It does look like the filter is being deadheaded, but it looks like there is also a tee behind the chlorinator. If that pipe on the right heading up the wall is the solar input, then the solar valve is blocking the bypass (when in the deadheaded position) and forcing the flow up the solar feed pipe on the right. Depending on the solar system you may or may not want 100% of the flow to pass through the panels, often the flow is adjusted to give the recommended flow rate for the number of panels that you have.