needed to.

During short outages, batteries are useful in powering low load, critical circuits such as lighting and refrigeration. However, most backup battery systems are not designed or capable of powering high electrical load circuits, such as heating, cooling, cooking, or drying, etc. 

Even with all these negatives, I did toy with the idea of proceeding with the battery installation. The financial incentives to install batteries are currently quite lucrative.

• There is (as of 2024) a 30% federal tax credit.
• Massachusetts has a Demand Response program that would pay me up to $7500 (cumulative total over 5 years). In return, the utility company would have the right to periodically pull power to the grid from my batteries during periods of high energy demand.
• My utility provider currently offers a 10 year, zero interest, loan program for the installation of batteries.

In short, the incentives would cut my costs by about half over time. However, even with these financial incentives, I elected not to proceed. Part of this was due to the hassle factor of replacing fire doors, moving a freezer, and installing an additional smoke alarm. — If I had (in 2019) known more about the code requirements involving the installation of batteries, I could have planned ahead better and avoided much of the above-mentioned hassles. In that case, I may have installed batteries, or maybe not….

It also seemed a little bit excessive to spend at least $32,000 to minimize the hassles of infrequent power outages. As one friend pointed out, my prior house was an 1880 farmhouse within which I had survived periodic power outages for over 25 years. In addition, the thought of spending $32,000 seemed counterproductive to the idea of being zero net-energy and zero carbon. In essence, I’d be using $32,000 of the earth’s resources, and increase the embedded carbon metric of my house. — While the cost to me would decrease after factoring in various subsidies, that argument felt somewhat specious as someone (somewhere) still must be directly or indirectly paying the full cost.

Anyhow, during my next power outage, I’ll probably be pissed for having not installed batteries.

So the moral of this story is:

If you plan ahead, make sure your plan doesn’t suck.