Solar Panels, the understanding thereof.

[Nightwatch]

We here on the good boat Nightwatch are confused.

 

We have, two 100watt solar panels. We have been reasonably happy with them.

Today, very sunny, hot and panels are unobstructed. Pointing towards the sun.

 

The gauge we use shows 7.5 amps going in to batteries. Didn’t seem a lot to me. So, out with a blanket. Covered one and gauge showed 1.75 amps. Expose covered panel, cover t’other, same reading 1.75 amps. Expose both and back up to 7.5 amps. All readings approximate.

 

Should I be getting more than 7.5 amps in these conditions with 200 watt of solar panels. Since we got them fitted the readings have been disappointing to me. Am I expecting too much?

Edited June 2, 2021 by Nightwatch

[David Mack]

7.5 A at around 14 V means you are getting around 100W into your batteries. The 200W panel rating is for ideal conditions, i.e. somewhere in the tropics, so half that in the UK sounds about right.

 

Are your panels wired in parallel or in series?

[Nightwatch]

Just now, David Mack said:

7.5 A at around 14 V means you are getting around 100W into your batteries. The 200W panel rating is for ideal conditions, i.e. somewhere in the tropics, so half that in the UK sounds about right.

 

Are your panels wired in parallel or in series?

This is where my knowledge of such things is exposed. They are connected ‘in line’ with a ‘Y’ connector.

[Tony Brooks]

Also how well charged are you batteries? As they charge up the charging amps drop off. They had probably been charging since about 5AM.

Just now, Nightwatch said:

This is where my knowledge of such things is exposed. They are connected ‘in line’ with a ‘Y’ connector.

So in parallel.

[Nightwatch]

The used amp hours used is indicated as -59 amp hrs.

Ihave flashed up the engine as we have washing to do. The alternator is pumping in 50+ amps on near tick over. We are berthed up.

Edited June 2, 2021 by Nightwatch

[Tony Brooks]

Something I noticed with my solar when I fitted an MPPT controller is that it was timed for the absorption phase and it tended to drop to a float voltage too soon. What battery voltage did the controller or voltmeter show before you started the engine. Unless you have fitted a fancy alternator controller the alternator will keep providing around 14.4V ish till the cows come home so you would get a higher charge than from  something that has dropped to float voltage.

[Nightwatch]

Will investigate Tony.

 

Thanks. Parallel or in series. Which is best? Please.

[Tony Brooks]

2 minutes ago, Nightwatch said:

Will investigate Tony.

 

Thanks. Parallel or in series. Which is best? Please.

 

No straight answer I am afraid and I suspect in most cases its not worth altering what you have got. If they were in series they may have started charging a bit earlier and stay charging a bit later each day but I have not seen it quantified. In series shading a panel may reduce the output more.

 

With large arrays series will allow you to use thinner (cheaper) cables but it increases the chances of getting a shock from the panel connections on the controller.

Edited June 2, 2021 by Tony Brooks

[David Mack]

36 minutes ago, Tony Brooks said:

 

So in parallel.

If they are in parallel, why did covering one panel not simply halve the current?

[Tony Brooks]

21 minutes ago, David Mack said:

If they are in parallel, why did covering one panel not simply halve the current?

 

No idea but he did say he has Y connectors so that is two into one so parallel.

[Higgs]

27 minutes ago, David Mack said:

If they are in parallel, why did covering one panel not simply halve the current?

 

It might be that the charge controller was able to work more efficiently with the two panels able to produce more current during DC to DC conversion. ??

 

 

 

Edited June 2, 2021 by Higgs

[sjc]

Why didn't it halve the current ?

 

Probably because the covered panel was draining some of it, assuming your panels do not have blocking diodes ?  The working panel was probably producing half your measured current, some of which went to your controller, the remainder was back-fed through your covered panel.  To measure one panel disconnect the other first.

 

As for % of max, we have had upto 90% on the right day, panels clean, properly tilted, batteries on bulk etc