At Rural Power Systems, our goal is to educate the consumer in order to make informed purchasing decisions.  In order to understand solar power systems, a few basic terms should be understood.

Below is a list of the most common solar power terminology, including their definitions and abbreviations.  The solar power explanations have been kept simple to ensure everyone can understand.

Many of the examples compare electricity to water running in pipes.  While not exactly the same, this is a great way to understand electricity and is simple way to explain electrical concepts.  Electricity can be hard to visualize, but everyone can visualize and understand water running in pipes.


Basic Electrical Terminology

Voltage (V)

Voltage is the electric potential between two points. This is usually expressed in volts. A standard AA battery is approximately 1.5 volts.  Just sitting there on a table, from the positive to negative terminal of the battery, exists the electrical potential of 1.5 volts.  Systems operating at higher voltages can transfer more power with less current.  It is common for high power solar power systems to operate at high voltages, anywhere from 24 to hundreds of volts.

If you think of water in a pipe, the pressure of the water inside the pipe is comparable to voltage.   With higher pressure water, more water can be transferred in a shorter amount of time.

Current (I)

Current is the electrical flow when voltage is present across a conductor.  This is usually expressed in amps.  A 1.5 volt battery just sitting on a table has no current flow.  Hook up light bulb (conductor) across the battery terminals to start the current flow.  There now current running through the light bulb.  In order to transfer more power, the current will increases.  To transfer this higher current larger wires are needed.

Current is comparable to the amount of water flowing through a pipe.  Water at high pressure in a sealed pipe will just sit there.  This is like our battery, there is voltage (pressure), but no current (water flow).  Hook up some pipes to the system and now water starts to flow through the pipes.  If more water needs to flow, larger pipes are needed.  This is the exact same for electricity, if more current needs to flow through a system, larger wires are required.

Power (P)

Power is the rate at which energy is transferred by an electrical circuit.  This is usually expressed in watts.  Power depends on the amount of current and voltage in the system.  Power equals current multiplied by voltage (P=IV).

Back to the battery sitting on a table.  Just sitting there, no power is being consumed.  This is because there is no current flow (1.5 volts multiplied by zero current is zero watts).  Connect the light bulb to the battery and now there is both voltage and current flowing through the light bulb, meaning the light bulb is consuming power and emitting light.  In a solar power system, the solar panels generate power in the form of voltage and current which is used by the electrical load.

Think of hose filling a bucket with water.  The bucket filling up is similar to power.  The bucket fills up at a given rate.  Turn up the pressure on the hose (increase voltage) and the flow of water (current) goes up too, filling the bucket faster.  Get a larger hose or even two hoses and with the same pressure there is more water flow and again the bucket fills faster.

Increasing either the current or voltage will cause the power of the system to increase.  In a solar power system this is achieved by adding additional solar panels.  By doing so, the total power of the system increases.


Solar Power Specific Terminology

Open Circuit Voltage (Voc)

Open circuit voltage is the maximum voltage a solar array panel can produce.  Open circuit voltage occurs where there is no current flow and the panel is in full sunlight.  Take the positive and negative leads of a solar panel, place in full sunlight and hook up a volt meter.  Because the two leads are not connected together (they are open circuit, hence the name) there is no current flow.  The voltage reading in this configuration is the open circuit voltage.

Short Circuit Current (Isc)

Short circuit current is the complete opposite of open circuit voltage.  This is the maximum amount of current a solar array panel can produce.  Take the two leads of the solar panel and short the positive and negative cables together (hence the name short circuit current).  Now place the panel in full sunlight.  Because the two leads are shorted together there is very little voltage.  If you measure the current flowing through the wires, this is the short circuit current.

Note: If you remember definition of power above P=IV, during open circuit conditions there is no power because current is zero and during short circuit current conditions there is no power because voltage is essentially zero.  To have power, both voltage and current are needed.  This brings us to our next set of terms.

Max Power (Pmax)

This is the maximum amount of power a solar array panel can produce.  The max power point is a balance of current and voltage to produce the maximum amount of power achievable from the solar panel.  Open circuit voltage conditions produces high voltage but no power, short circuit current produces high current but no power.  The max power is somewhere in between these two extremes with the correct balance of current and voltage.

Voltage Max Power (Vmax or Vmp)

Voltage max power is the voltage at which the solar panel is producing the maximum amount of power.

Current Max Power (Imax or Imp)

Current max power is the current at which the solar panel is producing the maximum amount power.

Maximum Power Point Tracking (MPPT)

Advanced controllers feature a maximum power point tracking feature.  Controllers with this feature determine the maximum power the solar array panel can produce and draws the correct voltage and current to maintain this maximum power condition.  If a controller draws too much current, the voltage is reduced, and power is reduced.  Likewise, if a controller maintains too high of voltage, current is reduced and again power is reduced.  A maximum power point tracker draws the right amount of current in order to maintain a high voltage and achieve maximum system efficiency.

Solar Panel Efficiency

Solar panel efficiency is a measure of how well a system converts light energy into electricity.  It is a ratio of light shining on the panel, versus the amount of electricity produced and is expressed as a percentage.

An ideal system would be 100% efficient, meaning all light energy is converted to electricity. This is not possible.  Most systems are around 16% efficient, meaning 16% of the light energy is converted into electricity.  If 100 watts of light are shining on the solar panel, 16 watts of electricity would be produced.


Solar Panel System Connections

Parallel Connections

Parallel solar panel connections are used to increase current.  Connecting two panels in parallel results in double the current.  Voltage remains the same.  A parallel connection involves connecting the positive terminal of one panel to the positive terminal of another panel and the negative terminal of the first panel to the other negative terminal of the second panel.  Connecting positive to positive and negative to negative will place the two panels in parallel.

Think of this as using two hoses as opposed to one to fill a bucket.  The amount of flow (current) doubles when there are two hoses filling the bucket, yet the pressure (voltage) of the hoses remains unchanged.

Schematic showing solar panels connected in parallel.

Series Connections

Series connections are used to increase voltage.  By connecting two panels in series, the voltage output is doubled.  The current remains the same as one panel.  A series connection involves connecting the positive terminal of one panel to the negative terminal of another panel.  The unconnected positive and negative terminals now have the same current but twice the voltage.  This can be expanded for multiple panels, meaning three panels in series will provide three times the voltage output.

Schematic showing solar panels connected in series.

Series and Parallel Connections

Solar panel systems are made up of solar panels connected in various series and parallel configurations to achieve proper voltage and current levels.    It is very common to have three panels connected in series to increase the voltage output by 3X and two sets of the 3 panels in parallel in order to increase the current by 2X.  Any number of panels can be connected in series and parallel configurations.

It is important to remember, in order to connect sets of panels in parallel each set should have the same number of panels in series.  Do not connect two panels in series to three panels in series.  Both sets should either have two or three panels in series in order to connect in parallel.

Schematic showing solar panels connected in series and parallel used for larger solar systems.

Solar Well Pump Systems, A Complete Overview

The following article describes the major components of a solar powered well pump system.  These are very simple systems, capable of replacing most utility connected wells.  They are capable of pumping water from hundreds of feet underground at many gallons per minute.  With a mere 6 hour of sunlight a day, these systems are capable of producing thousands of gallons of water every day, all without being connected to utility provided power.  Now more than ever before, solar well pumps can replace hard wired systems.

Basic Solar Well Pump System Components

All of our solar power well pump systems consist of three main components

  • Brushless DC Well Pump
  • Maximum Power Point Tracking(MPPT) Controller
  • Solar Panel Modules (if purchased as a complete kit)

Brushless DC Solar Well Pump

Brushless DC well pumpBrushless DC solar well pumps are made up of two main parts, the brushless DC motor and the pumping mechanism.  The brushless motor takes electrical power and converts it into mechanical energy, which provides the force required to turn the pumping mechanism.  This mechanism pumps water causing it to rise from deep beneath the ground to the surface, hundreds of feet above.

The brushless well pumps we carry are designed to operate on solar power.  They features a highly efficient brushless DC motor designed for years of use.  Brushless technology is the latest advancement in DC motors.  Brushless motor technology increases the energy efficiency and decreases the required maintenance, since there is no need to change carbon brushes which wear down over time in standard brushed DC motors.  Brushless motors have no brushes, hence the name, and are designed for many years of continual usage without maintenance.

The second major pump component is the pumping mechanism.  Our pumps feature a helical rotor pumping mechanism.  This consists of a stainless steel spiral mechanism, which spins against a rubber gasket.  This spinning motion against the gasket, forces water upward and out of the well.  The pumping mechanism is user replaceable in the field.  All of our pumps come standard with a spare, so the user never has to worry about pump down time.  Simply remove three screws on the top of the pump, remove the old pumping mechanism and insert in the new mechanism.  Unlike other designs, there is no need to send your pump back to the factory for costly repairs if pumping efficiency decreases.

The body of the pump is made out of 100% stainless steel.  Stainless steel is a hygienic material perfect for drinking water applications.  The other benefit of stainless steel is that there is no need to worry about the pump rusting or corroding.  The pump is designed to offer years of maintenance free service.

Maximum Power Point Tracking Controller

The maximum power point tracking (MPPT) controller is the brain of the entire system.  It takes power generated from the solar panels and supplies it to the brushless DC motor.  At the same time it monitors solar panel performance and makes adjustments as needed to the voltage and current in order to maintain maximum performance.  Other inferior systems use brushed DC motors connected directly to solar panels.  These systems waste energy since they are not operating at their maximum potential power.  The MPPT feature improves overall system efficiency, especially in low light, overcast conditions.

Solar well pump controller used to operate the brushless well pumpThe MPPT controller also features low well shutoff and storage tank overflow sensors.  If the well starts to run dry, the controller will shut off the pump in order to prevent damage to the motor.  The pump should never be run dry due to a drop in the water level, and doing so for even a few seconds can damage both the motor and pumping mechanism.

The storage tank overflow sensor will shut off the pump once the storage tank is full.  It is a very simple float that is installed in the top of the storage tank to sense when it is full.  Stainless steel probes may also be used instead of the float valve.  Once full, it sends an electrical signal to the controller to shut off the pump.  This is a very useful feature to prevent pumping of water when the tank is full and starting to overflow onto the ground.  There are two benefits to this feature.  First, water is not wasted and pumped onto the ground.  Second, operating life of the pump is extended, since it is not running unnecessarily.

An alternative to using the tank overflow sensor is to utilize the motor speed setting on the MPPT controller.  This consists of a simple dial which can adjusts the speed of the pump.  All of our controllers feature a digital speed controller which regulates the speed at which the pump operates.  The pump can be set to operate at any speed desired and can be fine-tuned to the amount of water needed on a daily basis.  If the full flow rate it too much, it can easily be adjusted to any lower flow rate by a simple adjustment of the regulator.

The MPPT controller is encased in a water resistant enclosure and is suitable for outdoor use.  It features water resistant wire pass-through ports on the bottom, to prevent both moisture and bugs from entering the electronics.  Power and external sensor connections are made easy by the use of clamping screw terminals.  Only a screwdriver is required to make the electrical connections to the controller.

Solar Panel Modules

Solar panel used to operature the solar well pump systemAll of the solar panels provided in our well pump systems are mono-crystalline silicon panels.  Mono-crystalline cells provide maximum performance in the smallest area.  Last generation technology, amorphous silicon, does not provide the same area to power performance.  We have chosen to use the latest technology of solar cells in order to provide maximum performance for each system.

The cells are connected as necessary to achieve proper voltage and current for each module.  The modules feature industry standard MP4 connector for ease of making series and parallel connections to increase system power. There is no need to splice wires in order to make these connections.  The MP4 connectors are water resistance and ideal for an outdoor environment.  Every panel has an aluminum frame and tempered glass to protect the solar cells.  The tempered glass is impact resistant to prevent damage in severe weather conditions.

All of our solar panel systems are sized to at least 1.6 times great than the pumps power requirements in order to maintain performance in low light conditions.  If you choose to purchase solar panels separately or have your own solar panels, we recommend a minimum of 1.4 times panel to pump power ratio.  All of our panels range from 80 watts to 100 watts as necessary to achieve proper current and voltage.  We tend to use the smaller solar panels since they are easier to ship and install by a single person.  If solar panels are sourced locally, our systems can use any size modules as long as the current and voltage are correct.

Recent advances in solar panels have really made these small scale systems possible.  High quality low cost panels can be produced in module form.  This means all solar cell connections are made at the factory and encased in protective glass and a rugged aluminum frame.  Only two power connections exit each module with easy to use MP4 connectors.  Series connections can be made easily with just the existing module connectors.  Parallel pigtail connections are provided as needed to connect panels in parallel.  This makes the solar panel electrical connections very easy to make.


Now is a better time than ever to install a solar power well system!  The technology has advanced to a point where system performance exceeds the requirements for large variety of usages.  From homes to farms, there is a cost effective solar well pump solution available.  Check out our available systems and as always please feel free to contact us for personalized assistance in choosing a system.