Solar Works on the Roof, Ground, or Far Afield
The 75% decline in the cost of solar electric panels over the past 10 years has turned solar into a practical investment that is accelerating New England’s transition to clean energy. Whether purchased upfront or financed, whether you own your home or rent, whether it’s installed on the roof, on the ground, or across the state, solar technology can help your household, business, or institution save money and the environment.
This section of the guide covers many of the solar options available today. The great news is that there is viable a way to go solar for everyone!
Rooftop Solar Basics
Rooftop solar installations are ReVision Energy’s most common installation and the form of solar people are most familiar with. But even so, there have been some advancements in the way we approach rooftop solar as equipment prices decline and electrical/fire codes become more rigorous.
Any roof facing between southeast and southwest makes a great solar roof. If you want to get scientific, use a compass or compass smartphone app to see which direction your roof faces. The perfect solar orientation in New England is 195 degrees (15 degrees west of due magnetic south on a compass, also known as ‘true south’) but any orientation between 150 and 240 degrees is within 10% of perfect.
With that said, as equipment costs have dropped, our tolerance for off-axis systems has increased somewhat. For example, a solar array that is positioned due west may (depending on the roof slope) harvest within 20% of its ideal annual production.
Since much of a solar project’s total project cost is fixed overhead (electrical connections, inverter, permitting, getting a crew on-site, etc.) it may be possible to simply add extra solar panels to make up for the production loss on a strongly east or west facing roof and still see a very strong ROI for your solar project.
The actual solar panels have become ‘cheap’ – relatively speaking – so there is a certain cost curve where adding additional solar panels does not significantly impact the fixed costs of the project but allows you to generate more power (and, accordingly, more savings) for a modest increase in the project budget.
What about the slope of the roof? Most common roof pitches, e.g. 4/12 to 12/12 are just fine for solar and do not significantly impact the overall yearly solar harvest. More extreme angles (mounting on a flat roof or an awning mount) require special hardware but are also good options in many cases.
Want to understand how this all fits together? See the graphic below, which compares the relative height of the sun in the skyline, to its orientation, at various times during the year.
Shading (Solar Access)
Ideally, we like to see a shade-free solar ‘window’ between 9am-3pm, year-round. When evaluating your site, a solar professional will use a tool such as a SunEye or Solar Pathfinder. These tools take a fish-eye photo of the open sky and then super-impose the sun’s arc (adjusted for longitude) onto the open sky photo. The results can be interpreted by software to develop a percentage figure of available solar access at a site; generally greater than 80% is required but we prefer to see access that is 90% or more.
Any significant shading during the ‘peak’ hours of the day will affect solar production and reduce the system’s ROI. That said, because ReVision Energy employs module level optimizers on most of our residential projects, solar systems are more tolerant of partial shading than ever before. We use the industry’s best site survey tools when conducting solar evaluations so we can generate an accurate analysis of potential shade issues and advise potential customers accordingly.
Ground-Mounted Solar Arrays (and solar trackers)
For all those situations where a roof-mounted system is not viable or wanted, another option is to install solar panels on the ground.
Due to the need to survive decades of punishment from harsh winters, ground-mounted solar arrays must be built particularly tough in the Northeast. The footings and wire management system must be able to handle hundreds of freeze/thaws, and the panels must be able to withstand uplift from the wind, multiple feet of snow, and pummeling from rain and hail.
Historically, that has meant that ground-mounted systems in the northeast involve heavy excavation to pour large concrete footers to support the solar array. The concrete work is not only CO2 intensive and disruptive to the site, but costly. As a result, ground-mounted solutions have historically commanded a significant premium over roof-mounted projects of a similar size.
Our engineering team, not to be deterred by the challenge of marrying absolutely perfect product performance with a need to reduce costs and gain efficiency, has evaluated hundreds of racking and foundation solutions over the years. In 2016, we made an investment that significantly improves our ability to install ground-mounted arrays: a Pauselli 900 solar pile driver, which allows us to install pile-driven posts or ground screws for solar arrays without the need for any concrete.
What used to take hours can now be done in a matter of minutes, and with far less disruption to the site!
With the new equipment in play, our premium for installing a ground-mounted solar array has dropped by over 26%, to the point where in some instances the ground mount solution will be comparable or cost-competitive with roof mounted installations.
Some advantages of ground-mounted arrays compared to roof mounts are:
- System can be oriented at perfect angle and shade-free area, no need to accept imperfect home orientation
- Array can be located in less conspicuous area than on the roof
- Array not hindered with on-roof obstructions like dormers, skylights, and plumbing vents
- No rooftop work required, so certain parts of the installation go much more quickly
We also are still fans of and installers of AllSun Solar Trackers, a dual-axis, GPS-driven tracking system that allows a solar array to harvest roughly 40% more electricity in a given location than a traditional, fixed-axis system.
Community Solar / Solar Gardens
ReVision Energy’s approach to Community Solar Farms, or CSFs, is a member-ownership model that follows the concept of community supported agriculture (CSAs). Rather than building the solar array on site at their own home (growing a garden), a CSF shareholder invests in a solar project somewhere offsite (at the solar ‘Farm’). Thanks to recent pro-solar legislation in Maine, solar farms can have 100+ members, where each member receives a share of solar production from the total array relative to their percentage of ownership in the Farm.
Billing-wise, a CSF share works identically to having solar production at your home. 100% of the solar electricity generated by the solar farm is sent back to the grid. Each shareholder gets a credit—based on their percentage share—that is automatically applied to their utility account, which can accumulate for up to a year and be used for any electric load, whether that be heating water, heating the home, or powering an electric car.
The CSF share is utility-specific. Should you move within your region and stay with the same electric utility, your CSF share simply transfers with you. Should you need to move out of the region, your CSF share can be transferred to a new owner. ReVision Energy maintains a long wait list of people eager to buy out existing CSF shares and can help set up the transaction.
Learn more about community solar farms here!
In addition to the hard and fast physics, it’s impossible to close a section on the many options of solar electric system design without talking about the ‘real world.’ In the real world, homeowners and businesses face choices about where to purchase their energy and what kind of solar array makes sense. So when we discuss solar with a prospective customer, we need to know a lot about them in order to design a system. For example:
- Is a rooftop array feasible? If so, how much roof space is there? If not, is a ground mount feasible?
- Beyond pure production economics, what other factors are important? Aesthetics? Carbon reduction?
- What is the rate currently paid for electricity? How much electricity is used per month?
- Has this building had efficiency improvements? Is there room to decrease their need for energy inputs?
- How many people live in the home? How much hot water do they use? How is that hot water heated?
In addition to offsetting household electric bills, we look to every opportunity to leverage affordable solar to reduce dependence on oil or gas by converting water heating and space heating equipment to solar, as we’ll discuss in the next section, SOLAR CAN HEAT AND COOL YOUR HOME.
Interested in learning more about your individual solar options?
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