Most SDHW systems are designed to provide approximately 50% of a home’s hot water heating load. The actual amount of money that can be saved is based on that percentage, on the type of fuel currently being used to heat your water, and on the cost of that fuel.
At present, a family of 3-6 people using electricity in the Kingston area ($0.105 per kWh) would save over $400 per year. A family using natural gas would save about half of that at current prices (although the price of natural gas is more volatile).
Adding collectors to achieve higher production levels does not work if the hot water load and storage volume does not change. For example, adding a third collector to a 2 panel system will not provide 50% more energy. Instead, a gain of only 20% to 25% would be achieved by doing this.