Usually toilets do not require hot water.
Is the plumbing divided into hot and cold water pipes?
If toilets are hooked to hot water, how many flushes and how many gallons per flush per day.
What is the expected consumption per each worker?
What is the latitude from equator, and expected solar input. Further north, and hazy atmosphere reduce input. Beijing has smog I believe.
How often is the solar panel going to cleaned of smog and dirt for maximum collection?
If the area has hard water, then the entire system is prone to sediment build-up and failure unless water is artificially softened.
Solar water heater temperatures can exceed 180 degrees at times. This temperature will damage storage tank that is not made for that temperature.
Most solar water heater systems have pressure regulating valve and expansion tank to accommodate occasional high temperature and pressure.
A good fellow to contact might be at following website:http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
Solar collectors are usually connected to a circulating pump, and then the heated water is stored in a tank.
The pump circulates water continually from solar collectors through a storage tank.
This type of system would use ordinary tank-type water heater for storage.
Most of these systems also utilize a back-up heating element inside the tank.
More complicated systems circulate special liquid through spiral tubes inside the water heater.
This type of heater would be an indirect water heater.
Indirect heaters are used for solar collectors, and used with boilers, or any outside heat source.http://www.bockwaterheaters.com/Products/products_coil_tank_water_heaters.htmlhttp://www.hotwater.com/products/residential/cirrex_solar.htmlhttp://waterheatertimer.org/images/solar-water-heaters-on-roof_lbiRv_5784111-500x282.jpg