Grid-Tie System Operation
For the sake of explanation, let's assume your monthly bill is around P6,000/month and that you want to install a 1.6kWp grid-tie solar system. Your daytime base load is around 1.5kW since you run an air conditioner most days between 8AM - 4PM. Let's have a detailed look at how the solar system works to save you money. The concept is exactly the same for any grid-tie system; even large commercial/industrial systems.
11 AM - Sunny, high load
It's a sunny day and the AirCon is running. The solar system is running at it's peak and covers most of your consumption. The load in the house is 1.5kW, the solar system is producing 1.3kW. You are only using 200W from the grid. Your meter is barely moving since your consuming very little grid power.
12:30 PM - A brief rain cloud passes over
You get a 30 minute rain shower so the solar system is no able to run at it's peak but the AirCon is still running. The solar system now only produces 500W, the load is still 1.5kW, you are using 1kW of grid power. Your meter runs faster as you're consuming more grid energy.
2 PM - Sunny, low load, with Net Metering
The sun is out again so your solar system can run at full power. However, you leave the house to go shopping and turn off the AirCon. The solar system is producing 1.2kWp but the load is only 300W since no one is home. You have net metering set up with your cooperative so we program the solar system to export excess energy to the grid. You export 900W to the grid and receive ~P5 credit on your energy bill for every kWh. The meter is spinning backwards.
2 PM - Sunny, low load, without Net Metering
The sun is out again so your solar system can run at full power. However, you leave the house to go shopping and turn off the AirCon. The solar system is producing 1.2kWp but the load is only 300W since no one is home. You do not have net metering set up with your cooperative yet so we program the solar system to prevent the export excess energy to the grid. The solar system automatically "throttles" itself to match the load. The solar system produces 300W and you neither use or export energy to/from the grid. The meter stands still. This export limitation program allows you to use your solar system and enjoy savings even while waiting for the cooperative to process your net metering application.
4:30 PM - It's getting close to sunset, load is high
You return home and turn the AirCon on again. The solar system can only produce 400W since it's late afternoon and the sun is not strong. Load is 4kW since someone is showering with an instant water heater and water pump is running. You import 3.6kW from the grid and the meter is running very fast until the shower is turned off.
10 PM - Solar system is off but load is medium
Everyone has gone to bed and you're running a 1HP split-type AirCon in the master bedroom all night. The solar system is also in "sleep" mode and does not produce any power. Load is 500W since the AirCon is running in automatic energy saving mode. You import 500W from the grid and the meter is running until the sun comes up the next day.
9AM - Sunny but the grid power fails (brown-out)
The solar system shuts down automatically within 2 seconds according to ERC safety regulations. This is known as anti-islanding and prevents the risk of the solar system feeding power to the grid while linemen are performing repairs. There is no power in the house since grid-tie solar systems do not have batteries for backup power. You would need a generator for backup power. When grid power is restored then the solar system will wait for 10 minutes, according to the regulations, before generating power again.