Solar direct DC application refers to Solar Panels directly connected to DC loads for operation without the need of battery bank as backup. This is the simplest and cheapest form of Solar PV System as it does not require expensive components such as battery and solar charge controller. It is also a long lasting system without frequent component replacement especially battery bank in an off-grid PV system.
However, DC direct application is only suitable for small DC power appliances within few hundred watts such as water switch, water pumps, exhaust fans, heater coil, LED lights, phone or small electronic chargers that need to operate only during daytime. Since the system does not store energy, the power generation is subject to intensity of sunlight.
Direct application is not an efficient system as we need to oversize the solar array to compensate the availability and fluctuation of sunlight. Normally solar panels are sized at least 2 times the size of total connected load wattage to overcome losses during conversion and fluctuation of sunlight. For example, charging a 5V 2A (10W) phone may require at least 20W Solar Panel to be effective; Running a 20W DC ventilation fan may require at least 40W Solar Panel.
100Wp Solar Panels
100Wp 18Vmp Solar Panel is commonly used for Solar DC direct and small Solar Off-Grid PV System. A good solar panel may last at least 20 years. Grab one at our affiliate link here !!!
20-30Wp Solar Panel 18Vmp
A good quality of Solar Panel can last more than 20 years. It is a portable and convenient power source suitable for small application such as Water Switch. You may consider getting one at our affiliate link here !!!
Solar Panel’s maximum operation voltage (Vmp) should be higher and near to the load’s nominal operating voltage since it normally does not involve MPPT mechanism. High voltage differences will contribute to the power loss when a solar panel is directly connected to a DC load. A typical 18Vmp solar panel for a 12V loads can lost between 22-33% due to voltage difference (assume operation voltage is at 12V) while 32Vmp solar panel for 12V load can lost between 56 – 62%.
There are typically 3 common ways of installing a Solar DC Direct System:
INSTALLATION METHOD 1 : DIRECT CONNECTED TO LOAD
Solar Panel is connected to a load without any other components. This method is used when solar panel capacity is designed to be less than the load requirement. The short circuit current (Isc) of the solar panel must not be more than operational current of the DC load. Solar Panel will adjust its generated current and voltage based on its I-V curve characteristic thus if the condition above met, the power production will not possible to exceed the load requirement.
The loads will operate under power all the time thus no protection is needed. This method is only applicable to 1 load per panel. If a solar panel is powering more than 1 load, it may have a chance of overpowered if one or more loads are not operated or faulty. In the later case, a DC-DC converter is required (method 2). For direct connection, the DC loads must be able to withstand high initial voltage and wide range of voltage fluctuation thus it is not suitable for sensitive or electronic loads which require stable voltage or narrow input voltage window.
Possible loads are LEDs, heater and motor based loads such as ventilation fan and water pump. The maximum operating voltage (Vmp) must be larger and near to nominal voltage of the load for efficient operation. This is the cheapest way of installation if the owner does not mind to have fluctuation of load performance due to different sunlight intensity throughout the day.
This installation method has lowest efficiency as it does not have power conversion unit to convert voltage difference to current gain especially for higher voltage solar panel. For example, 3 units of 100W solar panel (32 Vmp; 3.125 Imp) may only possible to operate a 12V 10A (120W) load at full power. Thus the panel voltage selection is critical.
12V/24V Bilge Pump Submersible Water Pump
DC voltage Bilge Pump is a submersible pump regularly used for water pumping application for irrigation and farm. It can be operated by Solar. Find out more at our affiliate link here !!!
2 Pin Waterproof Connector
It is the waterproof connector which is suitable to be used outdoor. It can connect up to 1..5mm square cable size. Grab a set of connector at our affiliate link here !!!
INSTALLATION METHOD 2 : CONNECTION VIA A DC-DC CONVERTER
This method involved a DC-DC converter or step down converter in between solar panel and load for voltage conversion and regulation. The DC-DC buck converter is used to step down the output voltage of a solar panel to a regulated and desired voltage which is the nominal voltage of the load. It is suitable to be used including electronic loads such as phone charging or operate other USB gadgets. The DC converter can also prevent overpowered to the load. In other words, more solar panels or bigger solar capacity up to 2 to 3 times the load total wattage can be installed to increase the operation time and stability of the output power.
There are few types of converter including USB converter module that charges USB gadget, CV converter for general purpose uses and CC & CV converter to charge a battery. Avoid operating large power loads as unstable power may frequently get them shutdown. Many loads can be connected together as long as the loads having the same nominal voltage. The output voltage of the converter must be set either same or slightly lower than nominal voltage of the loads. The converter capacity must be large enough to operate all the loads. while the input voltage range must be able to withstand the solar panel open circuit voltage.
The DC-DC converters do not have Maximum Power Point tracking mechanism. Thus the maximum operating voltage (Vmp) of solar panel must be larger and near to nominal voltage of the load for efficient operation. However, it is able to convert voltage difference (voltage change due to step down) into current gain at output but in condition that solar power generation is higher than load requirement. During low sunlight, the DC-DC converter just act as normal bypass as without any useful function when the input voltage from solar panel is lower than the set output voltage of the converter. Thus the load and panel are operating at same low level voltage.
In the case when the solar panel generation power is more than load requirement, a DC-DC converter will convert the voltage difference into current gain thus it is more efficient than method 1. Using same example as above, only about 1.5 units of 100W solar panel (32 Vmp; 3.125 Imp) may possible to operate a 12V 10A (120W) load at full power. As a result, an equivalent of 150Wp should able to support 120W load under very bright sunlight with some minor power losses.
DC-DC Boost Buck Converter
DC-DC converter is a device to step up / step down / to regulate output voltage. A boost buck converter can have a range of input voltage and the output can set to a desired voltage. It also can be used to stack in parallel to increase the total power or reduce burden without stressing the module. Get one at our affiliate link here !!!
12V Powerful Exhaust / Ventilation Fan
This is a very powerful and strong DC operated fan for building heat dissipation and space cooling. It is compatible with industrial grade and has high force thus may expect some noise. This is not a laptop ventilation fan. Check it out at our affiliate link here !!!
INSTALLATION METHOD 3 : CONNECTION VIA PWM SPEED CONTROLLER
This method connects solar panel and load via PWM speed control module to increase power generation. It is an enhancement from method 1. The power generation gain is actually the reduction of power lost due to voltage difference between solar panel (Vmp) and nominal voltage of load similar concept as MPPT mechanism. This method can only be used on motor loads such as water pump and ventilation fan.
Difference with Method 1 and method 2, under reasonably good sun radiance, the PWM controller has a potentiometer which user can manually adjust the power output of the Solar Panel via duty cycle concept thus indirectly adjusting the output voltage of solar panel based on its I-V curve characteristic.
However, the maximum point of a solar panel is constantly changing based on the changes of sunlight and temperature and user can set only one fixed point unless keep adjusting all the time. It is better to adjust for maximum operation when the sunlight is at optimum so that generation is improved on bright sunny day.
The PWM controller cannot be used together with DC-DC converter which can eliminate the performance gained. Without the protection of DC-DC converter, solar panel capacity is limited up to 120% of load wattage and only for 1 load per PV panel or array. Method 3 is favorable if Solar Vmp value is very high compare to nominal voltage of the load. Same to others, there is no difference during low sunlight condition.
PWM Control Module
PWM Control Module is a module originally used to dim DC LED light and to adjust DC motor speed. It also exhibit the benefit of power adjustment of the solar panel thus we can adjust the operating power based on the I-V characteristicd. There are wide range of PWM Control Module at our affiliate link here !!!
DC Energy Meter
DC Energy meter display important measurement units such as voltage, current, power and energy. It is very useful to troubleshoot or analyse an electrical or project performance. Grab one at our affiliate link here !!!
PWM Speed Controller can be manually adjusted or integrated to Arduino board for continuous tracking. Manually adjusted will be less efficient as the maximum power point of the solar panel will keep changing based on the irradiation and temperature. However, it is overall simpler and suitable for non-technical user. Best is to adjust during good sunlight. Once set, user can leave it forever. During setting, energy meter can be used. For smooth adjustment, it is best to add a capacitor parallel to the input connection of the PWM controller.
As for automated control using Arduino board, more material and wiring work are needed such as an arduino board, voltage and current measurement sensors. Some PWM Speed Controller support 0-5V as sensor thus suitable for micro controlling.
In summary, method 1 is more favorable due to simplicity and cost but the supported loads are limited. Method 3 is an enhancement and is more cost efficient if the installed solar panel has high Vmp compared to nominal voltage of the load. It also increases the power for moderate light level condition. Method 2 is the most commonly used in direct DC application. It provides regulation and protection from overpowered which could lead to load overheated or burned. It also can support larger loads and wide DC appliances.
Ferrule Lugs and Crimper Set
Ferrule lugs are used at terminals for tight and secure connection. Besides, it also prevent stranded cables accidentally touching adjacent power line that may cause short circuit. Grab 1 at our affiliate link here !!!
Terminals Crimping Plier Set
This is a crimping tool with interchangeable jaw for crimping many types of terminals. It is a must have for DIY electronic and electrical for professional installation work. You may choose at out affiliate link here !!!
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