Today the framing of the second floor began, and measures were taken to provide proper drainage from the building.
Today the framing of the second floor began, and measures were taken to provide proper drainage from the building.
Since there are no moving parts, PV doesn’t require any maintenance except cleaning the glass. The photovoltaic collector doesn’t fail. If a panel fails it’s usually because a solder joint connecting the cells fails. Most manufactures warranty their panels for 80% of rated output for 25 years.
Inverters have traditionally been the weak point in the system. Mean failure rate has been 5 years. 2 year warranties were the norm in the late 1990s. 5 year warranties are common now, and some manufacturers offer 10 year.
PV panels produce DC power which is either used directly by DC lighting and appliances or wired to a central inverter, typically located indoors. An NREL study (PDF page 41) found that inverters have needed to be replaced every 5-10 years while panels last 25 years or more.
Central inverter PV systems are wired in series like Christmas lights. Central inverters use a Maximum Power Point Tracking (MPPT) algorithm to determine the optimal output of the system. Therefore, the output of the whole system was only as good as the worst performing module. If there is one bad solder connection, one dirty cell, or one partially shaded cell the whole system is affected. Just like Christmas lights it is impossible to find a problem without testing every individual part.
German and Austrian central inverters are the best quality because their government incentive programs require installers to warrant the system for 10 years which put pressure on manufacturers to improve their reliability to stay competitive. North American manufacturers have not kept up.
That’s all changed with micro-inverters. They mount outside attached to each panel. With micro-inverters AC power leaves each panel. There’s less inefficiency due to DC voltage drop. The Christmas light problem is solved. Micro-inverters get as much energy out of each panel as it can produce, so partial shading is no longer a problem. If an inverter fails the rest of the system still functions, and it’s a relatively small replacement cost compared to a central inverter.
Micro-inverters are also designed to be much more reliable. Enphase credits four things:
Traditional inverters use electrolytic capacitors which are notorious for their short life. Microinverters still use them, but they use a more durable design. From Enphase Reliability Study for Electrolytic Capacitors:
“For traditional power converters, an acceptable useful life of capacitors is as low as 2000h at 85°C. Out of desire to increase the reliability of its inverters, Enphase Micro-inverters use capacitors rated from 4000 to 10000h at 105°C. The capacitor lifetime is very sensitive to temperature as its useful life doubles for every 10°C temperature drop.”
Enphase also parallels their capacitors. When one fails the quality of the current wave degrades because it gets a little more ripple in it, but it’s not catastrophic to the inverter.
Since micro-inverters are a new development there’s no lifespan data. In an Enphase white paper they compare their Mean Time Between Failures (MTBF) determined from accelerated lifecycle testing to other electronics:
“The concept of MTBF is often confused with a component’s expected useful life. In fact, these concepts are not the same. For example, a battery may have a useful life of four hours and have an MTBF of 100,000 hours. These figures indicate that in a population of 100,000 batteries there will be approximately one battery failure every hour during its four hour lifespan.”
Enphase has a 600 year MTBF goal, which would make integrating micro-inverters with solar panels at the factory the default. At that point solar panels will be truly plug and play.
The one downside to micro-inverters seems to be for off-grid systems. Since each panel is putting out AC power, you have to have another central inverter to convert it to DC to store it in the batteries.
There are at least a dozen companies working on micro-inverters, but Enphase is the only company shipping a product that we’re aware of.
These Thermeleon tiles are white when it’s hot and black when it’s not. When they’re white they only absorb 20% of incident sunlight, but when they’re black they can capture 70% of it.
They use a polymer suspended in water with a dark background layer. When it’s cool the polymer stays dissolved, and the dark background is exposed. When heated, the polymer condenses into tiny droplets which appear white because scatter and reflect the radiation.
The Thermeleon project won the 2009 MIT Making and Designing Materials Engineering Contest. They need to find out if their tile is durable enough to stand up to the harsh conditions on a real roof before they have a real product, but they say the ingredients are all cheap and readily available.
The Advantek subfloor for the ground level was installed today.
This is the second article in a series originally written for New Life Journal.
By: Clarke Snell
Let’s not beat around the bush. In this day and age, heating and cooling our houses amounts to spending a lot of money to create a lot of pollution. That’s because most of the energy we use for this purpose comes from burning fossil fuels. What’s worse, as a society our response to skyrocketing oil and gas prices has been to keep making the skies dirtier. The weird thing about this whole scenario is that everything we’re burning is just stored solar energy.
Here’s the process: Plants turn sunlight into energy which is turned into living tissue. Animals eat the plants. Plants and animals die. Wait several hundred million years. Drill deep wells and dig big holes to access resultant oil, gas, and coal. Transport all over the planet and burn copiously until supply begins to get scarce. Fight wars and panic until lights go out and heat goes off.
I don’t know, wouldn’t it make better business sense to skip the “middle man” and go directly to the source, i.e. the sun? Duh. The technique is called passive solar design: the conscious manipulation of the sun’s direct energy to affect the temperature inside a building. It is clean burning, runs for free after installation, has no moving parts, comes with a lifetime guarantee, isn’t susceptible to power outages or unexpected supply shortages, requires no special maintenance, and can be accomplished by simply rearranging the materials used in a conventional modern house at little or no extra expense.
Though its most effective real world implementation is a beautiful dance between science and art, the concept behind passive solar design is elegantly simple: if you want heat, let the sun in; if you want cool, don’t let the sun in.
Our loving star has made the process so much easier by methodically changing its path through the sky throughout the year. In our region, the winter sun rises to the southeast, stays low in the sky to the south, and sets to the southwest. The summer sun rises to northeast, stays high in the sky most of the day, and sets to the northwest. This is an amazing stroke of luck because it means the sun is low in the sky when it’s cold outside and high in the sky when it’s hot outside. Low sun is easy to let into a building, while high sun tends to be blocked by the roof and other protrusions of the building itself. Perfect!
With this basic observation under our belts, we’re ready to realize a passive solar masterpiece. First, we need to find the right place to build. In our region, that means a site that will give us unobstructed access to the low southern winter sun. Some trees or other obstructions to the east and especially the west would be great to block the hot rising and setting summer sun. (A ridge or evergreens to the north might block some winter winds, but wind is very site specific so we’d have to spend some time on site to make that call.)
Next, we’ll design our building to let in a lot of winter sun and block a lot of summer sun. Building shape is the most basic parameter. In our area, the best shape is longer on the east-west axis, creating more wall surface on the south and less on the east and west.
The main avenue for sun to enter the building will be through glass. From a heating point of view, only south-facing glass will create a net solar heat gain, so other glass should be minimized. However, north, east, and west glass are an important part of our natural ventilation cooling and daylighting strategies. This is where the delicate interplay of science and art comes in, in other words we’ll find beautiful compromises.
The heating equation, in any case, is straightforward, we simply have to carefully match the square footage of our southern glass windows and doors to the amount of “thermal mass” we place in the building. Thermal mass simply means something that stores heat, so technically everything is a thermal mass. Dense heavy materials usually store heat well. Water, concrete, stone, and earth are good examples. A great place to put mass in a building is in a concrete or earthen floor. Sun flows in through glass covered openings and is stored in the mass of the floor. The mass sucks up heat, thus preventing the house from overheating during the day, then slowly releases the heat after the sun goes down keeping the house warm at night. The trick is creating the right balance. Science to the rescue! We have everything from rule of thumb glass to mass ratios to computer assisted thermal modeling at our disposal.
Next, we’ll need to design our roof overhangs and other protuberances so that they follow our mantra: block sun when it’s hot, let in sun when its cold. The poster child for this is the southern trellis covered with deciduous vines (grapes and hops are two options for you vintners and brewers out there). Thick leaf cover that blocks the sun in spring and summer dies back in fall and winter to let the sun through. Since we know where the cooperative sun will be in the sky at any time of year, roof and window overhangs can be sized to interact with the sun exactly as we like. We’ll add covered patios on the east and west, again to block low hot sun, and one on the north to create an outdoor room that will be shaded all summer long.
Finally, we’ll work with the surrounding landscape to heighten our design. In tandem with our patios, we’ll add shade trees, especially to the west and north. Plants not only create shade, but evaporative cooling which is the natural technology mimicked by your refrigerator and clanking, polluting window A/C or HVAC unit. We’ll also create a focus to the south, perhaps placing an outdoor kitchen under the trellis with a kitchen garden in front of it. We’ll place doors and windows that encourage cross-ventilation and allow effortless transitions to outdoor rooms. Don’t forget that in our climate a little tweaking back and forth between sun and shade makes the outside comfortable for most of the year. Outdoor rooms are inexpensive access to the mansion of nature. Of course, we’ll also design a unified insulation strategy that includes measures to slow convective, conductive, and radiant heat loss through the building, but that’s another story.
Ta-da! A passive solar masterpiece that will supply a baseline of heat and cool at the right time of year which can then be enhanced to create the specific indoor environment of your choosing. Though you may not get the picture from this frantic overview, none of these design features need to control the look or feel of the building. Passive solar is flexible if you are. It’s a pivotal design concept, not an architectural gestalt.
Disagreement abounds even on some of the basics. For example, some people feel that our climate is too wet to allow for natural ventilation as a cooling strategy because open windows plus humidity can result in mold. In the end (here’s where you refer back to that lovingly pawed copy of my column from last month that’s taped to the fridge), the right approach to passive solar is going to have to match the specifics of who you are with the specifics of the place your house will sit.
I will however be unequivocal about one thing: you are going to heat and cool your house with solar energy one way or another. The only question is if you want it free and clean or expensive and dirty. This may sound like a laughably obvious choice, but a cursory glance at any cityscape or subdivision will show that the sun is presently laughing at us, not with us.
By: Clarke Snell
This is the first in a series of columns written for New Life Journal on the quickly propagating though illusive animal known as “green building”. These days it seems like there is such a frenzy to do “green building”, that few of us slow down long enough to really say what it is. I’ll remedy that problem right off. For me “green building” grows out of the broader concept of “sustainability”: the simple idea that the way of life we choose must not lead to circumstances that prevent that way of life from continuing. Bees have got it down, rabbits can do it in their sleep, but we humans just can’t seem to wrap our big brains around it. In order to even start moving in the direction of sustainability, I feel that we need to create buildings that balance five often conflicting traits:
Five Elements of Green Building
(1) Low Construction Impact. Building is almost always an initially destructive act. Land usually has to be at least minimally cut and reshaped, holes need to be dug, and materials refashioned to serve the building. A green building minimizes its construction impact on the local ecosystem through careful design that considers the building site as a partner rather than an inconvenience. It minimizes its impact on the ecosystem of the planet by utilizing replenishable materials that cause the least amount of environmental destruction in their use.
(2) Resource Efficiency Through the Life of the Building. After a building is built, people move in and use it. This hopefully long relationship usually constitutes the main period of impact that the building will have on the planet. Heating, cooling, lighting, bathing, and watching re-runs of “Survivor” all require resources that are often non-renewable and polluting. A green building creates the daily indoor environment for its human inhabitants in the most efficient, non-polluting, and renewable manner possible.
(3) Longevity. Creating a building requires natural resources such as construction materials and fuels as well as human labor and ingenuity. The longer a building lasts, the longer the time span before the natural environment will be asked to ante up resources to repeat the process. A green building, then, is designed to have a long fruitful life.
(4) Nontoxic. It’s a true testament to our dire straits that this one even makes the list. As bizarre as it may sound, we have to be very vigilant if we want to create a modern building that is nontoxic to its inhabitants or the environment at large. Okay, y’all, it’s pretty simple: a green building does not poison its inhabitants or the environment.
(5) Beauty. To be simplistic (give me a break, it’s just a short column), a sustainable system is one where component elements work together to create a self-regulating, self-maintaining cycle. The complex tangle of relationships that tend to create such systems in nature develop slowly over eons. Everything on the planet earth developed, changed, and adapted as part of a sustainable system.
Flash forward to today. We modern humans find ourselves out of the sustainability loop. What happened? Simply put, we left home. Once we cut ourselves off from a deep, cultural connection to a specific place, an exact climate, a complex matrix of relationships that slowly developed over time, we left the basic source of our sustenance, our sustainability. Now we are left with the daunting task of trying to rebuild that delicate connection to the web of life.
Hey, don’t look at me. I can’t begin to imagine the delicate negotiations we’re going to have make to get back in the club. It does seem to me, though, that to create a sustainable lifestyle, we need to stay put more of the time and derive more of our social, physical, and spiritual sustenance from our own backyards. For example, it takes a long time to build healthy soil to grow good food; to build a network of friends and compatriots that will be the basis for community; to nurture the trees and other plants that will be part of a house’s cooling strategy. These things simply won’t happen if we aren’t sufficiently seduced by our buildings to stay with them for the many years it will take to turn them into integrated places that nurture both their inhabitants and the environment. A green building, then, needs to be deeply and personally beautiful to its inhabitants, a place that is as hard to leave as a lover and as unthinkable to neglect as your own child.
From Theory to Practice
Okay, we’ve defined the task, let’s build some stuff! Unfortunately, we live in a place called the real world where things are never that simple. The fact is that the five elements I’ve outlined are often in conflict with one another. For example, to save energy using passive solar design on a forested site, you need to create a larger construction impact by cutting more trees to access the sun. On the other hand, cob, a mixture of clay soil, sand, and straw, can have an incredibly low construction impact, but isn’t the best insulator. Cob buildings, then, will often use more energy to heat, than comparably sized buildings using other wall systems. Even the seemingly no-brainer concept of building without toxins is harder than it sounds. When it comes to drain pipe, for example, you’re probably going to use PVC. It’s a non-renewable petrochemical product and highly toxic dioxins are released in its manufacture, but I have yet to find a truly practical alternative.
In the end, “building green” is a deeply personal process in which you make judgments as to how a building will best merge with your own personal mode of survival, be it computer programming or subsistence farming, to create the most beneficial impact on your environment, both local and global. An ideally “green” building, then, must be a very specific thing, matching your idiosyncratic personal needs with the fabric of your exact local environment. It’s a daunting challenge, yes, but what more important goal have you got on your to do list? In the coming months, I’ll be throwing in my two cents worth as to how you might go about creating that strange, beautiful animal known as the “green building”.
This week, Matt and his crew continued to frame. The bottom plate was bolted to the slab, and the TJI joists were installed.
Today, Matt and his crew started framing the lower level walls. The 2×4 wood studs are placed 2′ on center rather than 16″ because the 12″ of Hemcrete will provide enough stiffness to the structure.
Matt Schillig and his crew completed the termite barrier today. It consists of 2 pieces of brown aluminum flashing, a continuous adhesive membrane, 1/2″ Advantek and caulk.
Today, the concrete slab was scored on a three foot grid, to prevent cracking. David Madera and Greg Flavell of Hemp Technologies also helped us to perform a full-size Hemcrete test.