A customer recently asked this question, concerned that the utility was not giving her full credit for what she was producing.
The quick answer is that not all of the energy the array produces is exported to the utility grid. Thus the amount shown on her utility bill was only the amount of energy produced less the amount consumed in her home.
For a fuller explanation, read on...
There are a few numbers to consider when evaluating your solar array:
the energy you consume in your home or business,
the energy you import from the utility,
the energy your solar array produces, and
the energy you export to the utility grid.
The energy you consume is the total energy required to run all the electrical appliances in your home or business, whether you had a solar array or not, regardless of the source (the utility or your solar array).
The other three numbers vary depending on a number of factors including your demand, the time of day, and how clear or cloudy the weather is.
When your solar array is producing energy, all of that energy goes to powering your home or business, first. If your array is producing more than you need, then the excess charges a battery system, if you have one, and the remainder is sold to the utility. That is the amount of energy you export.
During times when your consumption is greater than the energy produced by the array, such as late in the day, at night or during cloudy periods, your system will import the energy needed from the grid to meet the consumption demand.
Some utilities show only the net amount you import on your bill. If you export more to the grid than you import. the bill usually shows zero, and the utility keeps track of the amount you exported for later credit.
Other utilities will show the amount you imported separate from the amount of energy you exported. These utilities provide a transparency that many customer prefer.
This customer asked why the export amount shown on the utility bill was lower than the total production for her solar array. In her case, almost half of what she produced during the billing period was exported to the grid. The rest was consumed in her home.
Feel free to follow up with comments or send any questions to us via the Contact Us link at the top right of this page.