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Passively Active Solar Heating

May 2014

Solar heating systems, as we know them today, have been around for a long time - well over 100 years. Solar collectors are placed in the sun and collect heat which is transfered into some fluid (air or water) which is transported though pipes or ducts to some other location where it is either used or stored for use later.

The concept has worked reasonably well given the capabilities of the hardware and the thermodynamics that limits its abilities. Designs were typically divided into "active" and "passive", where "active" meant that pumps or fans were involved and energy was consumed to transfer the solar heat from one location to another. "Passive" meant that the transfer of heat was self-driven by the temperature gradiant between the hot collectors and the cooler end use location or storage.

Over the past ten years PV (Photo-Voltaic / solar electricity) has started to dominate the solar scene and it does not use pumps or temperature gradiants, but has its own application divisions: grid-tied, off-grid, battery based, etc. Are these systems active or passive? Since they normally do not have any moving parts, does that make them passive? Does the use of inverters - which actively change the generated energy from one form - DC (Direct Current) to another - AC (Alternating Current) - make them an active system? Does using batteries, which changes the form of the energy from electrical to chemical and back again make those systems active?

Now we have new solar electric products that blur the lines even further - solar electric water and space heating systems - such as CyboEnergy's PV CyboInverter 1200H. This inverter, the first of its kind, takes solar energy and converts it to AC power which is fed directly into a heating appliance such as an electric water heating element or a resitive element in a baseboard heater, or an electric frying pan, etc. I would like to propose a new term: "Passively-Active Solar".

Passively-active solar systems do not use pumps or fluids to move energy around, but transfer electrons from PV panels directly to an end load - such as, in the case of the CyboInverter 1200H, to an electrical heating element of some kind.

The term Passively-Active Solar may never catch on - but is does accurately describe the unique characteristics of a new generation of solar heating systems.