Questions/frustrations re: Charging new GZ yeti 400 (only 40W input w/60W of panels)

[Waltzing Matilda]

I picked up a Yeti 400 yesterday, and it had about 80% charge when I opened the box. The instructions state: charge immediately! keep charging/plugged in at all times!! So I thought I would see how the panels I have manage this vs. constant wall charging.

Today I began charging it with my array of GZ panels (2-Boulder 15W's+ 1 Boulder 30W)...



The input is only showing 40w, when all 3 are linked together.


The read-out on the Yeti 400 panel is informative- but a bit discouraging. Even with a potential 60watts of panels, I'm only showing an input of 40 watts, at high noon, in full sun, in San Diego.

Conditions seem ideal- am I missing something? Is this the best I can expect?

I tried experimenting: covering 1 15W panel = loss of 10w (input dropped from 40 -> 30)
Covering the 30w, input dropped by 20W (from 40 -> 20)
Covering both 15's was same (from 40 -> 20)

So it appears the panels are only generating a combined input of 2/3ds of their "potential" maximum output, per the GZ rating.

Is this because they are chained together? Are they losing energy via their cables?
If so- is the only solution getting 1 single panel, as large as possible? (I think GZ now offers a 90w panel)

Hoping someone with a similar set up can report better results/offer advice.

 

[pugslyyy]

Most of the reviews are positive for the GZ panels, but the negative ones are that they don't make rated output. Does it charge more quickly when plugged in to AC (i.e. are you sure it is the panels)?

 

[Waltzing Matilda]

Haven't plugged it in yet- I'm testing the efficiency of the panels to help plan for future off-grid usage/charging capacity.

Display is now showing about 45W input via the 60W worth of panels, so it seems to be improving over time.

+They appear to be very sensitive to any shading- the input drops by almost 50% with even a small amount of a panel getting covered.

 

[dwh]

Solar module rated output is tested at STC (standard test conditions) which is 1000 watts of light per square meter at 25 degrees Celsius (77 degrees F) running at the Voltage of Max Power (Vmp) with the light arriving at an angle of incidence of 0 degrees.

When hotter than STC, they'll put out less than the rated power, when colder than STC they'll put out more than the rated power. They are black, glass and facing the sun - they are almost always hotter than STC.

Running at a voltage lower than Vmp they will not be at full efficiency. With a PWM controller, they'll be running at whatever the voltage of the battery is, and that will never be at Vmp. With an MPPT controller they'll run at whatever the Vmp is at the moment (it changes based on temp and amount/angle of light).

Flat will have a higher than 0 degrees angle of incidence, which is why they work best when tilted to face the sun dead on.



I have no idea if you have an MPPT controller or a PWM controller, but with what I see in the pics, with a PWM, you're getting just about what I'd expect.

 

[dwh]

+They appear to be very sensitive to any shading- the input drops by almost 50% with even a small amount of a panel getting covered.

Solar panels are made of cells wired in series. The cells are always around .5v. So it takes 30 cells in a "series string" to get 15v, 32 to get 16v, 34 to get 17v and 36 to get 18v.

Solar cells either generate power, or they consume it. When they consume it, they become little electric radiant heaters. When a few cells in a string are shaded, they'll start taking the power that is flowing through them from the other cells in the string and radiate it as heat. To prevent that, there are bypass diodes. Usually one per string.

When a few cells get shaded (can even be just one), the voltage drops and the bypass diode activates and now the string is at 0v.

0v won't push power through a battery.

 

[rayra]

well for starters flat on the ground is nowhere near the optimum angle. In fact flat on their back is pretty far off the best angle. That's a pretty fundamental aspect of solar power.

You need to factor in your latitude and the time of year. Right now, halfway between winter and summer solstice, your panels ought to be tilted up to about your latitude, ~30deg+

http://greenerenergy.ca/PDFs/Tilt and Angle Orientation of Solar Panels.pdf

 

[rayra]

Thing to keep in mind about solar cells themselves is they are NOT 'flat', they are a sandwich of different materials. And those layers themselves interfere with the efficiency of the panel and thus its output. The panel needs to be perpendicular to the sun to reach anything close to their maximum rating. So you can't just lay a panel out and forget it all day. If you are roughing it somewhere with a 'big sky', you ought to be re-angling the panel(s) several times during the day, to keep them generating closer to their peak rating.

 

[rayra]

here OP, read this too -
http://en.wikipedia.org/wiki/Solar_cell_efficiency

You also need to re-calibrate your expectations. Nobody gets the rated output from a panel. 2/3 of the rated output isn't even 'bad'.

 

[jonyjoe101]

I'm familiar with solar and 40 watts sound about right. Example with my first 120 watt panel hooked up to a pwm controller i get about 6 amps of charge power. 14.4 volts x 6 amps = 86 watts, extrapolated that would be about 43 watts for a 60 watt panel.

You never get the full output of the solar panel. You only see high amps / wattage going to your battery when the battery is almost empty. As the battery gets fulled the battery will limit the amps it receives.

The mppt solar controllers are rated at 97 percent or higher efficiency, that means you might get almost all the wattage the panel is rated. But these only work on high voltage panels 30 volts or higher. Mppt is also more expensive.

The 90 watt panel is very expensive for its output. You can buy a cheaper panel and a 20 dollar wincong 20 amp pwm solar charger and it will do the job. 90 watts while bigger will still take 9 hours to charge the yeti. The yeti is a 33 ah agm battery, any solar controller/panel combination will charge it.

Myself I upgraded to a 240 watt panel on the roof of my astrovan, that and a 20 amp ecoworthy mppt controller gets me 12 amps of charge power. It charges everything fast. a yeti 400 completely drained would take less than 3 hours to charge with that type of power. Nothing beats the big panels but they aint portable.

 

[dwh]

The mppt solar controllers are rated at 97 percent or higher efficiency, that means you might get almost all the wattage the panel is rated.

Actually, it means that 3% will be consumed by the controller and converted to heat. 97% efficiency means if you have 100w coming into the controller, you'll have 97 going out to the battery.

But these only work on high voltage panels 30 volts or higher.

No, MPPT works as long as the solar panel voltage is higher than the battery voltage. It doesn't require any "special" higher voltage to work.

 

[snowblind]

I picked up a Yeti 400 yesterday, and it had about 80% charge when I opened the box. The instructions state: charge immediately! keep charging/plugged in at all times!! So I thought I would see how the panels I have manage this vs. constant wall charging. Today I began charging it with my array of GZ panels (2-Boulder 15W's+ 1 Boulder 30W)...

The read-out on the Yeti 400 panel is informative- but a bit discouraging. Even with a potential 60watts of panels, I'm only showing an input of 40 watts, at high noon, in full sun, in San Diego.

Conditions seem ideal- am I missing something? Is this the best I can expect? So it appears the panels are only generating a combined input of 2/3ds of their "potential" maximum output, per the GZ rating.

Unfortunately that's how solar is sold. I doubt you'll ever see a full 30 watts from any 30 watt panel. The most I've personally pulled out of 2 x 15watt Boulders is 22 watts but it was Feb and the sun was not strong. Anything above 20 watts from a 30 watt panel and I will be happy.

Is this because they are chained together? Are they losing energy via their cables?

Not really. I measured a 1 watt drop across my 30' GZ extension cable so prob not an issue. Guessing your total panel cable length is less than 20' If you ARE seeing a bigger drop you can use a 4-port combiner to avoid daisy chaining the panels -> http://www.goalzero.com/p/45/8mm-input-4x-combiner

Hoping someone with a similar set up can report better results/offer advice.

Perspective - The wall charger can only supply 80 watts of charge using shore power. If you look at that as a "gold standard" benchmark of Yeti charging then you are currently 1/2 way there.

Aiming - GZ panels seem to be EXTREMELY sensitive to aiming. You will need to re-aim the panels every couple of hours to get peak charging. If you want something flat on the ground bring your checkbook! http://smile.amazon.com/Powerfilm-F...UTF8&qid=1427405002&sr=8-9&keywords=powerfilm

Consumption - I measured my energy consumption when camping and figured that I don't really need very much solar. If I'm only using an average of 30 watts per hour why deal with the size of 120 watts of panels? I'm not trying to live off the grid.

What was your goal again? Energy self-sufficiency or extending the capacity of your current, portable system?


Matt

 

[rayra]

Think of the multi-layer substrates of a solar panel like a polarizing filter. Like hitting at too much of an angle to the panel face doesn't even get thru to do anything. Keeping the panels as perpendicular to the sun as possible is very important. Or else you have to overbuild the system so the lower efficiency ( x moar panels) still meets your power requirements.

 

[robgendreau]

I seem to recall that the use of PET rather than glass also reduces the efficiency, but I can't say for sure.

But I'd say you're perhaps right about going with one panel. You're using about 40"x 18" of panel, right? For a supposed 60W? Go to CostCo and get Grapesolar 100w; it's 40x27 so a bit bigger, but lots more power and about the same weight, for $150. I swapped out three panels for one of these and love it. Quite sturdy; good frame. I dunno what all GZ gives you with those panels in order charge so much for them (more of a charge to your wallet than your battery), but pretty much all you need with the Grape is a controller in addition to the panel, and some wiring. The panel uses solar-standard MC4 connectors.

 

[snowblind]

Get Grapesolar 100w; it's 40x27 so a bit bigger, but lots more power and about the same weight, for $150.

That is a VERY low price for a 100w panel! $159 via Amazon Prime -> http://smile.amazon.com/s/ref=nb_sb_noss_1?url=search-alias=aps&field-keywords=Grape+Solar


Matt

 

[unseenone]

+1 on the Grape Solar You cannot go wrong with them.