The short answer is most of the time yes, but it depends.
In an Existing Home
If you're already living in a home that has roof trusses and no solar panels, the added weight of the solar panels won't have been considered when the trusses were designed. This doesn't mean they won't be able to take the weight—it just means there will be a limit. The LABC (local authority building control) states that: "small dead load increases to standard configuration fink trusses (of up to 9m span) will not overstress truss members or their connector plates to any significant degree. Installation of a single row of solar thermal or PV panels is considered acceptable, without further structural investigation."
This being said, they also state that:
"An installer should always carry out a basic assessment to establish a minimum level of robustness in the construction".
If your trusses were from us, you can contact us and we'll be able to advise how much additional weight your roof can take. If they're not from us, you'd need to contact your truss supplier, or failing that, a structural engineer.
You're Building a Home
In the words of James May, good news! If you're considering adding solar panels to a home you haven't built yet, we can design your trusses to take this additional weight. Just make sure whoever is installing your panels knows what they're doing, though, as the load of the panels needs to be evenly distributed across the trusses.