What’s So Zero-Energy About a House Connected to the City’s Electrical Grid?

One of the most common questions that people ask us about our house is what we mean by zero-energy. Let me begin by explaining what we don’t mean by zero-energy. Our house is not off the grid, like a house you might find out in the country, away from public utilities. And while we produce our own solar electricity, we’re still connected to the city’s electrical grid. We don’t have a bunch of batteries in the basement. But more on that later.

Now, let me explain what we are  building: It’s called a net-zero energy house. Quite simply, this means that we expect our solar panels to produce as much (or more) electricity over the course of a year than we use for heating and household use.

Like ours, all net-zero houses are connected to city power lines, but not all achieve the stringent standards we’re shooting for. In fact, the definition of net-zero can get a little muddy. For instance, some claim net-zero status for houses that produce enough of their own renewable energy to offset only that portion of their power that comes from dirty sources. In Seattle, where 91% of our electricity is hydroelectric, this is a relatively easy standard to achieve if you have electric heat. Other people define net-zero as zero energy bills over the course of a year, even if they are using more city power than they are actually producing. And in what seems to me like the most egregious misuse of the term, some so-called zero-energy homes simply produce enough solar electricity to power their sockets but depend on natural gas for heat.

Another question people ask us is whether all our power comes from the sun. It usually goes something like this: “If you’re connected to the grid, you’re still using dirty power at night and on cloudy days, right?” The answer is–sort of, but not really.

As I mentioned above, we don’t have a bunch of batteries in the basement (actually, we don’t even have a basement). Why? Because storing electricity is inefficient, not to mention expensive. When you charge a battery bank, you don’t get as much electricity back as you put in. Some of it is lost as heat. That’s why most houses that have solar panels hooked up to a battery bank rely on some other source for heat, like a wood stove.

It’s far more efficient and cost-effective to hook our solar panels up to the city’s electrical grid. That way we can put power into the grid during sunny days, when we’re producing more than we can use, and take it out at night and when it’s cloudy. It’s like we’ve set up our own little clean solar power plant, which means less natural gas needs to be extracted and burned and less electricity needs to be generated, avoiding all the associated negative environmental consequences.

Alex and I like to compare it to a bank. When you have an excess of cash, you make a deposit. For all practical purposes, it’s still your money when you go to withdraw it from the ATM later, even if it was mixing with everyone else’s money in the vault.

What do you think? Make sense, or do we need to keep searching for a better metaphor?

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3 thoughts on “What’s So Zero-Energy About a House Connected to the City’s Electrical Grid?

  1. Well said. Maybe get out some crayons and draw some graphics too. jk

    What a lot of people do not understand is that the times that solar is producing and supplying the grid with electricity is a crucial time to do so because of the marginality of the “time of use”. In the heat of the day is when power plants max out there capacity due to: cooling loads/air conditioners, business usage etc, and the marginal costs are huge. When power plants get near overcapacity then more plants must be built to meet the demand and typically the cheapest and cleanest options have already been used. It is cheaper for the power company to offer incentives (rebates, higher kwh costs etc) for people to use less during peak periods than it is to build additional power plants.

    So…not sure about Seattle but in many places such as S. Calif, the SW, etc your surplus power that you are putting into the grid is far more beneficial than that which you pull out in the evening and on cloudy days. Maybe in Seattle since you use hydro would mean a really big differential in the source of energy. If the hydro plant maxed out during in the peak hours then what is the next source of energy? Coal? Oil? Nuke? all of these are can be far worse than hydro, (providing the hydro is done responsibly)

    You are not only using a net 0 amount of energy but you are offsetting the dirty usage at a critical time of the day.

  2. You have learned well, Grasshopper! Very well stated!
    One very important thing you left out, though; your house was designed to hold up to 4 KW more solar panels than it will have initially, so if and when you do decide to buy a car, it can be an electric car, and you will be able to drive it up to about 9,000 miles per year, just with the energy produced by your home.
    Let the critics find fault with that!

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