The amount of energy from sunlight that hits the earth in just one hour is more than the worlds energy consumption for a year! Every hour, 430 quintillion Joules (that is 18 zeros after 430) of energy hits the earth. With the sun not going anywhere soon, it is quite clear that it can provide us with a vast amount of energy.
So why is only 2% of global electricity currently coming from solar power? Across the globe we simply aren’t capturing and using enough of the sun’s energy. This is due to various limitations which will be discussed later in the blog, but let’s start by discussing different types of solar power.
There are two main types of solar power, photovoltaic technology and solar thermal technology. Photovoltaic technology directly converts energy from the sun into electricity; in contrast, thermal technology captures the sun’s heat and uses it heat directly or converts it to mechanical energy for electricity.
Let’s look into these two types in a little more detail…
Photovoltaic (PV) Technology:
Photovoltaic solar power systems are made up of PV cells. An individual PV cell produces around 1 to 2 watts of power output. Many cells are assembled into solar panels and lots of panels are assembled into a solar array.
How does each individual PV cell work?
- Each cell is made up of positively and negatively charged semiconductors (usually silicon) sandwiched together, creating an electrical field.
- When photons (light particles) hit the cell, the energy is absorbed by the PV cell.
- This energy excites electrons (negatively charged particles) in the semiconductor material.
- The electrical field forces the electrons to flow in a specific direction, towards conductive metal plates.
- The current is then directed into wires.
- An inverter converts the direct current into alternating current (the type we can use in our homes).
The number of panels is directly proportional to the electricity output. A small solar array could be placed on the roof of a house to provide electricity to the house whilst a large solar array could be used to power thousands of homes.
Solar Thermal Technology:
Solar thermal technology can be broken down into two main types, low-temperature solar thermal power (used for heating) and concentrated solar power (to produce electricity).
Low – temperature solar thermal power:
This type of solar power directly uses the suns radiation to heat up water supplies. It is useful in domestic settings (hot water and heating) as well as industrial settings where hot water below 100 degrees (Celsius) is required.
The most common type are flat-plate collectors which have a dark surface to absorb sunlight. They have a layer of thermal insulation on top and a sheet of glass to generate a greenhouse effect.
Energy from the sun heats up a transfer fluid. The transfer fluid is pumped through a heat exchanger that is connected to the water supply.
Concentrated solar power (CSP):
- CSP uses mirrors to reflect and concentrate sunlight onto a receiver.
- The receiver contains a fluid that can hold heat well – this could be oil or molten salt
- The heat from the concentrated sunlight heats up the fluid in the receiver.
- The hot liquid heats water in a heat exchanger which causes the water to
- The steam then turns a turbine which spins a generator and the generator makes electricity
- The heated fluid is recycled over and over again and the steam is cooled and condensed to be reused.
So what are the advantages and disadvantages of solar power?
- It is a clean and renewable energy source: There are no greenhouse gases released in the conversion of solar radiation to energy and solar radiation is abundant.
- It is a flexible and accessible energy source: Solar energy can be produced in almost any location and allows the production of energy in remote areas where access to power lines is not possible.
- Maintenance tends to be simple and affordable.
- Solar power doesn’t produce noise pollution
Seems like a no brainer, right? Let’s look at the drawbacks
- Solar power can be unreliable: There are huge intermittency issues that come with solar power. The sun (particularly in the UK) doesn’t shine all day everyday and whilst energy can still be generated on an overcast day, the efficiency is greatly reduced.
- Storing solar energy is currently expensive and inefficient: as we are not able to produce solar energy at night or on a rainy day, we need to be able to store excess energy generated during the day. The current solar battery solutions are expensive and inefficient.
- The initial installation cost is high: whilst solar power reduces costs of energy bills, the initial investment is large.
- Transportation and installation can be associated with greenhouse gases so it isn’t 100% clean.
To sum up, the sun provides us with an incredible renewable energy source, but currently we just aren’t capturing enough of it. To overcome the major barrier of intermittency, we need to improve solar batteries to store energy for use at times when the sun isn’t shining, or store excess solar as hydrogen via electrolysis.
There is a great deal of hope for the future of solar panels. With the cost of solar technology reducing significantly over recent years and the ongoing research into improving efficiency and storage solutions, the future of solar power is bright.
If you want to check out how Hans-Olof Nilsson who has solved the intermittency issue at his house in Gothenburg, Sweden, check out the Climate Change series over at the BBC with Ade Adepitan: