Until recently, the most common use for a rooftop in the realm of solar power generation was for a solar water heating array. In the not-so-distant past, this made sense. Electricity-generating photovoltaics were expensive and had a relatively short life, while rooftop water heaters were inexpensive and simple. Using nothing more hi-tech than a garden hose left out in the summer sun and a holding tank, rooftop water heaters were capable of augmenting a household’s hot water supply for very little money. But the drawback to this technology is simple: hot water is all that it can produce.

Here are a few simple facts:

Today, the lifespan of a solar cell is 25 to 30 years and the cost recently dropped dramatically (PV warranties are typically 20 years while solar hot water systems are typically only guaranteed half the time or less). Solar cell production in the United States is growing at nearly 50% per year, and this is driving down the price. At the same time, companies such as General Electric and the German firm Stiebel Eltron have made extraordinary developments in “heat pump” technology, and are now marketing heat pump water heaters with up to 62% increases in heating efficiency.

Given this, if your home already utilizes a rooftop water heater, it makes sense to consider replacing it with a new, high-efficiency electric water heater and provide the needed electricity with a new photovoltaic array. If you haven’t yet invested in new, green energy alternatives, then – with all of the new technology emerging - this option is clearly the preferable choice.

There’s another way to look at this as well—it’s a matter of personal choice and options. With a rooftop solar water heater, you have dedicated your roof to the production of hot water. Now, this probably made sense when it was originally installed. After all, the electricity that would have been used to heat the water is conserved and results in some savings, but there are many downsides to these old units. In most systems, the water needs to be circulated through the pipes to avoid overheating and that requires the use of electricity to drive the pumps. Additionally, any time you and your family are away from home, the energy is wasted. On a vacation for example, when no hot water is used the system actually results in a net cost because of the continued action of the electric pump.

But with photovoltaics, the choice of how to use the electricity and savings is yours. Replacing the old rooftop water heater with solar panels allows the production of electricity which can be used as you please. It can heat water with one of the new high-efficiency heat pumps at an even lower cost than pumping an active rooftop system with an inefficient electric water pump. And when it comes time for that vacation, well, while you’re away nothing is wasted. The PVs continue to produce electricity and the hot water heater can be switched off.

Increasingly, your rooftop is becoming the most valuable piece of property you own. In the new green energy economy, your rooftop has the potential to be a money-making power plant, and so to commit it to the simple heating of water, particularly when there are so many other uses, is a short-sighted investment.

The new heat pump water heaters from General Electric, Stiebel Eltron, and others, allow for more choice than homeowners have ever had before when it comes to green energy production and use.