What is the Difference Between PV and Solar Thermal?

Photovoltaics (PV) convert the energy from the sun directly into DC power. From there the DC power is passed through an inverter and converted into ac power thus allowing electricity to be transferred to the residence and back to the grid. A meter is also added to monitor how much electricity is being taken from the grid and sent back to the grid.

Contrary to PV, solar thermal doesn’t produce electricity. Instead it uses a working fluid, typically a water and propylene glycol solution, to collect heat energy from the sun. This working fluid is circulated through the solar collector where is absorbs energy from the sun. From there the hotter working fluid then travels to a storage tank of some sort.

Many times this tank is a domestic hot water heater that is connected to a boiler as well to add supplemental heat when the working fluid cannot get the domestic hot water up to temperature. However, there are also solar thermal applications that allow for pool heating. Using solar thermal to heat a pool has very similar features to using solar thermal to heating domestic water.

How do Photovoltaic panels work?

PV panels are typically made of two doped silicon layers. These layers are stacked one on top of the other and are comprised of a positive (P-°©‐type) or negative (N-°©‐type)

Charge. When doping, the positive layer electrons are removed thus making the natural state of the cell positive. Similarly when doping the negative layer, electrons are added thus making the natural sate of the cell negative. When the sunlight hits the front of the panel, the energy from the sun in the form of photons knock electrons loose. These electrons that are knocked loose flow down towards the positive side to fill empty spaces. When an external path is added, in the form of a wire, this promotes electric current through the wire to the adjacent layer.

How do Solar thermal panels work?

The operation of a solar thermal panel in comparison to a PV panel is much less complex. A solar thermal panel is comprised of a few basic components seen on the left. These components consist of glazing allowing for the sunlight to pass through to the tubes that the working fluid is being circulated through. A dark colored absorber plate that promotes sunlight absorption, and insulation at the bottom of the panel to reduce conductive heat loss through the back of the panel.

The primary goal of the solar thermal panel is to collect as much heat as possible and transmit that heat to the working fluid. This working fluid is normally water that contains some percentage of propylene glycol. This mixture is more necessary in colder climates where the working fluid has a potential to freeze.

What are the benefits of Photovoltaic?

• 30% Federal income tax credit
• 25% NY State income credit on a primary residence up to $5,000
• NYSERDA’s capacity based incentive that offers $1 per watt up to 25KW (PON 2112)
• Reduced electricity bill

What are the benefits of Solar Thermal?

• $1.50 per KWH displaced annually, up to 80% of calculated existing thermal load
• Ability to produce hot water from the sun to heat domestic hot water or pool, etc.
• Reduced electricity bill

Note – everyone’s tax liability is unique and a tax professional should be consulted to confirm tax credit eligibility.