Therefore it is way simplier to calculate standard vs solar roads cost difference.
If standard roads are much cheaper then ok, we can forget about solar roads.
If the difference is reasonably small then we have to consider difference in maintenance cost for the two road types. And maybe then we can consider income from produced electricity. I expect this will be smallest figure here.
Anyway, I expect same results at the end :-)
Didn't Dave already do that?
The solar panels cost X amount of money. The "extra installation costs" (to make it a 'road') for the panel add X euro.
The solar panel earns X euro per year. Divide the cost over earnings and you get payback time over the initial investment, that excludes maintenance. The table shown for reworking existing roads may also get thrown off completely. What happens if a solar tile breaks down? Do you replace it instantly? Do 5 tiles <100m need to be broken? What if the glass is damaged you can't drive over it? You would need instant repairs then, but for 1 panel that may become costly.
Also, the 20cts per kWh is not correct (as also mentoined on the wordpress blog in a comment). That is the price for consumer homes, which is 6ct for the electricity and 14ct tax.
If you install solar energy on your own home you can reduce your "net consumption" with 20cts/kWh. When your net consumption becomes negative, i.e. you're overproducing (produced kWh > consumed kWh) you don't get tax paid out. The tax is something the government wants from consumers; we're dirty for using electricity at all! You only get the '6ct + a small fee' from your energy company:
http://www.energieleveranciers.nl/zonnepanelen/terugleververgoeding-zonnepanelenEon: 7 ct/kWh
Essent: <10MWh/year: 8ct/kWh. >10MWh: 4ct/kWh
NUON: 7ct/kWh
Qurrent: 10ct/kWh
In addition, to be eligible for reducing your energy bill ("salderen") you need to be connected to a standard home 3x 80A connection. As a road is owned by the government, they obviously will not carry those installations.
What this basically means that the earnings are roughly 3 times less as Dave predicted, and as it's the only source of income the payback time will be 3 times longer.
300 euro's investment with ~3,33 euro/year -> 90 years!
I think most solar panel installations are only rated for 30 years of operation, making it a completely unfeasible idea. Any improvements in solar panel will also help the roof installations.
To make the concept of solar roadways catch up with roof installations, all efficiency improvements and cost reductions need to be made in the roadway installation itself. I am not sure if massive mass production will reduce Dave's figures even more than is required.
The only way remaining for it to work is the cost of electricity to increase by an order of magnitude; but that would help roof installations as well. Moreover, the energy market is quite complex (it's a trade stock in the Netherlands, actually), and comes from multiple parties and sources. So that is not very likely to happen short to mid term I think.