A consumption rate ($/kWh) can be used to calculate a bill in different ways, depending on whether there is excess solar production and whether selling to the grid is allowed. Many utilities have designed complex meter structures to keep track of the purchases from grid and the sales to the grid. Feedin tariffs, Net metering, Buyall Sellall are all different types of consumption rates and have different definitions around the world. To keep it simple, we use the following five rate transaction types to define how a consumption rate is used to calculate the bill. A tariff can have many consumption rates and each consumption rate can have only one rate transaction type. Here’s a list of the possible rate transaction types:
Transaction Type 
How the bill is calculated 
Net Meter 
cost = Net kWh * $/kWh 
Net Excess 
IF Net kWh<0, the cost applies= Net kWh * $/kWh 
Net Purchase 
IF Net kWh>0, the cost applies= Net kWh * $/kWh 
Import 
For the sum of instantaneous energy (kWh) coming from grid, apply cost= Purchases kWh * $kWh 
Export 
For the sum of instantaneous energy (kWh) sent to grid, apply cost = () Sales kWh * $/kWh 
These transaction types are further explained below:
The diagram below shows the transaction between solar panel, house (customer) and utility using a single meter.
The house has only one meter, which can “move forwards” when buying power from the grid and “move backwards” when selling excess to the grid.
For the first hour in the month of January, the load was 10 kW, and the solar panel produced 20 kW. In that hour, the load after selfconsumption is 10 kW. Since it is a negative load, we could export energy to the grid. Therefore, in the first hour in January, the system sold 10 kW to the Grid. After the first hour in January, meter A now has “moved backwards” and has recorded 10.
In the next hour, the load after selfconsumption is 10 kW, meaning the system needs to purchase 10 kW from the grid. Now the meter will move forward by ten and will read zero (10 + 10 =0). This goes on until end of the month when the meter is read by the utility.
In this type of meter, only the monthly “net” reading affect the utility bill – not the instantaneous meter readings. If the total purchases at the end of the month have been greater than total sales, then the meter will have a positive value. If the total sales at the end of the month is greater than total purchases, then the meter will have a negative value.
To represent meters that record the “net” consumption over a period of time, we use the following three rate transaction types:
(1)Net Meter
A consumption rate with “NetMeter” will be calculated as = Net kWh * $/kWh.
In the above example, the Net kWh were calculated over the period of a month. Some utilities will have different charge periods. The charge period options for “NetMeter” rates are: Hourly, Daily, Monthly, and Annually.
(2)Net Purchase
A consumption rate with “NetPurchase” will be calculated ONLY IF Net kWh>0. The cost = Net kWh * $/kWh.
In the above example, the Net kWh were calculated over the period of a month. Some utilities will have different charge periods. The charge period options for “NetPurchase” rates are: Hourly and Monthly.
(3)Net Excess
A consumption rate with “NetExcess” will be calculated ONLY IF Net kWh<0. The cost = Net kWh * $/kWh
In the above example, the Net kWh were calculated over the period of a month. Some utilities will have different charge periods. The charge options for “NetExcess” rates are: Hourly and Monthly.
The diagram below shows the energy flows between a solar array, a house (customer), and the utility.
The system has two meters, each of which can only “move forwards”. Meter A will record any electricity sold to the grid. Meter B will record any electricity purchased from the grid. Another way to look at this is that Meter A and B will record instantaneous exports and imports, respectively. There is no “netting” at the end of the month or charge period.
To represent Meter A, we have:
(4)Export
A consumption rate with “Export” will be calculated as = () Sum of instantaneous Sales kWh * $/kWh
To represent Meter B, we have:
(5)Import
A consumption rate with “Import” will be calculated as = Sum of instantaneous Purchases kWh * $/kWh
The estimated cost for these two rate transaction types is calculated on a monthly basis. Comparing Transaction Types:
Below is an example of the different calculations by rate type with a monthly charge:



$/kWh 
0.5 
0.2 
0.5 
0.5 
0.2 
Month 
Energy Purchased 
Energy Sold 
Net Energy 
Net Purchase 
Net Excess 
Net Meter 
Import 
Export 

kWh 
kWh 
kWh 
$ 
$ 
$ 
$ 
$ 
Jan 
72,071 
61,007 
11,064 
5,532 
0 
5,532 
36,036 
12,201 
Feb 
59,490 
57,856 
1,634 
817 
0 
817 
29,745 
11,571 
Mar 
60,907 
67,186 
6,278 
0 
1,256 
3,139 
30,454 
13,437 
Apr 
52,656 
61,070 
8,414 
0 
1,683 
4,207 
26,328 
12,214 
May 
56,282 
60,666 
4,384 
0 
877 
2,192 
28,141 
12,133 
Jun 
60,384 
51,916 
8,468 
4,234 
0 
4,234 
30,192 
10,383 
Jul 
62,993 
52,762 
10,231 
5,116 
0 
5,116 
31,497 
10,552 
Aug 
68,213 
56,097 
12,116 
6,058 
0 
6,058 
34,107 
11,219 
Sep 
62,066 
63,651 
1,584 
0 
317 
792 
31,033 
12,730 
Oct 
61,313 
64,410 
3,097 
0 
619 
1,549 
30,657 
12,882 
Nov 
71,771 
52,437 
19,334 
9,667 
0 
9,667 
35,886 
10,487 
Dec 
72,843 
55,752 
17,091 
8,546 
0 
8,546 
36,422 
11,150 









The table shows that the estimated utility bill depends significantly on which transaction type is defined.
You can add multiple consumption or energy charges to your tariff. Click on the Add Rate button on the right corner under the consumption tab.
This will open a popup window as shown below.
Follow the steps below to add a consumption rate.
As discussed in the beginning of this article the following charge periods are available for each rate type
Rate Type 
Charge Periods 
NetMeter 
Hourly, Daily, Monthly and Annually 
NetPurchase 
Hourly and Monthly 
NetExcess 
Hourly and Monthly 
Import 
Monthly 
Export 
Monthly 
a. Flat energy rate  If it is a constant energy rate ($/kWh) then enter the cost in box for Cost ($/kWh)
b. Tiered energy rate If it is a tiered energy rate, then check the box that asks “Has Tiers”. This displays a table for you to enter the tiers and their costs. Enter the Limits for each Tier and the costs in $/kWh. The table in the picture below, has the following tiers  from 0 to 50 kWh, the rate is 0.5 $ per kWh. Between 50 100 kWh the rate is 1 $ per kWh. Any consumption above 100 kWh would be charges 2 $ per kWh.
So if a customer consumed 300 kWh in the billing period, then the cost = ( 50 kWh * 0.5 $/kWh) + (100 kWh *1 $/kWh) + (150 kWh * 2 $/kWh) = 425 $
Tip: Be sure to add a last tier with a really high upper limit for all consumption that exceeds the highest tier, will fall into this category
a: If this rate to only apply during the summer season, then change the starting and end dates accordingly.
b: If this rate has a Time of Use, then check the box that says “Has Time of Use”. You may add one or more days and times times to this rate.
You can specify the days of the week, and the time ranges in which the rate applies on each of those days. You can add multiple times of use by clicking the "Add a Time of Use" button.
If this is checked, it would mean that this rate would be applied to any grid purchases during the holidays. To add all the public holidays in your region, go to the Add Holidays Section.
If you want to import real time prices, then refer to this article.