Website for Turnkey Solar Solutions in Arizona

Frequently asked questions (FAQ).

Features

• Maximizes Power Transfer from PV
• Increases water pumping ouput by 30-40%
• Over 99% Efficiency in Direct Mode
• Over 90% Efficiency in Switch Mode
• Custom Models Only

The power produced by a photovoltaic (PV) system varies with the amount of sun shining on the array and to a lesser extent, array temperature. If temperature is held constant, this power variation results in a variable current at a fixed voltage. Increasing temperature reduces PV output voltage.

For photovoltaic applications that function over a limited voltage range, such as charging batteries, the variation in current with sunshine is acceptable and the use of additional electronic equipment beyond battery regulators is generally superfluous. Other PV applications, such as driving DC motors for water pumping, require variable voltage (for optimum operation) that is not compatible with the fixed voltage and varying current available from the PV array.  This mismatch in voltage can cause a substantial loss in power, resulting in reduced system efficiency.

The ETA Electronic Maximum Power Tracker (EMPT) overcomes this problem by electronically transforming the array power to lower voltage and higher current whenever it is necessary to match the array output to the load.  At other times the EMPT remains "on" with full power transferred directly to the motor. The EMPT operates to transform voltages only when there is inadequate array current to operate the load directly.  EMPT efficiency is above 90 percent when transforming power in switching mode and above 99 percent in direct mode. Generally, adding an EMPT to a PV pumping system will increase the annual pumped output by about 30 to 40 percent. The current into the motor can be 10 times higher than the array current when the motor is turning very slowly (for a DC motor, voltage is directly proportional to motor speed). A "Positive Displacement" pump has an almost constant torque (current) need and will deliver water in proportion to its RPM (proportional to the motor voltage). Therefore the EMPT keeps the pump turning usually down to 10 percent insolation. Appreciable savings are also realized with centrifugal type pumps especially in low "head" applications. The unit uses all solid state Electronic devices with no mechanical parts except for a "Mode" switch and the interconnect terminals. A remote high reliability linear integrated circuit temperature sensor is normally employed to measure cell temperature of the PV array. This covers all first order effects in determining the array Maximum Power operating point which is primarily determined by temperature. The high accuracy temperature sensor allows the EMPT electronics to "track" the ideal operating point as temperature changes. The change in ideal operating point with light intensity is small and can be neglected. It should be noted that on a cold windy winter day the ideal operating Voltage may be 20% higher than on a hot and still summer day. For this reason pumps using our system will run significantly faster in the winter than in the summer. This partially makes up for the fewer sun hours available. When charging batteries, the excess array voltage is "Transformed" down into additional charging current; an advantage that becomes even more significant at low battery voltage.

The EMPT Control employs numerous features to enhance safety, performance and long term reliability. The Temperature sensor is a isolated very high impedance constant current type which is clamped and filtered on the printed circuit board by R-C networks. This technique, though more expensive, is far more reliable than the more common thermister sensor approach. The PV power input is filtered by a large (low ESR) Energy Storage Capacitor which very effectively eliminates noise and input transients. The Control's power supply (12 VDC) is derived from the input capacitor through a one-way diode and an R-C filter network clamped by a Zener Diode. Additionally the circuitry employs a low supply voltage detect which prevents operation under very low power or start-up conditions. This further protects the power switching FET(s) which could be damaged with insufficient drive voltage. The Power FET(s) are protected from positive going voltage spikes with solid State transient absorber(s) rated at 1.5 joules of protection. Negative transients are clamped by the transient absorbers and the FET body diode(s). The FET(s) are driven by a low impedance CMOS driver circuit that can source or sink one Amp of drive current to minimize switching losses. The commutating (free-wheeling) diode has been selected for good reverse behavior and critical forward recovery characteristics.

How does a maximum power tracker work?