PV life cycle cost/utility tariff for rebate based on Dollar/kWh not Dollar

asked 2021-01-09 20:45:41 -0500

mattkoch's avatar

updated 2021-01-10 12:14:18 -0500

So, Austin Energy has a solar rebate that works on Dollar per kWh of PV energy produced, rather than being an up-front amount in Dollar. In addition, they have net-metering, so the customer only pays for whatever electricity they must purchase after offsetting the facility demand and usage by the PV power generation and energy production.

I am currently using a tariff that has the ElectricityPurchased:Facility meter and the BuyFromUtility option. Originally, I also had a tariff that has the ElectricitySurplusSold:Facility meter and the SellToUtility option, so I could buy and sell at different $/kWh rates. I realize I could probably also use the ElectricityNet:Facility meter and the Net-Metering option if the buy and sell rates were the same, as they usually are for net-metering.

However, this does not account for PV energy production itself. So I thought I need a tariff with the ElectricityProduced:Facility meter and the SellToUtility option for that. However, EnergyPlus issues a warning that the ElectricityProduced:Facility meter is not normally used with the SellToUtility option. And, in the EnergyPlus report under Meters, this tariff has a "Selection No" entry. So I think this is being ignored.

Additionally, the rebate stops after ten years, so I was hoping to use an escalation rate for the ElectricityProduced:Facility meter that is 1.0 for the first ten years and then 0.0 for the rest of the life-cycle analysis period. However, this escalation does seem to be ignored as well.

So, I was wondering if anyone had ever encountered the need to model life cycle cost with a rebate that is based on $/kWh and if so, what they might have done to account for it?

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This is also known as a Value-Of-Solar (VOS) tariff, by the way. EDIT: Well, not quite. Austin Energy distinguishes a VOS tariff, which I believe should combine an Electricity:Facility/BuyFromUtility tariff with an ElectricityProduced:Facility/SellToUtility tariff, and a Performance-Based Incentive (PBI), which I believe should combine an ElectricityNet:Facility/NetMetering tariff with an ElectricityProduced:Facility/SellToUtility tariff. The challenge for both is the same, i.e. how to make EnergyPlus "select" the ElectricityProduced:Facility/SellToUtility tariff.

mattkoch's avatar mattkoch  ( 2021-01-10 10:29:40 -0500 )edit

Have you tried using ComponentCost:LineItem with the type being PV and the cost being negative so it shows as a rebate?

JasonGlazer's avatar JasonGlazer  ( 2021-01-11 11:41:24 -0500 )edit

Thank you Jason. I am viewing the ComponentCost items as more of an answer to a "what's my building costing me to build" question, and the LifeCycleCost items as more of an answer to a "how do I best retrofit my building for efficiency" question. I may be wrong in that, but that is what I am thinking when reading the documentation. More importantly, ComponentCost seem to be determined once upfront and - for PV - only depend on rated power, not produced energy. So, I would have to calculate that upfront and then add it as a negative LifeCycleCost:NonrecurringCost. A workaround at best.

mattkoch's avatar mattkoch  ( 2021-01-11 17:29:06 -0500 )edit

What I am really looking for is a calculation coming out of EnergyPlus that applies the Dollar per kWh rebate to the monthly PV energy production and then calculates net present value to fall in line with all the other LifeCycleCost calculations. As a bonus, this could be "turned off" after 10 years (hence my thought on using escalation). Yes, manual calculations outside of EnergyPlus are conceivable, but for simplicity and reliability, really all LifeCycleCost items should be calculated in real time as necessary to account for any changes made to the model.

mattkoch's avatar mattkoch  ( 2021-01-11 17:35:02 -0500 )edit

You might be able to automate the process if you are comfortable programming. If you know Python, you can try eppy or if you are more comfortable with Ruby or C++, you can try OpenStudio.

JasonGlazer's avatar JasonGlazer  ( 2021-01-12 14:27:52 -0500 )edit