Australian network tariffs - Ausgrid demand charges based on kVA and rolling capacity

Hello All,

I am trying to model a PV system with financial model that is to be located in the Ausgrid network area of NSW Australia. The attached plant runs from 6:00am-4:30pm.

The Ausgrid network tariff for the attached plant is on is EA-305. This tariff basically has demand charges (peak capacity) that are based on the maximum kVA value (not KW) measured each month between the time of 2pm-8pm. If for example the maximum kVA value measured between 2pm-8pm in January is 100kVA the amount billed at the end of the month will be 100kVA x 34.668c/kVA/day x 31 days = $1,024.

To complicate things the recorded demand does not reset each month. That is if the maximum demand in February were to drop to say 80kVA the charged amount for February would be based on January's figure of 100kVA i.e. 100kVA x 34.668c/kVA/day x 28days = $970.

If the demand were to increase however to say 150kVA then February would be charged at 150kVA x 34.668c/kVA/day = $1456.

The process is known as ratcheting and the only time the recorded value lowers is if a site records lower values than the currently recorded maximum for 12 months in a row.

Based on that can anybody tell me if they have managed to somehow use SAM to model a system with kVA based demand charges and rolling capacity?

SAM is obviously made in general for US based demand tariffs.

The possible insurmountable hurdles I face are:

1) SAM uses kW. Using the sites known power factor I could convert the annual consumption data to kVA but in doing so that would skew the consumption calculations.
2) SAM currently uses the monthly recorded demand value and does not have a rolling capacity/ratchet feature.

The only way I think I can get any kind of estimate (without NREL adding a lot more features to SAM) of the impact of my PV system on the peak demand/rolling capacity charges would be to look at a worst case scenario. That is what amount of kW could my PV system produce on a cloudy/rainy day in the middle of winter at 4:30pm (the shut down time of the plant). I would therefore know at worst what is the minimal amount the PV system could reduce the kVA figure and could multiply that figure by the daily charge x 365 to get an annual savings.

Hope someone has been there before and can offer some advice.

Thanks,
Robert

Dear Robert,

Your observations of those limitations are all correct from my perspective. We may be adding demand ratchets to a future version of SAM. We are releasing a new version of SAM later today with two major improvements to the electricity rates model: There are now four metering options to handle net metering and feed-in tariffs, and the rate and demand structure inputs and results are now tables rather than large numbers of individual variables to make it easier to analyze the data.

Best regards,
Paul.

Best regards,
Paul.