City of Hamilton customer owned renewable generation

Size bands and what each one obliges

The screens that decide it

• Sized within Hamilton’s published consumption formula, which is severe Limit 25 kW.

  Annual production may not exceed the customer’s annual energy requirements, and where historical demand readings are unavailable the system in kW AC may not exceed the estimated average annual demand, computed as the annual kilowatt hours divided by 8,760 hours and then divided by 30 percent, or 25 kW, whichever is less. That arithmetic is annual kWh divided by 2,628. A home using 12,000 kWh a year caps at 4.57 kW AC, 18,000 kWh caps at 6.85 kW AC and 24,000 kWh caps at 9.13 kW AC. A typical ten kilowatt system needs roughly 26,300 kWh a year of consumption to qualify. Where a demand meter exists, actual average annual demand governs instead, which is usually lower still. Compute this from the customer’s bill before quoting anything in Hamilton.

• Fifteen percent on two denominators at once 15 percent of line section peak load, a figure only the utility holds.

  Both tests must pass: the aggregate may not exceed 15 percent of total circuit peak demand as most recently measured at the substation over the previous twelve months, and may not exceed 15 percent of the distribution circuit line section annual peak demand. Both need utility data.

• Ten kilowatt aggregate cap on a shared secondary Limit 10 kW.

  The aggregate generation capacity on a shared secondary line, including the proposal, may not exceed ten kilowatts. That alone rules out many duplex and shared transformer installations in older Hamilton neighborhoods, so check whether the service shares a transformer secondary before signing.

• Fault current and short circuit interrupting limits

  Aggregate fault contribution may not exceed 10 percent of the circuit maximum fault current at the nearest primary point, protective devices may not be exposed to fault currents above 85 percent of short circuit interrupting capability, and no additional facility may be interconnected on a circuit already above 85 percent of that capability. The last of those is an absolute bar rather than a study trigger. A single phase resource on a 240 volt center tap may not create imbalance above 20 percent of the service transformer nameplate.

Ask the utility this, before you sell it

1. What is this customer’s annual consumption and, if a demand meter exists, their actual average annual demand? The sizing cap is computed from those and usually binds long before 25 kW.
2. Does this service share a transformer secondary with another customer? The aggregate cap there is ten kilowatts.
3. What is the Parallel Renewable Generation rate schedule and what does it pay? Enrollment is mandatory as a condition of interconnection, the standards leave the ordinance number blank, and the rate schedule is not in any published document.
4. Is non export likely to be imposed here? If the facility exceeds the existing operating capabilities of the lines, a reverse power relay set to trip at 0.1 percent of the service transformer rating may be required, which on a 25 kVA transformer is twenty five watts and is effectively zero export.

Worth knowing before you quote

Two applications are required, not one: the interconnection application and the Renewable Energy Parallel Generation Application For Service. The utility will not approve an interconnection application that does not include the second. Credit is capped annually at the customer’s consumption from 1 January to 31 December. A feasibility analysis, if requested, requires a 50 percent advance on the estimate, with the system impact study following if an adverse system impact is found. No approval or permission to operate timeline is published anywhere in the 32 pages. Applications are reviewed in the order received and processing does not begin until the application is complete. The customer’s utility account must be in good standing, and the request is framed as the customer’s rather than the installer’s.

All Ohio interconnection rules