The first screen presented enables you to select or specify:
A month’s worth of actual data of the 60 watt module’s hourly energy output - from a particular year, January 2002 to last month .
An array size (rating in kilowatts peak), where "kilowatts peak" is the power the array would produce in response to a full sun - clear day radiation directed normal to the array. (The 60 watt module output is scaled accordingly)
The tilt of the array in degrees. (0 deg. is horizontal, 90 deg. is vertical).
The inverter efficiency.
The daily energy demand or "load" on the system (in kilowatt hours)
The cost of electricity in $/kilowatt-hr. (Note: Buy-from and sell-to the grid are taken as the same).
Clicking on the button "Submit" will then display a new "page" with a summary of your choice of system
parameters on the left and a graph to the right shoing the daily energy demand uniformly distributed over
the 24 hours of a day (in red). The message "Click onthe graph below to change any hourly value" will
appear and enable you to alter the hourly value (as in the standalone simulation).
Clicking on "Run Simulation" will execute the program and bring up
a new page with the results.
Running the Simulation
The green bars show the daily energy, in kilowatt-hours, produced by the array each day over the course
of the selected month/year for, in this case, the 31 days of the month of May,2002. For some time periods,
system output data may not be available. When this is the case, the day’s array output is shown in grey. The
height of the bar represents the total array output for that portion of the day for which we have data.
Displayed above the graph are:
The kilowatt hours produced by the array and the inverter output.
The kilowatt hours consumed by the load and the benefit accrued in dollars.
The surplus kilowatt hours sold to the grid when the hourly array output exceeds the load.
The deficit kilowatt hours bought from the grid when the load exceeds array output.
The net benefit/cost saving for the month in dollars.
In general,the total kilowatt hours produced over the month (after losses through the inverter) is equal to the sum of the total load, the monthly surplus, less the monthly deficit. If the selling price of the surplus is equal to the purchase price of the deficit, then the net benefit/cost can be taken as the product of the inverter output and this dollar value. This is the case currently in Massachusetts. But elsewhere (in the world) this may not be the case in which case one must cost out the surplus, the deficit and the load, then do the sum. For example, in France, the selling price can be as much as five times the purchase
price.
By clicking on any day of the month, a display of that selected day’s array output and load variation will be served up.
The particular hours (if any) for which data is missing is shown, again in grey, in this plot of hourly values and the fields on the right allow the simulation to be re-run, with different system parameters.
