The output of the solar energy plant depends on the particulars of the environment in which it is built. Small differences between one location and another can yield major differences in terms of the output of the plant. Sub-optimal decisions around the location and construction of a plant can have big consequences over the life of the facility. The costs of building the plant are more or less equal, whether it's built in "locale X" or at a different site just two miles to the east that could yield double the production of a sub-optimal site. This means that errors can be extremely costly and this risk may be prohibitive in some instances.
The key is to understand the micro-environment around the location of the power plant, the specifics of how the facility will be installed and then selecting the best technology to facilitate that specific environment. Each of these factors can create tremendous obstacles to building solar plants.
If you are a grid manager at a utility, your job is to keep the electricity coming so that when customers flick the switch the lights go on. The grid manager's job is not to go out on a limb with new technologies and take risks. Grid managers are not rewarded for that. They are rewarded for being reliable. The source of the electricity they distribute is not their concern as long as it keeps coming.
For this reason, those who favor solar adoption need to make the argument that solar is a much cleaner source. It’s a much more sustainable source, and, unlike wind power, the facilities are not eyesores. Solar is low to the ground. It has no moving parts, which require yet more energy to operate. It depends on a nuclear fusion bomb – the Earth's sun – 93 million miles away that is going to outlast the human race. All of these arguments need to be made, but there are enormous hurdles within the utility marketplace because the industry's DNA has little to do with taking risks.
Wind is truly an intermittent power source. We currently have difficulty predicting daily wind conditions. Solar on the other hand is much more predictable. The sun is coming up tomorrow – that is a given. With current technology we can forecast the amount of insolation (radiation from the sun that reaches the surface of the earth) which a particular site will receive over a year. This level of predictability is accurate enough to make financiers comfortable enough to finance 20-year power purchase agreements (PPAs).
Bankers don't like risk. Systems can be affected by temporary weather or environmental conditions. A large thunderhead could obscure the sun or a large fire could occur with enough smoke to impede insolation, causing production of energy to drop off temporarily. Grid managers still look at solar as too unreliable to bet too much of their sourcing on it. It still appears to be too risky. And the perceived value of having sustainable sources of energy is still weighted against the utility’s mission, which is to provide as uninterrupted a stream of energy as possible.
Cooperatives are generally in rural areas and are owned by its members. They buy their power through wholesalers and distribute it within their co-op. They typically buy the power from the closet transmission/distribution lines to the rural farmers and residents who own those distribution lines and transforming gear. There are some very successful co-ops across the United States driven by the membership mandate to buy the cheapest power possible. Thus, this model does not favor the adoption of solar until the price can be competitive and that remains difficult in most co-op areas.