Solar Panel Power?

[PAFred]

I'm starting to look into the possibilty of installing a solar panel aray to off set the rising cost of electric power. My current average monthly Kwh for a 30 day period runs about 2500 kwh. can anyone offer up any ideas for the size / (number of) panels and wattage that would be needed. And is there any way to off set the up front costs involved so as to make it feasible.

And what about payback from the utility for power you dont use during the day for example even though the amount generated back into the grid would be small.

And lastly is there any place on the web that has simple calculators for figuring out what you need to install such a system.

 

[itsmoked]

PAFred;

By far the best way to save money on your energy bill is to turn things off!!

Some serious consideration along these lines can go a long way in reducing the dollar drain.

There is really a very large amount of calculation that needs to go into deciding on a solar system for any particular case. Each case is totally unique.

Stuff like what state you're in, what county your in, what city you're in, and whether your power is tiered or not.

Also whether you have time-of-use billing or not. Whether your utility will do any buy-back or not? Whether your state is offering any tax incentives. What payback period will you swallow. And before all this, whether or not you would be willing to front the $15-$25,000 required?

Best suggestion for you would be to contact the local solar power installer. They would be happy to come talk to you. If there are any tax rebates or programs available in your area they would be the ones to know and give you the straight facts. Hopefully, you don't live under any big redwood trees.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[GregLocock]

As a rule of thumb in Oz you get between 4 and 7 kWh per day from a panel that is rated at 1 kW at noon.

Typically in Oz the insolation is around 1 kW/ m^2 at noon, and a typical panel might have an effciency of 10%. So you'd need a 10 m^2 panel, to generate 1 kW at noon.

So, to generate 100 kWh per day you will 100/5.5*10 sq m of panels, on an average day.

That's about 20 sq m, or 200 sq ft.

The cost of controllers and batteries is also significant.

I really suggest you do a web search for solar power, everything you have asked is well known. The details will depend on where you are.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[LionelHutz]

80kWH per day - that's a lot of solar panels.

I've seen/read about solar systems basically running in 3 ways. The first way basically runs the meter backwards during periods of excessive usage. The second uses a smart meter and involves buying and selling the hydro. The third involves charging batteries and using the power for yourself only - obviously, this is harder to do with a grid tied system. The first two ways use inverters directly connected to the panels which push out all the power they can harness into the grid. It depends on the usage and location as to which way is best.

Look up a website and magazine called Home Power. The usually feature a detailed solar panel installation every issue.

A very general number I've seen is 1kW of panels produces about 100kWH AC per month. This varies depending on location so just use this to get an idea of approximately how much panel you need before getting into the real calculations. Don't be surprized to find you need about 25000W of panels, give or take a few kW here or there. Unfortunately solar isn't cheap. You're likely talking in the $100's of thousands, not in the $10's of thousands for an installation of that size.

 

[IRstuff]

MIL-HDBK-310's Table 1 results in 386 kWh/m² in a hot climate. You need to include about 15% quantum efficiency and an 80% inverter efficiency gives you about 62 kWh/m² net.

For 100 kWh/day, you'd need something like 2160 m² of panel area.

MIL-HDBK-310's numbers are essentially BEST-CASE, e.g., with an overhead sun. The farther you are from the equator and the farther you are from your summer, the less power you get.


TTFN

 

[charcoal]

In There is a Standard which is useful. It is called
AS 4509.2-2002 Stand-alone power systems - System design guidelines. The appendix at the rear gives good calculation templates.

 

[IRstuff]

Oh, and to actually get those values, you'd need to steer the panels to continually face the sun. Otherwise, you'd take a hit on the angular subtense.

TTFN

 

[EEJaime]

PAFred,

I designed a demonstration project for the US Postal Service for one of their small facilities here in the Southern California Desert a few years ago. The system used series connected collectors to generate power which was then inverted to 208y/120v, 3ph,4w. With the inverter losses, the size of the arrays needed, the roof racking structures and supports and weather proofing, (it was a single ply membrane EPDM roof), coupled with Southern California Edisons balking, and protective relaying requirements, as well as the custom switchgear, etc.... Our study indicated somewhere around a 40 year payback. Photocells are somewhat more efficient now, but I wouldn't expect a whole lot of improvement.

We also have installed several municipal parking facilities with solar collectors to charge battery banks which power the facilities' lighting from dusk to dawn, but again that is out in the desert and these are very long covered parking lots with lots of roof area.

Your best bet would be to use single load photo arrays that power small remote devices such as battery powered lights, or to use solar illumination systems directly, which collect sunlight, focus it down a 12" tube to a skylight looking lens in your house. Water heating systems are workable, but require maintenance and a way to utilize the heated water efficiently. But I believe the real, high power level solar power for household use is still a few years off.

Regards

 

[GregLocock]

Sorry i've just noticed a factor of 10 error in my maths, but i don't see where then next factor of 10 for IRstuff's number comes from.

We got almost exactly 9 kWh per day from 8 sq m of 22% efficient cells, on sunny/fine days.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[IRstuff]

Arrgh...must remember how to do numerical integrations correctly...

try again. 310's best case is 9.3 kWh/m², assuming 22% efficiency and 60% conversion efficiency results in about 1.2 kWh/m² net output, which matches Greg's data point almost exactly.

Therefore you need a minimum of 82 sq meters to generate 100 kWh on a good day. If you make allowances for less optimum conditions, you'll be in the neighborhood of Greg's revised 200 m², as a bare minimum.

As a example, if you need to ride out 3 days of no sun as well, you'd need at least 328 m² to capture 4 days worth of juice.

Then, you need to store all that somewhere. A typical 80Ah car battery would be about 1 kWh of storage.

TTFN

 

[wfowfo]

Quote by Itsmoked:
"By far the best way to save money on your energy bill is to turn things off!!"

Although most people don't consider it an option, this is by far the best advice on the subject

 

[wareagle]

PAFred posted " My current average monthly Kwh for a 30 day period runs about 2500 kwh." At 10 cents/kwh = $250.00 / mo
or about $3000 per year.
IRStuff said "For 100 kWh/day, you'd need something like 2160 m2 of panel area." 100 kwh/day = 3000 kwh /mo which is about what Fred said he needed. If the panels cost $30k to install you need 10 yrs to break even and longer
if you have and break downs or replacements. 2160 sq meters
is a big area of about 100m x 21m or 300 ft x 60 ft. Most houses don't have a place to install something that big.
Thats not a very inviting solution to the problem.

Fred
What area do you live in?

 

[itsmoked]

Here's the most interesting solar power home site I've ever run across.

It describes another good reason to talk to a local solar company. The system history is an interesting read. It also shows just how little the local POCOs actually like solar users regardless of their multimillion dollar TV ads spouting their great love of solar.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[itsmoked]

OOOOOOOOPPPSS!

http://www.solarwarrior.com/

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

Given their relatively northern location near Salinas, CA, their net kWh numbers are consistent with a net 9% against the best case kWh values during summer months. Their winter numbers are about 1/6 of their summer numbers:

http://www2.solarwarrior.com/solarstatus.html

Oddly enough, their 2880 ft² array comes out to 267 m²!!!. Their photos do not show any sun tracking capability, so their winter output drops quite a bit.

As for their trials and tribulations with PG&E, that's hardly surprising. That's not any different that all those other energy companies that were supposed to have open access to PG&E's power lines to sell us power from anywhere in or out of California. Whatever happened to that?

Enterprise Rental, famous for never filling gas tanks used to reimburse a renter that came back with more gas than he left with. It was a great thing, since you could invariably find a gas station that sold you cheaper gas than Enterprise charged, thus you could always make a few bucks on a rental. Not any more!

TTFN

 

[z633]

2500kwh for a 30 day average period? =~100kWh/day. That is a lot. If this is a home you can probably reduce this in half or less. 10 kW/ day is sufficient. Do not let these so called experts (that have not lived-off the grid, less a camping trip or two) fool you. (ie. Solar trackers are more needed in winter, maybe true, for IR panels… what are that??. I have been off the grid totally for 18 years, power is less of an issue than telecom. My advice is cut the cord, go off grid totally. The power company would probably have a minimum monthly charge anyway ~$20. I do not want to give the power company $20 of power for free. Maybe, it can be arranged to sell power at the wholesale rate, when there is an excess. Often happens, as not. To much power. No “automatic” means of using it.

Now to the efficiency aspect. I have read the experts here bashing… say compact fluorescents. Well, I have not lost any, short of the very early magnetic ballast types (transformer died). But otherwise, maybe it is the power quality of the power. Modern sine wave invertors have better power quality that the pooch. Less outages also. Before satellite, the only way of knowing there was an issue was when the TV terrestrial air wave died. Now it would be the sweaty friends with no power, looking for a free shower.

So it requires some forethought and sacrifice, but it can be done with little or no impact to your current lifestyle. The scribbles of power figures given thus far are far from the whole picture.


BTW my main array is 750W of used ARCO panels that were 5 years old, 18 years ago.

 

[GregLocock]

Get off your hobbyhorse. Nobody in this thread even mentioned compact fluorescents until you did. In fact the first reply suggested that reducing demand was likely to be the best investment.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[LionelHutz]

z633 - You say 10kWh/day is all that's required but you must use much less power than that since 750W of panels isn't nearly enough to produce 10kWh per day. Or, you have about 2000W more power producing equipment? Saying you have 750W of solar panels and that 10kWh per day is all that you need in the the same post implies you're getting 10kWh per day from the 750W of panels which is somewhat misleading.

The reason many installations keep the grid connection is to get rid of the requirement of having a battery bank. Solar panels hooked to a grid tied inverter is fairly simple and almost maintenance free. Adding a large bank of lead acid batteries makes the system much more complex.

 

[z633]

Well, I guess the 1kW Bergy up on top of the 63’ stick helps a little too. The grid tie
method has been sold as an energy efficiency program. That is the customer’s net bill is lower, but, yet is still a consumer of, and indentured to, the utilities authority to collect overhead, taxes, and profit fee. Strange that with all the energy incentives, etc. that a typical non-grid connected power producer would get a red cent for their diligent effort.
The LEED program, we are having a new facility LEED certified… 10KW of solar power … and with a main power transformer of 3.5MW, so the solar is used to circulate the eddy losses? As for lead acid batteries, a good set can last 20 years, cost $5K, or about $21 per month. That would be around the minimum charge for the utility so it would appear to be a break even effort either way. However it is human nature to use more, and more, especially considering if they think they are getting the power for free. That is add a bunch of solar panels on the roof –(agreed – bad idea), and the more sloppy and power wasteful we become.