Answers to Common Questions about Installing Solar in Your Home in St. Charles

By Paul Hopkins, Electric Utility Engineering

The current tax incentives and solar renewable energy certificates program have significantly changed the economics of rooftop solar. Currently, almost two-thirds of the total cost of the installed system is covered by these credits, in most cases. We’re happy to say that the City has seen a swell in applications in the last six months.

For our citizens who might be interested in solar, we would like to share some of the frequently asked questions we hear from residents interested in installing solar.

Q: Are there any special considerations for St. Charles because the City operates a municipal electric utility?

A: Solar installers and developers are most familiar with installations on the ComEd system. There is no technical difference in the physical solar installation; however, there are other differences. Due to limitations with our metering and utility billing systems, the net metering process is different. Net metering refers to customers who generate unused electricity from their solar installation who then sell it back to the grid. Additionally, City code requires any residence installing a solar installation that is interconnected to the City’s utility distribution system to have an electric service utility meter enclosure that also has a service main breaker and meets all current codes for grounding and bonding.

Q: How does net metering work for energy sold back to the grid?

A: Solar production that isn’t needed at the customer site at the moment it is produced flows back to the grid. You will need to purchase a special meter that the City will install that measures how much energy flows into the building, and how much flows out of the building back to the grid. However, the meter does not immediately “spin backwards” when the solar array is pushing energy back to the grid. Instead, we read and calculate the value of the energy pushed back to the grid on a quarterly basis, and issue that amount as a monetary credit on your bill. This Renewable Generation Energy Purchase Policy can be found on the City’s website and is different than ComEd’s net metering process.

Q: How do I get started with solar?

A: Here are 7 basic steps:

  1. Seek vendor proposals. We recommend getting at least two quality proposals and notifying the vendor that St. Charles City codes must be met.
  2. Submit for a building permit. The permit type is a generic “Residential Alteration” for which we have created a streamlined permit process for rooftop solar. What you need for this building permit should be part of any contractor proposal:
    • Array size
    • Drawing showing where the panels are going on the roof
    • Electrical raceway and conductor installation details and calculations
    • Electrical drawings, including showing where the array is going to feed back into the main panel
    • Product cut sheets for the major elements:
      • Rack system
      • Panels
      • Inverter(s)
  3. Receive a Permit. Permits with the required information are typically reviewed within two weeks.
  4. Have your solar panels installed.
  5. Secure an interconnection agreement. The City will draft a custom interconnection agreement for each installation. Because your array will be connected to our electric grid, we have specific requirements that must be met. All of the requirements are standard and are not impediments to installation.
  6. Schedule a final inspection. Upon completion of the installation, the City will perform a brief visual inspection of the physical installation, and a grid disconnection test to insure that the inverter stops producing if connection to the City’s grid is lost. The City provides a Letter of Compliance and a Certificate of Completion that may be used to apply for the Solar Renewable Energy Certificates (SRECs) as part of the “Illinois Shines” program.
  7. Enjoy being green. 

Q: Why is the City concerned with the array turning off if the City’s grid goes down? I would like to keep powering my house if possible.

A: This is the most pressing safety issue for our linemen. Since the array is tied to the grid, if there is a power outage and the array keeps producing, the array will re-energize or “back-feed” the grid. This creates lethal voltages on the system for line crews who were dispatched to repair the power outage and believe the system is de-energized. Industry standards require inverters to cease converting DC to AC if the normal utility grid goes down. Technically there is a way to have your array produce during outages, but it requires additional, expensive components to maintain the safety for the line workers.

Q: Why doesn’t the City pay full retail rate for the energy put back on the grid?

A: The City’s rate breakdown is pretty simple. The cost per kWh of the City’s Rate 1 residential rate (currently $0.1208/kWh) includes:

  1. The purchase of energy
  2. All costs for maintaining the distribution system plus any overhead costs required to keep the electric grid reliable.

The rough breakdown is $0.08 for energy, and $0.04 for the system and overhead costs. The City views solar production as competition to our normal power supplier. Therefore, the energy the City buys from you is priced the same as the energy we would have paid to our power supplier.

But even though you are producing your own energy, you are still utilizing the City’s electric utility infrastructure. You need to be connected to the City’s electric distribution system to “sell” your excess energy back to the grid. You also need the City’s electric utility to provide your energy when your solar array isn’t producing enough energy for your needs (think nighttime hours and cloudy days). 

Q: Are there any limitations on the size of the array that I can install?

A: The maximum array design should be sized to produce 100% of your annual energy needs. City code requires case-by-case approval and testing for installations in excess of 10kW.

Q: Why can’t I install a system that produces more than 100% of my annual kWh needs?

A: This 100% limit reflects our current strategy to protect the distribution system. Our system and its transformers are sized to provide you and your neighbors all of your energy needs. If there were several solar installations all producing much more than 100% and backfeeding significant amounts of energy to the grid, there is the potential for transformers to be overloaded by all of the reverse flow.

Example: A standard 50kW transformer serves 5 residential customers (10kW per customer). If all 5 customers installed solar arrays which backfeed 20kW, that transformer would receive 100kW and burn out.

Q: Which is best: a string inverter or microinverter?

A: Each has benefits. The City has no preference. There are examples of each type in service in St. Charles.

Q: How long will it take me to recoup my investment in a solar installation?

A: Even though solar is making a surge and there are state and federal incentives, at this point in time it will typically take between 8 and 10 years to recover the installation cost of the system.

Common Solar Misconceptions

Myth: The City doesn’t allow solar.

Reality: There are already a number of solar arrays producing in St. Charles. Vendors may not be familiar with working in St. Charles, but we embrace solar. If you have questions, call Paul Hopkins in our Electric Utility Engineering office at 630.377.4407.

Myth: Your electric bill will go away.

Reality: Your electric bill can be drastically reduced, but there are still costs that the City needs to recover regardless of how much net energy you are taking from the grid. The City still has to maintain the service cables, transformer, mainline, and substations to provide you with power when the sun isn’t producing energy for you.

Myth: My roof faces east/west and I heard that it needs to face south to work.

Reality: A roof with clear access to the southern sky generally has the greatest amount of solar energy potential. However, east and west roofs are not significantly less efficient and the economics are not much different. Don’t let the direction your roof faces be a deal breaker. Trees and other shade are the most significant elements to consider.