Technical data

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OFF GRID

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General

Recommendations

for Inverters and Hybrid Systems

Inverter Selection Matrix

Pnom_inverter Unom_battery Battery capacity

200 W 12 V > 100 Ah

500 W 12 V > 200 Ah

1,000 W 12 V > 400 Ah

2,000 W 12 V > 800 Ah

2,000 W 24 V > 400 Ah

3,500 W 24 V > 700 Ah

3,500 W 48 V > 350 Ah

5,000 W 48 V > 500 Ah

7,000 W 48 V > 700 Ah

Sine Wave Inverters

In contrast to modified sine wave inverters, the

Steca sine wave inverters supply a pure and ac-

curate regulated sine wave to the load. Only this

pure sine wave technology allows the user to run

all types of AC loads within the off-grid photo-

voltaic system, which can normally be used in

grid connected mains power supply systems. Ad-

ditionally, this technology guarantees a noiseless

operation, which is especially important if critical

applications like radios, television and other sen-

sitive devices are used.

Modified

Sine Wave

Inverter selection

The inverter should be sized properly depending

on the type of application. The summary of com-

sumption should be covered by the continuo-

us power of the inverter while starting currents

should be within the maximal power.

To allow a future increase of consumption Steca

recommends to oversize the inverter.

PV generator and

charge controller selection

The solar module array has to be adapted to the

local solar irradiation conditions and the energy

consumption of the system. To avoid downtimes,

the PV generator must provide enough energy

even during months with low irradiance to meet

the needs of the loads.

The minimum size of the regulator had to cover

the maximum short circuit current of the modu-

le and the maximum load current. Sometimes

even technical feature had to be supported in the

application and a high end regulator should be

used in a low power system.

To keep the initial cost on a low level we recom-

mend to size modules and battery according to

the current consumption and to size the control-

ler corresponding to future refitting.

Battery rating

The battery has to be sized properly in order to en-

able the inverter also to supply high demanding

loads. Some critical loads like fridges, freezers,

pumps and motors draw extremely high currents

during a short starting phase. To run such loads it

is important to use a capable inverter with an extre-

mely high overload capacity especially during the

starting phase. The battery also has to be sized in

a proper way to be able to supply enough current

if requested by the inverter. The following formula

recommends how to size the battery: the batteries

capacity should be at least 5 times more than the

nominal power of the inverter divided by the nomi-

nal voltage of the battery

C_batt ≥ 5 h * Pnom / Unom

while Pnom indicates the nominal power of the

inverter in Watt and Unom the nominal voltage

of the battery in Volt.

Selection of system voltage

The system voltage of the off-grid photovoltaic system

should be selected dependently of the load demand. The

higher the load demand the higher the system voltage.

If no 12 V DC loads are connected, a higher system vol-

tage of 24 V or 48 V should be preferred to reduce the

DC-current in the system. Above around 2500 W, only

inverters with 48 V power systems can be recommended.

The higher the voltage, the lower the system currents.

Finally, lower currents result in higher system efficiency

due to less losses.

Selection of cables

DC currents are typically high in inverter systems. Due

to this fact, it is essential to use proper cables bet-

ween the inverter and the battery. Always connect

the inverter directly to the battery. Choose a DC inver-

ter cable as short as possible. Also, the thickness of

the cable should be sized properly. Choose a thicker

cable in case of doubt – this can have a significant

influence to the overall system behaviour. By using

thick and short cables the system losses can be redu-

ced – the results are higher efficiency and better per-

formance. If the inverter is delivered with a DC cable

never enlarge this cable or use a thinner one.

(V)

100 500 1.000 2.000 5.000 10.000

(W)

Single Phase Inverters

Steca SISteca AJSteca

Solarix PI

Steca SI 3~Steca

Solarix Sinus

Inverter - Chargers

Steca

Compact

Steca HPCSteca XPC Steca Xtender

XTH

Steca Xtender

XTH 3~

1.000 2.000 3.000 5.000

(V)

(W)

100.00010.000 20.000 50.000