Before you invest in solar energy, check out these tips on assessing your unique solar window to decide if solar energy makes sense for your site.
Solar power is rapidly becoming mainstream, and the options for investing in solar energy are staggering. A Solar Buyer's Guide for the Home and Office (Chelsea Green Publishing, 2010), by Stephen and Rebekah Hren, is the perfect resource for navigating solar power system options successfully, from understanding how solar systems work to knowing the right questions to ask a professional installer before choosing a system. The following excerpt from chapter 2, “What’s Appropriate for Your Site,” deals with finding the solar window of your site.
Free energy from the sun streams down upon us, and we need to take advantage of it! But to make an investment in solar worthwhile, you must have sufficient access to that free energy. Neighboring buildings, trees, and terrain can all be an impediment to sufficient sun. After all, you can’t live a life powered by the sun in the shade! Even if your home and yard are completely shaded, there are still opportunities to invest in solar energy (and especially solar electricity) through things like green-power programs.
To analyze a particular location such as your south-facing roof space or a sunny spot out in the yard, you’ll need to take stock of the six primary factors that affect any site’s unique solar availability—its solar window (See diagram in the slideshow). Doing so before bringing in installers to get project bids ensures that you understand what the potential limits and complications are for any solar installation at your site. These six factors are:
1. Existing vegetation and its potential growth
2. Average seasonal insolation and climate extremes
3. Position on Earth (latitude) relative to the sun
4. Orientation of your home and other existing structures relative to solar south
5. Terrain such as mountains and other potential obstructions such as complicated roof designs
6. Available area or square footage
If you haven’t already, it’s time to take stock of where your home, building, or office is in relation to the sun. When you get up in the morning, and over the course of the day, watch where the sunlight comes in and where it goes. Pay attention to where it is at midmorning, midday, and midafternoon. Which exterior walls are shaded? When does the roof get sun in the morning and when does it stop in the evening? What surrounding structures cast shadows on which part of your home, and at what times of the day? Additionally, which parts of the building shade other parts, such as dormer windows, vent pipes, and chimneys?
As the seasons change, many of these things will gradually change with them. When the sun sinks into the sky during winter, the number of obstructions will likely increase. On the other hand, trees will lose their leaves. Consider how these changes would affect efforts to access sunshine at that time of year. In midsummer, pay attention to the unexpected solar path that starts with the sun to the northeast at dawn, high up overhead at midday, and setting in the northwest at dusk. Each time you watch the path of the sun over the course of the day, remember that it will follow this exact same path on the other side of solstice, so that May 21st will be the same as July 21st, April 21st the same as August 21st, and so on.
Much of what you discover about the position of the sun over the course of the year may be counterintuitive. Since the Earth’s axis is at a fairly steep incline (around 23 degrees), and in addition to spinning like a top it’s also circumnavigating the sun, your relative position to the sun is constantly changing. Studying the intricate dance between your site’s unique solar window and the always-moving sun before trying to harness it will decrease the likelihood of missteps.
The amount of power (or irradiance) a spot on the Earth receives from the sun changes over the course of the day and year, because the angle of incoming sunlight through the atmosphere shifts, as does the amount of cloud cover (or what can be called microclimate). Although every individual spot on Earth receives the same total number of hours of daylight per year, the energy (also known as insolation or solar irradiation) a specific spot receives varies widely based on the local microclimate. This specific amount of energy can be quantified in peak sun hours, and is measured in blocks of 1,000 watts/m2. A chunk of energy adding up to 1,000 watts/m2 for one hour equals one peak sun hour (for example, 200 watts/m2 for one hour in the morning plus 800 watts/m2 for one hour in the early afternoon equal one peak sun hour). The National Renewable Energy Laboratory has been collecting data from weather stations for decades, and provides average peak sun hour numbers for different regions. For solar resources used year-round, such as solar hot water and solar electricity, it’s fine to just look at the peak sun hour number averaged over the entire year. For solar heating purposes, you need to separate out individual months. The next time you hop on the Web, take a minute to visit the NREL Web site and find the numbers for the research station nearest you.
What good will this “average peak sun hour” number do you? First, it allows you to compare your solar resource with other regions of the country, to get an idea of what to expect from any potential solar equipment. It also gives a solid foundation on which to base conversations with solar installers and gauge their knowledge and trustworthiness. Any seasoned installer should be able to converse with ease about your region’s solar resource, how that information fits into your location’s solar window, and the future performance of any solar technologies you have installed.
But the main reason for defining your sun hours is to combine that number with your unique solar window to understand the potential supply of solar energy for your site. With this information, you know how much solar energy is available at your site at various times of year, and you can then estimate how much energy a particular solar device will provide. You will already have an excellent idea of whether solar equipment will work for you, and this will make conversing with potential installers much easier. Many solar installations run into thousands or tens of thousands of dollars, so employing the same diligence as with other large purchases like cars or homes will greatly smooth out any difficulties.
The efficiency of a system depends first upon the available solar energy as described above—which is partially a factor of shading and partially a factor of precise location. Systems lose and gain power depending upon how perpendicular they are to the sun’s rays at any given time. So installers will note the azimuth of a site (how closely it is aligned with true south). They will also note the tilt angle of a fixed mounting structure, like a roof. The azimuth and tilt angle will be used in calculations along with peak sun hours to predict how much energy a particular solar device will deliver. See Table 2.1 (in the slideshow) for comparisons of different tilt angles, insolation, and production numbers.
Fortunately for us, engineers have designed amazing and effective solar site-analysis tools to make calculating the solar resource quick and easy for a particular location. On the first visit to your site, any solar installer worth their salt should do some preliminary analysis of your solar window using one of these tools. The most common of these nifty little devices is called the Solar Pathfinder. The Solar Pathfinder works by positioning a half-globe over an outline of the path of the sun. By leveling this half-globe and aligning it with true south, the reflection of any potential obstructions at any time of day for any month of the year can be outlined on the sun-path chart. Thus a reading can be made in one instant for a year’s worth of changing shadows.
Enterprising engineers have even written smart phone applications—homeowners with iPhones can download an application called the SolmetricIPV for less than twenty dollars that will do a decent solar site analysis. On the opposite end of the spectrum is the Solmetric Suneye, a digital tool that costs upwards of one thousand dollars. Watching a visiting installer use one of these tools (or downloading an app for your smart phone) will go a long way toward bettering your understanding of the sun’s movement over the course of each day and each season.
Since for the most part we have not planned our homes, buildings, and landscapes with the idea of solar accessibility, it’s not surprising that most of our solar windows will be less than wide-open. But it is also important to remember that we inhabit a human-made and human-altered landscape, including not just the shape and orientation of our buildings but also the placement of trees and other potential obstructions. What may seem like a permanent blockage of the sun can sometimes be manipulated and altered—just as the original landscape was. If you’re considering a large solar addition to your home, it might make sense to do some preliminary opening up of your solar window so that you get the most out of your investment.
Sometimes roof space will be perfect for solar except for some obstruction such as a chimney, a plumbing vent, or a small architectural flourish (such as a small window into the attic) that either shades the roof or significantly interrupts the roof space. For instance, our house contained an old chimney from the original coal-fired furnace. The existing gas furnace was vented out of this chimney, but before we reroofed we made the decision to take the chimney down and vent the furnace through a much smaller metal pipe. This made the job of reroofing easier, it removed potential shading, and it also removed a large thermal bridge that conducted interior heat to the outside, thereby improving the energy efficiency of our home.
If you’re considering large solar additions to your home that may require tens of thousands of dollars of investment, spending a few thousand on clearing the roof beforehand may be money well spent. Not only will it open up the maximum amount of space to solar equipment, but it is likely to make the job of installation easier since racking and panels will not need to be altered or disrupted. Small obstructions like plumbing or attic vents can often be moved quite easily, and even larger ones may not be overly costly to move, depending on the degree of their obstruction and the size of your solar project.
As a couple trying to make the world a sustainable place to live in, it’s painful to have to recommend some judicious pruning or harvesting of landscape obstructions such as trees. And yes—by harvesting we do mean cutting them down, hopefully to be used for one of the many purposes that trees are great for, such as lumber or firewood. Large trees near your house not only disrupt your and your neighbor’s solar window—often to the point of making it impossible to utilize solar energy—but they also ruin infrastructure such as sidewalks and roads, gas and water lines, and the foundations of buildings. They can also be a hazard during fire season and cause mayhem during large wind events, something we experienced firsthand during a hurricane. Remember, trees grow! New medium-sized trees (such as the amazing variety of fruit trees) can replace larger ones, and provide summer shade for the yard and walls of a house without ruining your roof’s (and your neighbor’s) solar access and causing the other dangers that large trees pose. If we are going to create a world powered by the sun and renewable energy, we have to be able to access the sun. If we remain in the shade, we will forever be dependent on fossil fuels—and the resulting climate disruption will likely destroy many of the forests of the world. Bear in mind that it may be necessary to harvest a tree or two to save the forest. And while harvesting large trees can be costly, it will make the payback on any solar investment much quicker, while simultaneously protecting your home and family from danger during storms. And the new fruit tree you plant will bear lots of delicious fruit!
Trees come in two types—deciduous and evergreen. While solar electric systems are very sensitive to even small amounts of shade, solar thermal technology can still function at a reduced level when the sun is only partially blocked, such as through the branches of deciduous trees in wintertime. As the sun sinks toward the horizon during winter, make a note of what trees will block your solar resource—and whether they are deciduous or evergreen. And keep in mind that tree size is not static; trees that are close to any solar installation can shade them out in a few years.
What if the trees blocking your solar window aren’t yours? Obviously, if you just go next door and ask your neighbors to cut down their trees, you’re unlikely to get a positive response. Feel them out first, and let them know that you’re thinking about investing in a solar system. If the opportunity arises, consider offering to pay for harvesting any offending trees and planting some smaller native or fruit trees instead. If this seems impossible, or they refuse you outright, don’t despair. It’s still possible to access solar electricity through green-power programs.
It’s also possible that future construction could block out your solar window, possibly after you’ve spent tens of thousands of dollars. See the “Solar Access Laws” sidebar, and visit the DSIRE Web site for more on your state’s solar laws.
Many folks are fascinated with solar energy and want to figure out how to integrate it into their lives, but aren’t particularly excited about altering the look of their house or other building with a few solar panels. It depends on the physical characteristics and orientation of your solar window, but for those with aesthetic concerns about solar panels the options break down as follows:
• Ask the installer to use a part of the roof that is flatter or more hidden for placing the collectors or modules.
• There are color choices for frames, rails, and other structural components of systems, as well as color choices available for solar collectors themselves; make sure your installer knows your preferences.
• Consider placement on a garage or other outbuilding, or a ground- or pole-mount in the yard.
• If your roof needs replacement, consider building integrated options, such as solar electric laminates that stick to metal roofing—or even solar shingles, which haven’t been common but are increasing in market availability.
Before contacting a solar installer, you should also check into your CCRs, or codes, covenants, and restrictions on solar for your building or neighborhood. You might encounter homeowners’ association rules against solar devices viewable from public areas, historic district covenants regarding aesthetics, or other zoning issues such as building height concerns. As mentioned in the “Solar Access Laws” sidebar, in the past few years we’ve seen many new laws restricting antisolar covenants—and more willingness on the part of homeowners’ associations and historic preservation groups to facilitate solar installations. If you have a restrictive covenant or code on your site, will it be worth the effort to fight it? Don’t forget the covenant could be outdated or written by well-meaning but uninformed committees in the past, and you could be setting a meaningful precedent by thoughtfully challenging it. It is also entirely possible that the covenant or restriction could be unenforceable because of new solar access laws. Sometimes homeowners’ associations will allow variances to their covenants if adjoining neighbors have no objection.
One important thing to consider before installing solar collectors of any variety onto your roof is the age and relative condition of your roofing material. Whatever type of solar installation you’re considering, it’s likely to last at least two or three decades, so it makes sense to have a relatively new roof before proceeding. If your roof doesn’t have about ten years of useful life in it, you should replace at minimum the section that will be directly underneath the solar device.
In our opinion, there’s nothing like adding some renewable energy supplies to the world right on top of everyone’s home. But there’s no doubt that beyond cost there are a wide range of factors that might make the idea of putting a solar system on your roof or in your yard a hard sell, or quite simply a bad idea all around. The first is not having an appropriate amount of sunlight. You can’t live off of solar energy in the shade! A responsible solar installer should caution you against a system if you have poor access to the sun, but an excess of solar zeal might prevent this discussion. It’s worth being diligent and checking yourself, probably before you make that first contact.
An important thing to note about solar electricity, as with all electricity, is that it is highly portable. Electricity is already produced far away from where it is consumed, with today’s large power plants often sending buzzing electrons hundreds of miles away. Solar electricity works well with distributed power generation, or having lots of small producers all giving to and taking from the grid. But solar electricity does benefit some from economies of scale, so large solar power plants can make economic sense.
If you don’t have a good spot for a solar system, the portability of electricity means that you can still support renewable energy through green-power or green-tag programs. These are programs that offer homes and businesses the opportunity to purchase a portion or all of their electricity from renewable resources for a small premium, offsetting fossil-fuel-powered generation. The renewable electricity is from a mix of resources like solar, wind, and biomass. While as a homeowner the actual electrons flowing into your home might still come from the coal plant, you can rest assured that the money you are spending to buy electricity is supporting renewable power generation, perhaps a large solar power plant hundreds of miles away. To check if your area is served by one of these providers, check the EPA’s Green Power locator.
Q. If I install solar, will it make my house look ugly or make it harder to sell?
A. No and no. Solar installers today work hard to install systems that blend in seamlessly with your roof contour and color, and don’t stick out. Plus, the Appraisal Journal reports that for every one thousand dollars saved in annual utility expenses, a home’s value increases from ten to twenty-five thousand dollars.
Q. Are these systems reliable? Do they need maintenance?
A. Solar systems need very little maintenance, not usually more than a once-a-year checkup. Dry and dusty regions might need panels hosed off a few times a year. Your system will be warrantied, and if installed correctly will last for decades.
Q. I’ve already got electricity, hot water, and heat—why would I need to buy this?
A. So you know your power comes from clean renewable resources. Fossil fuel-based systems pollute, result in energy dependence on rogue states, and leave the Earth a worse place. Solar energy has none of these issues, and you can actually save money on your energy bills in many places with great financial incentives.
Q. How much is all this going to cost me?
A. Good question! The issues of payback, financial incentives, and performance are detailed and (frankly) a little convoluted. To get it out there, the up-front cost of solar water heating is typically in the three to nine thousand dollar range, a solar electric system is typically ten to forty thousand dollars, and solar heating can range widely from one thousand dollars on up, depending on local climate and the size of the system. Keep in mind that some, and potentially all, of these costs can be recouped through tax credits, incentives, savings on fuel costs, and the like.
1. There must be sufficient sunshine! Look for little to no shade from 9:00 a.m. to 3:00 p.m. on average, year-round. Solar electric systems perform poorly in any shade, though solar thermal systems (systems that generate heat for hot water or interior heating) can handle a bit of dappled shade from leafless deciduous trees in winter.
2. The azimuth or direction the device faces. Generally south-facing for the northern hemisphere, although any direction other than north can work—especially west for solar thermal systems.
3. The tilt angle of the device or of the roof it will be installed upon. This is not critical for most systems as long as they are facing generally south (within about 30 degrees of “solar” south). PV arrays can be installed at any angle from flat to perpendicular. If facing east or west, a lower tilt angle is usually better to catch sun during more of the day. Solar thermal systems should not be installed flat if they are being used to provide heating during the winter.
Insolation or solar irradiation is the amount of solar energy that falls on a particular area for a specified period of time. Insolation is commonly given in watt hours per square meter (wh/m2) or in hours of sun per day. Peak sun hours are the number of hours per day that a site is receiving the equivalent of 1,000 watts/m2. Solar south refers to the direction of the sun halfway between sunrise and sunset on any given day.
All of the factors listed above help determine what is referred to as your solar window, a description of how much solar access one particular spot has available over the course of the year. Different parts of your home and yard will have different solar windows, and finding the one with the maximum amount of solar access will make sure your solar investment pays off.
Solar thermal refers to solar equipment that is intended to transform solar energy into heat. This can be heat for hot water, heat for the home interior, or both simultaneously.
In the later days of ancient Rome, a combination of enlightenment about the tremendous power of the sun and energy constraints resulting from overharvesting of nearby firewood led to the enactment of solar access laws. Many homes throughout the Roman Empire were heated by the heliocaminus, or “solar furnace”—a south-facing room that stayed warm in the winter. As the population increased and the built environment expanded, these rooms became shaded, leading to a ruling in the second century A.D. that a home’s access to sunlight could not be violated by one’s neighbors. This ruling was eventually incorporated into the Justinian Code of Law.
Likewise, English common law—upon which both United States and Canadian law is based—provided for solar access through the law of ancient lights. Essentially, this says that if a building has had access to the sun for twenty years, then no structure may be erected to shade it. It is also likely that this arose because of the incorporation of solar heating and lighting into English homes, and the resource limits of depleted firewood supplies. As of this writing, there are no known cases of the law of ancient lights being enforced in North America.
We believe we are at the cusp of a similar dynamic, where fossil energy’s limits (both its availability and its intolerable pollution), combined with an awareness of solar energy’s amazing potential, is leading to the adoption of laws that not only prohibit ordinances that stymie solar installations, but go one step further in guaranteeing a property’s access to the sun. Over time, such laws will allow us to rework our towns and cities to be powered by the sun, safe from the limits of fossil fuels and the planetary destruction they produce.
Reprinted with permission from A Solar Buyer's Guide for the Home and Office: Navigating the Maze of Solar Options, Incentives, and Installers by Stephen and Rebekah Hren and published by Chelsea Green Publishing, 2010.
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