Measuring word-of-mouth (WOM) results is not really very hard. It only becomes difficult if you try to use quantitative methods.
That's because WOM is a "qualitative" technique. Putting numbers on word-of-mouth communication is like using an apple to check the color of an orange.
To [qualitatively] measure the results of WOM marketing, just ask and answer the following questions:
1. Do prospective customers know: what makes your solar business different than all the others, and when you're the best supplier for the job?
2. Do members of the press (including bloggers) accurately reflect your competitive positioning and lend 3rd party credibility to it?
3. Do industry influencers understand your business strategy and support it to the press?
4. Does the target market see you as a reference source expert/counselor in the solar industry?
5. Do your business partners support your products and strategies?
6. Do your resellers (or channel partners) know where to spend their time, who to call on, and what to say?
7. Are key customers actively involved in testimonial marketing and serving as references?
I've been successfully using this 7-point checklist to evaluate WOM programs for many years. It's really not that hard. Really!