Solar PV, or Solar Photovoltaics is the process of converting sunlight into electricity utilizing at least 2 layers of semiconductors sandwiched into a solar cell. The semi-conductor layers differ in electrical charge such that when the sunlight hits the negatively charged (n-type) layer it excites an electron which will then be attracted to the positively charged (p-type) layer. This causes a chain reaction of electrons flowing from negative to positive causing a rate of flow or current of electrons.
Multiple solar cells are combined in series to create a solar module (a solar panel) and each solar module creates a certain amount of power depending on the number of solar cells it contains. The power created by the solar panel needs to be used as it is created which is fine when you need power, otherwise the power needs to be stored for use at a different time.
As with a vast majority of renewable solutions, energy storage remains the largest hurdle to overcome in our goal of replacing fossil fuels as a source of energy. Renewable Solutions such as Wind and Solar power depend solely on the presence of wind and sunshine to produce electricity; both of which are not always available when we need power – having a means of storing the excess power created during the day or times of wind is a current challenge. On small scale applications (home or office), the most economical solution today remains battery storage - the problem being that battery technology is severely lagging the pace of technology. For this, being connected to the power grid is still the most economical solution.
On-grid or grid connected solar pv systems utilize the existing electrical grid as a means of storage. During the daylight hours a solar pv system is generating electricity and distributing it onto the grid for use by anyone who is connected to it. At night, when the solar pv system is not generating electricity, you are obtaining power from the grid.
During the day you are selling power to the Utility and at night you are buying power back from the Utility, with the end goal being power sold = power bought.
The diagram below shows a brief overview of some of the components involved:
The Solar PV Array (1) converts the suns energy to DC electricity; DC is commonly used in electronics and anything powered by batteries (RV lighting, car stereo). For use in household/commercial applications, the DC electricity must be inverted to Alternating Current (AC) electricity and is done so through an electronic device called an Inverter (2). The inverter takes the incoming DC power and inverts it to AC. The AC power then gets thrown onto the utility grid after passing through the end users main electrical panel (3) and the Utility Bi-directional meter (4). The Bi-directional meter is supplied by the power Utility and is a means for the utility to track the power being sold to the grid vs the power purchased from the grid.
Pros: Cheaper, simple system components, lower maintenance, unlimited utility power, ability to sell power, carbon negative over lifespan
Cons: Utility connection required/reliability on Utility, loss of power upon Utility power outage.
Grid connected systems are the most common installations in North America, however, there are situations where being connected to the grid is not possible, or desirable. With a grid connected system, if there is a power outage, power is no longer being fed to the grid, nor is it being bought from the grid. In remote situations, grid connection might not be a possibility, or cost prohibitive.
An off-grid solar pv system utilizes some of the power generated throughout the day while storing excess energy in batteries, then at night, power is drawn from the batteries. Off grid systems are typically coupled with standby generators to ensure power is available during periods of prolonged darkness or high consumption periods. A drawback of off-grid systems are the general cost, maintenance and short(er) life span of the storage system. A great deal of planning and design is required in order to minimize the size and in turn cost of an off-grid solar PV system.
System components depend on the requirements of the end user, the diagram below shows a brief overview of a typical off-grid installation:
As with the gird connected system, the solar Array (1) still converts the suns energy to DC. The charge controller (2) is the first piece of an off grid system required for storage. The charge controller is the brains of the system and is responsible for maintaining a charged state in the battery bank (3) and also handles distribution to any possible DC loads - such as lighting, appliances or DC motors. The battery bank is sized to store all of the energy required by the end user to function over a specified period of time (typically 3 days). When needed, the stored DC power is inverted (4) to AC and directed to the distribution Panel (5), for use by all other appliances or devices that require AC power. For end users that have high-power requirements, live in low sunlight areas, or want added reliability, a generator can be utilized to ensure the batteries are topped up.
Pros: Independence from utility (connections costs, fluctuating/rising cost in power), power backup and reliability. Cheaper, simple system components, lower maintenance, unlimited utility power, ability to sell power, carbon negative over lifespan.
Cons: Expensive, higher maintenance, complicated system and installation, limited available power.