When looking at electric appliances, we hear the words volts (V), amps (I) and watts (W). Voltage, expressed in volts, measures the amount of “pressure” that pushes electricity. On the other hand, amperage, measured in amps, is the electric current that flows through a system.
A useful analogy is to think about electricity voltage and amperage in terms of water flowing through a pipeline. If the pipeline is wide, it will allow for more current to flow through it (higher current). Likewise, if there is a water pump or a slope that moves water from a higher pressure area to a lower pressure area (higher voltage).
When we multiply amps (I) x volts (V), we can calculate power. Power is normally expressed in watts (W). Depending on the situation, we can think of power in terms of kilowatts (kW), megawatts (MW), gigawatts (GW) or even terawatts (TW). A 1,000 W is equivalent to 1 kW. Likewise, 1,000 kW is equal to 1 GW and so on. You can think of power as the rate of doing work at a given moment in time. For example, I have a lamp at home with a label that says:
7 V DC 1.9 W
With this information, I can measure the current or amperage required. This can be easily calculated as: 1.9 W divided by 7 V which is 0.27 amps. If I want to know how much energy my lamp consumed today I can simply multiply the wattage (W) times the time turned on. If I used my lamp for 4 hours, I would multiply 1.9 W x 4 hours which is 7.6 Watt-hours. This measurement is known as energy.
Henceforth, we can define energy as the amount of power during a given period of time. This is very useful when needing to calculate how much energy a photovoltaic panel can produce. For example, if the PV solar manufacturer specifies that my panels outputs 40 volts at 5 amps, I can calculate power by multiplying them 40 x 5 = 200 W.
To simplify, I could calculate the average number of hours where my panels can generate electricity during the day, let’s say it is 4 hours per day. To obtain an estimate of monthly electricity output generated we would multiply its power 200 W x 4 hours * 30 days = 24,000 W or 24 kWh. While this is far from a precise number, it is a good start and the fundamental principle by which we can start understanding how these systems work.
In practice, there are more technical details to take into account. These include external factors such as weather and temperature patterns and internal factors such as inclination (known as tilt angle) towards the sun, materials and production process used or the charge controller used in the PV system. We will be going into more details as we move forward in this course.
Key takeaways:
- Energy measures how long a device is being used or how long it is producing power.
- Power measures the instantaneous consumption, which is calculated by multiplying amps x volts.
- Voltage can be thought of as the “pressure” that pushes electricity through a system or conducive material whereas amperage is the amount of electric current that flows through it.
- There are many energy units such as joules, british thermal units (BTU) and calories. These will be discussed as we cover more materials in the courses.
- Solar PV systems require sunlight to generate electricity. External factors such as sunlight levels, seasons, temperature, wind speeds among others influence the amount of energy that they will produce. Internal factors such as materials used for production, types of chargers used will have an additional impact on efficiency and its product lifecycle.