Enphase AC Battery Review

I’ve been so itching to write an Enphase battery review. The AC coupled Enphase battery seems to be gaining significant interest although its release date still three months away. It’s a revolutionary concept: a battery that can be fitted to any solar system – any inverter. Imagine that. Any solar system in Australia. You don’t have to have the fancy pants “battery ready” inverters that sales people are banging on about. No longer feed your power back to the grid for a miserable 6 cents. For about $2500, you can store it in a battery and use it at night. The battery revolution has begun, or has it?

When I review a product, it generally entails me sitting down with the manufacturer and compiling a list of pro’s and cons of the product. I shared lunch and a few beers with Florian from Enphase at the Hamilton hotel. We exchanged emails, sometimes vehemently. Finally, last Friday I had a tense Skype conversation with the bloke who is worth his weight in gold. This time, my apologies Florian, I’m not going to share the pros and cons. I’m just going to point out one glaring downfall of the Enphase AC Battery.

AC Coupled Definition

AC coupling simply means your battery will be charged from the output of the inverter. The battery is charged by using 240 volts AC. Because every inverter produces 240volts AC, any inverter can be linked to the an AC coupled battery such as the Enphase. More commonly, batteries are charged with the DC power direct from the solar panels. While there are many advantages to DC coupling, a downside is you will need to have a true battery ready inverter, and match it with selected batteries.

Enphase smoke and mirrors

After reading Grant’s comments below, I should point out that the logic I am using works for South East Qld. If however, you have a “time of use” tariff with low off-peak and high peak charges, then the battery could be charged a second time during off peak, and discharged twice during peak times. What follows is my logic with a flat tariff of around 25c/kWh.

So let’s do the maths the Enphase way. We’ll do as they suggest and get 3x 1.2kWh (1.1kW usable) batteries. This means you have 3.3kWh of usable storage. “But wait,” says Enphase, “because you can cycle the battery twice a day, effectively it is 6.6kWh of storage.” So now you have a battery solution that is theoretically a bit bigger than the Tesla or LG, and for around $7500 installed. And you have a better warranty. And, because it is AC coupled you can connect it to any solar inverter. We’re on a win, win, win … right?

Enphase AC Battery smoke

Bugger, there is a catch. The 1.2kWh Enphase batteries charge and discharges at 270W each. Three batteries will charge and discharge at 810W. To do two cycles of these three batteries, you need to have.

• 800w of excess power between 6 am and 10am to perform a charge cycle.
• 800w of deficiency between 10 am and 2 pm to perform a discharge cycle
• 800w of excess power between 2 pm and 6 pm to perform a charge cycle.
• a piddly little 3.3kWh of discharge at night.

This is not even remotely realistic.

It obviously depends on your load. If your solar production curve is frequently intersecting you consumption curve, you may be able to get 1.5 cycles. This type of usage pattern may happen occasionally if you are at home during the day. But really, this is not the problem we are trying to solve with batteries.

Look in the mirror

My logic is:

• If you want to store power you want to first oversize your solar system. Oversizing your solar system in most cases means installing 6.5kW of solar on your roof. Oversizing is cost effective.
• After you oversize your solar system, the next most cost effective measure is to load shift. This means using the inverters intelligence to turn on or off your hot water or your pool when you are exporting power. Load shifting will always be more cost effective than storage. Enphase does not offer an interactive load shift solution like the Fronius smart meter and relays.
• Once we have oversized your solar and we have implemented load shifting, we then look at excess production and excess demand. Batteries are there to buffer, to soak in excess solar production and to deliver when demand exceeds solar supply – generally at night.

The piddly little 810w of power absorption that Enphase offers does not fit what a 6500w solar system on a standard home requires.

There are so many factors that Enphase want to discuss. The safe LiFePO4 chemistry, AC Coupling vs. DC coupling,  scalability, safety, and warranties. But if it does not work, it does not work. It does not work. Enphase, the concept is there. I love the flexibility of AC coupling. In time Enphase (or their competitor) will release an AC coupled battery that will meet the aggressive charge and discharge market demands.

Sonnenbatterie may be one example. The AC coupled battery will be available before the end of Q2 2016. I’ve posted a review on sonnenBatterie since I wrote this post here.

I’ve been wrong before

Most recently I was wrong when I bagged out the Redback inverter prematurely. I’m more than happy to take comments from Enphase or from my competitors that back the Enphase battery for what I see as no more than opportunistic reasons. Leave your comments below!

Mark