Solar hot water heating is the cheapest way of supplying your home (or even your workplace) with steaming hot water, just the way you like it. And it's cheap to run.
When you have a solar hot water heating system installed, large electricity bills or gas bills for heating that water will be a thing of the past. This is because on sunny days you will be get your household hot water for free. It is powered by the sun.
On cloudy days or during the winter months, you will still be using electricity or gas to warm your hot water, in most cases. But this will only be only as a boosting function, to raise the temperature of the already-warm water to a hotter temperature.
Solar hot water gets its free heating from solar hot water panels that are mounted on the roof. Ideally, they need to be positioned so they face the mid-day sun. So in the northern hemisphere, like the USA or Europe, the panels should face south. In the southern hemisphere, like South America, South Africa, Australia and New Zealand, they have their solar panels facing north for best results. But in situations where you can't get the noonday sun, the next best thing is to have your solar panels facing west, so they get the afternoon and evening sunlight. This works both for solar hot water panels and for solar electricity panels as well.
Remember, there is always some heat hitting your solar hot water panels from the sun's natural light and warmth. The solar hot water heating system just needs some help on the dull days when you want that water to be steaming hot. Some folks have the booster function turned off to save money, and still find the solar hot water is warm enough to for them and their family to take a shower.
So whether you need to use electricity or gas (natural or bottled) to increase the heat all depends on where you live, the time of year and how much sunshine you get where your home is located. And naturally it also depends on how warm or hot you like your shower or bath to be 'just right' for you.
Solar hot water heating is recognized by many countries and governments as being very 'Green' and energy efficient. So much so that they sometimes offer rebates on the installation costs. You should find out if there are any being offered where you live. And if it isn't offered by your local government, I'd be asking them, 'Why not?'