M&V professionals have been using utility bills to track energy and cost savings for energy efficiency projects since the 1980s. However, with the advent of solar photovoltaics, using utility bills to track energy savings has gotten more difficult. Often the photovoltaic system will have its own meter. This may be useful at times, but sometimes it just adds to the confusion. There are several sets of data:
- Solar PV Production
- Energy from the Grid to the Building
- Energy from the Solar System to the Grid
- Net Energy Usage
- Building Energy Usage
More data is not always a good thing. If you have all this data, now you have to determine which data you need to use. This is where thinking comes in. If you throw in battery storage, it can get even more complicated. And to top it off, we get to deal with how the utility is handling the energy you are sending or receiving from the grid—and this is not so simple.
So you can see that there is not just one problem, there are many problems, and the confounding part is that different combinations of problems will lead to different solutions. To me, this is what leads to the confusion. The human mind can handle one problem, but when asked to handle three problems that each have many different possible answers at the same time, the mind gets flustered. If you have been flustered by tracking utility bill savings when there is a solar PV array involved, then you are not stupid, you are merely human.
The purpose of this paper is to address this issue and solve it step by step. It is my hope that this paper will serve as a manual that will guide you as you track your energy savings when it gets confounded by solar PV.