// Define the calculateGridCharge function
function calculateGridCharge(estimatedKwhProduction, batteryCapacity) {
    // Calculate the amount of kWh produced by the solar system during the day
    var kwhProduced = estimatedKwhProduction * 24;

    // Calculate the amount of kWh that needs to be stored in the battery to reach capacity
    var kwhToCharge = batteryCapacity - kwhProduced;

    // If the amount of kWh that needs to be stored in the battery is negative, set it to zero
    if (kwhToCharge < 0) {
        kwhToCharge = 0;
    }

    return kwhToCharge;
}

// Use the calculateGridCharge function to calculate the number of kWh to charge from the grid
var estimatedKwhProduction = msg.payload;
var batteryCapacity = 28;
var kwhToCharge = calculateGridCharge(estimatedKwhProduction, batteryCapacity);

// Set the output message
msg.payload = kwhToCharge;

return msg;