Also called grid-interactive, grid-intertie or utility-interconnected. Grid-tie solar systems are built onto your building and/or property and connect directly into the electric utility feed. Ths type of system provides no backup power when utility power fails. This is possible in areas that allow:

• Net metering: Whereby the solar system stores excess solar generated electricity with the utility in the form of energy credits when it is producing more power than you are using.
• Feed in Tarrifs: Whereby the solar system electrical power generation is separately metered from your electrical load and you are paid for the solar energy recorded by the meter. In Ontario, this program is called the "Standard Offer Program, or SOP".

Design Issues:

1. Net Metering: Sizing battery-less grid tie systems against electrical load demand is done using your average monthly kWh usage on your utility bill and your average sun hours per day (yearly). Knowing these two values allows you to define your solar system size in a net metered environment to net zero your utility bill over a one year period. If we estimated an average home energy usage at 1000 kWh per month, then the calculation for this would be:

(1000 kWh monthly usage / 30 days) / 4.2 hrs* = 7.9

The above solution identifies that a 7.9 kW nameplate rated solar array** would be suitable for completely offsetting 1000 kWh per month average electrical usage under a standard net metering agreement.

2. Feed in Tarrifs: Sizing battery-less grid tie systems against electrical load demand is done similarly to a net metering application, with one important distinction: The feed in tarrif must be weighed into the calculation of solar system size. The easiest way to do this is to divide your average monthly electrical bill in dollars by the feed in tarrif price. For instance, if we use the Ontario Standard Offer Contract solar price of 42 cents per kWh we discover that:

($ 150.00 per month bill) / ($ 0.42) = 357

The above solution identifies that a solar system producing 357 kWh per month (on average) would provide an income of $ 150.00 per month (on average). We can now take this number and the average sun hours per day (yearly, as discovered in the solar resources section here) to define your solar system size. For example:

(357 kWh per month / 30 days) / 4.2 hrs*= 2.83

The above solution identifies that a 2.83 kW nameplate rated solar array** will provide an average of 357 kWh per month in electricity. This energy would then be sold to the utility to offset your electrical bill of $150 per month.

Step 1 - Size your generation: Sizing battery based grid tie systems against electrical load demand is the same as sizing grid tie systems under a net metered application. Using your average monthly kWh usage on your utility bill (or less, as other factors such as money or location constraints) and your average sun hoursfills contents)

Step 2 - Size your battery bank: Sizing battery banks for grid tie battery back-up requires:

• identifying the critical loads that you want maintained during a blackout, and
• identifying the desired run time for your critical loads

Sizing these systems requires:

• a complete load evaluation of every piece of electrical equipment that is commonly used by the system,
• a solar array capacity based on matching load against your lowest solar resource months resources, keeping in mind that the lowest resource month is dependant on application. Summer-only cottages can be sized against summer resources, whereas year round loads need winter resource design.
• a battery bank design that provides autonomy to keep your loads up and running even during poor weather, 3 to 5 days autonomy typical for cottages, up to 10 days typical for telecom or other critical applications.