Solar Blanket output

[EddieF Member Find all posts View Profile Close EddieF]

Hi all, I'm after some real world experienced advice about a solar blanket I'm looking at. My confusion is knowing if the reported output seems reasonable. I'm looking at a 200wat iTech solar blanket. The size would be around 1.2 Meter squared. The spec also says the max current is 10.8 amps. So I'm thinking roughly 10.8 amps at say 12volt would provide 130 watts. But the specs also say open circuit 22 volts so I guess using this the calculated watts using this would be higher than 200Watts (before passing through the regulator I guess). Any Input greatly appreciated.

[sparksy Senior Member Find all posts View Profile Close sparksy]

Ive got a 200W solar blanket, and no matter where I try it I cant get more than 12 amps out of it through a decent mppt controller. Im thinking of getting rid of it and replace with 2 flexible panels that can slide under my rear shelf.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

10.8A is the maximum output under lab conditions, ie plenty of light on the panel and the panel kept cool at around 22C. In real life as soon as you put the panel in
the sun it heats up and output drops. Also as above if it is not a quality MPPT type controller you'll loose power there too.

I would work on around 60-70% of the rated power so around 7A under ideal conditions.

[EddieF Member Find all posts View Profile Close EddieF]

Thanks for your input Sparksy and Leigh. I'll be looking at MPPT (or DC to DC) later on. Sparksy, there is a sale on at Hardkorr for their Heavy duty solar mats, not sure if this is what your looking for?

[Piggy Water pistol pilot. Find all posts View Profile Close Piggy]

They are missing some numbers from the panel data. Maximum power voltage etc. But yes, quickly doing the area calculations of the panel, it will likely produce a maximum of around 10.5 amps at around ~18-20 volts. This would line up with the other specs. The downfall however is the cheap PWM regulator, I'd be ditching that quick smart for an MPPT.

As much as some may not like it, For the $399 price tag of the itech, I would personally buy a KINGS 200 W folding blanket with an MPPT reg included for $229.

Why do I say this? I've tested the Kings extensively, as we have dozens (Actually hundreds) of remote sites using solar power to run telemetry gear and other electronic items. When doing maintenance on them, we will use the cheapy Kings units to top the batteries off so we can load test them. We have proper solar meters that test outputs of panels in Volts, Watts and Amps and have a built-in MPPT to see the throughput. I've tested 7 kings panels, and they are all pumping out higher specs than they list on the website.

I've also personally used them on my vehicle top up the House and twin batteries, Even though its average looking MPPT, it works efficiently.

I choose Victron MPPT units, as they log everything and have adjustable parameters from your phone. It doesn't matter what solar panel you use with them either.

[EddieF Member Find all posts View Profile Close EddieF]

Excellent sum up Piggy. Ok perhaps I'll give the Kings a try. Can't go too far wrong for the price.

[EddieF Member Find all posts View Profile Close EddieF]

Just ordered the Kings 200W kit. $179. Can't go wrong for that price :-)

[Piggy Water pistol pilot. Find all posts View Profile Close Piggy]

Just ordered the Kings 200W kit. $179. Can't go wrong for that price :-)

Good price. If you have a Multimeter, I can post a way you can also check its output specs on a sunny day.

[EddieF Member Find all posts View Profile Close EddieF]

Thanks Piggy, really appreciate your help. Unfortunately my meter has gone to heaven. So I have also ordered a Wattmeter with anderson plugs from Tentworld.(150amp). Looking forward to giving it a try.

[GeeWhizz Senior Member Find all posts View Profile Close GeeWhizz]

As mentioned previously, the solar market is full of many 'ambitious' claims. The Kings '200W' blacket falls into that category.

You cannot expect low-end (read: "cheap") solar panels, of any sort, to provide more than around 155 Watts per square metre of actual collection area. The Kings '200W' solar blacket is 1255 x 940mm edge-to-edge. Being a folding blanket made of 6 panels, each with a 20mm border, the actual collection area is 0.96 sq.m (not looking good, is it?). My estimation for this blanket is about 150Watts in ideal conditions (slanted directly at the sun, north of the 30 degrees south parallel, with the panel cooled to 25 degreesC).

King's claimed efficiency is >21% - that's not going to happen. In typical conditions when you're out camping, you'll probably get around 120Watts out of this blanket on a sunny day.

[Piggy Water pistol pilot. Find all posts View Profile Close Piggy]

Solar panels can vary greatly, and new designs like shingled panels have more output for the smaller panel size.

A good rule of thumb is a square metre of solar panel, will produce around 1000 watts (1 kW) per day of sunshine. (That is between 150-200 watt panel size.)
Basically, a solar panel at 15% efficiency is around 150 watts per M2. A 21% efficiency will be around 210 Watts per M2, naturally dependent on which cells, shingled vs Bus Bar, Poly vs Mono etc.

STC ratings (Standard test condition) are done in Labs, working at a perfect 25 degrees, and a light source at the optimum angle (Directly above panel), and at exactly one sunlight spectrum.
So in testing in theory if a panel was 100% efficient, we would see a 1000 watt output, 20% = 200 watts, and so on.

There is an equation you can do, this works for some cell types (Bus bar) but Shingled stuff is a bit higher output vs panel size.

At 17-18% efficiency every watt should equal 0.0064 m2. So a 1 square metre panel = 156.25 watts output. (at 12 volts). Higher efficiency cells/panels also have more output, and higher voltage = more output.
Bump this up to the normal 16-20 volt output of a panel, and you are suddenly 50+% over the 12-volt output specs. (EG that 156.25 watts suddenly becomes 234 watts). This is why you often see large numbers on panel tags and advertising specs.

Solar panels very rarely are sitting at 12 volts. I see around 18-21 volts out of mine daily. This is why you see higher claimed figures for the same size panel.

If your calculations are reasonably correct put the Kings panel (classed as a cheapy) at .96 of a square metre. ( This is about right) Then decent brands such as Victron or Redarc which are up to 6 times more expensive. Should be of the stated size for the wattage. But… Not every solar panel ( Or Cells) and these panels are made of multiple cells are of the same quality or output.

Let's have a look at some cheap vs expensive solar panel sizes.

Kings adventure store. 200 Watt claimed size: .96 of aanM2.
Redarc ($1100 panel!) 200 Watt claimed: .911 of aanM2. (Yep, smaller than the Kings and over 5 times the price). Redarc also has a $2450 112-watt solar blanket!!
Victron (One of the best solar mobs) 200 Watt, .992 of an M2.
Low energy developments (Again a reputable good company) .95 of an M2 for 200 watts

So some of the “top end” companies that sell solar, are actually smaller sizing than the king panel.. Didn’t see that one coming did we?

Depending on the voltage output, depends on what “wattage” they decide to rate their panels at. They likely average this out a lot as well.
It’s a total world of twists and turns, even with the expensive brand name panels, that one would expect to perform better than a “kings” brand.

The Kings panels specs are: Operating voltage 19.1 (Vmp) x 10.42 Amps (Imp) = 199.02 Watts. Obviously rounded to 200, remember this is in perfect test lab conditions!
The Redarc: Vmp 20.0 volts x 10.0 amps (Imp) = 200 watts.
Victron came out to 199 watts as well.


We run as stated before, multiple solar panels for remote work, and have found the Kings cheapy, to be the best bang for the buck. I regularly see upwards of 40+ amps a (Full sun) day coming out of it when I have to top up flat site batteries.

In regards to the claim of .96 not being enough size, Check any manufacturer including the really expensive good brand ones, Redarc, low energy developments, Victron etc and you will find they are all around the .95 of a M2 size.
Again remember, solar panels don’t run at 12 volts, hence again higher outputs.

I run a full-time 50-litre fridge in one of my work vehicles, Average daily draw is between 80-160 watt-hours. It is on a 50 Ah lithium battery, and is independent of the vehicle and gets solar charge only, it’s been running for over a year, and never had an issue with low voltage. I have a 110-watt panel feeding it, the most I have ever seen produced on the Victron logs, was 93 watts. By 9 am most mornings or earlier, the Bulk charging is complete, with 30-minute absorption, and then it goes off to float charge for the rest of the day. A total overcast day may see the Bulk charge stretch out to 5-6 hours if really really grey. This 110-watt panel is a shingled style, and by using the above calculations should be around .704 of a metre square. It's not, it's .536 of aanM2 (24% smaller) and with our test gear, I’ve seen 104 watts coming out of it. Shingled panels are 15-25% smaller than bus bar panels.

Bottom line is, Yes! there are some very dodgy panels and advertising out there, if a panel looks great because it's small, and claims 300 watts, do some calculations and check reviews.

On a random note, Swapping from an AGM to a lithium battery, which has a higher float voltage (13.5 volts), than the AGM at around 12.7, the amperage the fridge uses is reduced by around an amp. Something to remember when choosing batteries, a higher float voltage of lithium battery can reduce the overall current consumed. As the solar panel outputs 19-21 volts, its no issue in charging higher as the MPPT reg steps it up or down as needed.

[GeeWhizz Senior Member Find all posts View Profile Close GeeWhizz]

Firstly, I need to say that I’m an Electronic Engineer and do know my subject in both theory and in practice. You have provided a lot of detail, which I’ll address below in blue. I am not trying to pick a fight - just correct a few inaccuracies for forum members who may read this thread.

Solar panels can vary greatly, and new designs like shingled panels have more output for the smaller panel size. A generalisation, however as I stated above, most cheap panels are among the low performers.

A good rule of thumb is a square metre of solar panel, will produce around 1000 watts (1 kW) per day of sunshine. (That is between 150-200 watt panel size.) Watts are an instantaneous value - Watts per day has no meaning. Unless you’re trying to say something else, this is not a rule-of-thumb.

Basically, a solar panel at 15% efficiency is around 150 watts per M2. A 21% efficiency will be around 210 Watts per M2, naturally dependent on which cells, shingled vs Bus Bar, Poly vs Mono etc. Correct

STC ratings (Standard test condition) are done in Labs, working at a perfect 25 degrees, and a light source at the optimum angle (Directly above panel), and at exactly one sunlight spectrum. Correct
So in testing in theory if a panel was 100% efficient, we would see a 1000 watt output, 20% = 200 watts, and so on. Correct

There is an equation you can do, this works for some cell types (Bus bar) but Shingled stuff is a bit higher output vs panel size. This depends entirely on the makeup (material technology) of the panels

At 17-18% efficiency every watt should equal 0.0064 m2. So a 1 square metre panel = 156.25 watts output. (at 12 volts). Higher efficiency cells/panels also have more output, and higher voltage = more output. Watts is a measurement of power and is what it is, regardless of the voltage of a panel. A higher voltage on the same panel will not deliver more power, just less current. Read below.

Bump this up to the normal 16-20 volt output of a panel, and you are suddenly 50+% over the 12-volt output specs. (EG that 156.25 watts suddenly becomes 234 watts). This is why you often see large numbers on panel tags and advertising specs. Not correct – you can’t “bump up” a panel’s power by just reading a higher voltage. The science does not support your assertion. The formula for power (watts) is voltage times current: W = V x A. Have a look at a performance graph of a credible solar panel: as the current being drawn goes up, the panel’s terminal voltage comes down.

Refer to the attached chart, courtesy of Mr Google. If you draw too much current (I), the panel voltage decreases, and the power delivered (Ie V x A) drops away. Similarly, it you draw too little current, the voltage climbs but the power delivered (again, V x A) decreases.

An MPPT charger will control the current being drawn from a panel (or bank of panels) to keep both the panel’s voltage and current close to its ‘sweet spot’ or MPPT point. It is therefore doing MPPT, “maximum power point tracking”. If the sun goes behind a cloud or the panel is partly shaded, the MPPT charger will change the current draw to get the best the panel can deliver in those conditions.

Solar panels very rarely are sitting at 12 volts. I see around 18-21 volts out of mine daily. This is correct. This is why you see higher claimed figures for the same size panel. Nonsense – refer to my previous answers
If your calculations are reasonably correct put the Kings panel (classed as a cheapy) at .96 of a square metre. ( This is about right) Then decent brands such as Victron or Redarc which are up to 6 times more expensive. Should be of the stated size for the wattage. But… Not every solar panel ( Or Cells) and these panels are made of multiple cells are of the same quality or output. Correct – Too many cheapies (like Kings or iTech) are overstated

Let's have a look at some cheap vs expensive solar panel sizes.
Kings adventure store. 200 Watt claimed size: .96 of aanM2. 0.96 x 15.5% = 145W

Redarc ($1100 panel!) 200 Watt claimed: .911 of aanM2. (Yep, smaller than the Kings and over 5 times the price). Redarc also has a $2450 112-watt solar blanket!!
Not sure where you get your figures from here: Redarc’s SRP0240 200W panel ($442) has an area of 1.02sq.m. Its claimed efficiency is 19.6% - credible for the price.

Victron (One of the best solar mobs) 200 Watt, .992 of an M2. I can’t comment on this one but Victron is also a credible brand. I can’t find a 200W monocrystalline panel on Victron’s website.

Low energy developments (Again a reputable good company) .95 of an M2 for 200 watts I haven’t research Low Energy Developments panels.

So some of the “top end” companies that sell solar, are actually smaller sizing than the king panel.. Didn’t see that one coming did we? Yes, we did. Put simply, higher efficiency panels are more expensive.

Depending on the voltage output, depends on what “wattage” they decide to rate their panels at. They likely average this out a lot as well. Not correct – see previous answers.
It’s a total world of twists and turns, even with the expensive brand name panels, that one would expect to perform better than a “kings” brand. Correct.

The Kings panels specs are: Operating voltage 19.1 (Vmp) x 10.42 Amps (Imp) = 199.02 Watts. Obviously rounded to 200, remember this is in perfect test lab conditions! As I’ve said previously, you’ll be battling to get more that 155W/sq.M out of a cheap Kings panel.

The Redarc: Vmp 20.0 volts x 10.0 amps (Imp) = 200 watts. As I mentioned previously, credible at the price.
Victron came out to 199 watts as well. Credible at the price.

We run as stated before, multiple solar panels for remote work, and have found the Kings cheapy, to be the best bang for the buck. I regularly see upwards of 40+ amps a (Full sun) day coming out of it when I have to top up flat site batteries. 40 amps is an instantaneous measurement, 40 amps a day is meaningless. To put a current of 40 amps into a 12v battery, you will need about 500 watts of solar panel/s.

In regards to the claim of .96 not being enough size, Check any manufacturer including the really expensive good brand ones, Redarc, low energy developments, Victron etc and you will find they are all around the .95 of a M2 size. Reputable companies generally charge significantly higher prices for their more efficient panels

Again remember, solar panels don’t run at 12 volts, hence again higher outputs. If you are referring to Watts, this is an incorrect assumption. When dealing with solar panels, a higher voltage from a panel does not mean more power (except for very low light levels, when a solar panel is just starting to operate).

I run a full-time 50-litre fridge in one of my work vehicles, Average daily draw is between 80-160 watt-hours. It is on a 50 Ah lithium battery, and is independent of the vehicle and gets solar charge only, it’s been running for over a year, and never had an issue with low voltage. I have a 110-watt panel feeding it, the most I have ever seen produced on the Victron logs, was 93 watts. By 9 am most mornings or earlier, the Bulk charging is complete, with 30-minute absorption, and then it goes off to float charge for the rest of the day. A total overcast day may see the Bulk charge stretch out to 5-6 hours if really really grey. This 110-watt panel is a shingled style, and by using the above calculations should be around .704 of a metre square. It's not, it's .536 of aanM2 (24% smaller) and with our test gear, I’ve seen 104 watts coming out of it. Shingled panels are 15-25% smaller than bus bar panels. An 110 Watt panel is about the right balance for a 50Ah battery. If your system is completing its bulk charge by 9:00am, either (1) it is summer, (2) you are in the tropics and/or (3) your battery was still reasonably full (Eg 80-90%) at dawn. I can’t comment further, your figures sound credible.

Bottom line is, Yes! there are some very dodgy panels and advertising out there, if a panel looks great because it's small, and claims 300 watts, do some calculations and check reviews. That was all that I was stating in my previous post. Vendors of many (most?) cheap panels/blankets are making “ambitious” claims. If you buy a “cheap” solar panel then it is very likely to underperform, as I quoted with the Kings 200W.

On a random note, Swapping from an AGM to a lithium battery, which has a higher float voltage (13.5 volts), than the AGM at around 12.7, the amperage the fridge uses is reduced by around an amp. Something to remember when choosing batteries, a higher float voltage of lithium battery can reduce the overall current consumed. As the solar panel outputs 19-21 volts, its no issue in charging higher as the MPPT reg steps it up or down as needed. Only if the MPPT charger has a “Lithium” profile setting. Otherwise, the system is a compromise and you won’t be doing your expensive Lithium battery any good in the long term.

Finally, some cheap panels may actually offer good value for money (measured in watts per dollar). However, don’t expect to get their claimed power out of them.

[Pradopolous Junior Member Find all posts View Profile Close Pradopolous]

Geewhiz, what would you recommend, as im wanting to but a 200watt solar blanket

Ie whats a decent blanket without spending a small fortune, is this possible in Aus

cheers

[gunda Member Find all posts View Profile Close gunda]

Are Hardkorr and Renogy regarded as credible brands? I have a Hardkorr 200W mat, and it's claimed cell efficiency is 20.38%. Is that credible? Is the claimed maximum working current of 11.11A credible?

(I had a faulty under-performing HK mat that has just been replaced under warranty, and I'm waiting for enough sun to assess the performance of the replacement mat I have been sent. I want to know what its best performance is realistically likely to be, although I may not see it in the middle of winter.)

[GeeWhizz Senior Member Find all posts View Profile Close GeeWhizz]

Are Hardkorr and Renogy regarded as credible brands? I have a Hardkorr 200W mat, and it's claimed cell efficiency is 20.38%. Is that credible? Is the claimed maximum working current of 11.11A credible?

I have not personally tested either the Hardkorr or Renogy solar blankets. However I looked at the specifications for this Hardkorr 200W mat kit and it's specifications are realistic. If Harkorr's specs are correct, I calculate that it could deliver close to 200W, with an efficiency of 16.4% - credible. I'm not sure where your figure of 20.38% comes from - another model perhaps? For me, the big unknown is, what is their quality and how well do the suppliers support their product. When buying rigid panels, you have to also consider how well they stand up to rough roads etc.

Solar panels can work quite well in winter, due to the cooler conditions but you do need sunny weather. It depends on how far south you live and how cloudy the sky is - both of which reduce the output.

I did a search for Renogy panels and blankets but could not find any comprehensive specifications for them. Ebay and Amazon are not good places to do research on solar panels! They may be fine but without decent specifications, I would not be considering them for myself.

My suggestion is that you read reviews and owner feedback on their experiences with their panels and blankets. And, be aware that some owners sing the praises of their particular solar setup because they don't want to lose face. Buying the latest and greatest is often not the best move - I prefer to use proven products, even if they were released a year or two ago.

I have to say that my first folding solar panel was a Kings "160W", purchased 5 years ago. I connected it in parallel with the 120W fixed panel that came with my camper trailer, bypassing the folding panel's PWM regulator and ran the cable into an Anderson double adapter connected to the camper's Projecta IDC25 DC-DC charger. It never performed as well as the camper's 120W no-name brand fixed panel (it's about the same size as the camper trailer's fixed panel). I still use it but it only delivers about 100W when working alongside the fixed panel. I should have known better but was in a hurry to get away into the bush camping. You live and learn!