19-0516 v3.x Energy Monitoring Methodology

We are pursuing Energy Petal certification for an accommodation site in Glenorchy, NZ. We request confirmation regarding the acceptability of our site metering configuration. Effectively, we are a small community site with two main sites, one of which has PV generation and is aiming for Petal certification, and another that benefits from the excess energy exported from the PV renewable power generation on the LBC registered site. We will also have a battery to serve both our LBC resilience requirements and additionally aid in load shifting and peak load shaving. The Petal registered site also has its own smaller internal battery (Tesla Powerwall) which was used as an experimental resource for the project team and will be used as an educational resource for tours and visitors. The overall goal of our configuration is to support another community site during (regular) external grid outages and to reduce the distance over which our power is exported to the end user(s).

Our site path supply goes through the following systems in succession (from the external grid to internal power usage as can be seen in the metering diagram):

1. The National Grid
2. A full site transformer
3. A full site utility/tariff meter (on the consumer side of the transformer)
4. A full site approved back up generator
5. Supply to the other community site (through individual site meter B)
6. A full site battery (on order)
7. Individual Petal site meter (A)
8. PV arrays and inverters
9. Internal small battery (Tesla powerwall)

As our utility meter serves two sites we will be providing a letter signed by both the owners and the energy engineer substantiating that this is the case (as per I06-3) and monitor our generation through another meter.

We seek confirmation that our proposed monitoring methodology as outlined is acceptable.

We will measure and record the import/export of power from the Individual Petal site meter (A).

We will also monitor each PV grid array and sum the generation to record as our total production. We will also monitor our use through building meters on our site as our consumption (we also have a lot of downstream submetering to monitor and optimize our power use).

The losses incurred over the distance from the LBC site meter (A) to the utility meter (about 10 meters of a shared path) and through the transformer and main full site battery will not be accounted for. Is this acceptable?

The powerwall battery supply and return are metered by a separate electrical meter (not the Tesla app which we have found to be irregular). There are losses incurred while storing energy in the battery, thus the amount supplied to charge the battery is less than the amount drawn for use from the battery.

Consider Batteries a component (usage):
The Tesla Powerall battery system consumes power through inverter and battery losses. We propose to treat this as energy use. Our Telsa meter measures charge and discharge energy of the Tesla as separate "registers". The energy use of the Tesla Powerwall will be calculated as "charge energy" less "discharge energy". The energy discharged from the Tesla will also be metered as 'use' by the subcircuit that uses it.

Electric Vehicle Charging:
Energy consumption from electric vehicle charging stations will be deducted from the overall annual energy demand calculation as per theEnergy Petal handbook.

The proposed metering configuration is acceptable. Please note that the site battery energy losses must be included in the project's energy budget, if the battery is used in standard site operations. 

In order to demonstrate net positive energy performance, the team must demonstrate how the losses incurred from the site battery will be pro-rated to the Petal and Non-Petal site. In addition to the standard Energy Petal Documentation Requirements, the team must provide documentation to reconcile the difference in energy use measured at the utility meter versus the total energy use for the individual site meters.

Electric vehicle charging may be excluded from the project energy budget. 

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