Question: How to assign new unit rather than default

I was trying some calculations for a solar installation.

4.9kW system. 3.5 h sun/day.  $0.27/kWh

restart:
with(Units:-Standard):
                     "maple init loaded..."
4.9*Unit(kW)*3.5*Unit(h/day)

714.583333333333*Unit('W')

but I want it to output 17.15 kWh/day

I looked up previous questions, and got this rather convoluted solution:

restart: 
Units[AddSystem]( NewSI, Units[GetSystem](SI), kWh/day );
 Units[UseSystem]( NewSI ); 
combine( 4.9*Unit(kW)*3.5*Unit(h/day), units ); 


17.15*Unit('kWh'/'d')

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