Beyond Net Zero, Part II
By Dan Bihn
NOTE: Last week and this week, Energy Currents is excited to feature a two-part series by one of Enerdynamics' long-time facilitators and Smart Energy specialist Dan Bihn. This content was originally posted in January 2019 by Solar Oregon. Our thanks to both Dan and Solar Oregon for allowing us to share this valuable insight with our readers!
Last week's post Beyond Net Zero, Part I looked at how net metering helped launch the solar electric industry, and then Net Zero Energy brought together onsite renewable power generation and energy efficiency. But the next challenge that our energy system faces is affordably accommodating large amounts of solar and wind energy. This requires some smart thinking and strategic program details. Here’s one example that might offer some insights. Let’s go to Japan and see what they’re doing . . .
Japanese Net Metering
Japan, reeling after the earthquake, tsunami, and nuclear meltdowns of 2011, amped up its renewable energy game. Japan has never had simple net metering. They’ve always required 2 meters — one for purchased inbound power and a separate meter for outbound excess power. While this may sound a bit cumbersome, it offers some interesting opportunities.
Separate meters for buying and selling electricity (photo by Dan Bihn)
Having two meters allows for asymmetric ‘net metering’ — purchased electricity can be priced differently than exported electricity. And that’s exactly what Japan has been doing. In 2012, largely due to the unpopularity of nuclear power, the excess energy selling price was set to $0.41/kWh, while the retail purchase rate was hovering around $0.27/kWh.
That policy — and a companion commercial feed-in tariff — have proven very popular and effective. Japan went from less than 1% solar in 2010 to well over 6% solar in 2018. However, in some parts of Japan this policy has been a bit too effective. Much like California, some regional utilities have had to curtail PV output on mild, sunny weekends when low demand and high solar production exceed the grid’s ability to accommodate all of that solar energy.
The economics are changing. As solar costs have declined, so too have the tariffs. Today export rates are close to the retail purchase rate (making it equivalent to simple net metering), and they are heading down further, to a bit below retail this coming year.
The 2011 tragedies also accelerated Japan’s nascent zero energy home program. Today a $7,500 ZEH subsidy is waiting for those who play by some very forward-thinking rules.
Advertisement for one of Japan’s net zero energy home builders (photo by Dan Bihn)
Naturally the home must annually produce as much as it annually consumes. It also must exceed existing energy efficient building codes. And the home must use state-of-the-art heat pumps and appliances. But what sets this program clearly in the 21st century is the requirement for a sophisticated home energy management system (HEMS). These systems, which look like a wi-fi router, use a recently standardized home network protocol to control just about everything from lights, heating, and cooling, to home security and fancy bathtubs. And the HEMS must communicate with the smart meter and the PV inverter.
Typical installation of a Japanese Home Energy Management System (HEMS) (photo by Dan Bohn)
As solar penetration increases and the buy-back price of rooftop solar decreases, the smart ZEH homes are ready!
Back when export rates exceeded retail purchase rates, the smart homes benefited their home owners by shifting consumption away from times when the solar panels were producing so they could cash in on the generous export rate. As export rates drop below retail rates, it is in the home owners' best interest to shift their consumption to times when solar panels are producing to avoid buying more expensive grid power (effectively a self-consumption tariff).
Wall-mounted HEMS user interface (photo by Dan Bihn)
But it takes more than a smart HEMS system to do this. It takes flexible loads. While shifting lighting from nighttime to the middle of the day may not be a very bright idea, what about loading your clothes dryer in the morning and have it wait until there’s enough rooftop energy to run? Or, if you have an electric vehicle (and it’s at home), charge it when the sun shines.
But maybe the best idea is cranking your heat-pump water heater when the sun is shining. As it turns out, Japan is ready for this!
Japan had already pioneered the ideal water heater — the EcoCute (the word “cute” sounds likes the Japanese word for water heater). It is a high-performance heat pump that uses CO2 as the refrigerant, allowing it to operate at higher temperatures. And if it leaks it won’t lead to the ozone-depleting problems of conventional refrigerants. On top of that, since the CO2 was initially captured from the air, leaks won’t increase atmospheric greenhouse gas levels.