public void setPercentagesOnOrientations(Double north, 
			Double west) throws SolarPowerSystemException {
		if (!isValidPercentage(north) || !isValidPercentage(west)) {
			throw new SolarPowerSystemException("Percentages on orientations " +
												"should be valid percentage.");
		} else if ((north + west) != 1) {
			throw new SolarPowerSystemException("The sum of the percentages " +
												"on both orientations should be 1.");
		} else {
			this.percentagesOnOrientations = new Double[NUMBER_OF_ORIENTATIONS];
			this.percentagesOnOrientations[NORTH] = north;
			this.percentagesOnOrientations[WEST] = west;
		}		
	}