Category Archives: Solar Power

Not So Complicated

Castleton charger

The new Level 2 chargers at Castleton State College, grid-tied to a 10 kw PV array.

A quickie post here, in the middle of writing a more complicated one. Today I needed to attend an unexpected event in a town an hour from here, and didn’t quite have enough charge in either of the cars to get me there and back. I went anyway, with the idea that on the way home I would go find the new charger I had read about that has been installed in the beautiful, tiny town of Castleton, VT. Bingo; this worked out perfectly. The installation is an impressive setup. Quite a few chargers are grid-tied to solar arrays, but this one has the array directly behind the charger. It makes for quite a visual statement—there’s no doubt where the power’s coming from, and no doubt what it’s being used for. Sunshine, propelling vehicles. The system was installed, in this case, by Castleton State College (with grants from Same Sun of Vermont, and Green Mountain Power), but here’s the kicker—a system this size would fit on virtually any average-size house, or in any average-size backyard. And, with a system this size, most American households could power their houses, AND an EV. It’s just not that complicated. Other than an inverter, which is about the size of a suitcase and isn’t visible in this picture, that’s the whole system.

So, no thorium reactors needed, no superconductors, no not-yet-invented gizmos. And on the other extreme, no horses and buggies and kerosene lanterns needed, either. Just some PV panels, an inverter, and an EV. Yep, not so complicated.

Not Sexy

La Bastilla Ecolodge cropped

Off-grid or grid-tied—that is the question. La Bastilla Ecolodge, Nicaragua. Hmmm, there’s no ice there…

Something’s become more and more apparent to me lately as I ponder our off-grid setup—being grid-tied is inherently more efficient than being off-grid. I know, nothing too sexy here with this technical point, but it’s an important realization, and it has implications for the larger systems that nations need to be working toward.

In my case, as I add generation to approach net-zero, each additional kilowatt of capacity will be needed less and less. Some numbers to illustrate—we are off-grid, and have about 3 kw of solar PV installed in two large arrays. On a sunny day in the summer, when the days are long and the sun is high, the system can produce over 20 kwh’s of power. We tend to use about 7 kwh a day, which means that in the summer we’re often making about three times the amount that we use or can effectively store. The batteries tend to be full by 10:30 in the morning on such days, and then the panels do very little for the rest of the day. In December, however, it’s quite the opposite, with much shorter days and a lower sun angle. At that time of year we only average about 4 or 5 kwh’s of generation each day, which is a bit shy of what we need, and so we run the gas-powered generator off and on, especially in November and December. Usually by mid-January the skies are clearer and the days start lengthening a bit, and we start breaking even again, and continue that way for the next ten months.

So, our house is close to net-zero, but I’d like to completely eliminate those hours where we need to run the gas-powered generator. If I added 2 more kw’s of PV capacity, I’d probably get really close. BUT—that investment (probably $4,000 if I did it myself) would only be needed for about two months a year. Thus, for about 80% of the year it would just sit there essentially unused, which would equate to hundreds of kwh’s of uncollected, and therefore lost, power. In short, the closer I approach being fully net-zero in the off-grid setup, the less efficient the total system becomes. Needless to say, this isn’t good—in addition to the expense, everything has environmental costs when produced, even technology that we need more of like solar PV, so it seems like it would be a case of not using our resources wisely.

If our house was grid-tied (which it never has been, due to the potential expense, because we’re something like 1,500 feet from the power lines), the story would be dramatically different. All those hundreds of kwh’s that I currently am forced to waste would flow into the grid, which would enable to power company to generate less. At other times, when our demand exceeded our production, I would draw these “banked” hours back from the grid. This is actually another of those win/win/win situations. It would be more efficient—it would keep my solar production from being wasted, the losses incurred by transforming power to and from a chemical state in the batteries would be avoided, and when generation is required, it would be done by the power company’s much-more-efficient stationary natural gas plants, or by grid-scale wind or hydro.

Yet another win/win---power companies on both the Canadian and U.S. sides of Niagara Falls generate 4.4 gigawatts of hydroelectric power, without destroying the beauty of the falls.

Yet another win/win situation—power companies on both the Canadian and U.S. sides of Niagara Falls use the river to generate 4.4 gigawatts of hydroelectric power, without destroying the beauty of the falls. This is the equivalent of about four nuclear power plants.

The power company benefits as well—peak solar hours often overlap with peak grid demand, so grid-tied solar inputs tend to reduce peak demand on the grid. The opposite tends to be true when grid-tied homes are pulling from the grid, say, in the middle of the night to charge EV’s, during times of very low demand. The net effect is that grid-tied systems help level the grid. Many power companies, like Green Mountain Power (GMP) here in Vermont, seem to be embracing distributed generation for another reason—taking the long view, they seem to recognize that the role of power companies is and will be changing, away from the old idea of generating power and distributing it in one direction for a single price, and to the model of the power company as a manager of a complex grid that buys power from many sources and distributes it, as needed, in all directions, perhaps with time-of-use (TOU) pricing. (See earlier post “Cloudy Day Pause” for more about how grids might function in the future.)

Remarkably, being grid-tied would probably be a better choice even if I had to use a power company, like some in the Midwest, that rely nearly 100% on coal. Being grid-tied does not change the total amount of fossil fuel that is burned—the companies burn less when grid-tied homes are feeding power in, and then burn more later, when such homes are pulling power out.

Now, while being grid-tied is more efficient when viewed system-wide, what would happen if everyone was grid-tied, in a future situation where fossil fuels might be nearly totally phased out? It’s easy enough to see how the grid can work as a virtual (and unlimited) “battery” for a small proportion of customers, but where is the upper limit? The short version—we’re not quite sure. One thing is for sure, though—U.S. power companies are nowhere close to this limit. In Vermont the electric utilities are currently allowed by law to have up to 4% of their generation from grid-tied systems, but that number was established somewhat arbitrarily in years past, and the legislature is currently expected to soon raise it to 15%, a move that is being welcomed by most of the power companies. A better case study of high RE penetration would be the situation in Germany, though it’s complicated enough that the topic really warrants its own post. Short version—their solar feed-in is around 35% on sunny days, and due to vagaries in the international coal market (coal has become cheaper due to plentiful supplies of natural gas in the U.S.) it has caused disruption in the business models of German power companies, which has had economic costs and, as of yet, fewer than expected CO2 reductions (see Economist article, “How to Lose Half a Trillion Euros“. I personally think The Economist is quite one-sided in this article, but that, again, would probably be a whole other post.) Eventually grids worldwide will need to move toward 100% RE generation as we phase out fossil fuels, and much of this will be distributed generation from point sources. But, 1) we’re not even close enough to worry about it now, at least in the U.S., and 2) power companies will change their business models over time. Indeed, companies like GMP have already started. Fortunately, moving to a smarter grid isn’t an all-or-nothing propostion, but rather evolutionary change over time. (Again, previous post “Cloudy Day Pause” discusses some of this in more detail).

So, back to where I started—it isn’t sexy, but the higher efficiency of grid-tied systems is an important point as we work out our workable vision of the future. We’ll eventually need a smart, flexible grid that efficiently connects renewable generation from million of sources to millions of destinations. In the much shorter term for me, tying to the grid might be the easiest, if not the cheapest, way to achieve net-zero. Much to ponder…

Top image by La Bastilla Ecolodge/Creative Commons at http://www.flickr.com/photos/75904527@N05/6789926688/in/photolist-bm19Dw-bHQZjr-hgdJBV-bBhSJ4, image has been cropped.
Niagara Falls image credit: pierdelune / 123RF Stock Photo

Net-Zero is Possible

An interior view of Middlebury College's 2013 Solar Decathlon entry, a net-zero house.

An interior view of Middlebury College’s 2013 Solar Decathlon entry, a net-zero house.

Until this past summer, I had more or less assumed that a net-zero house, one that didn’t use any fossil fuel to function, could really only be achieved in some ridiculously expensive research and development setting. That may have been true a decade ago, but it isn’t true now. A combination of technical advances and cost reductions has now put a net-zero house within the reach of nearly everyone. Even better, net-zero can be achieved in most buildings in stages, and are investments that are likely to outperform the market in today’s investment climate. The result is a win-win-win situation.

First, what exactly is “net-zero”? There isn’t a hard-and-fast definition, but, in general, net-zero buildings create as much energy as they consume. They typically combine highly efficient construction and appliances with some form of renewable energy generation, usually on-site. But, this can be done in different ways, and sometimes with different goals in mind, and the result is a wide variety of net-zero terms, as delineated in this list from a designer in Waitsfield, VT (his house is in the list below)—

“Net-zero carbon, net-zero cost, net-zero source, net-zero site, near net-zero, net-zero ready…there are many terms used to describe a certain category of buildings that are referred to as “net-zero energy buildings” (or NZEBs).”

In the last six months I have seen or heard about no less than six examples of net-zero buildings, and the variety of approaches in these buildings will give you some sense of the term, I think. (Some of these details are from memory, so forgive me out there if I get something wrong).

Building #1— Kim Quirk is the owner of Enfield Energy Emporium in Enfield, CT, an architectural firm, and she bought and renovated this house and has turned it into a net-zero office space and living quarters. I saw her presentation about this at Solarfest this past summer, and if I recall, the house was originally built in the mid-19th century, and was mostly gutted when she bought it. She had the basement foamed, and did a deep-energy retrofit that included increasing the thickness of the exterior walls and filling them with cellulose insulation. She added a 5kw PV system in the yard, which is net-metered. And here’s the unusual part—for heating, she dug a huge hole under her driveway, about 10 x 12 feet by 10 feet deep, lined the sides with a liner and foam, filled it with sand, water, and tubing, and then buried it. (My rough calculations—about 60 tons of insulated mass). This thermal mass is a huge “Thermos” that can store an entire summer’s worth of heat gathered by a largish array of evacuated-tube thermal collectors. So all summer long they run and pump hot water through this thermal mass (pics here), which brings the temperature up to something like 180 degrees. In the winter another set of tubing pulls the heat out, where it’s radiated into the house in a system of low-temperature (90 degree F) baseboard heat. An interesting approach. One of her goals was zero-combustion in addition to net-zero, and from her talk this summer it sounded as if the building was on its way to achieving her design goals.

Building #2— Architect Bill Maclay’s Dartt House, in Waitsfield, VT. I saw Bill give a presentation about this building last week at Renewable Energy Vermont’s Expo in Burlington. This is another older structure, renovated in much the same way as Kim Quirk’s house. It is actually two or three net-zero projects together—a building that serves as an office, and an adjoining building that he been turned into two apartments. Unlike Kim Quirk’s solar-heated thermal mass method, these buildings use air-to-air heat pumps for both heat and cooling, all powered by a combination of larger PV arrays—one 17kw array that serves as the roof of a carport (last pic on this page), smaller arrays to the rear of the house, and another large net-metered array that is off-site.

Our house, under construction in 2004. Timber-frame construction with R-40 walls and R-60 roof panels.

Our house, under construction in 2004. Timber-frame construction with R-25 walls and R-32 roof panels.

Building #3— Oddly enough—our house. Technically a “near-net-zero building” as it is now, as we still use propane for hot water. But we’re on our way to net-zero, via yet a third approach—using sustainably-gathered biomass for heat. In our case, cordwood. Our house is off-grid, with a 3kw PV system and a 1kw wind turbine. With the addition of a bit more PV and solar hot water, we should get all the way to net-zero. Even as is, the building uses only a fraction of the fossil fuel that most Americans use. The house also has a fair amount of passive-solar design features—it is oriented to the south, and most windows and living areas are on that side of the building, and closets and utility areas are on the north. The site is shielded to the north by hills and trees, and open to the south. The building has performed admirably—on sunny days in the winter I can leave home for work with the house at 63 degrees, and come home to a house that is well above 70, all with no heat on, even if outside temps are in the 20’s. We typically use about 2 1/2 cords of wood per winter for heat, which we burn in a single wood stove on the main floor of the open-floor-plan design.

Building #4— Well, “buildings”, plural. A company called Vermod is making net-zero single-wide modular homes to address the need for efficient low-cost housing in the state. With 12-inch-thick walls and triple-pane windows, and a 6kw PV system on the roof, Continue reading

Cloudy Day Pause

snowy DC

Gray days to deal with.

Mr. X thinks my vision of a future without nuclear power is “too hard” (“Needed: The Hard Path“). I was all set to write a post arguing about it, but something that’s not too uncommon here has given me pause—a dark and cloudy day. This is because a big part of the entire argument of whether we need nuclear power hinges, for most people, on whether or not we can make enough power from renewable sources. And THAT entire argument hinges on the question of intermittency, which is what the cloudy day reminded me of. Solar arrays can make plenty of power on a sunny day, and wind turbines can make plenty of power on a windy day, but what about all those other times? If we depended entirely on wind and solar and hydroelectric, what would we do on short winter days when the entire East coast might be having a cloudy and windless day? Or worse, a week of such days? If the energy constraints in such a system were dramatic, or if such a system was too difficult to build, it might result in that path that would be “too hard”.

So, Mr. X had a variety of points, but his main ones, including whether or not I was being consistent in my thinking, hinge around this “too hard” piece. In general, there are two broad lines of thinking here-

Line-of-thinking #1—We will need nuclear power as we move toward carbon-free sources, because wind and solar and other renewable sources are intermittent, and we will need nuclear power for baseload power. Or, related, we will need nuclear power as a transitional power source, until we build out enough wind and solar and/or develop grid-scale storage capacity.

Line-of-thinking #2—We can indeed switch over to renewable power, and the intermittency problems can be solved, and the money we would have had to spend developing safer “Gen IV” nuclear power would have been better spent on developing the truly safe and sustainable renewable system that we will need for the long term.

So, who is right? Could we make the system work with just renewable power? After some contemplation, I’ve decided that we probably can, though I admit that it will be difficult, as it will involve some fundamental changes. Some factors that make me lean in this direction—

— I think we need to undergo a paradigm shift with regard to how people expect their electricity to be delivered; the new systems will not just mimic the old. Customers today expect electricity to be generated by the utility and made continually available, in any amount, at a set rate. The system of the future might function dramatically differently from this, with the utility companies buying power from thousands or tens of thousands of producers, aggregating that power, and then making it available at a continually varying spot price. Consumers will be able to monitor this price via smart meters, and will be able to use this information to shift their demand.  And, they will indeed shift their demand, because prices might vary dramatically. (And, because the generation is so dispersed, it will help moderate demands on transmission infrastructure.) This change alone would go a long way toward solving the intermittency problem—we might someday see tremendous electricity consumption during sunny hours, as people choose that time when power is plentiful (and cheap) to charge their EV’s, heat or cool their homes, run their water heaters, run their air conditioners, or, factories choose that time to conduct energy-intensive operations.

— Wind and solar complement each other really well. Germany is a good example of this—the country has 32 gw of installed solar, and about 30 gw of wind. Their solar peaks in spring and summer months, when daily solar production is about eight times higher than in December and January. But wind production is nearly the exact opposite, and the seasonal fluctuations largely balance out. (For a visual of this, see pages 13,14, and 16 of this presentation. It takes half a minute or so to load this page, but worth the wait.) Other factors also help, such as the fact that daily demand peaks in most systems during midday hours, and seasonally during the summer, exactly when solar production peaks.

Kaprun hydro-electric dam, Salzburg, Austria.

Kaprun hydroelectric dam, Salzburg, Austria.

— Hydroelectric power could be held back during the day, when solar power is at its maximum, and used during nighttime hours. In many locations it can even be held back seasonally, if required. Pumped-storage systems are used in similar ways; filled when power is cheap, then used for generation when power is expensive. Other forms of utility-scale storage are being developed at a rapid rate, from compressed air storage in abandoned mines, to grid-scale liquid-metal batteries, to ideas about lifting whole mountains (TEDx Talk here), or putting together used EV battery packs in stationary locations for grid-scale battery storage. In all storage situations, the higher the difference between low and high electricity rates, the more profitable the storage—another prime situation where market-forces will help to solve a problem.

— Roofs everywhere need solar panels, even if they don’t have optimum orientations. Panels facing east and west on rooftops (and not just south) spread solar production more evenly across the course of the day (…though in the Southern Hemisphere they put solar on the northern sides of their roofs).

— The larger the geographic area that is tied together by a smart grid, the easier it is to balance power and loads. Over large areas, solar insolation averages out, as does wind production. DC transmission lines are capable of delivering power for well over 1,000 miles, and such transmission corridors could link the production from the windiest areas in the Midwest and offshore to urban centers where it would be needed, and from the sunniest parts of the country to the less-sunny (see post “This is Interesting…“). Continue reading

Urban Rooftops

On top of those skyscrapers...

On top of those skyscrapers…

First, I don’t want anyone to think I have been disparaging distributed, rooftop solar in some of my recent posts. Having solar on every roof would be a fantastic thing, and I think it’s a logical first step toward carbon-free power. PV panels are affordable, roof space is already present, and photovoltaic arrays don’t lose efficiency when they’re installed in smaller arrangements. But my point, every time distributed solar comes up, is that even if every rooftop were covered, this wouldn’t produce the amount of renewable power that we will need, and there isn’t enough rooftop space in cities to even begin to produce enough power to meet the demand of the people there. But, this doesn’t doesn’t mean it wouldn’t be worth doing—rooftop space in the sun is rooftop space in the sun. However, in cities, photovoltaics might not be the best use of this valuable real estate.

So, to back up a bit, let me sing some praises for solar hot water. In terms of efficiency, solar hot water collectors dramatically outperform solar photovoltaic panels. Capturing heat from solar insolation is just a fairly efficient process, compared to converting light into electricity. And, until just recently it didn’t make any sense, in terms of price, to install photovoltaics to make electricity that would then used to heat water. In recent years, however, heat pumps have become efficient enough, and PV systems have become cheap enough, that in many situations it might be a better choice to use photovoltaics and a heat pump to make hot water, instead of thermal collectors. (Good article here.)

Evacuated tube collectors for solar hot water.

Evacuated tube collectors for solar hot water.

However, regardless of the price of photovoltaics, it is likely that the best use of rooftops on large, tall buildings in the city will be thermal solar hot water, at least in any building where hot water or space heating is required. Though prices between the two systems are close to equitable today, the higher efficiencies of solar hot water make the physical footprints of such systems much smaller than that of  PV panels. My rough estimate is that the PV panels required to run heat pumps would take up four times the area of modern, evacuated-tube solar hot water collectors.

So, I suppose I have a rather small point to all of this—that down the road, we might need to use rooftops in cities for solar hot water. The footprints of such systems are smaller, and we could maximize gain from that limited rooftop real estate. Electricity can be produced remotely and then brought in on transmission lines; such a task with hot water would be fairly unworkable.

My second point might be that for some people in some situations, that advances in PV systems and heat pumps have made it less of a clear choice whether installing thermal solar hot water systems is the best way to use solar to heat water. But, as I was walking through small-town Vermont last week and pondering the fact that many people in town have quite-limited roof space with appropriate southern exposure, it could be that thermal systems, due to their smaller footprints, might remain a pretty good choice for many, whether they live in the city or not.

Blog note: Welcome, Australia, Canada, and Great Britain! My post about perennial agriculture seems to have been spread all over facebook, and I have been getting hundreds of views from all over the world, with clear groupings from these places. I write about my corner of the United States sometimes, but my focus is always on ideas and systems for the whole world, so it’s great to have you on-board. We’ve got a whole planet to fix, and we’re going to need people from every corner of it to get it done.

Image credit: ssuaphoto / 123RF Stock Photo
Image credit: packshot / 123RF Stock Photo

Free Lunch and the Holy Grail

Beautiful things...

Electric motors, beautiful things…

We had a charging glitch with the cars today—my wife plugged the red one in at work, but came back after eight hours only to find that it must not have been plugged in right, and hadn’t charged at all. So, after work I took it to Middlebury to one of the public chargers, and put my bike in the back and rode the seven miles home. A great ride. It had rained earlier in the day, and the weather was cool, and the sun was shining huge sunbeams out from under the retreating clouds, and everything was about as green as it can ever be. Quite bucolic, with the farms and the fields and the Adirondacks in the distance. I wish I had taken a camera.

So I rode along thinking about the energy the Leafs use. They go about 4 or 5 miles per kwh of charge. To put that into perspective, our solar panels make about 3,000 watts in full sun, or 3 kwh’s. So, in an hour the panels make enough power to propel a Leaf, which is slightly heavy at something like 3,500 pounds, somewhere between 12 and 15 miles. As I pondered the effort it was taking to propel 190 pounds (me plus bike) for half that distance, this seemed quite impressive. To move a weight that is approaching two tons for a distance of 15 miles, with the sunlight that hits a quarter of our barn roof in just one hour—that seems like a free lunch. Continue reading