Page 48 - Green Builder January 2017 Issue

Building

Innovative Solutions for High-Performance Homes

Net-Zero Trifecta: Solar, Heat

Pumps and Smart Controls

Getting to net zero is within easy reach with new technologies.
The only real hurdles are politics and ignorance.

ABY MATT POWER 15 or more and an energy efficiency ratio (EER) of 12.5 or more, with
FEW MONTHS AGO, I SPOKE TO BUILDER variable output.
Gene Myers of Thrive Home Builders (www.
thrivehomebuilders.com) in Denver about whether For example, the outdoor component of my multi-zone (three mini
mini-split heat pumps could be powered by solar split) Mitsubishi system draws about 3,800 watts at peak demand. My
PV panels, essentially converting electricity into 6-kW solar array will sometimes deliver that wattage and more—but
affordable, clean heating and cooling for homes. not consistently.
“We’re doing that on all of our new homes,”
Myers told me. “We have been for a couple years now.” This need for a buffering technology narrows the options for
residential solar, and also explains why so many companies are
That took me by surprise. getting into the energy storage arena. PV’s path to heating and
At the time, I hadn’t looked closely at how such a marriage of cooling—the biggest energy users in the home—is limited to two
technologies would work. Since then, I’ve been putting the pieces indirect routes: net metering or batteries.
together, planning a system for my own building with a solar
array and mini splits, all managed through a
smartphone app.
What I’ve learned is that the path to net zero
with solar heating/cooling is possible, but the devil
really is in the details. Some of the devils, however,
are elected officials.

INDIRECT, NOT DIRECT POWER PHOTO CREDIT

It’s important to understand that solar PV panels Mixed blessings. Darker areas show where net metering allows owners to trade energy
do not directly power mini splits—at least, not credits at retail value.
yet. Even the best new DC-to-AC inverters, made
by companies such as SMA (www.sma-america.
com), can’t overcome the inconsistency of how
weather patterns affect PV power generation.
According to Zach Nugent of ReVision Energy
(www.revisionenergy.com) in Portland, Maine,
weather and seasonal issues (along with the Earth’s
rotation) mean that power output from PV is not
consistent enough to take over the high demand of
a mini-split system’s outdoor condensing unit. This
limitation applies even to a super-efficient model
with a seasonal energy efficiency ratio (SEER) of

46 GREEN BUILDER January/February 2017 www.greenbuildermedia.com