Can solar electric panels (PV) be used for water or space heating?

No! Well, not without great expense. Photovoltaics (solar electric panels) convert the sun's energy into DC electricity at a relatively low efficiency level (14-17%), so trying to operate a high power electric heating element from solar electric panel array would be very inefficient and expensive. Solar thermal and passive solar design is the direct heating of air or water from the heat of the sun and is much more efficient (55-85%) for heating applications than solar electric panels.