Aggregate Metering in Maryland

Farms, churches, schools and local governments rarely run on a single electric meter. A farm might have a barn, a shop, a well pump and a grain dryer, each billed separately. Aggregate metering lets one solar system cover several of those meters, so the customer doesn’t need a separate array behind each one.

Aggregate metering in Maryland is available for eligible customers. A utility “shall provide meter aggregation” to an eligible customer-generator who asks in writing (PUA §7-306.3; COMAR 20.50.10.07).

Who Qualifies for Aggregate Metering?

Aggregation is not available for everyone. State law limits aggregate metering to:

• Customers using electric service for agriculture
• Nonprofit organizations
• Municipal or county governments
• State government
• Public higher-education institutions

Homeowners and for-profit businesses don’t qualify.

How Aggregate Metering Works

The solar connects behind one meter, called the host meter. Each billing period, production first covers the host meter’s own usage. Extra kWh then roll to the customer’s other meters in a set order, usually chosen by the customer (COMAR 20.50.10.08).

For example, a solar system produces 10,000 kWh in one month. The barn meter (the host meter) uses 4,000, leaving 6,000 kWh of credit. The shop meter is first in line; it uses 3,500, and all of it is credited. The grain dryer meter is second; it uses 5,000, gets the last 2,500 kWh of credit, and pays for the other 2,500.

Aggregation can happen on paper, with the utility adding up usage and credits across the accounts each billing period. Where services are close together, it can also happen physically, by rewiring them to a single meter (COMAR 20.50.10.08).

Aggregate Metering Requirements

1. One customer. Every account in the group has to be held by the same customer or legal entity as the account with the solar. If a farm’s meters are split between family members, or between a person and an LLC, they need to be retitled before applying.
2. The solar has a location rule; the other meters don’t. The solar must sit on the customer’s premises or contiguous property (PUA §7-306); however, the meters receiving credits can be elsewhere in the utility’s territory.
3. Size. A system can’t produce more than 200% of the combined baseline annual usage of the aggregated meters, where baseline is the prior 12 months of use. State law caps net metering at 2 MW, but allows up to 5 MW for an aggregated facility and more than one system feeding a single aggregation (PUA §7-306(g), (i)).
4. Ownership. The customer can own the system, lease it, or contract with a third party that owns and operates it (PUA §7-306).
5. Everything in writing. The customer requests aggregation in writing and tells the utility how to split credits among the accounts before aggregation starts (PUA §7-306.3(c)). The utility then has to allocate credits “per the instructions of the eligible customer-generator” (COMAR 20.50.10.08).
6. Utility Specific Requirements: Each utility writes its own version of these rules into its tariff, and the differences matter when designing a system. Below are some of the key differences:
   1. BGE covers aggregation in Rider 18, Net Energy Metering, pages 98B–98C. It doesn’t limit how many accounts can join, but every account must be “within the BGE service territory.” If any account buys power from a third-party supplier, the host and every aggregated account must use the same one. BGE may take up to 90 days after it receives the signed Certificate of Completion to start aggregating.
   2. Pepco uses a separate rider, Rider “ANEM”, pages 52–52.3. It’s the only one of the four that merges the accounts: every host and aggregated account moves to a single account with a new account number, served by one energy supplier. A Pepco customer can have up to three host accounts and must aggregate at least two others. Allow up to 90 days after Pepco accepts the application.
   3. Potomac Edison‘s Virtual Meter Aggregation Service (tariff pages 26-4 to 26-5) describes their policy. By default, PE credits the highest-usage accounts first. PE signs the aggregation form as approved, or rejected with a reason, which gives the customer written confirmation of which meters are in.
   4. SMECO uses Rider NM-A, Net Metering-Aggregation, Sheets 165–170. Its biggest difference is a PJM study: if the system is sized above the host account’s own baseline annual usage, the customer must enter the PJM queue and get written approval. The rider application is due at least 90 days before the system is turned on. SMECO allows one host account and one system per aggregation group. It may rank accounts largest-usage first, and the group takes accounts until their usage reaches 110% of the system’s expected annual generation.

Next Steps

Aggregate net metering in Maryland can let one well-placed solar system cover a farm, church or county facility’s full set of meters. The catch is in the details: each utility writes its own rules, and something as small as an account name or a meter-reading cycle can decide which meters get credits. Energy Select has designed and installed solar across Southern and Western Maryland for more than two decades. Contact us or call (301) 200-1130, and we’ll review your meters against your utility’s rules and size a system around the accounts that qualify.