Solar Power Day & Night

You are probably wondering how is it possible to have solar power both day and night if all we have in Trinidad and Tobago is approximately 12 hours of sunlight a day.

Over the years talks of renewable energy went from murmurs to whispers to full conversations as declining oil, gas and coal reserves negatively impacts the world.  In T&T, with the abundance of sunshine available, solar power seems to be the most plausible type of renewable energy for the twin island. The most popular way to generate electricity from the sun is through the use of solar panels. Solar panels also known as photovoltaic (PV) panels, which are made of photovoltaic cells that use photons from sunlight to excite electrons, causing them to move, producing electricity.  Electricity is basically a flow of charge which is carried by free flowing electrons through a conductor such as copper. Solar panels, contrary to popular belief, does not operate on the heat coming from the sun. The hotter the temperature of the sun, the less efficient a solar panel can become as its ideal operational temperature is around 25˚ C to 30˚ C.

Conventional solar (PV) panels

We all know that we have been experiencing temperatures that are higher than 30˚C in Trinidad and Tobago. In the generation of electricity in T&T, natural gas is burned to achieve really high temperatures in order to generate steam to operate turbines to drive generators for electricity. The burning of natural gas for power generation emits dangerous greenhouse gases which contribute to global warming. Since heat is a major requirement in the generation of electricity then there must be a way to use the sun’s heat to generate electricity. Solar thermal technologies is the use of technology in order to harness the sun’s heat energy for any useful purpose. This has been in existence for ages, however it has evolved from practical uses such as drying to more technical uses such as electricity generation. This is done using “Concentrated Solar Power” technologies. This technology use mirrors called heliostats, that are specially programmed to track the sun so that sunlight can be reflected to a single point called a receiver on a tower that is made up of a highly conducting material. By placing hundreds, even thousands of heliostats around a tower all angled at one precise location on the tower the temperatures can reach up to 600˚ C.

Heliostats at Crescent Dunes power plant designed by SolarReserve

The heat absorbed by the receiver on the tower heats a fluid, generally water, to create high pressure steam to drive turbines, similar to that of a natural gas power plant. This still does not explain how we can have 24/7 solar power. If the water is replaced by another fluid that has a high thermal conductivity and then stored in a highly insulated tank to maintain its heat for a long period. After the sun sets this heated fluid can be used to heat water to generate steam for the turbines. Molten salts are used as the fluid which is also referred to as the thermal transport medium and also the heat energy storage medium. It is made up of calcium nitrate salts which is a cost effective thermal absorber that is also non-toxic and non-flammable. The storage capacity is calculated so that there is enough molten salt to be heated and stored in the storage tank to provide electricity for when there is little or no sunshine, such as night time or during high cloud cover. The storage tank is so well insulated that it loses only 1˚ F per day.

Concentrated solar power plant designed by SolarReserve

This technology offers a stable and constant source or power that other forms of renewable energy technologies cannot. It is not intermittent in nature as solar panels or wind turbines and uses the same technology that already exists at coal, natural gas or nuclear power plants. With the heat being generated by the sun there are no harmful greenhouse gases being released by the power plant, making it 100% renewable. The Crescent Dunes power plant located near Las Vegas in the United States consists of 10,347 heliostats and provides 110MW of power with 1.1GWh of storage which is enough to power 75,000 homes during the peak electricity use hours.

As with all projects there are challenges to building such a power plant like this as the land space required is great. With Trinidad and Tobago being a small island there are not much sites available for the construction of such a plant. In other areas of the world a major stumbling block with concentrated solar power plants were birds being killed by the heat around the receiver tower by following bugs that were attracted to bright light at the top of the tower. This problem was solved with the invention of a special frequency generator that would trigger birds to fly in a different direction rather than to go towards the tower.

This technology is 100% applicable in Trinidad and Tobago and is readily available. Should this be the first step toward turning T&T green?