Why 100 watts are not equal to 100 watts?

This is tricky, the initial question was clear and while nobody owes nobody anything, it was... a bit of work to see the thread going the wrong direction. The tricky thing is how this can confuse a reader with the same question. I guess at the end the story will repeat itself over and over until the reader buys the stuff whatever ratings are printed, do the math, calculate some safety margins and then see how in real life the numbers just won't match. And it has nothing to do with lab ratings or lab conditions. It's was confusing to me, not it isn't, but it's tricky to explain without realizing it would be easily taken out of context or off topic.

notifications off. See ya.

Well, I just joined the forum and I have read most of the responses here and I think the moderator, SDOLD summed things up pretty well to answer this post. I experienced the same things with my first 100 watt panel having a 18 volt rating and 5.6 A maximum current output. I typically only got 4-5 amps out of it. Maybe 5 in the cooler weather, but closer to 4 in hot weather. At 4 amps I was doing 48-52 Watts. I recently found using a MPPT controller really improves my efficiency because it converts the unused voltage into usable power with up to 35% Amps. I definitely see a big difference charging at low voltages. So that has helped me. Also, you may check your inverter efficiency. It may be low and costing you extra wasted power. Mine is around 90% efficient, so not too bad. I'd encourage you try the MPPT controller as it will really help your efficiency.

Perhaps you mean 18 VOLT rating? It starts by getting your numbers and your units right, or you are lost.
Then its about efficiency, energy gets away every step of the way. As someone once said

You can not win

You can not break even

You can not get out of the game.

Bruce Roe

"Originally posted by Supernova532
I experienced the same things with my first 100 watt panel having a 18 watt rating
and 5.6 A maximum current output."

Yes, typo, not big deal. Iif you read the context of the post anyone would know I was referencing voltage not power.

Maybe in horseshoes, typos don't matter. With engineering, terminology has to be precise, if you want precise answers. Several years ago, a joint ESA & NASA Mars lander crashed, because some of the software measured in meters, and some in feet. I'm sure everybody knew what was supposed to happen, but the terminology never made it to the spacecraft properly.

Hey Bob, I borrowed some of the hold down bolts last night :

noaa_n_prime_satellite_on_the_floor_700x621.jpg

Maybe not a big deal to you. Typos or not, others not as astute as you who may take your written stuff as accurate can go astray by your error.

Typos happen to all of us, me probably more than most, but considerate posters still check a post before pulling the trigger on it and know why.

I suggest you take the constructive criticism, proof read your stuff more and move forward.

Already checked to unsubscribe from notifications about this thread, but still receiving them... unsubscribed again.

Mod - I tried, but my level of moderator does not allow me to alter your subscriptions. Sorry, Mike

Could it be a typo?LOL

Lucky for me I was not launching the NOAA satellite, just testing my $75 solar panel, typing a message late at night and made a typo. Yes, even engineers make typos. Time to move on. I corrected the typo in the post. Thanks.

I will simplify it for those non-technical people - there are basically 4 components to a Solar Power system:

1) Solar Panel
2) Charge Controller
3) Storage Battery
4) DC to AC power Inverter

From my years of experience with Poly type panels they produce about 81-83% of their STC rating in full sun and 77 degrees F air temperature. In the winter on a clear day and very cold the power can approach the STC rating but that is not the norm. Some areas of the world receive more than 1000 W/m^2 sunlight and can be as high as 1300 W/m^2 near the equator or at high altitudes but again that's not the norm.

Where you can really loose power is in the other 3 components:

Charge controllers come in 2 types - PWM and MPPT with the later doing DC-DC power conversion and operating at the Maximum Power Point which moves during the day. PWM controllers do not do power conversion so they never operate at the most efficient point and typically loose 30-50% or more of a panels power depending on configuration over what an MPPT controller can extract from the panel. A good controller matters and the ones we make are 98-99% efficient on power transfer.

The Storage Battery can also loose power if its a Lead Acid type (Deep Cycle, AGM ect.) and I have measured their Energy Return ratio to be at best 70%. This means if you put in 100 amp hours during charge you will only get 70 back on discharge.... Another type of battery I have been using is the Lithium Iron Phosphate for 7+ years now. I also measured this Energy Return Ratio... this battery chemistry is 99.8% at returning what you put in. I metered this carefully several times to make sure I was not getting bad data. After over 7 years our 600 amp hour pack comprised of 24x 100 amp hour lithium Iron Phosphate cells in a 4 series 6 parallel configuration (12 volt setup) was metered at 608 amp hours. brand new it measured 615 amp hours. Can't say enough good things about this battery chemistry. There are many other benefits I will not go into here.

Finally the DC-AC inverter matters.... cheap ones are maybe 85% efficient and good ones are 90-95%. The Xantrex Pro Watt 2000 I use measured at 95% at 1000 watts output which is half power and the most common average load. At 200 watts is measured 92%. The spec is 90% from the Manufacturer. The no load draw is also real low and measured 0.35 amps on a 12 volt setup (13.4 volts actual due to the Lithium Iron Phosphate Battery)... So about 4.7 watts draw in standby (No Load).

So in summary using a cheap controller, inverter and Lead based battery you end up with:

Controller (70%), Battery(70%), Inverter (85%) = 41.65% of the Solar Panels Energy makes it to the AC output !

Using a good MPPT controller such as ours, Lithium Iron Phosphate Battery, and a good inverter at 92% or better:

Controller (98.5%) , Battery (99.8%), Inverter (92%) = 90.43% of the Solar Panels Energy makes it to the AC output - or more than 2x the output in Watt-Hours with the same solar panels.


Cheers,

Rob
< moderator deleted signature > Rob, please leave your self promotion at home