Whether we are talking about money or energy, a big part of keeping costs low is being able to track them. To accomplish this, I have a spreadsheet that has different tabs for each of the sources of energy inputs and outputs that we track for our primary residence.

• Grid Usage – Our utility company allows you to track how much energy we used on a daily basis, and is usually updated next day with information from the former. So I log in weekly and plug those into one tab.
• Solar Production – I log on to Solar City’s website (the website pretty much mirrors the iOS app), go to the monthly view and then download a CSV to get the raw numbers. I copy-paste that info into the spreadsheet.
• AC Usage – When we had our photovoltaic system installed, it came with a free Nest thermostat! This allows us to set the high and low range for our days and nights, set the system to ECO mode when no one is at home and more importantly it tracks how many hours either the heat or AC ran on a given day. I plug those numbers into the spreadsheet, and while it’s not an exact science, I assume that each hour that the AC runs (heat is a gas furnace, so not applicable here) uses roughly 3.5 kWh. The tricky thing with Nest is that, for some reason, they only store the past 10 days of information for your system, so I make sure to check this every week and add the usage numbers to my spreadsheet.
• Car Usage – As I have mentioned on the blog before, we have two electric cars that we use for commuting. We have a JuiceBox Pro 40 which we use to charge the cars. This has an EV Juicenet iOS app (and website) that allows us to gather the information on each charging session.

I take all of these numbers and total them (SUMIFS is a helluva function) in a tab that compare all of the numbers in a row for a given day. This gives me a thousand foot view of how much energy we used in a given day, how much we generated and where that energy went. The following is a run-through of what our energy tracking process looks like on the daily level, using example data from August 18.

I get the Total Energy Consumption for the day by adding the kWh generated from the solar panels to the number reported back from the utility company for that day.I then take the Total Energy Consumption and subtract the kWh (if any) that was used to charge the cars for the day – this gives me the Total Non-Car Energy Consumption.If the AC didn’t run for that day, then the Total House Energy Consumption will be the same as the Total Non-Car Energy Consumption. Otherwise I subtract the Total AC Energy Consumption to get to that number.Admittedly we don’t run this process manually for each day, we just plug data into our spreadsheet every week and it gives us the results, laid out a little more like this.

This process of data collection has allowed me to analyze our energy usage to the extent that I know what the house needs to run on when we aren’t there (so fridges and freezer and maybe two lightbulbs), a normal weekday (lights only on in the evening, maybe some TV, microwaving food occasionally) and a normal weekend day (more time at home, more lights, potentially more TV).

If we have a really high usage day I can normally identify the causes of an outlier – 9 times out of 10 it is because of multiple loads of laundry / needing to run the dryer a few times. Other times it is because someone left the computer and monitors on all day and night.

I also have totals broken out by calendar months and even by billing periods, so I know what to expect for the current billing cycle. This allows me to compare numbers for different months, see how much we used in terms of energy and money on charging the cars, running the AC, or just powering the house.

It isn’t a perfect system, and I certainly want to spend more time analyzing the results and taking action based on what I find, but it is far and away better than not tracking our usage and being flabbergasted by a $200 electricity bill every month.