Before you start harnessing the elements to heat, cool or light your home, caravan, tent or truck, it is worth considering your motivation as it will determine what systems are best for you. You will also need to assess your site as you may not have suitable resources. Are you able to connect or remain connected to the national infrastructure as a backup? Do you need to have an uninterrupted power supply (UPS)? Are you relocating daily or is it a more permanent arrangement? What is your budget?
We recommend that you focus on what you consider to be essential and then be prepared to compromise if nature temporarily leaves you a bit short. Establish what are your MUST and WANTS are. Once you have established your MUST and WANTS you can calculate your energy requirements and usage. We also recommend that you develop a modular and scalable approach so that the system can be easily changed as your requirements or financial circumstance changes.
The photovoltaic (PV) cells of a solar panel harvest sunshine in the form of photon rays and converts them to direct current (DC) electricity. The life of a solar PV system is impressive as there are no moving parts to convert the solar energy into electricity.
How Solar Panels Work
Each solar panel is a remarkable lattice of layers of silicon-based cells. When the sun’s photons hit a layer of silicon that has free outer electrons around the atoms, these move to the layer beneath, which comprises atoms with electrons missing. The resulting flow causes a small current, but because there are many cells linked together, the whole panel produces a useable voltage of DC electricity. It remains as DC current it is going straight to a battery. This is a 12V system.
Solar PV systems are specified as having a ‘peak power capability’, because they depend on how much sun shines on the panels. The systems do still make electricity on overcast days, though obviously make more power on a sunny day.
Solar panels are extremely useful for charging batteries and so are ideal for powering “stand-alone” or “off the grid” systems that are remote from mains supply. For a stand-alone system, it is important to be sure that your solar panel can provide enough energy to power whatever you intend to use it for. As long as your panels are a suitable size and you have sufficient batteries you should seldom have an occasion when there is not enough power. You should aim to have enough stored energy for those “just in case” situations.
In a battery, a chemical reaction occurs and then electrons travel through a wire from one terminal to the other, and the result is Direct Current (DC) electricity. Batteries are particularly useful for standalone systems as they are fairly cheap and power can be stored and used when needed. If you wish to store electricity that you have generated in the battery bank then deep cycle batteries are designed to deliver less current for a longer period of time. Once flat they are designed to be recharged.
Car batteries can be used but they are not suitable as they are not designed to be fully discharged. The deep cycle batteries are designed to be recharged once flat and will last longer.
The amount of energy that a battery can supply is specified in ampere hours (Ah). So, a 12-volt battery that is specified as 100Ah can theoretically deliver 1 amp for 100 hours or 100 amps for 1 hour.
Multiplying the volts and amps, gives you the power (watts) the battery will produce.
So for our 12 volt battery it is possible to have:
- 12 volts X 1 amp = 12 watts for 100 hours
- 12 volts X 100 amp = 1200 watts for 1 hour
Back in the real world, these numbers don’t quite add up as you can’t expect to get more than 80% capacity from your battery, i.e. 80 Ah.
The smaller deep cycle batteries are not designed to deliver masses of current so you shouldn’t really drain more than about 10 -15 amps (that’s a device of about 120 – 180 watts). So if a pump needs 60 watts to function we divide 60 watts by 12 volts, which gives 5 amps.
If you use the pump for 2 hours a day, a fully charged battery therefore lasts about 8 days.
How to work out Watts, Amps and Volts
Common sense states that a larger Solar Panel will collect more energy than a smaller solar panel, but what size is correct for your needs?
Most power consumption of appliances is given in Watts. It is a relatively simple calculation to work out power your energy use, just multiply the power consumption by the hours of use. For example:
100 watt device used over 5 hours equals 100 x 5 = 500 Watt hours (Wh)
Converting Watts to Amps
If you want to figure out if your 100W solar panel is capable of running a fridge that draws 2A, then it’s a matter of one formula. You cannot directly convert watts to amps, since watts are power and amps are the current. It’s kind of like trying to convert litres to kilometres. But because the voltage in a 4WD is fixed at 12V then converting the watts into amps becomes achievable via the following equations:
So in the event of the 100W solar panel, 100W / 18.97V = 5.28A. That shows that the 100W solar panel can provide a maximum unregulated output of 5.2A whilst the fridge is drawing just 2Ah. A common mistake people make with solar power is taking the wattage of the panel and dividing it by 12V, this is the wrong calculation to make as no solar panel is 12V they are generally between 18V and 21V. False statements about 120 Watt panels being able to produce 10 Amps per hour are un true, un realistic and an unfortunate selling point used by people in the industry who do not fully understand solar power. To combat the “cowboys” out there all iTechworld solar panels have the full power ratings clearly marked on each and every panel we produce.
If you would like to find out more about Solar Power then please do not hesitate to get in touch.
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