1. Cost – the single largest hurdle solar energy faces is that competing energy sources have always been cheaper in terms of dollars per kilowatt-hour (a standard measure). Compared to electricity from coal-fired power plants, solar is more expensive – if you don’t consider the environmental costs (which typically are hard to asses a dollar amount to).

But in recent years solar power is becoming closer and closer to grid-parity on price especially with the introduction of new types of solar panel chemistry like Cadmium telluride.

2. Site suitablity – many sites don’t receive enough solar energy to make solar energy cost effective. Cloudy areas with frequent rain are often not as well suited for solar panels because typically solar panels need direct sun to produce the most power. That’s changing though, new panels can now use diffuse light on cloudy days to still produce power. With prices going down steadily, more sites would be feasible that once were not.

3. Embodied energy – It takes a tremendous amount of energy to produce a solar panel. Because of this – depending on the type of panel and the way it was made – the panel itself may have required 11 years worth of its energy production just to make it. So if that’s the case, the panel won’t begin making ‘new’ energy until it has been operating for 11 years. It takes energy to make them, and you can think of this like taking out an ‘energy loan’ and so the loan must be paid back before an ‘energy profit’ can be made. Again, this is changing, new panels are made more efficiently, and require less material than older technologies so the 11 years is highly dependent on the type of panel and the manufacturing process.

4. Production and Demand – Typically solar panels produce the most energy during the middle of the day and somewhat less before and after than. Also, solar panels produce the most power during the summer. To the extent that demand for power does not coincide with this production curve, other sources of energy must be used to fill in, or some sort of storage (like batteries) is needed.

5. Materials – The material used to make solar panels is in short supply or the supply has fluctuated. This, again, depends on the type of panel, some panels don’t have this problem. Shortages in materials mean it can be hard for producers to meet demand – thus pushing up the cost – which is the main stumbling block for the adoption of solar energy.