Because solar hot water has been so dominant in New Zealand for the last decade, when you say "solar" most kiwi's assume you are talking about solar hot water and don't know there's a distinction between the two. They are quite different technologies! The simple difference is solar hot water is plumbing and solar power is electricity. You will have plumbers on the job if you are getting a solar hot water system installed and if you are installing a solar power system you will have electricians on the job.
So what is the difference between the functions of a solar hot water system versus a solar power system?
A solar power system produces electricity for your entire home that is normally run by electricity. For example it runs your toaster, your electric heater, your vacuum cleaner and your hot water system (only if it's powered by electricity). A solar hot water system only heats water for your home.
Should I install a solar power system or a solar hot water system first?
Both types of systems compliment each other very well. A solar hot water system will meet your hot water needs while a solar power system will meet your electricity needs. Whether you get one type of system first or choose one over the other largely depends on what you are willing to invest and what your current circumstances are.
A solar power system could completely eliminate your power bill, but the average New Zealand home would need to invest around $23K up front and the payback period is approximately 10 years. For many New Zealanders this is the ultimate goal. You can always go for a solar power system that is a bit smaller and might only half your electricity bill and you can always scale it up later.
A solar hot water system costs between $4K and $8K and will reduce your power bill by approximately a quarter and the payback period is approximately 5-8 years. If you already have an efficient hot water system like a gas heating or a wetback a solar hot water system might wouldn't make a big enough difference to warrant a solar hot water system.
I hope this article clarifies the difference between solar hot water and solar power for some people. If you have any other questions on this topic please let me know.