Minneapolis – The free, self-guided 16th Annual MRES Solar Tour Saturday, October 1, includes open houses at about 50 Minnesota homes, businesses and organizations that have solar and other renewable energy installations. Organized by the Minnesota Renewable Energy Society (MRES), the tour includes open houses in the Twin Cities and several other Minnesota communities from 10 a.m. to 5 p.m.

For the first time, this year the online guide to sites at www.MNSolarTour.org will list each site’s additional eco-friendly features. Besides the usual pictures, maps and details about alternative energy technologies for each site, the guide will list eco-friendly features such as urban chickens, electric cars, rainwater storage systems and the like. Tour guests must register at www.MNSolarTour.org to obtain addresses of the tour sites.

“The solar tour is popular with people who are thinking about purchasing some kind of renewable energy technology because it gives them a chance to see lots of systems and talk to lots of owners,” said Laura Cina, managing director of MRES. “The lists of other eco-friendly site features this year should draw even more people to the event.”

The owner, representatives from TE Studio, as well as representatives from Energy Concepts will be on site during the day to answer your questions.

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The March electricity bill and meter readings show that the home was zero energy during the month. After a long and cloudy winter we are now observing surplus energy generation, which will offset the winter-use of electricity.

On a related note, the energy monitor is showing that the PV systems produce at near the nominal output they are rated. Over the last week we’ve seen 4.4kW and more out of the 4.68kW-rated arrays.

Meanwhile, we are on the quest for carbon-neutral operation. Again, with a very cloudy winter that yielded neither great passive solar heat gains, nor plentiful active solar electricity and hot water, we are excited to see all sources pick up now on the way to carbon neutral operation.

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Photovoltaic Tracker

Solar thermal panels on the roof

We are happy to announce that the solar photovoltaic system at the Passive House in the Woods produced the first 1/2 kWh of electricity yesterday. Both the solar electric and solar hot water systems will help this home achieve carbon-neutral operation and offset its footprint.

[Update] Midway through day 2 of operations, the PV system has now generated in excess of 50 kWh. It is exciting to see the power generation meter spin up and start to offset the consumption meter!

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Electrical

Wiring bundles

Electrical box

Both line and low voltage wiring are installed by EHS. They take great care in a clean installation that is easy to understand. Low voltage and line voltage lines are run in separate bundles in an effort to keep signals within undisturbed.

The electrical system in a Passive House is similar to ordinary electric systems with the exception that any protrusion through exterior walls or the roof are being sealed for air-tightness and uninterrupted insulation.

Gary chose to have a lighting control system by Lutron installed. This is not required by the Passive House standard but can help reduce lighting-related energy loads.

Plumbing

Plumbing with air-admittance valve

Insulated water supply lines

Wall-hung toilet rough-in

The plumbing system is very simple. The design of the home puts most of it in one single wall that extends vertically from the basement to the second floor throughout the home. This means short waste and supply pipe runs, and an economical installation. The supply lines are copper, and continuously insulated for efficiency. The waste lines are PVC, and mostly insulated. Warm waste water is used to pre-warm the well-water that is being pumped into the hot water tank, upping the efficiency of the hot water system. Additionally, hot water is being pre-heated by a solar thermal collector on the roof. Last but not least, an electric on-demand water heater can boost the water temperature if the combination of waste-water heat recovery and solar thermal pre-heating do not make it hot enough. 85% of the hot water needs will not require the on-demand unit.

The plumbing system in a Passive House is similar to ordinary plumbing systems with the exception that pipe runs are continuously insulated, and that air-admittance valves are being used instead of vent stacks.

Ventilation

Ventilation system (duct and ceiling box)

Passive House certified Lüfta ventilation machine

The ventilation system is at the heart of each Passive House. This building will utilize a Passive House certified Lüfta heat recovery ventilator from Germany, supplied by Peak Building Products. It will be combined with a 600 foot PEX earth loop provided by Rehau—buried below frost on the property. This system will pre-warm, or pre-cool and dehumidify the incoming ventilation air and boost the system’s efficiency to well above 90%. The Luefta machine will supply the entire home with outside air year-round, and exhaust air from the bathrooms and kitchen. The ductwork comes from Inno-Products and is comprised of a home-run layout with 3″ diameter plastic flex-ducts. The systems throughput is being adjusted by sensors that measure both CO2 and humidity levels in the air. This setup means that the homeowner does not have to adjust ventilation rates, and that the system will ramp down when it’s not needed to conserve energy.

Backup Heating

Nuheat standard mats

Nuheat is supplying electric in-floor heating mats on room temperature thermostats. There are 7 zones throughout the home that can be individually adjusted. The entire system is sized to supply a peak heat load of 10 kBtu—about 3,000 Watts, or the equivalent of running 2 hair dryers at the same time. This represents a 90% reduction in heating system over most conventional construction today.

The heating system in a Passive House is very different from ordinary heating systems. It is merely a backup for long stretches of extremely cold and cloudy days in the winter and does not compare to conventional systems in terms of its capacity.

Renewable Systems

PV tracker, underside

Stand-offs for solar PV and thermal systems

Energy Concepts helped with the design of the renewable energy systems. There are three systems that will go into the building: A solar photovoltaic tracker, a photovoltaic panel array, and a solar thermal domestic hot water system. The photovoltaic systems are scheduled to produce about 6,750 kWh of electricity annually, while the solar thermal panel has the capability to pre warm enough domestic hot water to provide 85% of the annual demand. The remaining portion of heat needed will be supplied with the help of a Stiebel-Eltron booster heater.

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Pouring a footing for the solar tracker

PV tracker similar to this project

Gary decided to use solar electricity and generate it on site with the help of a solar tracker as well as a fixed array of panels on the roof top terrace. Sized and engineered by Energy Concepts, these two systems are projected to make 6,750 kWh of clean electricity per year. The home is currently projected to use only a total of about 4,200 kWh—including Gary’s household electricity. This means that the building will become a solar power plant—making more energy than it consumes.

Backside of PV tracker

According to the energy model we used, any carbon emissions generated by an average fuel mix used by the utility (meaning electricity made from some portion of coal, gas, nuclear, and renewable resources) will be offset by the electricity provided by the solar panels. This works without batteries. The power grid essentially becomes the battery. The home will consume solar power first if it is available, and use grid-supplied power when it is not. Whenever it makes electricity it will feed it back into the power grid for consumption.

Pedestals for the PV system

PV panels similar to this project

We are installing an energy monitoring system in the home to measure both the incoming and outgoing amounts of electricity. This will allow us to verify the energy calculations, and Gary to understand how his lifestyle affects the overall performance of his power plant.

Tomorrow: Indoor Environmental Quality

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As sustainable design moves out of its infancy and tries to establish norms and standards for new construction, one of its central challenges is how to create energy that can power an entire house–and where possible–feed any surplus back to the grid.

Energy Concepts (ECI) was contacted early on as the Passive House in the Woods project concepts were being explored. As 2009 Focus on Energy Market Provider of the Year, ECIʼs veteran engineer Craig Tarr has the kind of experience and technical background to make a “carbon neutral” building become “carbon negative”–that is, a building that produces more energy than it consumes.

There is nothing more sustainable than creating a building that is a net producer of energy rather than a consumer. Given the problems of fossil fuel electricity production, this is likely to be the “gold standard” in sustainable design going forward. Quite simply: if we are not part of generating societyʼs solutions, than we are part of its problem; or at least, are certainly subject to its problems.

With that in mind, ECI set out to design a system that would meet a high standard: producing at least as much energy as it consumes. Passive House in the Woods is an all electric home, so the issues were reduced to providing electricity. But, because it is much cheaper to heat water with the sun than to produce electricity from the sun to heat water, a secondary system to provide solar hot water was planned.

Generating electricity in a rural area comes down to two choices: wind or solar. In this case, since the electric needs were fairly modest and the wind resource not particularly abundant, a solar photovoltaic system was the clear preference.

ECI and its installation partner Steiner Plumbing/Heating/Electric of River Falls, have developed a specialty in solar PV Top of Pole Mounts (TOP). Essentially, rather than using a buildingʼs roof for mounting PV panels, the TOP uses an 8ʼ x 8ʼ steel beam anchored in cement and then mounts a rack of panels on top of that. The system maximizes efficiency when it is paired with a dual axis tracker, as explained in this post about how TOPs are actually installed.

Tarr and the other engineers and contractors examined the likely electric use at Passive House in the Woods and determined that while meeting as much as 90% of the buildingʼs overall electric use, the TOP mount would likely fall short of zeroing out the bill completely. So, an additional four SunPower 210 panels were mounted, along with the solar hot water panel, a 4ʼ x 10ʼ Solar Skies SS40, on the buildingʼs roof.

Letʼs take a moment to talk about solar PV panels. SunPower panels were selected for this site because they are hands down the best, most productive solar panel commercially available. Likely you will hear a lot of hew and cry about solar innovations– nano-solar, thin-film solar, Chinese panels at $1.00 a watt –but what needs to be understood is that, as a long-term investment that will provide an essential

service to a house, solar PV is not about messing around with things experimental or cheap. The last thing any homeowner wants or needs is to be left without electricity after a long day at work. Thatʼs why SunPower is far and away the best solar panel in todayʼs market. At 31” x 61” the panels mounted on the TOP system produce 230 watts instantaneously– at least. And, as has been verified in independent 3rd party testing, SunPower panels often outperform their nameplate rating–meaning they produce more than they are rated to produce. Thatʼs a new spin on the old idea of “free energy”.

But, the point is this about solar PV: a homeowner only has so much space, either on their roof or in their yard, and they have to produce as much power as they can. Given that, the best, most powerful and reliable way to do that is to use SunPower modules. And thatʼs what the best and brightest clearly understood when designing the electric generation system for Passive House in the Woods.

So, for the electric needs of Passive House, there are 16 — 230 watt panels mounted on the Top of Pole system, governed by a dual axis tracker which is constantly maximizing production by aiming the panels directly into the sun. As the sun moves, the panels track the sun; as the season changes sun angle, the panels adjust as well.

The 16-panel system should produce in the range of 6,000 kWhs annually. But, because Passive House set a high standard of being completely carbon neutral, if not carbon negative, an additional 4 SunPower 210s were racked up on the roof. That will provide at least another 1,000 kWhs annually, thus putting the Passive House in the Woods over their anticipated power needs on an annual basis.

By the way, generating electricity with solar is not, right now, competitive with current generation methods. Meaning: yes, it is cheaper to sit back and allow the power company to provide you with electricity. The problem with that though is, we donʼt really understand all the costs that are accruing to the environment and the human population as a result of burning coal. If we truly understood those costs, and could price them, the odds are good that solar would not only be competitive with coal, but actually outperform coal. So, while a system like the one described here is in excess of $50,000, before generous State and Federal incentives kick in and knock the costs under $30,000, the real question should not be about the costs of solar: it should be, what are the real costs of coal? And are we leaving those costs for future generations to pay?

Next time: understanding the solar hot water system at Passive House in the Woods.

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