Can I Recommend Ground Mounted Systems?
Primarily this page is for microFIT projects, however there is some useful information for net metering projects as well. Initially anyone could have a ground mounted system if they chose, now only rural residents can have a new ground mounted microFIT approved. If your property, or any of the parcels of land that border your property are zoned for residential use, a ground mount is not permitted. (This does not apply to net metering)
Primarily this page will focus on fixed ground mounted systems. With the summer of 2010 change by the OPA to provide a lower rate of 64.2 cents per kWh, many people are asking if they should put their system on their roof to get the higher rate. The current price is lower. In 2017 the price will be 21 cents per kWh, and at this price, a ground mount is not attractive for microFIT. However a ground mount still makes perfect sense for net metering installations.
The main reason the OPA gave for introducing the new ground mount category was that on average ground mounted systems produce more power for about the same cost as a roof mounted system, and the lower rate provides the same rate of return for both types of installations.
The logic behind this is that most roofs do not face the ideal direction, and do not have the ideal slope. In addition they usually have shading issues that can’t be remedied. All of these tend to lower the electricity yield below that of an ideal installation. On the other hand, a ground mount can be positioned and constructed with an ideal panel orientation, and can be positioned to avoid sources of shading. Therefore the average ground mount is more productive, and at 80.2 cents the OPA was concerned that it would be too profitable, at the energy consumer’s expense.
Most people in the industry accept that ground mounted systems typically produces more electricity than the average roof mounted installation and that is why most of the applications prior to July 2, 2010 were for ground mounted systems.
Now I would like to examine the topic of choosing between ground and roof mounted systems.
First, two points about how much electricity is generated. If the cost of installing either type of system is nearly the same, and more importantly if the amount of the cheque that you receive is the same for both systems, what other factors should be considered?
- The ground mounted system is delivering more kWh to the grid, and so is providing a greater benefit towards the goal of eliminating coal fired peaking generation plants and is greener.
- After 20 years, no one knows if the IESO will offer another contract at a lower rate. Let us assume they do not. Then you as a home owner have two choices, the first is you can sell the power to your local hydro distribution company at the current wholesale market price, and still continue to generate some income. The second and perhaps better option is that you switch to “net metering” where you use your own power and use the grid as a logical storage element to “store” electricity that is surplus to you daytime needs, and consume power from the grid at nightime or on cloudy days. You only are charged for any amount of electricity that you consume that is in excess of that which you generate, averaged over a ling period of time. Any extra that you generate in excess of your consumption, on a long term average is not paid to you, the surplus is provided free to the grid. Net Metering hopefully drives your electricity bill to zero. The important point with net metering is that you are displacing electricity that you otherwise buy at the retail price with that generated from your own panels, and if your system generation matches your consumption you are receiving the retail price for all of your solar generated electricity. Today that is about 12.5 cents, in 20 years it probably will be more. When time of day metering comes into use, solar electricity is inherently generated during the peak periods, and so attracts the peak rates.
Once you select which route you will take in 20 years, the best system at that time will be the one that generates the most electricity. Therefore these two points favour the choice of a ground mounted system even when the dollar amount of electricity produced today is about the same for roof and ground based systems.
Now for some other considerations in choosing between roof and ground mounted systems.
Ground Mounted Advantages:
- Safety – Ground mounted systems are safer to build and maintain
- There is much lower risk to the installation crew due to falling when a ground mounted system is installed.
- On a roof mounted system, the homeowner is at a risk when they try to clear snow from their panels
- During the summer. bird soiling does not requires climbing the roof to clean the panels
- In the winter the home owner may climb the roof to clear snow from the panels, which typically have a lower slope and so are more prone to accumulate snow. A ground mounted system is much easier to keep free of snow.
- Increased risk of lightning strikes due to a grounded metal surface higher than the existing roof. On most residential roofs, they are wood frame construction, and therefore are an insulator. THe solar panels turn your roof into a conductor.
- The higher the panels are mounted, the higher risk due to wind damage.
- Repairs in the winter are much safer, if a roof mounted panel or microinverter fails, you may have to wait for spring to safely service them, if you can’t gain access by renting the use of a cherry picker.
- The panel orientation can be due south, for maximum yield.
- The panel slope can be set at the ideal angle for maximum yield.
- There is less of a size constraint than on a roof, so an installation is more likely to support a 10kW system.
- With less area constrains the lower cost per watt polycrystalline panels can be used, to reach the 10 kW maximum. Conversely a rooftop system with limited space may have to use more expensive monochrystalline panels to reach 10 kW capacity due to insufficient space.
- With a ground mounted system it often is practical to install slightly more than 10kW STD rated panels, with a 10kW capacity inverter and operate in an inverter limit mode. Note the OME has stated that they require a REA assessessment for all ground mounted installations with more than 12 kW of panels. Please see the MOE website for the full text of the regulation.
- There is no concern about roof leaks due to panel mounting
- The roof shingles can be replaced without removing the solar installation
- Appearance: for some installations a ground mount may be located out of site from the home.
- Warranty concerns, some homeowners are concerned that a roof installation might invalidate the homebuilder’s warranty.
- A ground mounted system may be easier and safer for the do it yourself enthusiast to do some or most of the work themselves, driving down the cost of the system.
- Some type of roofs, such as tile roofs or metal roofs require a more specialized mounting system which will increase the relative costs above that of asphalt shingled roofs.
Roof Mounted Advantages
- If your roof faces nearly due south, and has a 7/12 to 12/12 pitch slope and is big enough to hold all the panels you wish to mount, and there are no obstacles such as pipes chimneys or dormers causing shade, then more revenue could be generated.
- A higher location may be less subject to shading, and its attendant reduction in productivity, particularly in a non-rural environment.
- A roof installation is a little less expensive than a ground mounted system
- A roof mounted system can be installed in less time, particularly on a bungalow.
As part of a site assessment I use a tool called a Solar Pathfinder to analyze the impact of roof orientation and shading to determine the solar harvest at a particular location. If both a roof and ground mount are being considered, this can be done for both locations to determine the revenue generated from each type of mounting.
An alternative type of ground mounted system uses a tracking mount, which costs more (About $25,000 more on average according to the OPA in 2010) and get about a 30 to 40% increase in the amount of electricity generated with a dual axis tracker. Note that in order to achieve the upper end of these gains with a tracker, there must be a clear view of the sky right to the horizon for about 248 degrees of arc so the panels can be unshaded from sunrise to sunset. This precludes nearly all urban locations. Note that with a tracker there are more things to go wrong, the system no longer has the simplicity of no moving parts.
Size of a system
If you have about 630 ft2 of area on your roof or ground mount, then you can only install the highest efficiency and considerably more expensive monochystalline panels to reach a nominal 10kW capacity. You would need about 750 ft2 of area to install enough polychrystalline panels to reach the same capacity.
Net Metering Financial View
A ground mounted system will produce more power, if the roof does not have the ideal orientation. Over the lifetime of the system, typically 25 years, a little greater installation cost to achieve more power due to optimal orientation will pay for itself. Also if you wish to maximize your revenue, clearing the snow in the winter is much simpler on a ground mounted installation.
Ground mounted systems are not a good investment at current rates for microFIT. If there is no possibility of mounting panels on an unshaded south facing roof with a 20 to 45 degree slope, and at least 750 ft2 of area, then a fixed ground mounted system will generate more electricity. For net metering, a ground mount makes a lot of sense.
If it makes 39.6/29.1 or about 33% more electricity for almost the same installation costs then a ground mount will be a more productive investment.
There is a lot of piece of mind when a solar system is installed with a ground mount, since the roof is not disturbed. For a roof mounted system, unless the roof has been recently re-shingled a new shingling job should be done before the solar installation, and that should be factored into the cost.