Solar Panel Power

[BruceM]

I’m attempting to determine the theoretical wattage of the solar panel fixed to my recently acquired van. There’s no documentation and the panel carries a serial number but no brand mark. The pictures may provide a clue. It’s a 2003 van but I’ve no idea when the solar panel was fitted. The panel is 120cm x 55cm . Can anyone offer any guidance?

 

Many thanks.

[Charles]

Size wise it's about the same as a 100w monocrystaline.

[StuartO]

Good luck with the elderly solar panel which came with your MH - bear in mind that these panels don't last forever and older ones may not perform as well as newer, better types.

 

My pair of panels failed last year (after about five years service) and I took it back to the original supplier, who took them down off the roof and replaced the blocking diodes, which restored what appears to be normal service.  The diodes are inexpensive components but the panels have to come down to access them from the compartment on the back, so the £120 I paid was mostly labour.  It took them a couple of hours. 

 

The supplier said that if the diode change doesn't fix the problem it is expedient to scrap the panels and replace them because they are not economically reapirable in themselves.

 

Both panels and regulators have come down in price and improved in quality quite a bit over recent years.  It might be expedient to change your regulator for a more modern one even if you existing regulator still works since the better type boost the charging output by 15-20%.

 

So test the output of your existing panel/regulator combination and evaluate whether it is enough for your needs.  Unless it's still good enough to serve, take care not to spend good money on an old failing system. 

 

[BruceM]

Thanks both for the advice.

 

I’ve been reading up on how to measure the power output of my panel ( http://www.reuk.co.uk/wordpress/solar/measuring-the-power-of-a-solar-panel/ ) . It requires the use of power resistors which I don’t have.

 

However, I was thinking . . . I would have thought that my solar regulator (Sunsaver 10) should be holding the panel at its ‘operating point’ so if I park the van in bright sunshine and measure the voltage across the panel where it is connected to the regulator then a simple IxV will provide me with the panel’s peak power output in a real life situation.

 

Does that make electrical sense?

 

I’m actually getting 18.92v . Trouble is when I use my meter to measure the current being drawn the solar regulator does not appear to recognise that the solar panel is connected so no current flows. Scratching my head a bit on that one. Back to the drawing board!

 

 

 

[aandncaravan]

A cheap and easy way of checking the real power is a Wattmeter or Power meter, at £12 on eBay they are not exactly a lot of money?

They not only show you the Amps and Volts, but because they incorporate a timer they can calculate the Amps over time to give you a daily Ah reading, which is probably more useful than any other figure?

 

They are four wire connect, 2 'In' 2 'Out', and can go between the Solar Charger and the Battery or between the Panel and the Solar Charger.

 

Between the Solar Panel and the Charger is the most efficient place as the unit will cease to draw power when the Solar panel goes idle, as it obviously loses the power source it needs to drive the LCD display.

 

Wired in between the Solar Charger and the battery it will draw power continually from the battery to run the display, even when Solar Charge ceases at night time.

It's not much current draw, but during the short days, low gain of Winter it can make the difference between the battery staying charged and dropping down.

 

But then again it might be useful to see just how few Ah are being harvested?

 

Despite it's small size, it will supposedly handle 100a peak but I personally wouldn't put more than 40a through it.

 

 

 

They can be used to monitor the efficiency of any charging system, like the Alternator, etc.

 

There are cheaper versions but they are sometimes more complex to wire up. There is also a 150a (peak) version but we have no experience of those

 

 

[Charles]

BruceM - 2017-06-17 9:37 AM

 

Thanks both for the advice.

 

I’ve been reading up on how to measure the power output of my panel ( http://www.reuk.co.uk/wordpress/solar/measuring-the-power-of-a-solar-panel/ ) . It requires the use of power resistors which I don’t have.

 

However, I was thinking . . . I would have thought that my solar regulator (Sunsaver 10) should be holding the panel at its ‘operating point’ so if I park the van in bright sunshine and measure the voltage across the panel where it is connected to the regulator then a simple IxV will provide me with the panel’s peak power output in a real life situation.

 

Does that make electrical sense?

 

I’m actually getting 18.92v . Trouble is when I use my meter to measure the current being drawn the solar regulator does not appear to recognise that the solar panel is connected so no current flows. Scratching my head a bit on that one. Back to the drawing board!

 

 

 

You usually have to use a different socket on the multimeter when measuring current, and make sure it's set to DC current.

[Charles]

Personally I find it more informative to see what current the panel will deliver rather than wattage. Batteries are rated in amp hours so it's more relative.

[BruceM]

Meter ordered, I'll be back when I have some results.

 

Thanks to all for the pointers.

[colin]

I have 3 decades of experience of using solar panels, in all that time I've never bothered with a perminatly connected meter, I consider it to be the same as an alternator, if it doesn't work I'll investigate.

Whilst the price of solar has dramatically come down in price compared to the early days, I see no increase in quality with low price panels.

[BruceM]

Charles - 2017-06-17 11:59 AM

 

Personally I find it more informative to see what current the panel will deliver rather than wattage. Batteries are rated in amp hours so it's more relative.

 

That’s a good point. As I have a Fox-D1 fitted it’s an easy reading to take. Of course it varies with the drain on the habitation batteries (fully charged at the moment) so I think I’ll drain the batteries down a bit so that they take maximum solar charge, and tomorrow when the panel is back in full sun I’ll check what current is coming off the regulator.

 

So here’s the additional question, if the solar panel is the equivalent of a modern 100W panel, and if the regulator/charger were the latest/best technology, what current might I expect to see available on the Fox-D1?

 

 

[Charles]

BruceM - 2017-06-17 1:30 PM

 

Charles - 2017-06-17 11:59 AM

 

Personally I find it more informative to see what current the panel will deliver rather than wattage. Batteries are rated in amp hours so it's more relative.

 

That’s a good point. As I have a Fox-D1 fitted it’s an easy reading to take. Of course it varies with the drain on the habitation batteries (fully charged at the moment) so I think I’ll drain the batteries down a bit so that they take maximum solar charge, and tomorrow when the panel is back in full sun I’ll check what current is coming off the regulator.

 

So here’s the additional question, if the solar panel is the equivalent of a modern 100W panel, and if the regulator/charger were the latest/best technology, what current might I expect to see available on the Fox-D1?

 

 

If the panel is in good Nick and you have a standard charge controller (not mppt) I would expect 6.5 amps in full sun. You'd probably get a bit more with a mppt controller, how much more I don't know maybe 10%?

[747]

I think 6.5 amps is a tad over optimistic to be honest.

 

I used to have a good quality, quite new(ish) 100 watt freestanding panel and got around 6.5 amps max with it angled towards the Sun. A flat, roof mounted panel will not be as good.

 

As it is Midsummer and we are set for a glorious weekend, I would reckon 5 to 5.5 amps. If the Leisure battery is (batteries are) well discharged, a truer picture of the charge rate will emerge.

 

A handy tool for noting charge rates is the Car Current Tester from Maplin. I have used mine for many years. It is permanently wired in to the solar circuit. It runs off a small battery and has an On/Off switch. Be aware that it comes in two blade sizes.

 

http://www.maplin.co.uk/search?text=car+current+tester&x=13&y=17

[aandncaravan]

Charles - 2017-06-17 11:59 AM

 

Personally I find it more informative to see what current the panel will deliver rather than wattage. Batteries are rated in amp hours so it's more relative.

 

 

Charles, The meter has both Watts and Amphour measurement. Just been pointed out they are on ebay for as little as £6 including postage.

 

The difference between an MPPT charger and a PWM charger would be small in your full Sun example. Even possible the PWM would out perform MPPT at the Equator? But a very different matter in low light or low Sun, then a good MPPT charger, like the Votronic might be up to 40% more efficient.

Note there are currently on eBay some 'make believe MPPT' units. One company we challenged stated that the product has a name of MPPT, it is not a description of the Technology it uses.

 

 

I have a friend who drives around with a broken fuel gauge, he manages perfectly well and never runs out of Fuel, but I would want the gauge working.

 

 

 

 

 

[colin]

aandncaravan - 2017-06-17 4:04 PM

 

I have a friend who drives around with a broken fuel gauge, he manages perfectly well and never runs out of Fuel, but I would want the gauge working.

 

 

I do have a 'fuel gauge' for the leisure battery, it's a volt meter and gives an indication of the charge remaining, but it's interesting to note that esp. in winter the prime method for charging batteries is alternator and/or EHU, with just a LT410 panel I have not the foggiest what charge is being put in by these and I suspect most other van owners are in the same position, but many will be able to monitor the solar input which could well be best part of bugger all. ;-)

[aandncaravan]

A voltmeter has almost zero value to someone charging a battery, as all it shows is the charge voltage at the battery, not the actual battery voltage. When Solar is permanently connected it is pretty worthless method.

Even when the Solar charge stops as the Sun Sets, the battery voltage will be artificially high from just coming off charge

 

To see a batteries true State of charge voltage, you would probably need to make the check several hours after the sun went down, like at midnight?

 

A voltage check any other time will be inaccurate, sometimes leading many to believe the battery is fully charged when it may be anything but.

 

Putting a £6 Wattmeter in both the Solar charge cable and one in the battery supply cable will show exactly what has been taken out of the battery and what has been put in, to allow a check, not only there is a match, but that the battery efficiency is still above 80%.

 

 

 

[BruceM]

From the Fox-D1 in bright sunshine it maxes at 1.8amps.

 

When I receive the watt meter I'll check the solar panel output and see how it compares to the regulator output. A couple more amps would be handy though.

[aandncaravan]

Hello Bruce, With your description of the set-up and it's age, I would have expected nearer 3amps this time of year.

 

Maybe the battery wasn't drawing the max it could from the Regulator?

You don't need to run the batteries down to get the Solar Regulator to work at it's peak, just put a greater load on the battery than you expect the Solar system to be able to deliver. That should then be 'picked up' the Regulator which will then go to max output.

 

If you have a Hob Extracter Fan, Roof Light Fan, Halogen lights, etc. then that should exceed a 5 amp load.

 

 

 

 

 

 

 

 

 

[BruceM]

All the lighting is now LED and the only real load is the extractor fan for the gas heater.

 

So I turned on absolutely everything for an hour, then went back, left everything turned on and reconnected the solar. That’s what produced the reading. I'll have to work out whether I was drawing at least 5 amps though. I agree, it does seem low given it was in the height of bright sunshine – just about the max I could expect to get I suspect.

 

Once I’ve confirmation of the state of play by the watt meter I’m minded to replace and re-site the regulator/charger and if the watt meter indicates it necessary, replace the solar panel. I’m thinking that I might over-spec the regulator to give me the option of adding an extra panel in the future – I can get a Voltronic MPP 250 for £111 delivered on Amazon so the cost would be viable (subject to consultation with the other half in case she reads this).

[aandncaravan]

If you had drained down the battery with even that small load for an hour and then activated the Solar I would have expected the Solar 'Charger' to work flat out pulling all it can from the Panel?

 

Of course this assumes you have perfect batteries?

 

Old VRLA Batteries, like Gel and AGM can become 'exhausted', but if they don't have a secondary issue, like a Cell short, they may hold a steady voltage for weeks.

They appear perfectly healthy in many respects, but they won't take charge at anything like the rate they did when new. Typically, they also have a much reduced capacity as well, acting like much smaller batteries.

 

 

One G80 battery we took out, was 'still going strong at 6 years old' (according to the owner) because it always sat at 12.9v.

Yet after being fully charged the battery gave back just 22Ah when we discharged it to 12.0v.

 

A battery loses a tiny bit of it's capacity every time it is charged and discharged, so it is chemically impossible for a battery that has been regularly used for more than 6 years, "to be still going strong"'.

 

Or to look at it slightly differently, how yours might appear to be?

 

 

What I am trying to say, probably not very well, is that battery condition is absolutely key to a good solar solution. There is no point building a 100% efficient Solar Solution, as seems to be your intention, if the batteries are only 60% efficient and 'throwaway' 40% of every precious amp you harvest.

So may I suggest have these at the forefront of your investigation?

 

 

Ignore the rest of this if you are now bored, but because you are relatively new to the game you may not realise that when it comes to efficiency, some batteries are far more efficient than others.

Bosch/Varta claim up to 70% better electrical efficiency on their Powerframe batteries once the batteries are aged.

 

In non Powerframe batteries (that is all Lead Acid technologies Wet, Gel and AGM) the Plates corrode resulting in a build up of 'Growth' on the plate that inhibits the flow of electricity both into and out of the battery.

That is, the Electricity is obstructed both when you charge the battery, and when you draw that charge out.

Which may help you understand one of the reasons why some batteries that are aged take reduced charge? See the photo below of a Powerframe battery and a conventional battery that shows the corrosion.

 

A 70% difference between the best and the worst would have quite an impact on a Solar Solution. probably the difference between it 'working' and working brilliantly.

Because most don't have any metering of the systems efficiency, they may not be aware that it is only performing at 30%.

 

 

You have grasped, and seen it on your own system, that Solar Power rarely performs to 100% out of the box, especially so if installed prior to the beginning of 2016.

I personally think you are off to a good start, because you not only want to learn, but see the need to put in place tools to help you measure your progress.

 

Keep up the questions!!

 

 

[BruceM]

With the watt meter installed and some bright weather I’m finally able to collect some data.

 

To ensure correct interpretation I’ve attached photos.

 

Today at midday it’s sunny with some high altitude mistiness so not at max solar but not a long way off it.

 

One pic shows the set up at No Load – ie 19.47v on the panel with the watt meter measuring solar output and the FOX-D1 measuring the SunSaver-10 Regulator output.

 

I then added a load of approximately 5 amps .

 

The result is

Solar output 36.4W

Regulator output 2.8 amps

 

If I do indeed have a 100W solar panel then the solar output looks somewhat low – but then maybe it’s what’s should be expected.

 

Advice and comment would be appreciated.

 

[aandncaravan]

That does seem low, but how old is the Solar panel and is it clean?

 

The Solar Regulator voltage is a lot lower at 12.97v than I would expect from 19v going in? The best Solar Chargers would be giving nearer 14.4v in those conditions?

 

Remember you are not just measuring amps when looking at charger efficiency.

While 12.97v might supply a load for a light bulb, it isn't going to charge a 13v Gel battery very well at all, you want significantly higher voltage for that, every bit of the 14.4v a good Solar charger can deliver.

 

Your test is flawed, you are looking at how many amps a 12v load can pull from a Solar regulator, not is there enough 'oomph' to charge a 13v battery that may already be 'up to 12.8v' but need a crucial 15% more charge before it is 'Full'.

 

You need to be applying a load to the battery to discharge it to say 20% discharged, then monitor how much the batteries draw. The load should be to just discharge the batteries, not pull directly from the regulator.

 

If a battery is at 12.8v but the Solar charger can only manage 12.8v then no charging will take place, even if the Regulator has 3 amps 'available'. But a load, like a light bulb, needing as little as 11v might happily draw 3 amps at 12.8v.

 

Remember here that modern batteries are not 12 volt batteries, the best Motorhome batteries are 13v.

in order for any current to flow into a 13v battery that has a 'State of Charge' voltage of 12.8v, the voltage must be higher. The higher the better, but obviously too high will cause gassing and damage.

 

Ford batteries with Silver technology get upto 15v from the Alternator so they charge faster. The best Solar chargers will be up there at least 14,4v one putting out 12.9v isn't going to do much at all.

 

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One point, if the Solar was wired as recommended by the Motorhome manufacturer, the current would show on the Display unit ammeter as well as charge the Starter battery directly.

 

 

[BruceM]

Gotcha. I'll discharge the batteries and then revisit - we're expecting bight sunshine tomorrow so the timing should be good.

 

[aandncaravan]

How did you get on?

 

Sorry I had lost track and forgotten that you were still on the first test, when both tests are important.

 

In the test we suggested first, the idea was to see how much power you can pull from the system in amps to work out the panel size, it's overall capability to see if it has degraded, etc.

So you want to see how many amps you draw as a peak, by loading it anyway you can. Hopefully that will give you 5 amps'ish.

 

You then want to see how good the set-up is in charging a battery, which is quite different. For that you are concerned more about volts than amps, as stated above. This then tests the Solar regulator and cabling efficiency.

 

 

Sorry, in the later reply I thought we had already moved on to testing the Solar regulator, cabling, etc. I see, speak and email so many people about Solar failings I lose track of which 'conversation'. A side effect of being 63.

 

 

So your first test was valid and indicates that the Solar Panel (or cabling to the Solar regulator) may not be as good as it might be?

Which isn't unusual, Solar Panels generally have a guarantee of providing 80% output at 20 years. However experience suggests that this is optimistic.

 

 

Your second test will see how much of the power generated by the Solar panel actually makes it through to the battery as useful charge, primarily assessing the Regulator and cabling.

 

 

I think what you are doing and the approach you are taking will be of significant value to others, if not now, then certainly in the future?

 

When you have finished, please may I summarise your work and put it on our Solar Panel Hints and Tips page with the other Solar Info? http://www.aandncaravanservices.co.uk/solar-power.php

 

 

 

 

[BruceM]

You’re welcome to use any of this on your web site as you see fit – if it assists others then that’s a good thing.

 

My analysis so far

Under load of over 5amps

With a clear blue sky I was able to achieve a max of 44W from the solar panel with a current showing on the Fox-D1 of approx 3.4 amps

So here’s a question, what wattage should I expect a new 100W solar panel to provide? Given your 5amps observation should I expect approx 90W?

 

Off load with partially discharged batteries

The charging voltage sits at a fairly constant 14.1V

 

When we get some brighter weather I’ll discharge the batteries and measure power out of the solar charger compared to power out of the solar regulator to provide some gauge of its efficiency. I’d have expected it to be reasonably efficient, although moving to an MPPT featured regulator would no doubt up the power a bit.

 

Where I’m going with all of this is to determine whether there would be real benefit to

 

1/ Replacing the solar panel

2/ Replacing the solar regulator and or re-siting it close to the EBL

 

Our preference in the UK is for more traditional grass campsites without electrical hook up so a reasonably efficient solar system would be an advantage.

[colin]

BruceM - 2017-07-03 11:00 AM

Where I’m going with all of this is to determine whether there would be real benefit to

 

1/ Replacing the solar panel

2/ Replacing the solar regulator and or re-siting it close to the EBL

 

Our preference in the UK is for more traditional grass campsites without electrical hook up so a reasonably efficient solar system would be an advantage.

 

Obviously having the system working as efficiently as possible is a benefit, but I would point out the following.

You have not indicated if the set up produces sufficient power for your needs at the moment, even if the panel is down on output, if it's enough for you replacing it is an unnecessary expense, i.e. on our last van we had a 30w panel, it did all we wanted of it, on our present van we have a 85w panel, for most of year it does what we want, in depths of winter (like last new year) we use an EHU which for those few days of year is probably cheaper than buying enough panels to supply us (also we use electirc heating from EHU instead of gas).

MorningStar, a respected manufacturer do not recommend using MPPT regulators unless you have over 170w of panels.

As for moving the regulator, I've put together several solar set ups, and the regulators have had temperature compensation so have sited them next to battery as per instructions, I don't know if this applies if going throu a EBL, if it does then I guess putting it next to battery still applies.