Sync node-red sensor values

SyncNode-Red_SensorValues.md

// Wait for both messages to arrive
// Calculate delta between consumption and PV

context.power = context.power || {};
switch (msg.topic) {
	case 'power_cons_sum':
		context.power.cons = parseInt(msg.payload);
		//node.warn("context.power.cons " + context.power.cons);
		msg = null;
		break;
	case 'pv_bwp_sum':
		context.power.pv = parseInt(msg.payload);
		//node.warn("context.power.pv " + context.power.pv);
		msg = null;
		break;
	default:
		msg = null;
		break;
}

if (context.power.cons != null && context.power.pv != null) {
	var surplus = (context.power.pv - context.power.cons);
	context.power = null;
	return {topic:'surplus', payload:surplus};
}
else return msg;