We can also look at the payback period (years needed to pay for the initial installation) and maybe power grids, if he teams up with his neighbors. More barn roofs, more angles to South, the more the merrier!)
Here is some basic information on solar power calculations:
Calculate Your Solar Power Payback Period - Energy Sage (US-centric, so must account for local currency and local cost of materials)
Are The Netherlands offering subsidies or tax breaks for home owners? Yes!
See Government of the Netherlands - Stimulating the growth of solar energy
Looks like tax cuts, a grant scheme, grants, and credits.
Excerpt: (the easier financial stuff)
- Gross cost of solar panel system: The gross cost of installing solar on your home is dependent on the size of the system you select and the equipment that makes up that system.
- Value of up-front financial incentives: Tax breaks and rebates can dramatically reduce the cost of going solar.
- Average monthly electricity use: The amount of electricity that you consume monthly is an indicator of both the size of system you need and the amount of electricity that you can offset each month with solar. The higher your electricity bills are, the shorter your estimated payback period will be, as you can reduce or eliminate this bill as soon as your panels are operational.
- Estimated electricity generation: While solar installers will try to provide you with a system that matches your electricity consumption, practical constraints like the size of your roof and seasonal weather variation may impact the amount of electricity that you can produce on-site.
- Additional financial incentives: Depends on country, but can be significant.
Mass. Solar panels - guide to solar incentives, costs, and savings (Again, US-centric, but gives you some ball park figures for materials, even if obtained in the EU).
Surface area available
Pitch of roof (in degrees)
Orientation of roof - N, S, E, W
Weather conditions there historically and also adjust for any recent noticeable changes (climate change making it sunnier, cloudier?)
Sample cash flow chart for an X kW system (note you can purchase various types of kW systems - not all systems are created equal)
Not fully complete as a brainteaser, but it's a start!
Original thread by Cuchulainn: Solar panels - how many do I need? - W OT