Purchasing a new hot water system can be a big investment and the installation may include both gas and electrical components. You may need an electrician as well as a plumber but in just about every case, you will need a plumber.
The technology surrounding solar hot water systems has advanced rapidly over the last 20 years and has resulted in the development and supply of solar hot water systems that are cheaper, more reliable and have a longer expected life span.
The reliability of your hot water service will be dependent on the quality of your water heaters and the security of your fuel source. No matter how expensive your electrical hot water system is; if there isn't any electricity then you have no hot water.