According to the Solar Energy Industries Association, 92% of Americans want us to invest in solar energy. This association also reported a record number of rooftop solar panels in the year 2012.
An obvious drawback is fluctuations in sunlight. Solar pumps are powered by solar panels, many of them are quite good quality, but they all require sunlight. When a cloud passes over, the fountain shuts off. Batteries are available for many, but the larger batteries are expensive, and some have switches that do not allow the pump to run at the same time the battery is being charged.
It is not that a customer is usually saving much in electricity. Small plug-in pumps only use two and a half watts. To save electricity, it makes more sense to change all the house's light bulbs to LED or fluorescent.
Oftentimes, a customer does not want to have to pay an electrician to run electric outside. This is especially true in rural areas and for large ponds. Ponds need aeration or the algae gets to be bad, fish die, and the pond smells. However, ponds need most aeration at night after sundown. And if you do end up going solar for a large pond, you are going to pay a premium price for all the panels and backup batteries.
Probably the optimum use of a solar pump is for the kind of fountain that can go on and off all day without looking awkward doing so. A bamboo deer scarer (shishi odoshi), for instance, would probably look natural going on and off intermittently, as would many small pond spitters. A traditional concrete fountain, however, may look strange and sound strange if it goes off whenever a cloud passes.
The problem in customers' expectations may be the widespread use of outdoor LED lights. But these bulbs are tiny and use a very small amount of electricity. It's not like powering a toaster or a pump or even a one-watt light bulb. In fact, it is not uncommon to find a one-watt bulb system selling for sixty dollars.
If solar pumps were very often a good option for customers, then big box stores would probably be selling them, but there is probably good reason they are not. There would be too many returns.
And remember, even in Germany where solar is extremely popular and widely used, the people still have to plug appliances into the wall.