Hot water accounts for more than 30% of energy used in the home. 
I’ve had solar water heating for a year. I wanted a gas booster, rather than the electric booster which was installed. My dad (who is my landlord) has had bad experiences with a gas booster, so he didn’t get one. He also told me that the person who installed the system said electric boosters are better, but I wonder if that’s just what the installer likes, or something.
A brochure from the gas company said (admittedly this may be biased because gas it what they sell)
Solar power systems are the most energy efficient if you choose a gas-boosted system. Electric boosted solar systems emit nearly the same amount of CO2 as hot water systems which run [solely] on gas. 
From February last year when the system was installed, the booster wasn’t turned on until winter. The weather usually breaks in May in Perth, but April last year was very wet, so the booster was probably used then. June was very dry, so I think it would have been turned off for a lot of that month.
During winter we didn’t use the electric booster in the same way other people might, so the electricity use wasn’t so much (and it is electricity from renewable sources). The booster was only turned on for half an hour before use and if the day was sunny it wasn’t turned on (Perth’s winter has quite a few sunny days). When we first started doing this last winter we would often forget to turn it off afterwards, but it became a habit after a while. Showering and dish washing are the only uses we have for hot water (washing clothes in cold water works well). I do mop the floor with hot water, but that’s something that doesn’t happen as much as it should. Last time I mopped, the dog drool marks didn’t come off (Sheeba the dog drools a lot in hot weather). I decided I had to scrub them. That still hasn’t happened.
Since October 2007 the booster’s been turned off and the sun is heating all the water. I’m hoping the booster won’t be needed until May. With the very hot weather of the last couple of months this means the water is burning hot, but you just have to make sure you add cold and it’s ok. The very hot weather also means I’ve been having cold showers, so even the solar heater is not getting much of a work out. But it’s not like the energy is being wasted – the sun will shine no matter what (and I’m looking forward to it shining a little less sometime soon). There’s an outlet valve for when the hot water tank gets too hot from that shining sun, but it drips into a bucket and I water the plants out the back with the cooled water every morning.
- “Hot Water Systems” (2007) Advantages magazine, Summer, p.2.