RTA bus shelters ACs by Solar – Not a good idea

Dear All,

It was recently reported in the local news paper that the local transport agency of Dubai (RTA) is considering using solar energy for running air conditioners within the bus shelters.  Here is the reason why I think it is not a good idea

1. Economics: The average size of each air-conditioner is about 5KW.  Let us say that it is going to run for 12 hrs/day; so the total energy required per day is 60KWhr.  To have solar power (off grid – it seems like this is what they are referring to in the article), the initial set up cost adds up to about $150,000.00 (conservatively).  Compare this to the prevailing cost of electricity in Dubai of $0.07 per KWhr.  Savings per day is 12 x 5 x 0.07 = $4.20.  Breakeven point for the initial investment is $150,000 / $4.2 = 35,700 days or 97 years!  Anybody needs a calculator?

2.  Feasibility: In order to deploy a system of this kind, you would need installation of about 14KWp.   Total area required for installing a system of this size, you are looking at 140m2.  Assuming typical width of footpath next to the shelter where the installation is done to be of 5m, it’ll need 70 meter (unobstructed) footpath for doing the installation.  This is close to a typical city block! Unless, RTA plans to elevate and provide shading to the pedestrians using PV modules, no reasonable solution is possible to put these modules.  Add to this complexity in finding unobstructed locations for mounting PV modules within the city with high rise buildings.

Here is what is possible, however.

It is known that a direct air ventilation creates a feeling of temperature about 20 degrees lower than ambient.  If fans could be mounted inside the shelter along with vents (all DC rated highly efficient motors), then you could essentially provide relief to the passengers from scorching heat outside.  PV modules should only be used in places where grid supply is not available.  The shelter roof could be used for mounting PV modules for this load.Can solar power be used for these shelters?