Having direct experience in this area I would suggest using a combination of D&B data, trade association lists, email opt-in tactics and straight up cold calling. The key is to reaching the right people within the solar firm based upon your target message.

First of all, if you want to reach out to solar industry professionals, you have to think like a solar industry professional.

Start asking yourself these question:
1. What personality types are usually associated with solar industry professionals?
2. What social media platforms do solar industry professionals like to use?
3. Where do solar industry professionals like to go?
4. Who do solar industry professionals frequently contact?
5. Why would a solar professional use my website instead of someone else's website?

In any successful business, you not only have to buy your equipment and information, you also have to buy customers.

Did you spend any money on marketing?
Have you attended any solar industry related trade shows/conferences?
Have you contacted notable people in the solar industry to get them to endorse you?

These are just a couple questions you should ask yourself, once you answered them. You should have some idea of what you should do and where to go.

Hi, you should identify solar trade groups or associations and connect with solar professionals through those channels. If you qualify, join an industry association and attend national and regional meetings. Also research state solar organizations. Other professionals who could help you connect would be those involved in wind energy and LEED certification.

Hi. The easiest way for this is to use the power of "Social Media Marketing". To achieve your target reach:
1. Identify the business groups in solar industry, your target countries, stereotypes etc.
2. create some ad sets and campaigns (yes everything can be regarded as an advertisement) and follow their leads to see how effective is your ad in that group.
3. if the conversion rate is good and the performance of the leads are positive, continue publishing the ad sets and you will get more people showing interest in your website.

if you need their feedbacks and assessment, you can still use the social media. Before starting social media marketing targeting the public, find solar-industry related business people / influencers and send some quick surveys to them (please keep in mind that time is very important for everybody, so you should be convincing them in some way, the common method for this is to provide them some promotional giveaways or industry-related information).

Last but not the least, Facebook and Linkedin seems to be the most powerful media for your targets. Consider having some marketing budget and premium accounts, or hiring some professionals who have already this kind of database.

Thanks.

veyis

As with any industry, the solar space is broad and multifaceted, with a spectrum of professionals working across all kinds of geographic regions. Your biggest question right now is "who will see the most value in my website?"
Then, you proceed as others have suggested: determining how to best reach these folks.
To gain early traction, it helps to identify that ideal customer, since that should be your easiest "sale."
If you wish to discuss, send me a PM through Clarity for 15 free minutes.
Cheers,
Kerby

On-line promoting of your site, will bring to you many PR specialists, some sales guys, and similar of the sort.
Best way is to investigate and find the real solar professionals, those are tough guys, they talk about wattages and voltages, about USD and square foot of land or house roof. Sometimes they are not much friendly, but are in the core of the business.
all the best
Val