Published on March 16th, 2016 | by Guest Contributor


The Flaw Of “Zero Energy Buildings” Without Energy Storage

March 16th, 2016 by  

By Mark MacCracken

Conceptually, a Zero Energy Building (ZEB) design is simple to understand and dozens of projects have undertaken the challenge of becoming zero energy. Some of them have even “succeeded.” The reason for the partial success is that there hasn’t been a clear, concise broadly accepted term or definition of what ZEB means. As a result, to some extent, designers, contractors and property owners have not grasped the entire scope of what it means to be zero energy or its larger implications beyond the building.


California’s State Lottery Headquarters’ pavilion uses ice storage and solar panels to achieve net zero. Photo credit: CA Lottery

To help bring clarity across the industry, the Department of Energy released its definition for ZEBs. The new definition states that a ZEB is “an energy efficient building, where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy.”

With ZEBs, as with other buildings, off-site energy resources such as oil, gas, electricity, steam and district heat and cooling, are delivered to the building to power operations. What makes buildings “zero energy” is what happens on-site. At a zero energy facility, the energy generated by these off-site resources is matched or even exceeded by on-site renewable generation, which can be designated for the building or exported to the grid.

Since ZEBs rely less on fossil fuels and more on carbon free renewable energy resources, it is a great step toward even greater environmental design. However, for renewables to truly be able to dramatically reduce our dependence on fossil fuels, we need to address the other vital characteristic of fossil fuels: storage. Fossil fuels are a form of stored energy, while renewable energy is simply energy. In order to reach their full potential, renewable energy collection must be coupled with storage technology, either on the grid side or building side of the electric meter, so that it can be dispatched as required.

Understanding the Larger Implications of Zero Energy Buildings (ZEB) on the Grid

Along with the major benefits of ZEBs, the rise of ZEBs will present major challenges for the grid. The best way to explain this is by example. Assume for a moment you have a ZEB building that is not connected to the grid or what is called “off-grid.”  In this scenario, to keep the building operating, the site will need many forms of energy storage connected directly to the building: battery storage for regular nighttime operation, thermal storage for heating and cooling and fossil fuel for backup generation when all other forms are depleted. However, most ZEBs do not install storage and instead use the grid for their storage needs. The problem is the grid essentially has no storage capabilities. Therefore, the grid needs to have instantaneous backup fossil fuel generation available for the ZEB, even though the ZEB, on an annual “net” basis, will not need any energy from the grid.

Consequently, the inconsistent nature of renewable energy resources creates problems for utilities as annual energy consumption dwindles, but peak demand (maximum energy consumed during a 15 minute period within a billing cycle) does not change. Utilities quantify the relationship between average annual usage and peak demand with a term called “Load Factor (LF)” or “Capacity Factor.” It is a simple number that shows how well their assets of generation, transmission and distribution, are being utilized.  In the 1960s they were at almost 70 percent LF, but the increase in the use of air-conditioning has resulted in creating higher peak demands on summer afternoons so that the LF is now below 50 percent in the US.  If we look at the LF for a ZEB, by definition, its LF is ZERO (average load for the year is zero divided by any peak demand). So for the grid, the ZEB is the worst type of load.

In order to remain profitable as renewable generation increases, utilities are identifying energy storage as key to their future success. Energy storage is being rapidly added to both the grid and buildings. Businesses that don’t manage demand and/or utility energy storage are charged at a higher penalty for peak demand energy consumption, which most often occurs on hot summer days when utilities are pushed to their maximum capacity. It’s during these peak demand periods that the utility’s most expensive peaking plants come online for just a few hundred hours a year.

Energy Spikes, Demand Problems and Stored Cooling

While commercial ZEBs are energy efficient buildings with low carbon footprints, they still have large peak demands that they get charged for. To avoid high peak demand costs, energy storage allows buildings to virtually become their own batteries, storing energy when it is at its lowest price and calling upon it when they need it most, which is also when it is most expensive. Thermal energy storage specifically stores what has caused the most demand problems for buildings and the grid, namely cooling.


CALMAC’s IceBank® energy storage tanks provide the California State Lottery Headquarters with nearly 2,000 tons-hours of cooling capacity. Photo credit: CA Lottery

To understand the impact of “stored cooling” let’s use the backyard barbecue as an analogy. Most would agree that it is a bad idea to wait to start making ice cubes until the guests start walking through the door.  It turns out you need about 1 pound of ice per person for the party to keep drinks cold and make mixed cocktails. Your refrigerator would have to be giant to handle that kind of production, so most people would create ice the night before. To cool an office space for that same person it takes the equivalent cooling of 150-300lbs of ice per person.  As ludicrous as it sounds, most buildings do not store their cooling ahead of time, and instead rely on the instantaneous creation of cooling, which has caused the majority of the electric grid’s problems. In fact, 35 percent of peak electric draw on summer days is due to the instantaneous creation of cooling.

A Major Key to Making the Business Case for Zero Energy Building

When coupled with thermal energy storage, renewable generation can become a more cost effective source of power. For instance, a ZEB can reduce its peak demand by making ice using excess grid energy generated during cheaper, off-peak hours when electricity is plentiful, or when the building has excess solar energy. The ice can then be melted the next day to cool building occupants during expensive peak periods, if the cooling demand cannot be met by onsite generation.

On the other side of the meter, using cool storage with a ZEB, allows the utility to lower its peak demand and improve the grid’s load factor. Additionally, this practice will help the grid more effectively utilize renewables and make the energy available when needed so that the full benefits of ZEB and renewables can be realized.

Mark MacCracken is the CEO of CALMAC.

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  • Tom G.

    Unfortunately in the not to distant future, grid tied Zero Energy building may just become nothing more than what was once thought to be a good idea. We are already seeing public utilities adding fees for being tied to the grid; e.g.Nevada and some Arizona utilities. The next step which is already being discussed will be to institute a minimum grid fee for each property even if that property is not connected to the grid. That should just about kill off any battery storage system[s] and any financial benefit such systems might provide.
    Its hard to fight billion dollar utilities and their teams of attorneys and lobbyists.

    • philofthefuture

      That is called a death rattle. Once a substantial portion of customers have solar, they will make their voices heard and utility meetings and ballot boxes. Forcing people to pay for grid connect just makes off grid that much more viable. The problem is continuing cost reductions in both solar and storage. Utilities can whine a lot but they can’t hold out forever, it’s the snowball effect and once it starts rolling it can’t be stopped. That’s why they are trying so hard to stop it early before it get’s going but with 50%/year growth it’s already too late. I think extending the tax credit was the final nail in that coffin.

  • JamesWimberley

    A clear statement of the Storage Fallacy: high renewable penetration absolutely depends on storage. It seems hopeless – INTERMITTENT entails STORAGE – but it’s just wrong. Look, the old centralised grid had small amounts of storage, but basically it coped with the 2:1 or more range of demand variation with OVERCAPACITY and demand management. The same solution is available for wind and solar.

    Ah, say the adherents of the Storage Fallacy, but wind and solar are not despatchable. True, but the cheapest ways to back up the rather short periods of time when neither wind nor sun are available are demand management and gas peakers (which you already have lots of). A fair number of countries also have the option of importing hydro power, which is geographically localised. Storage only becomes a necessity when you move from 90% renewable to 100%, so it’s a problem for ten years ahead at the most optimistic reading. It’s definitely worth researching. But there simply isn’t a short-term constraint. The developers of the Ivanpah CSP plant could easily have added a lot of cheap hot salt storage, but decided against: it’s just not that valuable today.

    • GCO

      Indeed, renewables don’t need a storage breakthrough.
      (I know, I posted this video before, but I find it beautifully made and I think it really gets the point across.)

  • GCO

    I think that the last line of the article is the most important:

    The author is the CEO of the ice-storage AC company shown in the article.

    This explains some of the less-than-truthful blanket statements made, like saying that no renewable is “stored energy” (someone needs to go see a dam sometime…), that ZEB are “the worst type of load” (huh??), or ignoring details like how solar tends to peak at the same time as cooling loads…

    I believe that thermal storage will become economical, and therefore more popular, as electricity pricing becomes more dynamic (smart grid bringing us TOU on steroids); “net zero” considerations won’t have much to do with it.

  • Freddy D

    One of the main benefits of ZEB is pushing the efficiency way up. Building climate conditioning uses a HUGE fraction of the worlds energy supply and is reasonable for an equally huge fraction of emissions. PassivHaus caliber insulation takes the efficiency so high that consumption is down by 90% in many cases. The load becomes much smaller in the first place and the storage problem is much smaller.

    The results of this super high efficiency building are truly stunning when one looks at the final energy consumption. These buildings just sip energy.

    The proposition is much more than simply throwing enough PV on an existing building. And the economics tend to be fantastic too because efficiency is so often the “cheapest form of energy”.

  • neroden

    *Net zero* building is the term usually used. Which means they use imported energy sometimes, they generate energy and export it sometimes, but the *net* is zero.

    With storage, you can have a *gross zero* building. Occasionally known as a “off the grid” building.

  • vensonata

    Yes, zero energy just means you produce energy using solar, and ship some back to the grid and when you want energy you use the coal fired or gas fired generator located 100 miles away. Off grid you produce energy using solar, store excess in batteries for later use (or in hot water) and then use a natural gas generator located 15 feet away to provide the energy lacking. Take your choice of generator…100 miles away or 15 feet away, coal, gas, nuclear.

    • GCO

      I’ll pick the grid any day, absolutely no question about it.
      You (purposely?) forgot several important points:

      – Grid power increasingly comes from zero-carbon sources, like wind, hydro, nuclear and geothermal, while on-site backup generation is usually limited to diesel or natural gas (hmm, fracking…), and with generators which are less efficient and more polluting than larger-scale installations.

      – The energy exported by a on-grid building (e.g. during sunny days) displaces other sources typically including at least some fossil fuels, making it carbon negative during those times.

      – The manufacturing, transport and disposal/recycling of batteries is resource-intensive (read, very polluting); see Renault and Nissan’s life-cycle analysis for their EVs (will post links when I get a chance).

      – Batteries are completely impractical as storage for seasonal variations. Outside the tropics, an off-grid site with enough PV capacity to go through rainy/snowy months without running a generator constantly will see most of this PV wasted during the sunny part of the year.

      • John Ihle

        There are those pesky issues relating to storms, cyber security, etc. that may take the grid down and until the powers that be make energy storage a larger part of the grid off grid systems offer comfort which to some, including me, is valuable.. of course there are different ways to do that whether your on or off grid. At some point in the distant future energy storage will be economical for many. It will be interesting to see how the grid develops over the next several years and how it incorporates behind the meter solar and storage, ev’s, etc.. with larger scale and more localized RE and storage.

      • philofthefuture

        The only viable solution is hydrogen storage, both homes and grid level. With excess renewables hydrogen generation is basically free, just add water. Hydrogen is the ONLY solution to season shift energy, batteries don’t stand a chance of that.

        • Bob_Wallace

          Correct. Hydrogen is the only viable long term storage solution. As long as one ignores pump-up hydro, flow batteries, synfuels, and biomass.

          Hydrogen does win the least efficient sweepstakes. Also the most difficult to store.

          • philofthefuture

            Pump up hydro is only viable in certain areas, flow batteries will not do seasonal storage last I checked, synfuels and biomass are complete non starters, they will go nowhere. Take 100% of US arable land for biomass and even that wouldn’t replace 10% of oil usage. Exxon has been working for years to crack synfuels, (for obvious reasons), and like most other things it’s proved much more difficult and expensive than promised.
            With excess renewables energy spot prices are zero, even at 50% efficiency hydrogen is still the cheapest fuel long term because of that. Hydrogen is stored and transported handily, TX has 1800 miles of hydrogen infrastructure. The EU and Japan are going the hydrogen route, we will be forced to play catch up as usual.

          • Bob_Wallace

            Phil, please list the places where PuHS is not viable.

            Also tell us why we could store very large amounts of low energy per volume density but not store dense energy chemicals for flow batteries.

            And tell us why biomass will not work

            And tell us why synfuels will never work.

            You’re spouting junk, Phil.

          • philofthefuture

            Biomass ‘works’ of course. But again it cannot be scaled to even make a dent in our gas usage. Synfuel ‘works’ of course. But there is no path to making it economically viable. Unless a miracle occurs neither is viable. Pumped water ‘works’ but unless you have a huge dam laying around it is not feasible. Tell me how pumped water will work in the middle of Iowa. You need elevation and a vast reservoir.
            It is you that is spouting junk, these limitations are no secret by any means. Corn is the only ‘successful’ biofuel and that requires both subsidies and tariffs and increases food costs while it generates more CO2 than it saves. If you call that working then we’ll agree to disagree.

          • Bob_Wallace

            First, is there a law that storage must be within the state’s borders? Second, any abandoned rock quarries in Iowa? Third, there are 250 foot high bluffs along the Missouri River in Iowa.

            Some think there’s a route to making synfuel affordable. And it’s a lot cheaper and easier to store. When you claim “synfuel will go nowhere” you’re making a foolish statement. You cannot know the future.

            Wood is a commonly used biofuel. We’re currently running converted coal plants on wood.

    • Bob_Wallace

      Kind of jumped the shark there. We need to be working toward getting rid of all fossil fuel generation. A net zero energy house can produce its own electricity from solar, even store enough to cover a day or two if the economics work. But when solar and storage isn’t enough the NZEH needs access to wind, hydro and long term storage (pump-up hydro and flow batteries).

      I’m off grid as you are. For the last two weeks my generator has run for 4+ hours every day. My solar resources apparently are not as good as yours. I wish I could have accessed cheap wind during those two weeks.

      Today it’s sunny, my batteries are full, and I could be shipping some electricity to the grid for someone else to use. Or use it to build up deep storage. I’ve got a solar resource going to waste. All summer long I could be supplying the electricity for someone’s AC but I’ll just toss it away.

      • vensonata

        Absolutely… I would like to figure out how to use my excess. I am sitting here with two feet of snow and the battery is full by 10 am and stays at 100% until about 5pm everyday from Feb until November. So the next move is a plug in hybrid Mitsubishi coming this year. That will save a couple thousand in gas and use some of this damn clean energy. I can also heat domestic hot water now since there is so much extra and that should actually get us to a balanced use for the 9 months of enormous production vs 3 months of minimum production. So this is new in off grid living; skillful use of abundant production due to cheap solar overpanelling. I am sure there will be forums springing up with ideas. Maybe bake bread using excess solar and sell it?

        • vensonata

          By the way, this may not be relevant to this topic exactly but Neroden has pointed out that the Tesla 10 kwh powerwall has is no more. Only the 7 kwh powerwall remains. That is some news.

          • neroden

            Yeah, Tesla surveyed everyone who made a Powerwall reservation, and apparently the vast majority wanted the “daily cycling” version — so they ruthlessly got rid of the other one. (They’ve repeatedly cancelled options and variants of the Model S when not enough people ordered them, such as the S40, the S60, the aero wheels, the black roof — if they don’t have volume, they drop it.)

            This survey result says something fascinating about the *market*. Apparently people really want daily cycling. OK, good to know. Makes sense to me.

          • GCO

            Interesting and surprising. SolarCity planned on only offering the “10” kW⋅h backup version, stating (correctly IMHO) that in most of the US, daily cycling doesn’t make economical sense.

        • Bob_Wallace

          What I’d really like to know is how many kW of panels one would have to install in order to generate a kW in an hour on a cloudy day.

          I found one site where someone had plotted his daily production over a year. It looked like the general low was around 30% of the best days. There were a few days where it dropped to about 5% – I wondered if those were days the panels were covered with snow.

          I do fine on sunny days with 1.2 kW of panels. Could probably get by with less. I wonder how much more I would need to avoid all (almost all) generator use.

          Or with a grid system, how much would one need to overbuild in order to avoid more than one night’s storage? If solar drops to 3c/kWh might it be possible to install 3x as much along with about 20 hours of storage and be done?

          (Sort of babbling to myself here….)

          • vensonata

            First overkill the pv, who can regret it. My formula: one hour of full peak rating equals 80% of one days demand. I have 12 kw PV and use 16 kwh per day. Next, start with 1.5 days battery storage, measure generator use for one year. If generator runs more than 100 hours add one more day of storage (but lithium). It is possible to zero the generator with 5 days storage and thermal load shifting to propane or wood for heat, cooking, hot water during low winter production. It is carbon fuel but not through a generator and can be 90% efficient, silent, clean and automatic.

            Cloud cover is only about 50% reduction from March to October but gets worse as the sun goes lower and has to penetrate through more atmosphere November to February. In December in heavy cloud it might be 5% of possible.

          • GCO

            Check out stats on e.g.

            What it calls “efficiency” is kW⋅h produced per day, per kW of PV capacity.
            The site is a bit unintuitive but you should be able to find interesting data on some systems near you nonetheless. (Also note that the listed weather conditions often don’t reflect reality, but are merely inferred from the PV output).

          • neroden

            Interesting questions. I’m impressed with all y’all who are off grid.

            This is partly because I’ve been taking a different strategy: I’ve been getting rid of all *local* fossil fuel use first, which has been ramping up my electrical usage massively. Eventually I’ll have an all-electric house.

            I’ve already done a lot in the way of efficiency — LEDs, superinsulation — but frankly I like to keep my house hot, and I like my appliances. So I’m still an energy hog; I’m pulling 33 kwh / day and my heat isn’t electric yet.

            With our crappy insolation, it looks like I would need over 500 square feet of *before* accounting for heating. And I don’t have that much roof. So I’m fairly dependent on the grid.

          • vensonata

            All electric house in the Northeast would be difficult to supply from rooftop. At this point there is not a single example I can think of, although there is a house in Nova Scotia that theoretically could do it. A very good all electric house in the Northeast can come in at about 6000 kwh year. A 5 kwh pv array can Zero that. But winter demand will exceed production. With seasonal hot water storage for space heat, air source heat pumps, and heat recovery ventilation it would be possible with about 10 kw of PV. Panels at 24% efficiency would require less than 500 sq ft. If one wanted to go off the electric grid one could easily do it with a little gas back up for heat.

          • philofthefuture

            10KW on the roof, the rest on the ground! 😀

          • philofthefuture

            I have 30KW and have replaced most everything with electric equivalents. Gas stove and barbeque will stay. I use a wood stove overnight during winter nights. That makes me energy neutral. I live a few miles from the Canadian border. Most of my home I keep at 70 but there are a few rooms I keep at 65, I have per room radiant heat.
            I’m all LED as well but do have spray foam insulation, 6″ in wall and rafters.

          • Frank

            Wouldn’t mind if this site had links to descriptions of peoples cleantech stuff, like your solar system, including the parts you used to put it together including comments, including things like why you chose them, and what you learned. I’m grid connected. I don’t yet have a solar system, but would like to install one myself. I’m really interested in the StorEdge Inverter, and want to use power optimizers with the pannels, because I have a 4 sided roof, and would like to put pannels on 3 of them. Also interested in figuring out how to reliably hit the rafters through the shingles.

          • vensonata

            Look at “Home Power Magazine” for all your needs off grid and on.

          • philofthefuture

            I used SMA America Sunnyboy inverters. Go to their site and you can download a fantastic system design program. It takes account of your location, roof or ground mount, azmuth and orientation, high and low temps for your location. In addition you can input a range of solar panels or manually enter one that not in their database. You can design the entire system and simulate the results for YOUR home. I planned my entire system with it.
            Of course it only has SMA inverters but there are a ton to choose from, including some that will give power even without batteries as long as the sun is shining. They have grid voltage battery backup so you can add it later if you choose.

          • jonesey

            My 2.8 kW array routinely makes 15 kWh per day in June and July and 50-60 kWh per MONTH in December and January (less than 1 kWh per day is uncommon but happens a few times per month). Welcome to the cloudy Pacific Northwest, where we depend on giant hydro dams for our “storage”.

            Also, we don’t need residential AC here, but we need heat in the winter, so the PV generation and house electricity consumption curves overlap quite poorly on an annual basis.

          • philofthefuture

            I’ll second that! 😀 Huge output in summer, huge draws in winter. Grid backup makes it all work. Our AC is ‘open the windows!’ :<)

          • philofthefuture

            I have 30KW of solar 27KW out of three 9KW inverters. That 27KW is on a sunny day, on a rainy/cloudy day that can easily drop to 2.7KW or 10% sometimes even less if it’s particularly dark and stormy. Day storage is easy, week storage is extremely expensive, two weeks absolutely prohibitive. Using the grid I am energy neutral, I do have overnight battery backup for the occasional outage only.

      • Freddy D

        Precisely. It’s actually far less capital equipment (therefore far less global warming pollution) if society builds the renewable generation to meet demand. As opposed to massively overbuilding systems and batteries for the “low water mark” day of the year. And use the existing rid to move it all around.

        • philofthefuture

          Low cost hydrogen generation will change that.

      • Robert Pollock

        And a penny saved is a penny earned, it’s true. We can spend on new tech but I’ve always found that making the building more efficient first had just as good a return on investment, as any equipment upgrade.

        • philofthefuture

          Just switching to LED’s can make a huge improvement.

      • philofthefuture

        Search ‘hydrogen house’. Home hydrogen generation/storage and fuel cell generation. That’s on my bucket list within the decade.

    • Robert Pollock

      Factor in an electric car and everything re-images; My Spark holds only 21kw, about what the house uses in a day on average. Our next electric might be the Tesla X at 80 kw, or what the house would use on it’s worst (Air Conditioning) day. You can’t size a solar PV array to accommodate fluctuations like that. Using the car as backup storage might make sense, but any appliance that uses lots of power could/should have a dedicated storage system if it’s more feasible than one big powerwall in the garage. Cooling an over heated pool with the ground, or ice chests for the AC, or a car that runs on the stuff, and especially thermal mass in your houses’ design.
      If you drive electric you’ll know that the car’s charging plan is an integral part of your schedule. It’s not difficult, it can all be done while you’re sleeping or at work or out for dinner. It’s not uncommon to bring home a few dozen kw’s. I can easily see a routine that charges a Tesla and ‘brings home’ 20 kw or 30 kw daily that might go wasted or could be used if you could find a way to get current/electricity back out of the car’s battery. They make them so you can’t, or did at first, because they were afraid of people connecting them to the grid ‘unannounced’. Dangerous to others. Lots of possibilities when your giant storage battery is mobile, and most of the power on the grid goes to ground or resistance (wasted) anyway.

      • Robert Pollock

        Some liked the old Norton motorcycles because the handle bars were empty and you could store a piece of hose in there. Never out of gas. Just lay the bike down behind any license plate gas filler inlet and syphon. Stealing it would be if you didn’t know the car’s owner, otherwise, it was just an emergency back up for when the reserve didn’t work, which was always with the Nortons. I carried one more for the esteem, but had to use it once on a friend’s pickup.

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