Electric Load Modeling and Defining Custom Load Profiles
About Load Modeling
When SolarNexus calculates utility bill savings from installing solar, sometimes it's sufficient to know the annual electricity usage, but more commonly SolarNexus needs to know the monthly customer electricity usage or even hourly electricity usage. Monthly usage is important for getting an accurate savings estimate in cases where a tariff has seasonal rates. Hourly usage is important in cases where a net metering tariff has time of use rates, differential import/export rates, or no export compensation (such as self-supply tariffs in Hawaii).
Monthly Load Modeling
In cases where monthly usage is required, you can get the most accurate analysis results by entering usage amounts for the past 12 billing periods or the past 12 calendar months on the Energy Use screen. However, if you don't have complete data for the past year, you can enter either a partial year of data, estimated average monthly usage, or total annual usage and SolarNexus will model the expected usage for each month according to an assumed monthly load profile.
A monthly load profile defines how total annual usage is spread across the twelve months of the year and is used to either extrapolate partial year data to a full year or interpolate average monthly usage to get 12 monthly values. For example, if you know only that November's usage was 750 kWh, SolarNexus might model July's usage as 1000 kWh if using a monthly load profile in which July usage is 33% higher than November usage.
Sample Monthly Load Profile
Hourly Load Modeling
In cases where hourly usage is required, you can get the most accurate analysis results by uploading actual historical interval data on the Energy Use screen (Green Button File), where supported by your utility (primarily limited to California as of 2018).
When you don't have historical interval data, SolarNexus models expected hourly usage by distributing the entered or modeled monthly usage over each hour of the year according to an assumed hourly load profile. An hourly load profile defines how usage is spread across one or more typical days in a year. A "24x12" load profile, for example, defines 24-hour usage for a typical day in each of the 12 months, modeling seasonal variations in usage. For each typical day, it specifies the percentage of total daily electricity consumed in each hour. For a residence, usage might peak in the morning and evening, with a later evening peak in the summer, for example, while for a school, usage might peak and hold steady during school hours, except during the summer.
Sample Hourly Load Profile
Default Load Profiles
SolarNexus automatically chooses default, "geo-typical" monthly and hourly load profiles for a project based on the building type and project location. The geo-typical profile for a building type/location represents the average, or typical, usage for buildings of that type in the area.
Often, the default load profile is good enough for a reasonable analysis. But if you have more specific information about the customer's usage pattern, you may be able to get a more accurate savings estimate by specifying a custom load profile for the project. For example, if you know that a customer is usually home during the day and has an air conditioner, that implies higher daytime use and higher self consumption than average, which might result in higher or lower bill savings than a customer using the same overall amount of energy but who is away during the day and charges an EV at night.
Specifying a Custom Load Profile
To define a custom load profile for a project, use the Load Profile options at the bottom of the Consumption Information section of the Energy Use screen. Both options default to "typical for location", as described above.
You can define a custom monthly or hourly load profile in one of two ways:
- Select "[custom]" from the drop down and then click the arrow icon to the right of the drop down to view/edit the profile. The custom load profile will start as a flat profile (the same usage across all months or hours), which you can then edit to reflect the customer's usage pattern.
- Select a pre-defined load profile from the drop down, click the arrow icon to view the profile and click the Customize button in the top right. This is useful if you want to start with an existing profile and then adapt it to the project at hand. Select the "[typical for location - OpenEI]" pre-defined profile to start from the geo-typical profile for the project's location and then edit from there.
After starting a custom profile using one of the methods above, edit the profile by grabbing any of the bars by the triple line at the top and dragging it up or down to change the percentage. As you drag a bar up or down, the rest of the bars adjust accordingly to keep the total of all bars adding up to 100%.
When you are done editing the profile, be sure to click Save at the bottom of the Energy Use screen in order to save your custom profile. When returning to the Energy Use screen, you should see the custom profile you previously saved.
After editing/saving a custom profile, you can always switch back to the default profile by selecting "[typical for location]" from the profile drop down.
Hourly Profile Resolution
When viewing/editing an hourly load profile, you can select the resolution you wish to use.
Available resolutions:
- 24x12x2 (default): Define a separate 24 hour load profile for weekdays and weekends for each month of the year. Each monthly profile will be used for each day of that month. This allows you to build a detailed profile that captures fine grained seasonal and weekday/weekend differences, but is time consuming to enter since you need to separately define the profile for each of 12 months.
- 24x1x1: Define a single 24 hour load profile that applies to both weekdays and weekends. The same profile will be used for every day of the year. This doesn't allow you to capture seasonal differences, but is easier to enter as you only have to define the relative usage for a single 24 hour day.
In both cases, you can specify the relative difference between weekday and weekend usage. So, for example, if you know that the site tends to use half as much electricity on weekends as on weekdays (e.g. for an elementary school), you might set weekday usage to 67% and weekend usage to 33%.
You can switch back and forth between resolutions while editing. So if you want to enter a baseline profile and then slightly tweak it in each month, you can start by defining the baseline profile in 24x1x1 resolution, then switch to 24x12x2 resolution to add seasonal variations. You'll notice that when switching from 24x1x1 to 24x12x2 resolution, the single 24-hour 24x1x1 profile is copied to each 24x12x2 monthly profile.
Be careful when switching from 24x12x2 to 24x1x1 during editing! When doing so, the 12 monthly weekday/weekend profiles are all averaged to get the single 24x1x1 profile. If you've made edits to the monthly profiles, those will be averaged out to get the 24x1x1 profile and when switching back to 24x12x2, you'll see the same averaged version applied to each month. So in general, once you start editing in 24x12x2 resolution, you should avoid switching back to 24x1x1 resolution before saving unless you want to effectively lose (or average away) your edits.
After you save Energy Use with a custom profile, you can go back to the Energy Use screen to view the profile and switch between resolutions without worrying about losing data, as long as you don't click Save again with the new resolution.
Creating Pre-Defined Load Profiles
If your company has a few different custom load profiles that you commonly use, you (or an administrator for your account) can create pre-defined profiles that you can simply select from on the Energy Use screen rather than having to define a custom profile from scratch for each project. Even if you want to specify a custom profile for each project, you can start by selecting the pre-defined profile that's closest to the customer's usage pattern and then modifying as appropriate.
To manage pre-defined load profiles, go to the Admin > Energy Profiles screen.
Creating a New Load Profile From Scratch
To create a load profile, click the Add Energy Profile button and enter a name and description for the profile. Energy Type should be set to Electricity and Domain should be set to Consumption. Select the Sector (Residential or Commercial) that the profile applies to. For Annual Baseline, enter the typical annual consumption for sites using this profile. This amount is only used for informational purposes at this time, but may be used in the future for establishing the default consumption quantity for analyses when no actual customer usage value is given.
Then, define the monthly and/or hourly consumption percentages in the same way as described in the Specifying a Custom Load Profile section above. Click Save when done.
NOTE: If you only intend to ever use the profile as a monthly load profile, you only need to edit the monthly consumption percentages and you can leave the hourly consumption numbers as-is. Likewise, if you only ever intend to use the profile as an hourly load profile, you only need to edit the hourly consumption numbers and can leave the monthly consumption numbers as-is.
Creating a New Load Profile Based on an Existing Profile
Rather than starting from scratch, you can create a variation of one of your existing profiles by clicking the copy icon next to the existing profile. This is often a faster way of going about defining a load profile.
Give the new profile an appropriate name and description, make any edits to the monthly/hourly consumption percentages, and save it.
Creating a New Load Profile Based on a Geo-Typical Profile
To create a pre-defined profile starting from the geo-typical profile for a nearby area, start by clicking on the Geo-Typical Profiles tab, put the zip code in the location box at the top, and hit Enter. You should see a list of OpenEI geo-typical profiles associated with weather stations around the zip code. Pick the one you want to use as the basis for your new profile and click the copy icon next to it. Give your new profile an appropriate name and description, make any edits to the monthly/hourly consumption percentages, and save it.
OpenEI is an open resource for energy data that includes geo-typical usage profiles for weather stations around the country compiled by the DOE. SolarNexus has loaded these profiles -- 1 typical residential and 7 typical commercial load profiles for each TMY3 weather station in the US -- and made them available for use on your projects and as starting points for defining your custom and pre-defined load profiles.
Analyzing the Impact of Load Profiles
Bill Savings
Depending on the tariff, changing the customer load profile might have a large impact on bill savings and financial return, or it might only have a modest impact.
To see the impact, after entering energy use, designing the PV system and running an initial analysis, you can go back and update the load profiles on the Energy Use screen and re-run the analysis. In order to compare results, after updating the load profile on the Energy Use screen, you can clone the original solution and re-run analysis on the new solution. Results for that solution will reflect the updated energy profile, and you can compare the effect of the updated energy profile vs. the original energy profile by comparing analysis results for the new solution with the original solution.
When comparing results, pay attention to the "Avg. Monthly Bill with Solution" line in the Analysis Cost & Benefit table. While the energy profile won't impact the net post-solar utility usage, it may impact the average cost per net kWh by shifting utility usage to different time-of-use periods or by altering the balance of imports, self-consumption and exports. You can see the average cost per net kWh on the Utility Bills tab on the Analysis screen.
Self Consumption
When using a custom or pre-defined load profile, you can also see the exact self consumption percentage for a solution in the System Summary of the Analysis screen. The self consumption percentage is the percentage of the site's total electricity consumption that's sourced directly from the PV system during its operation.
Running the Numbers
As an example of how self consumption and bill savings can vary depending on the load profile, consider a site that has an annual usage of 10,000 kWh and a proposed PV system estimated to produce 9,000 kWh. The load offset for the proposed system is 90%, meaning that we expect 1,000 kWh in net utility usage after solar is installed.
Assuming the utility charges $0.10/kWh for electricity, the total annual bill before solar would be $1000. If the utility has retail rate net metering with no time of use billing, the total annual bill after solar would be $0.10/kWh * 1,000 net kWh = $100, for a bill savings of 90%. In this case, the load profile is irrelevant since the bill is calculated based only on annual net usage.
However, consider a tariff that charges $0.10/kWh for net imported electricity in each hour but only credits $0.08 for net exported (excess, or surplus) electricity in each hour. The load profile matters in this case since the more usage that takes place during the day, the more the household can self consume and the less it will need to import and export and the fewer differential (import - export) charges it will incur.
Consider the following three residential load profiles:
- Load Profile A: Nightly EV charging, with significant usage during 12am-4am
- Load Profile B: Average usage profile with typical morning and evening peaks
- Load Profile C: Heavy daytime use with a mid-day peak due to air conditioning
For Load Profile A, most consumption is happening when the sun isn't shining. Let's say that self consumption is 35%, meaning that 35% of total household consumption occurs during daylight hours when the PV system can cover it. In our example, that means that 3,500 kWh are self consumed from PV and the remaining 6,500 kWh are imported from the utility when the sun isn't shining. That also implies the remaining 5,500 kWh of PV production are exported back to the utility as excess energy. Using the rates above, the total annual bill would be ($0.10/kWh * 6,500 kWh) - ($0.08/kWh * 5,500 kWh) = $210, for a bill savings of 79%.
For Load Profile B, somewhat more of the household consumption happens during daylight hours, let's say 45%. Self consumption is 4,500 kWh, meaning that 5,500 kWh are imported and 4,500 kWh are exported. Using the same rates as above, the total annual bill would be ($0.10/kWh * 5,500 kWh) - ($0.08/kWh * 4,500 kWh) = $190, for a bill savings of 81%.
For Load Profile C, a significant portion of household consumption happens during the day, let's say 55%. Self consumption is 5,500 kWh, meaning that 4,500 kWh are imported and 3,500 kWh are exported, for a total annual bill of ($0.10/kWh * 4,500 kWh) - ($0.08/kWh * 3,500 kWh) = $170, or a bill savings of 83%.
You can see that in this example, the difference between a load profile resulting in a 35% self consumption and a load profile resulting in a 55% self consumption amounts to 4% in annual bill savings. Not necessarily a huge impact, but enough to lead to a meaningful difference in the overall financial return for the project over its lifetime. This suggests it can be worthwhile, depending on the project, to spend the time to define or select a load profile that accurately reflects actual customer usage. Obviously, the larger the differential between import and export rates in a tariff, or the larger the differential between peak/off-peak rates, the larger the impact from accurately modeling customer usage.