4 100 watt panel system

satman · April 2017

I have 4 100 watt solar panels (HQST) brand,also 30 amp HQST MPPT charge controller.The panels are wired in series (83.5V , 5.6 A.(OC)
Today was rather cool but it was bright and sunny.I may not be understanding this. I was only able to get about 240 watts from the 400 watt panels.60%. I was running my mini fridge from a 1200 watt inverter as a load.It draws 91 watts. My confusion is, does the load determine the actual output of the solar panels?

mike95490 · April 2017

2 things control the PV output.
A place to put the power (low battery, heavy loads)
(a partially or nearly full battery will not accept a lot of power)
How much sun and angle of Sun vs Panel

When my batteries are full and loads are light, 5Kw of panels only puts about 20 amps out

Photowhit · April 2017

satman said:
Today was rather cool but it was bright and sunny.I may not be understanding this. I was only able to get about 240 watts from the 400 watt panels.60%.

This is a bit low, even on cool days the surface of the solar panels will heat up, typically we see about 75% of the panel name plate rating, if the system is in "bulk" (basically taking all the energy the array can produce. You may have been past the "bulk" stage and already in absorb, at which point the charge controller limits the voltage passing to the battery and the battery may have begun to accept less current.

satman said:

I was running my mini fridge from a 1200 watt inverter as a load. It draws 91 watts. My confusion is, does the load determine the actual output of the solar panels?

It can at times, There are 3 basic stages in battery charging (for most charge controllers).

Bulk, where the batteries are accepting pretty much 100% of the current from the charge controller, this continues, depending on battery type and amount of incoming current, until the battery is about 80% full and the voltage reaches maximum safe level. At this point the charge controller will limit the voltage and switch stages.

Absorb, Where the charge controller limits the voltage to a safe level, to prevent excessive out gassing and heating of the battery. During this stage the battery begins to accept less current from the charge controller. Once the charge controller has been at this stage for a set amount of time or the controller determines a very minimal amount of current is flowing to the battery. It drops the voltage and begins the next stage.

Float, In float the charge controller maintains a lower voltage, high enough so that the battery doesn't lose energy, but low enough so that there is very limited charging. During this stage if a load is applied, the charge controller will allow more current from the array to pass, to maintain the set 'float' voltage.

An applied load will be reflected in more current passing from the charge controller, to maintain the voltage set points during both the Absorb and the Float stages, so in effect it does play a part in the output of the charge controller. If the load is greater than the solar array can handle the voltage will drop below the absorb or float levels as some of the current is supplied by the battery bank.

mcgivor · April 2017

One additional note, is that the sun doesn't suddenly come with full intensity, so the initial current, along with the voltage, will rise as the sun gets higher, depending on the depth of discharge, the battery may be approaching full charge by the time noon arrives, so the full potential of the array may never be seen. This has been my observation on my system 1, on a typical day by 11 am, the current the battery will accept has tapered down to around 6 amps, if I introduce a load of 1000 watts, the current the array will supply, will rise to 40 amps. Normally at 9 am, the charge current is around 25-30 amps, rarely will I see it higher, so without a substantial load, would never see the full potential.

So technically loads do have an influence on the maximum potential, if the maximum potential is masked by factors such as the example in the preceding paragraph, for example.

DConlyGuy · April 2017

since your like me and only running 400 watts of solar. i would run the panels in 2 sets of 2 at 40 volts and that way you start with the potential of 10 amps instead of the 5 your doing now. that how i run mine on a 24 volt system. it has worked very well for me with my tiny system

satman · April 2017

I have been testing individual panels for output today.Two tested at 80% and two at about 30%,All the tests were at about hi noon my time. All other factors being the same I can only conclude that the two lower output panels are drawing down my system.Is that a fair assumption ?

Estragon · April 2017

Maybe. You might get better production putting the two better panels in one string, and weaker ones in another.

Is there any crud on the weaker panels? Dead bugs, bird bombs, etc can cut production a lot.

BB. · April 2017

And shading. Any shading, partial shading (twig, antenna, overhead wires, etc.) can kill solar pv panel output (until shading is removed).

- Bill

satman · April 2017

Estragon said:

Maybe. You might get better production putting the two better panels in one string, and weaker ones in another.

Is there any crud on the weaker panels? Dead bugs, bird bombs, etc can cut production a lot.

satman · April 2017

Followup : I bought another 100 watt panel(poly this time).I wired the 2 mono in series with it and now are getting about 260 watts out of this array, at peak of solar day.Then as another test I wired the low producing panels in // and could only get 25-30 watts. I have talked to HQST about this at length . They were really no help. They even questioned the watt meter that had a external shunt . I even tested the diodes and they are normal. Gonna give them a call again in the AM This is getting frustrating after spending over 200.00 on panels that only put out about 30% of rated output.

4 100 watt panel system

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