Solar thermal or solar photovoltaic?
Solar thermal as in producing heat for household hot water, heating swimming pools, heating buildings (yes it's possible with proper design) etc. It's also possible to convert ANY source of reasonable grade heat sufficient to produce steam into electricity.
Indeed this is exactly how coal-fired and nuclear (and biomass, most oil-fired and older gas-fired) power stations work. Burning fuel or nuclear reaction produces heat to produce steam which spins the turbine to turn the alternator = electricity. Only difference with solar thermal electricity (or nuclear versus coal etc) is the source of heat.
Another form of solar thermal energy is to use the heat to create natural convection currents via a tall "chimney". Simply hot air rushing up the "chimney" drawing air in the bottom. The exact same principle as how an open fire "draws" smoke up the chimney and air into the fireplace (and the reason why open fires are incredibly inefficient and resource hungry as a means of heating - they suck huge volumes of cold air into the house to replace that drawn up the chimney). In the case of solar you just install wind turbines at the base to take advantage of constant wind. A conventional (albeit very large) greenhouse warms the air and with proper design it will run day and night (though output falls at night but then so does electricity demand). In practice it's like a hydro scheme run backwards using hot air instead of water. Note that the industry prefers the term "tower" instead of "chimney" to make it clear that it's a clean technology with no smoke.
Solar photovoltaic as in "solar panels" which convert sunlight directly into electricity. These are far more expensive (both $ and resources consumed) than solar thermal technologies for equivalent energy production. I don't have the figures in front of me but some time ago Hydro Tasmania calculated the total fossil fuels consumed in the life cycle of practically every available power production technology. Bottom line is that hydro is the winner with wind coming a close second. Wave, geothermal, tidal etc (in which Hydro Tasmania has no vested interest) are not far behind. But solar photovoltaic has a pretty big environmental impact due to the enormous amounts of fossil fuel energy used in production of the panels. The overall impact wasn't a great deal less than a best efficiency (available technology) fossil fuel power station from memory.
Given the financial and resource costs I personally think solar thermal is the way to go for using solar energy in the absence of a truly dramatic improvement in solar photovoltaic technology.
It's worth noting that hydro, wind, wave, biomass, tidal etc are all indirect means of using solar energy. In a technical sense coal, oil and gas are a form of stored solar energy but in this context they're best referred to as non-renewable fossil fuels.
If you are interested in using solar energy at home then don't forget that the point is to reduce the use of conventional energy sources (electricity, gas, oil, wood, coal) rather than using solar energy per se.
For hot water the basic options you have are electricity (off-peak or continuous supply), natural gas, LPG, oil (rarely used in Australia), solid fuel (wood, coal), heat pumps (which use electricity but not much of it compared to conventional electric heating) and solar which will usually require boosting by one of the above means.
Depending on your location and usage, the most efficient option will usually be either (listed in no particular order) solar with electric boost, solar with gas boost, heat pump or continuous flow natural gas. I left solid fuel off that list since for most it's not really an option but it certainly does work. Off-peak electricity is cheap but not efficient in a technical sense (though it works fine in that the shower will be hot as long as the tank is properly sized).
Be aware that under some circumstances solar with electric boost is well down the list. It depends on climate and whether or not you have access to mains gas. Assuming you buy a commercial system then in general, if gas is an option the most efficient system will be solar with a gas booster. If gas is not an option (LPG is rather expensive so I wouldn't use if for water heating if you've got either mains gas or mains electricity at a reasonable price) then in cooler climates go for a heat pump and in warmer climates go for solar with electric boost. For intermittent or highly variable use continuous flow gas (just gas, not solar at all) is likely to be the best option.
For houshold heating the first rule is to minimise the need. If it's an existing house then this basically means insulation and not leaving windows open unnecessarily etc. With a new house you have more options for passive solar design which in many climates means you will need no heating at all. But for most people the most efficient option will be either a heat pump (reverse cycle air conditioner), gas, or solid fuel burned in a proper wood heater or pellet fire (not an open fire or "pot belly" stove).
For swimming pools certainly go solar IMO even in cool climates such as Tasmania (not that private pools are common in Tas...). As for the boosting, either a heat pump or natural gas will be the most efficient in most cases although if solar is going to provide the vast majority of the heat then direct electric boosting on the off-peak rate would be acceptable. Any form of non-solar pool heating will be expensive to run and an an all-electric system (not a heat pump) on the continuous tariff might literally send you broke.
Note that I'm taking about technical (and environmental) efficiency and not cost. The most efficient isn't necessarily the cheapest. I'm happy to answer personal questions on the subject but suggest posting them somewhere (separate thread?) rather than a PM so that everyone who is interested can read the answers.