cutandpolished61 Posted March 7, 2020 Report Share Posted March 7, 2020 Hi All. having purchased my narrowboat late last summer i had not much time to look into my solar set up. But this year will be all about solar for me and I would appreciate your advise. Currently I have 2 x 100 watt solar panels linked to my 24 v bank which is used for the inverter and fridge. With a battery voltage of 24.5 volts I noticed on yesterdays sunny day the solar panels producing just 2.7 amps at 12:00. No shading, no clouds. Should I be satisfied with the amperage this time of the year? Could the cheap PVM controller the reason for the low amperage? Link to comment Share on other sites More sharing options...
ditchcrawler Posted March 7, 2020 Report Share Posted March 7, 2020 At 100% efficiency those two panels will only give you about 7 Amps, so I would say nearly 3 isnt to bad. What is the open circuit voltage of the panels ? Link to comment Share on other sites More sharing options...
MtB Posted March 7, 2020 Report Share Posted March 7, 2020 The current and voltage are irrelevant. You should be concerned by the power. You should also consider the meaning of "Wotever's Law" of solar: "However much solar you have, it will be too much in summer and too little in winter" I have 560W of solar and it is enough to power the fridge and everything else from about now (early March) to early November. When I had 300W it was good from April to September. Link to comment Share on other sites More sharing options...
cutandpolished61 Posted March 7, 2020 Author Report Share Posted March 7, 2020 3 minutes ago, ditchcrawler said: At 100% efficiency those two panels will only give you about 7 Amps, so I would say nearly 3 isnt to bad. What is the open circuit voltage of the panels ? No idea Brian. How can I find it out? With the voltmeter from the panels? Link to comment Share on other sites More sharing options...
Alan de Enfield Posted March 7, 2020 Report Share Posted March 7, 2020 2 minutes ago, cutandpolished61 said: No idea Brian. How can I find it out? With the voltmeter from the panels? It should be stated on the panels, or you can see the panel voltage on the controller / monitor You can see on mine the Panel voltage is 103 volts at 0.8 amps, when this is taken down to 14.7 volts by the controller it takes it up to 5.9amps. This is with a 'low-light' 170 watt panel. Link to comment Share on other sites More sharing options...
ditchcrawler Posted March 7, 2020 Report Share Posted March 7, 2020 Remember he is running at 24 volts. Link to comment Share on other sites More sharing options...
Alan de Enfield Posted March 7, 2020 Report Share Posted March 7, 2020 1 minute ago, ditchcrawler said: Remember he is running at 24 volts. Yes, it was just to show how he could identify the panel voltage. Link to comment Share on other sites More sharing options...
cutandpolished61 Posted March 7, 2020 Author Report Share Posted March 7, 2020 1 hour ago, Alan de Enfield said: It should be stated on the panels, or you can see the panel voltage on the controller / monitor You can see on mine the Panel voltage is 103 volts at 0.8 amps, when this is taken down to 14.7 volts by the controller it takes it up to 5.9amps. This is with a 'low-light' 170 watt panel. Link to comment Share on other sites More sharing options...
Alan de Enfield Posted March 7, 2020 Report Share Posted March 7, 2020 (edited) 12 minutes ago, cutandpolished61 said: So you have 21.6volt panels feeding into your 24 volt battery bank. Are they wired in series or parallel ? When your panel is putting out 5.8 amps it is only producing 17 volts. Ideally you want to have panels several times the voltage to your system allowing the controller to 'step down' the voltage and 'step up' the current. My panels have a VoC of 120 volts (10x the battery voltage). This means (as per the picture) that when the panel is outputting 103 volts at 0.8 amps, the controller changes that to 14 volts at 5.9 amps 'More bang for your buck'. If (for example) your panels are 12v and they are putting out 0.8 amps, then you are only charging the battery (at best) at 0.8 amps I think the suggestion to get an installer to 'source and install' is probably a good one, you'll get a system that works to the best possible - but - being in London you will struggle (as you have found on the LB facebook page - if they do not know anyone …………………….) Can you take a couple of weeks and move the boat up towards the Midlands - you'll have a choice of installers. Edited March 7, 2020 by Alan de Enfield Link to comment Share on other sites More sharing options...
TheBiscuits Posted March 7, 2020 Report Share Posted March 7, 2020 3 minutes ago, Alan de Enfield said: So you have 21.6volt panels feeding into your 24 volt battery bank. When your panel is putting out 5.8 amps it is only producing 17 volts. I suspect they are connected in series Alan, so 34.4V at 5.8A theoretical rating, feeding the PWM controller. Link to comment Share on other sites More sharing options...
Alan de Enfield Posted March 7, 2020 Report Share Posted March 7, 2020 Just now, TheBiscuits said: I suspect they are connected in series Alan, so 34.4V at 5.8A theoretical rating, feeding the PWM controller. I suspect so as well. And with a PWM being about 30% less efficient than a MPPT. If it is a PWM I'd suspect that yesterdays clear sky producing 2.7 amps is probably not far off the Summer maximum. Link to comment Share on other sites More sharing options...
MtB Posted March 7, 2020 Report Share Posted March 7, 2020 8 minutes ago, Alan de Enfield said: So you have 21.6volt panels feeding into your 24 volt battery bank. Are they wired in series or parallel ? I think they MUST be is series. AFAIK a controller PWM or MPPT will not step UP the panel voltage to charge a battery of higher voltage than the panel voltage. Link to comment Share on other sites More sharing options...
Alan de Enfield Posted March 7, 2020 Report Share Posted March 7, 2020 PWM vs MPPT charge controller test We often get asked about the actual difference you get between an MPPT and a PWM controller so we setup a side by side test using our Yingli part used panels onto 2 separate 12V batteries, 1 with a PWM controller and one with our tracer MPPT. Panels were set-up side by side angled south. With early March sun the MPPT was giving 3.7A into the batteries while the PWM gave 2.5A which was 32% lower than the MPPT. In cloudy conditions the MPPT was giving 1A when the PWM was giving 0.8A (20% lower with PWM) Both charged the batteries well, but 20%-32% more power was gained by using the MPPT. Link to comment Share on other sites More sharing options...
MtB Posted March 7, 2020 Report Share Posted March 7, 2020 (edited) 1 hour ago, Alan de Enfield said: Both charged the batteries well, but 20%-32% more power was gained by using the MPPT A common arithmetic error. If a value (say 1A) is reduced by 20% to 0.8A, it takes an increase of 25% to get back to 1A from 0.8A. 1 minus 20% = 0.8 Yet 0.8 plus 25% = 1 Edited March 7, 2020 by Mike the Boilerman To clarify 1 Link to comment Share on other sites More sharing options...
cutandpolished61 Posted March 8, 2020 Author Report Share Posted March 8, 2020 21 hours ago, Alan de Enfield said: So you have 21.6volt panels feeding into your 24 volt battery bank. Are they wired in series or parallel ? When your panel is putting out 5.8 amps it is only producing 17 volts. Ideally you want to have panels several times the voltage to your system allowing the controller to 'step down' the voltage and 'step up' the current. My panels have a VoC of 120 volts (10x the battery voltage). This means (as per the picture) that when the panel is outputting 103 volts at 0.8 amps, the controller changes that to 14 volts at 5.9 amps 'More bang for your buck'. If (for example) your panels are 12v and they are putting out 0.8 amps, then you are only charging the battery (at best) at 0.8 amps I think the suggestion to get an installer to 'source and install' is probably a good one, you'll get a system that works to the best possible - but - being in London you will struggle (as you have found on the LB facebook page - if they do not know anyone …………………….) Can you take a couple of weeks and move the boat up towards the Midlands - you'll have a choice of installers. How did you achieve the 120 voltage? By connecting the panels in series? Link to comment Share on other sites More sharing options...
Alan de Enfield Posted March 8, 2020 Report Share Posted March 8, 2020 Just now, cutandpolished61 said: How did you achieve the 120 voltage? By connecting the panels in series? No, the individual panels are rated at 120 volts. You can buy 12v panels, 24 volt panels ……………………………….. all the way up to 200+volts. My panels are classed as 'low-light' and are specifically designed for UK use where the Sun is lower in the sky and therefore hits the panels at a different angle. It is important to understand the differences and which is why it may be best to let your installer buy the 'right ones' for you. With a higher voltage panel (which has fixed watts) you get more amps when taken down to 12v to charge your battery. Watts = Amps x volts. So for example a 120 watt panel at 120 volts will produce 1 amp. When you take that output and your controller takes it down to 12 volts you get 10 amps going into your battery. 1 Link to comment Share on other sites More sharing options...
Chewbacka Posted March 8, 2020 Report Share Posted March 8, 2020 2 hours ago, cutandpolished61 said: How did you achieve the 120 voltage? By connecting the panels in series? In my case I have two 37v panels (ex solar farm) in series, so on a bright sunny day when the batteries are full the voltage is about 70v. Link to comment Share on other sites More sharing options...
Featured Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now