There are three types of solar radiant heating systems.

    First is heating the water directly, this is difficult because the solar heat is not available when the heat is needed.
    Second is to store the heated water until it is needed. We have installed a few of these systems, the cost of the storage system makes this type not practical.
    Third is to install a gas or propane combo heating and hot water system  and supplement it with a solar panel. These systems work very well and are very cost effective.

You do not need a southern climate to take advantage of solar
but you do need a home with a very low heat loss and a carefully designed system.
In a solar assisted system the heat loss of the structure is the most important part to consider. 

You should not buy solar equipment online, your local solar installers are familiar with your local requirements and which systems are feasible. A local installer will be more responsible. Remember if it does not work properly or needs service an online supplier will be no help. Unlike radiant where the plumbing trade has forced people to seek alternate sources to find affordable supplies, local solar suppliers have maintained good value for their service.

Smaller homes that are extremely well insulated and protected from solar gain in southern climates could benefit from combining solar and radiant, but they would need the structure to be designed around the heating and cooling system. In other words you design the heating and cooling system to take advantage of the available climate and geo features and then design the structure within those limits.

See page 84 as one example for solar cooling.