Congratulations, you’ve installed a battery storage system in your commercial building. Your team already has the greenest building around, and after struggling with construction and interconnection, you’re up and running!
Now the first invoice has arrived, and it’s your job to review it. You leveraged your capital and signed a shared savings deal. That’s great for capital but you know you better be able to explain every dollar because you’ll have to explain the same charges to tenants.
Never fear, here’s our handy guide to reviewing a battery storage invoice.
No Free Lunch
A battery isn’t an energy source. Because of system losses, it’s not possible to charge the battery without increasing kWh usage and in most cases kWh expenses. Your invoice should list this consumption specifically, and those amounts should correspond to your understanding of the battery operations. One tip–compare the total increase in consumption in off peak hours to the battery size. That will give you a high-level sense of how many hours the battery charged.
What’s the baseline?
Consumption increases are the bitter tax on what should be delicious demand savings, especially if your building is a market like California with high demand charges. To calculate your demand savings, one has to compare what prior demand was without storage to the demand with storage. Energy nerds call that a baseline.
This should be defined in your contract, but the gold standard of a baseline would be to simply combine the battery charge/discharge load data to the interval data of the building. If you don’t have access to that data or can’t make sense of things, use a tool like Gridium to review prior demand for a similar month. Does the baseline make sense? Have you hit that high demand before? Were there other projects or changes in the building that would increase or decrease demand since the battery was installed?
If things aren’t adding up, then its time to escalate and ask the hard questions from the project owner about how the baseline is calculated.
The layer cake of savings
You know how to read a commercial utility bill. It’s arcane and complex and tedious. There isn’t just one demand charge, there’s one for each TOU period as well as a facility demand charge. Some demand charges last a year, some are from the highest usage a year before. Some are when you peaked, some are when the grid peaked. These should all be clearly listed in the invoice and your utility bill. Make sure all the line items are there and clear.
Pennies Matter
Rates change constantly–that’s one of the reasons you installed the system to control escalating demand charges. But rates also change in very subtle ways that can affect your project returns. Make sure that the invoice uses volumetric rates that exactly match the rates shown on your utility bill. Very small changes here can have big impacts that could lead you to overpay.
Those four tips will set you in the right direction. If you’re a Gridium building, we’ll also show you a few other ways to check savings automatically and help review those first invoices. Just reach out if you need some help.
