For a few years, search for solar modules (because of fast growth of market), is bigger than offer.
Because of that, prices of modules are very balanced although the big differences in quality between
manufacturers still exist.

At buying, the most important is to determine how much power (W) we will really get after paying the
certain price. Calculation is very simple using just two always known data:
- rated power of module(every manufacturer must specify the rated power)
- the tolerance of rated power (every manufacturer must specify the tolerance limits of rated power)

Example:
If the price of module is 3000,- kn, rated power is 100W, and tolerance of power is -10%.
This means that you can count just on 90W. The price for 1W according to that is 3000 : 90 = 33,33 kn.

If the price of module is 3100,- kn, rated power also is 100W, but the tolerance of power is -0%.
For that module you can surely count with all 100W. The price for 1W according to that is
3100 : 100 = 31,- kn.

Obviously the first module is more expensive altough his price for the "same" rated power is lower.
Its price for guaranteed rated power of 100W according to that is 100 x 33,33 = 3333,- kn!

Conclusion:
At buying you first need to determine the price for 1W considering the tolerance of rated power.
The cheaper module is whose price for real 1W is lower!!

Comment: In text under title "What you must ask the reseller before purchase?" (see under "News"),
we indicated few additional data which are useful to know before finall judgment of purchase.

Solar controllers with MPPT tehnology are more expensive than other controllers, but for the same
battery charge current needed less solar modules (see under news Novosti "What you must ask the
reseller before purchase").

As the price of solar modules in system is much higher than price of the controller, it's easy to calculate
the repay of installing controller with MPPT technology. If the power of solar system is bigger, the
saving in total price is bigger. Here drastically valid: "I am not enough reach to buy cheaper"!!

a) Wave form of output voltage
Inverters are divided in two basic groups according to wave form of output voltage:
- pure sine voltage (such voltage is also from electric grid. The price of this devices is higher.)
- "modified sine" (trapezoidal or square), voltage
Devices with pure sine voltage can supply all type of loads, but their price is significantly higher.

b)Rated output power
Continuous output power certainly need to compared. Because of preasure on prices, manufacturers
more often specify output power which is not continuous. Usually is specified power which device can
supply during period of 30min or even shorter.

c)Overloading
The bigger possibility for overloading, the inverter will easier run loads with high starting currents.

d) Stand-by mode
In solar systems it is important that device consume less power when there are no connected loads.

a) Number of charge-discharge cycles which battery can handle during lifetime
That is by far the most relevant data for comparison of solar batteries. Together with number of
cycles, depth of discharge has to be stated. Example: 1200 cycles with discharge of 70% capacity.

b) Rated capacity
Together with rated capacity, discharge time with constant current should be specified. Example:
500Ah at 10-hour discharge time with constant current. Capacity with 100-hour discharge current
is for the same battery always 20 do 25% higher than capacity with 10-hour discharge current!

c) Weight
As a rule-of-the-tumb: more weight for the same capacity, more you will get from the battery.

d) Hermeticaly sealed battery or battery with liquid electrolyte?
If it's possible, battery with liquid electrolyte should be used. Liquid acid batteries are (for the same
quality compared), about 10% cheaper, resistantce to charging with increased voltage and currents
is higher and are by far more durable under condition of increased temperatures. Also, if regulator
overcharge liquid-acid battery, simply add distilled water. If that happened with hermeticaly sealed
battery, it will be irreparably damaged.