High Power MPPT Solar Charge Controller Request for Proposal (RFP) Template

High Power MPPT Off-Grid Solar System Proposal

Choosing the right charge controller is one of the most important decisions associated with designing and building an off-grid system.  This sample template was created to help installers, designers, engineering, procurement & construction personnel to create an RFP that will attract responses from qualified parties that can meet key High Power MPPT charge controller specifications to help ensure deployment of a reliable, high-quality off-grid system.  A charge controller is considered to be the brain of a Photovoltaic (PV) system and an ineffective controller can cause premature battery failure and failure in the whole system.  In addition to the sample template below, we invite you to view the GenStar MPPT Solar Charge Controller RFP template which addresses load control, shunt current monitoring, relay control, and battery management systems for lithium and other battery chemistries.


  • The controller design life shall be 15 years or greater.
  • The manufacturer’s warranty period shall be 5 years.
  • The controller shall be 100% solid-state.  Mechanical relays and cooling fans are not acceptable.
  • The maximum allowable open circuit voltage on the solar input shall be 150V or greater.
  • Load control requirements can be met with a 100% Solid State option or a dry contact relay switch option.


  • Peak efficiency must be >= 99%.
  • Efficiency at full power >= 94% with Vmp = 60V with 12 volt systems.
  • Efficiency at full power >= 96% with Vmp = 90V with 24 volt systems.
  • Efficiency at full power >= 97% with Vmp = 90V with 24 volt systems.
  • At a minimum, there should be 7 battery charge setting options for various battery types.
  • The battery settings should also be fully programmable allowing the adjustment of charge voltage, float voltage, equalization and temperature compensation. and custom programmability for optional voltage setting adjustments to accommodate a variety of battery types including sealed, flooded, and gel batteries.
  • Auto-equalization shall take place every 28 days or there must be an option for manual equalization for sealed or flooded batteries.
  • Voltage accuracy must be < 160 mV.  Controllers which do not list accurate information will not be accepted.  Battery sense must be included to eliminate voltage drop inaccuracies (Battery voltage sense terminals must directly measure battery voltage at all times.  Inaccurate measurements of voltage drop can cause the controller to enter into absorption stage too early and disconnect loads during low voltage disconnect (LVD) prematurely).
  • The thresholds for all the battery charging settings (absorption, float, and equalize), must be temperature compensated and adjustable. Default temperature compensation = -30mV/C @12V.  Custom settings must be available.  The controller shall include a built-in temperature sensor and a remote temperature sensor (RTS) for more accuracy.
  • MPPT Tracking Algorithm should be capable of sensing multiple maximum power points utilizing full sweeping at all times and continue operating with the highest power.

Switch Options

  • DC Load Control (Low Voltage Disconnect) to protect batteries from over-discharge. 100% Solid State option or dry contact relay switch option.
  • High voltage disconnect protection for Solar charging and Loads to prevent overcharging or high voltage conditions to load from the battery. 100% Solid State option or dry contact relay switch option.
  • A means to establish dry contact alarm notifications (this can be established by connecting to a compatible relay switch accessory.)
  • Generator start option with dry contact relay switch(es)
  • Multiple switches for prioritized loads

Custom Settings

The following settings must be able to be customized and adjusted:

  • Charge voltage regulation setpoints (Absorption, Float and Equalize).
  • Absorption extension time. The absorption time should automatically be extended when the depth of discharge (DOD) goes below a certain defined voltage to ensure full battery charge the following day.
  • Float timeout
  • Equalize time with Equalize timeout setting (max. time > Absorption Voltage ) to prevent partial equalizations for extended periods of time.
  • Manual Equalize or Automatic Equalize settings (Auto includes frequency (# of days) between Equalize).
  • High voltage disconnect for Solar charging and Loads
  • A maximum regulation voltage setpoint limit to protect voltage-sensitive loads.

Environmental Requirements

  • The controller’s circuit board shall be protected with a conformal coating.
  • The terminals shall be marine-rated. All fasteners shall be stainless steel.
  • The controller shall be rated for operating temperatures from -40 °C to +45 °C.
  • The controller can operate to the rated maximum battery current at 45°C without derating.
  • The controller shall be rated for 100% humidity non-condensing conditions.
  • Case studies must be available to demonstrate the reliable and long-term performance of the controller in warm and tropical environments.


The controller must be equipped with the following protections:

  • Solar Input: overload, short-circuit, high voltage warning, nighttime reverse current
  • Load Output: overload, short-circuit
  • Battery: high voltage
  • Other: High temperature
  • The controller shall continuously perform “Self-Diagnostics” and report any faults or alarm conditions as they happen.
  • Automatic recovery without fuses
  • The controller shall be transient overvoltage protected with nanosecond response Transient Voltage Suppressors (TVS’s) rated at least 4500 watts. Both the solar input and the load output shall be protected.
  • The controller will not be damaged with high input power levels. The controller is also able to continue operating continuously without exceeding the rated output current of the controller.

Meter Display Interface

  • The digital display should be included with the controller
  • The controller’s meter should display the following information
  • Battery Voltage, Charging Current, Target Voltage, (Load Current with solid-state load controller option)
  • Charge State (Bulk, Absorption, Float)
  • Load State (LVD, ON/OFF) – (with solid-state load controller option)
  • Alarms, Faults
  • Solar Current, Array Voltage, Array Vmp, Array Voc
  • Today’s Min/Max Voltages, Charge Ah, Minutes in Absorption/Float/Equalize, (Load Ah with solid-state load controller option)
  • Digital and Graphical Historic Daily Logged Min/Max Voltages, Charge Ah, Minutes in Absorption/Float/Equalize (Load Ah with solid-state load controller option)
  • Digital Meter
  • Multi-controller display options
  • Aggregated system data option (load with solid-state load controller option)
  • Backlight (on/off)
  • Self-consumption < .5W (42.5mA (backlight on)
  • Backlight Timeout
  • Operating Temperature -40ºC to +60ºC
  • Storage Temperature -55ºC to +85ºC
  • Humidity 5-95% (NC)
  • Conformal coated circuit board


The controller must accommodate:

  • Maximum wire size is 35mm. (#2 AWG)
  • 1/2″,3/4″, 1″, 1-¼” conduit or M20, M25, M32, M40 gland sizes to be offered in the enclosure.
  • Access to terminals must be possible while the controller remains mounted.


Controller must support the following communications capabilities:

  • Remote monitoring options for all system parameters including but not limited to operating Array Volts, sweep Vmp/Voc/Pmax, Charge State (Bulk MPPT), Absorption, Float, Equalize, Night, Fault, Disabled), Battery
  • Voltage, Target Regulation Voltage, Charge Current, Battery temperature, Heat Sink Temperature, Charge Ah, (Load Ah with solid-state load controller option)
  • Ability to download daily logged values for the last 100 days or more.
  • Remote data logging in real-time.
  • The following daily logged values must be stored internally by the controller:
  • Min./Max. Battery voltage
  • Ah charge/load
  • Max./min. Array voltage
  • Alarms
  • Faults
  • The time that the controller has regulated battery charging in absorption, float, and equalize charging stages.
  • (Daily logged values must be stored internally and available for download into a spreadsheet or viewable with an optional graphical meter.  Additional communications adapter accessories may be required to view this data).
  • The ability to program and control (System Reset/ Disable Charging and/or Load) the system remotely


  • The controller must be compliant with the requirements of CE, RoHS, EIA-62109, UL 1741, UL 62109, IEC 62109-1, US FCC Part-15 Class B,
  • The controller shall be manufactured in an ISO9001 certified facility