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Introducing the Enphase AC Battery

It’s been about six weeks since Net Zero Solar installed our first Enphase Energy AC Battery at our office/warehouse. Although this is a small test system, this exciting new product allows for a lot of flexibility in how energy is generated, stored, and consumed in your home. And although it’s not necessarily justified in pure economic terms at this point, the Enphase AC Battery can be a great addition to a solar electric system.

So what does it do?

It’s pretty simple—the Enphase AC Battery stores electrical energy from the sun for later use. Inside the attractive package, you’ll find a 1.2 kWh lithium iron phosphate (LFP) battery, a 280-watt microinverter, and some additional controls and safety equipment. The microinverter can convert the AC energy from your Enphase solar electric system to DC energy, which is used to charge the battery. It can also convert the DC energy in the battery to AC energy, which can be sent to the electrical loads in your home. It’s possible to install just one AC battery, most homes will need two or more to effectively store solar energy.

Net Zero Solar’s Enphase AC Battery system in operation.

The screenshot above shows operation of our system for a recent Sunday. On the left is the most important info—for this day, our only interaction with with the grid was to buy 0.38 kWh of energy. 92% of our energy came either directly from the sun, or from our two AC batteries charged from the sun!

The orange line shows how much energy was consumed in the office, with dark orange coming from either the AC batteries or the grid, and light orange coming directly from solar. Blue is solar. The lighter blue is solar production, while the dark blue is solar energy that’s either used immediately, or used to charge the AC batteries (You might be wondering why the solar output is greatly reduced in the afternoon—see below for more about this “zero export” system).

At the bottom in green, we see the state of charge for the AC batteries, or how “full” they are. From midnight on, the state of charge slowly drops, as energy from the batteries is used to power loads in the office. When the sun comes up, the solar powers the loads in the office, and then starts charging the battery too. By the time it’s 10:10am, the batteries are about 40% full. By about 2:00pm, the batteries are completely full.

Sunday night, the batteries are ready to contribute, and cover the energy use of the warehouse and office. The system is smart enough to carefully follow the load profile of the office, greatly reducing the energy used from the grid overnight. By midnight, the batteries are about 50% full. Not to spoil the story too much, but for this weekend there was enough energy stored to keep running off the batteries until 6:00am, when we came into the office and turned on lights, computers, and other loads.

You can see what happened Monday morning below. As it turns out, our weekday loads are large enough that our small solar electric system can’t both charge the battery and meet the load. We’ll be installing more solar soon to remedy this.

The system in operation Monday morning.

But Why?

So why would you want to install Enphase AC batteries? First off, it’s an amazing technology. Enphase AC batteries let you store your energy, onsite, and use it later! You’re increasing your own energy independence. You’re also buying a piece of the future, as you help build the nascent home energy storage market.

But will the Enphase AC battery save you money? Probably not. For the moment, consumers in Arizona have the ability to take advantage of net metering, which essentially allows you to use the grid as a virtual battery.

Net metering will go away later this year, as rate case hearings for TEP, UNS Electric, and SSVEC continue this summer. In fact, Trico customers already are only compensated at about eight cents for each kWh of energy they send to the grid, while they have to pay about twelve cents for each kWh they buy from Trico. So when energy is sent to the grid, rather than used or stored, they lose about four cents of value. But unfortunately, total lifetime costs for storage are currently much higher than this lost value.

Can I go “off-grid” with the Enphase AC Battery?

Well, sort of. The Enphase AC battery allows you to reduce your interaction with the utility grid, since you’ll store some or all of your solar energy on-site, and use it when you need it. But the Enphase AC battery is designed to use the grid’s voltage and frequency as a reference. If the grid goes down, the system will not provide backup (though Enphase is working on this).

What’s it like to have Enphase AC Batteries installed?

The installation is a simple process. First, we’ll find a spot to mount the batteries. Unlike microinverters, they must be mounted in an indoor space, away from the weather. A garage is ideal.

Jim and James check out the AC Battery wiring boxes in preparation for installation.

Like any other electrical infrastructure, we will obtain a building permit. Although these batteries are extremely safe, this permitting process typically takes a little extra time, because this system is new to not only homeowners and installers, but also to building departments.

When our technicians arrive on site, we’ll first install mounting brackets with wiring boxes to the wall. We’ll then install conduit between your existing electrical system and the wiring boxes, pull wire through the conduit, and connect the wires inside the AC Battery wiring boxes, and to a circuit breaker on the other end.

Rob, James, and Bobby install the Enphase AC Battery mounting brackets.

The technicians will place each AC Battery on the bracket, plug in a couple connectors, and turn on the switches. After a short commissioning procedure using a smartphone, the system will be up and running!

Bobby completes the wiring.

If you currently have an Envoy-S metered, you’re all set to go. If you don’t, we’ll need to upgrade your Envoy. Although this is an expense, the great news is this also typically adds energy consumption monitoring to your home.

Bobby and James secure the batteries to the mounting bracket, and plug in the DC connectors.

A Note on Zero Export

When looking at the first images in this post, you might have noticed that the solar electric system didn’t seem to produce as much energy as expected in the afternoon. This is partly from some clouds in the afternoon, but there’s more to the situation.

In some parts of the world, there is so much solar that utilities and policymakers have ended net metering, and systems are required to be “zero export.” This means that solar electric systems are allowed to produce energy to be used immediately in the home, or to be stored in batteries, but they can’t send energy to the grid.

This “self-curtailment” isn’t required in Arizona, but we wanted to test this zero export scenario out. So how does it work? Enphase’s Envoy-S Metered measures the energy flow in the system multiple times each second. If the energy consumption in the home or business is more than the solar is producing, things continue as normal. But if solar production is more than the loads, the Envoy-S Metered commands the microinverters to reduce power output. This architecture only works with the S280 or newer inverters.

Toward a New World in Energy

The Enphase AC Battery is just the first step toward some truly incredible technologies. In the future, we expect to have a wide variety of energy products in the home.

Yes, solar electric systems will produce energy, and energy storage will step in at night, or when it’s cloudy. But load control products will also intelligently choose when to perform various tasks in your home, such as when your heating and air conditioning should run to both keep you comfortable, and save you money. These systems might also control when your pool pump runs, or when you charge your electric car, for example.

The completed Enphase AC Battery installation!

And where’s the grid in this scenario? There are at least two possible paths. The first is that consumers minimize or eliminate their connection to the grid, running mostly from solar and storage, and using backup power source such as a generator.

The more likely path is that the grid evolves into providing a different set of services, which are much more tailored to customer needs and desires. In this world, the grid and home energy systems could communicate intelligently, helping each other as needed. For example, a home energy system could minimize the energy that they take from the grid during peak usage times. Maybe they can even send electricity from energy storage to help support the grid when needed.

Where from Here?

Are you interested in learning more about the Enphase AC battery? Please get in touch. We’d love to talk more details. We’d also like to hear your questions about the system, and your thoughts on energy storage in the future. Please share them in the comments!

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6 thoughts on “Introducing the Enphase AC Battery”

  1. I am puzzled as to why your above screenshots shows that you draw something from the grid at all. I see your usage is peaking at 110W per 15mins on 9th April and only very briefly, i.e. 440W max usage per hour and you have two batteries that should provide you with at least 500W output, any idea why the batteries did not cover 100% of your needs?

    1. Hi Gaetano, This system is set up as zero export, so that no energy is sent to the grid. To do this, the Envoy-S Metered used a pair of CTs (see https://en.wikipedia.org/wiki/Current_transformer for more info) to measure how much energy is coming from the grid, and tries to minimize grid use with any available solar energy and energy from the batteries. The Envoy-S Metered cautiously draws a small amount of power from the grid, to make absolutely sure that any small CT inaccuracies don’t lead to energy export,

  2. Is it possible to charge the battery from the mains? We have a cheap overnight tariff, to charge the electric car, we also have emphases PVs. So it would be desirable to charge the battery overnight on cheap electricity in the winter months.

  3. I am a current solar owner using enphase microinverters and envoy interface. I have been waiting for the right time to upgrade our system to be integrated with battery storage. Net metering though PG&E works for the most part but we all truly would love it to be able to use each and every kWhr we generate! We are one year away from our ROI date mid-2018 so our modest system has almost paid for itself already. Having an electric car has proven we need even more solar and a better way to charge during peak hours. I know a battery pack in some form is the answer. I am very interested to learning more about your solution.

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