Our electric provider here in North Reading, Reading Municipal Light Department (RMLD) (http://www.rmld.com/), offers time-of-use and net metering as two alternative electricity tariffs to the standard flat rate. If your electric provider has these two options, how could you determine if either or both of these options would reduce your electric bill?
Net metering is typically used by people that are generating as well as consuming electricity, for instance if you had a solar photovoltaic system. If you had solar you would very likely already have net metering, without a meter that supported net metering your solar system could be generating power and you wouldn't receive any credit for it.
Time-of-use (TOU) tariffs vary electric rates based on time of day. TOU rates are commonly used by electric companies to help shape electric demand by increasing the cost of electricity during some periods and discounting it during others. Discounts for off-peak usage can result in the movement of some electric usage away from peak hours.
We are currently on the flat rate metering plan but I wanted to see if, and how much, we might save with TOU metering. In our case it seemed likely that we had a good electric usage profile to save money with TOU metering. The house isn't occupied during the day. We have two electric cars that are scheduled to charge at night and in the summer the air conditioning is set to only run in the evening and during the night.
This might be enough information to decide to switch to the TOU approach but in our case we have a whole house energy monitoring system, the Neurio. We can use its hour by hour data to perform a detailed analysis and determine whether TOU would save money..
Currently RMLD's flat rate is $0.16 per kWh. TOU peak is between noon and 7pm at $0.19 per kWh with all other times, including weekends and holidays at a rate of $0.14 per kWh.
There are also customer charges that differ between flat rate and TOU rate billing. RMLD has a customer charge of $4.50 per month for flat rate billing and $7.00 a month for TOU billing. You'll want to keep this additional $2.50 for TOU billing in mind when comparing costs.
RMLD also requires that you lock into TOU metering for a minimum of one year, so its important that you understand your usage profile. I hope they would consider making exceptions if something changed that drove your bill up.
Here is a chart to illustrate flat vs. TOU rates throughout the day:
The rate difference between flat and TOU is an increase of $0.03 during peak hours but a $0.02 discount for off-peak.
Here is how our electricity consumption and cost lines up for summer and winter.
Note that the winter numbers are projected by using the summer consumption and removing the energy used for air conditioning. It is likely that the energy used to commute to/from work with the Model S will increase in the winter but no adjustment has been made to account for this increase.
You can see that some of our summer electricity usage is inside of the peak zone. This is air conditioning that is cooling the house to the temperature we sleep at. If we could shift this air conditioning to later in the evening we might save even more with TOU metering.
If you wanted to see whether TOU made sense for your house you might want to get the TOU specifics from your electric provider to understand peak vs. off peak and any additional costs per-month. Then look at your daily electric consumption to see how much falls within peak hours. You could reproduce your daily household energy consumption without a whole house energy monitor by looking at various electric devices and when they typically run. Does your AC runs during the day in the summer? If you have electric heat when you typically use it? Do you have an electric clothes dryer that runs during the day during the week? Electric hot water heater? Is anyone using water during the day? If you aren't sure enough of your consumption profile you might want to look at Neurio or one of the several other home energy monitoring systems to provide solid numbers.
It looks very likely that we will save some amount on electricity each month, both in the summer and winter and we plan to switch to TOU metering in the near future.
Update: Called on 9/12/2016 and our TOU meter was installed on 9/13/2016. TOU bills split the usage numbers into peak and off-peak amounts so it should be simple to check that we are saving by calculating the cost at the flat rate vs. the cost listed on the bill.
Net metering is typically used by people that are generating as well as consuming electricity, for instance if you had a solar photovoltaic system. If you had solar you would very likely already have net metering, without a meter that supported net metering your solar system could be generating power and you wouldn't receive any credit for it.
Time-of-use (TOU) tariffs vary electric rates based on time of day. TOU rates are commonly used by electric companies to help shape electric demand by increasing the cost of electricity during some periods and discounting it during others. Discounts for off-peak usage can result in the movement of some electric usage away from peak hours.
We are currently on the flat rate metering plan but I wanted to see if, and how much, we might save with TOU metering. In our case it seemed likely that we had a good electric usage profile to save money with TOU metering. The house isn't occupied during the day. We have two electric cars that are scheduled to charge at night and in the summer the air conditioning is set to only run in the evening and during the night.
This might be enough information to decide to switch to the TOU approach but in our case we have a whole house energy monitoring system, the Neurio. We can use its hour by hour data to perform a detailed analysis and determine whether TOU would save money..
Currently RMLD's flat rate is $0.16 per kWh. TOU peak is between noon and 7pm at $0.19 per kWh with all other times, including weekends and holidays at a rate of $0.14 per kWh.
There are also customer charges that differ between flat rate and TOU rate billing. RMLD has a customer charge of $4.50 per month for flat rate billing and $7.00 a month for TOU billing. You'll want to keep this additional $2.50 for TOU billing in mind when comparing costs.
RMLD also requires that you lock into TOU metering for a minimum of one year, so its important that you understand your usage profile. I hope they would consider making exceptions if something changed that drove your bill up.
Here is a chart to illustrate flat vs. TOU rates throughout the day:
The rate difference between flat and TOU is an increase of $0.03 during peak hours but a $0.02 discount for off-peak.
Here is how our electricity consumption and cost lines up for summer and winter.
Note that the winter numbers are projected by using the summer consumption and removing the energy used for air conditioning. It is likely that the energy used to commute to/from work with the Model S will increase in the winter but no adjustment has been made to account for this increase.
| Summer | Winter (projected) |
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 |
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| Daily savings: $0.50 | Daily savings: $0.67 |
| Monthly savings: $12.49 ($14.99 - $2.50) | Monthly savings: $17.60 ($20.10 - $2.50) |
These charts were created with Google Sheets, each chart was sized to be about the same size and then saved as an image. It would be great of Google Sheets had a way to set the chart dimensions numerically so they could all be set to the same size.
To build this comparison I used the kWh values from Neurio and built a table along with the hour of the day. Then added a column for flat rate and for the TOU rate at that given hour. The rate at a given hour of the day was then used to calculate the cost of the energy consumed during that hour, producing a set of costs for the flat rate and TOU rate. The cumulative savings chart is the running sum of the difference between the flat and TOU cost. I've shared the Google Sheets document in case you'd like to review it.. Please let me know if you find mistakes. It wouldn't be the first time there were errors in a spreadsheet that altered the results.
To build this comparison I used the kWh values from Neurio and built a table along with the hour of the day. Then added a column for flat rate and for the TOU rate at that given hour. The rate at a given hour of the day was then used to calculate the cost of the energy consumed during that hour, producing a set of costs for the flat rate and TOU rate. The cumulative savings chart is the running sum of the difference between the flat and TOU cost. I've shared the Google Sheets document in case you'd like to review it.. Please let me know if you find mistakes. It wouldn't be the first time there were errors in a spreadsheet that altered the results.
You can see that some of our summer electricity usage is inside of the peak zone. This is air conditioning that is cooling the house to the temperature we sleep at. If we could shift this air conditioning to later in the evening we might save even more with TOU metering.
It looks very likely that we will save some amount on electricity each month, both in the summer and winter and we plan to switch to TOU metering in the near future.
Update: Called on 9/12/2016 and our TOU meter was installed on 9/13/2016. TOU bills split the usage numbers into peak and off-peak amounts so it should be simple to check that we are saving by calculating the cost at the flat rate vs. the cost listed on the bill.
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