Question on ratings

[Jay64]

I just want to make sure that I'm getting this right. If a system is rated at say 240 watts, that is 240 watts per hour with full sun exposure, correct? So in a day of 6 hours of full sun exposure that system will give 1440 watts?

[bigmoose]

Jay, sort out watts and watt hours. I think you are co mingling the two. Watts are instantaneous volts X amps (power). Watt hours is the integral of watts over time (energy).

This may help http://en.wikipedia.org/wiki/Watt#Confusion_of_watts.2C_watt-hours.2C_and_watts_per_hour

[SamTexas]

If a system is rated at say 240 watts, that is 240 watts per hour with full sun exposure, correct? So in a day of 6 hours of full sun exposure that system will give 1440 watts?

Except for the terminology, you got it right.

A system rated at 240 watt(W) is capable of generating 240 W, if that power rate is sustained for 1 hour then you get 240 watt-hour (wh). For 6 hours you'd get 1,440 wh.

Solar panels rating are done under ideal condition when the sky is perfectly clear and the rays are hitting the panels at the optimal angle. In real life, expect no more than 50% for the duration of the day.

[Jay64]

Yeah, that's what was throwing me off. I was expecting to see something along the terms of watt/hours. But most of the systems I have seen only list watts. So if a system is only listing watts instead of watt hours, would it be sort of safe to use this as a watt/hour rating for VERY GENERAL calculations? I'm looking to make about a 10kw per day (give or take) system in very sunny conditions. So I'm looking at getting around 10 panels in the 240 watt range. I'm generalizing the watt/hour expectancy based on the watt rating.
So if these panels are able to do:
240 watt/hour=1440watts/day*10 panels=14.4kw/day=7.2kw (50% efficiency) to 11.5kw (80% efficiency)

I'm also probably over estimating the daily usage requirements for this planned use based on my current household use. But I'm thinking the planned use can be brought down to much lower than 10kw/day.

[SamTexas]

Sounds right to me. Don't forget to include the loss associated with charging lead-acid battery and the loss associated with the 12VDC to 120VAC inverter.

BTW it's wh, not watt/hour. See the link provided above by BigMoose.

[Jay64]

Yes, those losses have to be considered also. I'm just trying to get a real general idea of what size system I would be looking at. And I'm thinking of trying to keep it as a 12v system for the house. When I was growing up we had a 12v system in our house. We were so happy to get rid of that system when we finally had enough money to bring public utility power into our neighborhood. Back then we only had a wind generator, and I'm planning on also building another one of those, to have a double edged system. My property back home in Hawaii has tons of wind and sun. I'm also looking to build solar water heaters, so that will take about a 30% chunk out of the electrical usage.

But, yes, those losses are often over looked in the final planning. Thanks for bringing that up.

[amberwolf]

As long as you actually *have* full 6 hours of sun exposure at the right angle to the panel to give the full output....

My guess is that they rate the panels with max exposure at noon on the best sunny day when Earth is tilted so the sun is directly overhead at that spot. Most optimistic rating possible. If I were doing calculations to figure out possible output, I'd cut at least 10-20% off of the rating and work from there, and then be happy if it got better than that.

[Alan B]

If a panel is rated at 240 watts, that is the peak power output it makes under pretty optimal conditions (full direct sun, panel cool, etc). If you run it that way for an hour you will have produced 240 watt-hours. So the panel produces watts, you collect that into your battery or load in watt-hours.

To get the maximum power out you need to use a Maximum Power Point Tracking Charge Converter that adjusts to the maximum power point. If you don't use one of those you should instead look at the ampere output of the panel, not so much the voltage output. A typical panel might have a maximum power output at 17 volts of 14 amps for 240 watts. If you use this to charge your lead acid battery with a conventional charge controller you will get 14 amps but the voltage will not be 17 volts - it will be at the battery voltage. So the actual power to the battery will be only about 180 watts at 13 volts. The extra voltage is not converted into extra current unless a tracking charge controller is used.

[CrazyJerry]

And I'm thinking of trying to keep it as a 12v system for the house. When I was growing up we had a 12v system in our house. We were so happy to get rid of that system when we finally had enough money to bring public utility power into our neighborhood......

For what it's worth, keep thinking seriously about a 12 volt system. Currently I run a dual system, both 12 volt dc and 120 volt ac (can use either at will). The dc has essentially made the entire ac control panel (inverters and such) obsolete. This is the 1st winter during this 10 year experiment that I have not needed to run the Listeroid. The dc direct lines are running all the necessities (lights/fridge/computer/ceiling fans/circulation pump/etc...) Good luck in your quest!
~CrazyJerry

[Alan B]

If you want a bit more power you might consider a 24 volt system. Easy to make 12V with converters, and you get regulated 12V instead of varying voltage. Larger inverters are more efficient on 24V. Easy to make battery banks at 24V. For a small system 12V is ok.

[Harold in CR]

Crazy Jerry
Have you converted the TV and Fridge to run directly off 12V or, do you run Inverters for those appliances ??

12V Fridges don't exist down here, and, I would like to use 12V to run the Compute/modem, and TV, besides all the lights.

Just finished cutting up big chunk of Pork, using the lights from my homemade LED bulb and UPS battery.

[Hillhater]

.....Just finished cutting up big chunk of Pork, using the lights from my homemade LED bulb and UPS battery.

Wow ! .. you mean you have made a LED "laser cutter" to chop up animal carcases ??

[CrazyJerry]

Crazy Jerry
Have you converted the TV and Fridge to run directly off 12V or, do you run Inverters for those appliances ??

12V Fridges don't exist down here, and, I would like to use 12V to run the Compute/modem, and TV, besides all the lights.

Just finished cutting up big chunk of Pork, using the lights from my homemade LED bulb and UPS battery.

Harold in CR,
Here's a quick rundown of the 12 volt side of the system here:

I have a few televison sets. One is a run of the mill color 12 volt CRT from about a decade ago. The other two are lcd. One of those came manufactured as a 12 volt tv with an ac adapter (it's an RCA). I can run it direct into my 12 volt outlet so no ac necessary. If you find a flat screen tv that has an external ac adapter, simply look at the output of the adapter and you might find one that is 12 volt - there are many around (eBay rings a bell!)

12 volt fridges don't exist here either. After many unsuccessful attempts (or marginally successful attempts) at building one from junk parts, I splurged for a Sundanzer (made by Electrolux). Is is truly an energy miser by design. It is now about 9 years old and have had zero issues - it hardly ever runs. It will also run directly off the two wires that come off a solar panel with nothing else between the two.

Most any laptop is a good choice for a 12 volt system. If the laptop is not 12 volt by design, then simply to find a laptop car adapter (12 volt cigarette lighter type) for said laptop (or a universal adjustable voltage one) and you're in business! For several years I've been running an ACER laptop in this manner that is also hooked to an external HP flat screen monitor that is also running right off the 12 volt feed (it's ac adapter had an output of 12 volts so it was great candidate!) Internet cable modem is a motorola and it's ac adapter output is 12 volts so it now is running direct off the 12 volt dc feed lines.

Next to the ac powered led room lights, are also 12 volt direct fed led lights. All the 12 volt led lights are on pwm dimmers.

The circulation pump which is used to dump hot water from the woodstove heated tank into a 40 gallon secondary tank is an El Sid (uses a 10 watt driver) and is hooked direct to a 12 volt feeder line.

For times when I am not home, there is a Multi-Camera day/night cctv surveillance system (all 12 volt) and I can access it from any internet connection. It has a small 10" flat screen tv/monitor also. The 12 volts to the flat screen is dropped to 9 volts per it's power requirement but still dc direct.

The recumbent power-generator is 12 volt, and the am-fm stereo/mp3 next to it is 12 volt automotive (Kenwwood!) hooked to some casket sized speaker boxes. It sounds every bit as good as the ac powered separate component Technics home stereo that sits on the next shelf down.

Two 52" ceiling fans are also 12 volt (speed adjustable and reversible) use only a scant measured 7 watts, and come on automatically in the winter when the ceiling temp hits about 72 or so... or with a bypass switch.

The Go-One3 has a 48 volt system - however - I can charge it with one simple hookup directly from the 12 volt feeder line.

If my car battery goes dead, I can just jump it with the house (both are 12 volt!). If by some miracle the house bank goes dead, I can jump it with the car!

I still use the inverters for: the wash machine, woodsplitter, and mig welder (although I do have a dc direct welder/battery bank charger that runs right off the Listeroid).. The inverter run time is very minimal (possibly a total of an hour a week maybe.)

At one time I thought about having the woodsplitter with a dc motor but after some use, the ac motor is handier if I need to take it elsewhere where ac is more readily available...

This is a bit long winded but wanted to give an idea of what the pieces are for anyone thinking of going 12 volt. The 12 volt side is very hearty with a proven track record. I no longer worry about inverter failure.

~CrazyJerry

[Harold in CR]

Excellent info, Jerry. Thank You. You are correct, in that, anyone that wants to get serious about self energy efficiency, can use your info for very good results.

Also, there are many Marine appliances, such as Blenders and mixers and such, that work directly off 12V. I am going to be getting a Schumacher 12V 1000w Inverter. Know a guy in Wisconsin that swears by them. They go on sale at a VERY good price, occasionally, at a Farm Supply Store up there. Fleet, maybe ??

Thanks again, Harold.

[Harold in CR]

Hillhater, yes. The LED carcass processor is the same as the ones the Aliens use for bloodless sampling in remote locations. They run an extension cord from their space craft, to run them. Works a treat.

[CrazyJerry]

Excellent info, Jerry. Thank You. You are correct, in that, anyone that wants to get serious about self energy efficiency, can use your info for very good results.

Also, there are many Marine appliances, such as Blenders and mixers and such, that work directly off 12V. I am going to be getting a Schumacher 12V 1000w Inverter. Know a guy in Wisconsin that swears by them. They go on sale at a VERY good price, occasionally, at a Farm Supply Store up there. Fleet, maybe ??

Thanks again, Harold.

You're Welcome Harold. Not the definitive source here but I live this experiment every day. I know the inverter you have mentioned. Not to get off topic, but I've noticed a thing or two regarding inverter ratings. There are currently 7 inverters wired in here (4 sine wave and 3 modified sine wave). Using a Kill-A-Watt meter, all of the inverters show a nice 120 volt / 60hz (or a close 59.x something) output, however, all of the modified sinewave inverters will: Make appliances run measurably hotter (everything from motors, ac adapters, etc...) They will also make motors noticeably louder (like the washer, ac ceiling fans and such.) I have run into a couple of appliances that will absolutely reject a modified sinewave by going into "error". (One example is a backup computerized Toyotomi/Toyostove heater.) Just something to keep in mind when shopping for an inverter.

By comparison, the Listeroid will generate a true sinewave (via rotation not electronic manipulation) and even though there is a larger voltage and hertz variation, items listed above do run cool and quiet.

I have found all of the modified sinewave inverters to be quite reliable. 2 sinewaves (not listed above) were not so lucky!

Merry Christmas / Happy Holidays ES!
~CrazyJerry

[dogman]

Back to the watthours discussion. In general, you can count on calculations of a yearly average of wh per day. There are average insolation maps of the USA avaliable. So take the average insolation for the year and multiply by the wh listed on the panel. This method will give you a guide to how big a stationary panel setup has to be to get a wh per year number you are aiming for. To maintian that daily wh you need in the winter, you'd need to greatly increase the system size. That is why grid tie can be good, you can draw power in winter, and provide power to the grid in summer. No need to upsize the whole thing to last 3 sunless days.

It's shockingly small daily insolation, here in the desert soutwest, where we go, " Wow look, a cloud!" it's still only about 5.5 hours a day average. The average insolation takes into account that your panels are stationary I think as well as typical weather. You only get 100% for a few hours at noon. The rest of the day is much less.

[Alan B]

Tracking panels make a huge difference in collected solar energy.

Our large inverter is 24V and will produce up to 3KW sine wave with accurate 60hz. The same unit in 12V will produce only 2500W. We produce 12V from the 24V battery bus with DC-DC converters. The 12V is regulated and the converters are quite efficient, over 90% as I recall.

The particular inverter (Victron) I selected has the capability to work with the generator and produce additional power. It phases up with the AC from the generator and adds to it. This is useful in the RV for starting the Air Conditioner. The inverter and battery bank help with the starting power surge which the generator alone has trouble with. This allows a smaller generator to be adequate.

The generator also produces accurate 60hz with inverter technology.

[dogman]

Yeah, tracking panels for the win. There is a large commercial pv array that just went on stream this fall near El Paso. Acres of panels. All of them have a little parabolic mirror concentrating on each cell, and the whole panel tracks. Acres of em, and more in the works.

[jonescg]

On the subject of running a dual AC and DC system - I highly recommend it. Try to run a convenient DC voltage; at least 24 volts. This way the wiring doesn't need to be as thick. Run all of the lights in the house off 24 V and the fridge too, if you can. A good brand of 24 V compressor style fridge is the Eutectic fridge:
http://www.autofridge.com.au/page/products.html

With a dual system, if your inverter craps out, you still have lights and cold beer to wash your worries away.