How Our Solar Savings Calculators Are Programmed

How Our Solar Savings Calculators Are Programmed

DATA:
$default_cost_matrix = array(
 ’70’   => array(‘cost’ => 21085, ‘number_panels’ => 15, ‘watts_per_panel’ => 280),
 ’90’   => array(‘cost’ => 23170, ‘number_panels’ => 17, ‘watts_per_panel’ => 280),
 ‘110’  => array(‘cost’ => 25255, ‘number_panels’ => 19, ‘watts_per_panel’ => 280),
 ‘130’  => array(‘cost’ => 27340, ‘number_panels’ => 21, ‘watts_per_panel’ => 280),
 ‘150’  => array(‘cost’ => 30340, ‘number_panels’ => 24, ‘watts_per_panel’ => 280),
 ‘170’  => array(‘cost’ => 32410, ‘number_panels’ => 26, ‘watts_per_panel’ => 280),
 ‘190’  => array(‘cost’ => 35500, ‘number_panels’ => 29, ‘watts_per_panel’ => 280),
 ‘210’  => array(‘cost’ => 37600, ‘number_panels’ => 31, ‘watts_per_panel’ => 280),
 ‘230’  => array(‘cost’ => 40710, ‘number_panels’ => 34, ‘watts_per_panel’ => 280),
);
$texas_cost_matrix = array(
 ’70’   => array(‘cost’ => 19000, ‘number_panels’ => 13, ‘watts_per_panel’ => 280),
 ’90’   => array(‘cost’ => 21085, ‘number_panels’ => 15, ‘watts_per_panel’ => 280),
 ‘110’  => array(‘cost’ => 23170, ‘number_panels’ => 17, ‘watts_per_panel’ => 280),
 ‘130’  => array(‘cost’ => 25255, ‘number_panels’ => 19, ‘watts_per_panel’ => 280),
 ‘150’  => array(‘cost’ => 27340, ‘number_panels’ => 21, ‘watts_per_panel’ => 280),
 ‘170’  => array(‘cost’ => 30340, ‘number_panels’ => 24, ‘watts_per_panel’ => 280),
 ‘190’  => array(‘cost’ => 32410, ‘number_panels’ => 26, ‘watts_per_panel’ => 280),
 ‘210’  => array(‘cost’ => 35500, ‘number_panels’ => 29, ‘watts_per_panel’ => 280),
 ‘230’  => array(‘cost’ => 37600, ‘number_panels’ => 31, ‘watts_per_panel’ => 280),
);
$federal_rebate_amount = 0.3;
$loans = array (
 144 => array ‘interest_rate’ => 0.0299, ‘interest_only_months’ => 0, ‘loan_months’ => 144 ),
 198 => array ‘interest_rate’ => 0.0399, ‘interest_only_months’ => 18, ‘loan_months’ => 180 ),
);
$increase_rate = array(
 $areas[1]  => 0.025,  //Utah
 $areas[2]  => 0.030,  //Reno
 $areas[3]  => 0.030,  //Reno
 $areas[4]  => 0.02,   //Texas
);
function calculate_state_rebate ($areas, $cost_matrix, $location_area, $electric_bill) {
 switch ($location_area) {
    case $areas[1]: //Utah
       return 1600;
       break;
    case $areas[2]: //Nevada
    case $areas[3]: //Reno Metro
       return 0.15 * $cost_matrix[$location_area][$electric_bill][‘number_panels’] * $cost_matrix[$location_area][$electric_bill][‘watts_per_panel’];  //15 cents per Watt
       break;
    case $areas[4]: //San Antonio Metro
       return 0.62 * 0.96 * $cost_matrix[$location_area][$electric_bill][‘number_panels’] * $cost_matrix[$location_area][$electric_bill][‘watts_per_panel’];  //The rebate will be calculated as: [number of PV modules] x [PVUSA Test Condition (PTC) rating per PV module (Watts)] x [inverter efficiency] x [rebate level]
       break;
  }
}

How the Terms Are Grouped

$system_cost    = $cost_matrix[$location_area][$electric_bill][‘cost’];
$total_cost             = $system_cost; //Get the cost from the Matrix
$federal_rebate          = $total_cost * $federal_rebate_amount;
$state_rebate           = calculate_state_rebate ($areas, $cost_matrix, $location_area, $electric_bill);
//Figure out what the cost will be over 20 Years with standard increases.
$total_electric_cost      = round(calculate_20_year_electric_bill ($increase_rate, $location_area, $electric_bill), 2);
$electric_annual_increase  = $increase_rate[$location_area];
$options[‘cash’][‘net_cost’]         = round($total_cost – $federal_rebate – $state_rebate, 2);
$options[‘cash’][‘net_savings’]          = round($total_electric_cost – $options[‘cash’][‘net_cost’], 2);
$options[‘cash’][‘payback_period’]    = round(calculate_cash_payback_period ($options[‘cash’][‘net_cost’], $electric_annual_increase, $electric_bill), 1);

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