Our journey to power redundancy at the office

One of our primary goals with HQ v2, which we moved into over the summer, was to provide an office environment that supports our team’s best work—something that can only be accomplished if that work is free from sudden interruptions! That’s why we knew from the early days of designing our new office that we’d need to incorporate power redundancy in some form or fashion. This endeavor ended up being more difficult than expected, with several pitfalls, so I thought I’d write about the journey so others can achieve power redundancy with fewer headaches.

Choosing the backup source

There are plenty of resources available to guide people through choosing a backup source, so this section will just briefly explain our context and initial decision making.

In the event of a power outage, there are two major types of backup sources: batteries and generators. From a maintenance, sustainability, technology, and convenience standpoint, battery backup was the obvious choice for our company.

From there, we needed to decide what equipment we’d keep online during a power outage, how much power that equipment would draw, and how long we wanted to be able to keep that equipment running, which, when factored together, pointed us toward larger battery storage options. Tesla Powerwalls are the most notable product in this category, though other choices exist from brands like Generac, LG, and Enphase. We opted for Tesla’s offering due to its price per kWh, technology, and aesthetics.

Choosing a mounting location

When choosing where the Powerwall will go, there are many prominent considerations to make, like choosing between an indoor vs. outdoor location, proximity to breakers, and logistics with running conduit and wires. But one thing that wasn’t made known to us very early were the specific requirements for clearance in various directions for proper ventilation. A late discovery of these requirements unfortunately necessitated architectural changes to accommodate them. Taking these into consideration early, especially while the premises are still under construction, can prevent extra costs down the road.

Installing the Powerwall

Due to high demand, Tesla shipped our Powerwall directly to us, and it was up to us to find a Tesla-certified installer. Here’s where you can avoid a whole host of headaches: find a certified installer who also has sufficient experience installing Powerwalls in your particular setting. Tesla’s certification program seemingly doesn’t provide adequate preparation for contractors, as the certified installer we chose ended up being relatively unfamiliar with how to install Powerwalls—particularly in a commercial setting—and it led to extensive delays, confusion, and cost overruns.

Achieving uninterrupted power

Despite Tesla’s marketing language implying Powerwalls are capable of switching to backup power so quickly connected equipment won’t power off, this is not always the case. In our testing, and that of others we came across during our research, there’s can often be a 500–1000 millisecond delay between losing power and having power restored by the Powerwall. This is enough of a gap that connected equipment will power cycle and possibly require several minutes to power back on.

To mitigate this, we purchased a commercial uninterruptible power supply (UPS) unit to bridge this short delay, and inserted it between the Powerwall and our critical networking equipment. But, this introduced a new problem: the UPS never reverted back to drawing energy from the Powerwall, and continued to operate off of its own internal battery indefinitely.

This took quite a bit of research to diagnose, but it turned out that when Powerwalls are close to 100% charged, by default they output power at 65 Hz instead of the usual 60 Hz. This leads many UPS products to believe the input power is dirty, triggering the use of their internal batteries.

Luckily, Tesla’s Powerwall support team can remotely change this setting to 62.5 Hz, which will alleviate this problem for many UPS units.

EDIT: After publishing this article, and after several months of our Powerwall operating at a maximum frequency of 62.5 Hz, our Powerwall unexpectedly reverted back to 65 Hz—without any notification from Tesla. Given that the frequency change is clearly not stable, we opted to purchase a different UPS that tolerated higher frequencies. Eaton, in particular, makes several models that tolerate frequencies as high as 70 Hz.

TL;DR

1. Power redundancy is important for preventing unexpected work interruptions at the office.
2. Tesla Powerwalls are a solid solution.
3. Choosing a certified installer isn’t enough; find an installed that’s also experienced with your setting.
4. Powerwalls don’t offer truly uninterruptible power, you’ll also need a UPS for critical equipment.
5. The UPS must be able to tolerate at least 65 Hz, otherwise, it will not draw power from the Powerwall. (Lowering the Powerwall’s max frequency is possible, but not stable.)