Eager to learn

[zog]

Hey guys, been trying to educate myself on residential solar systems on "that other forum" but can't seem to get any technical answers (Just insults). So I find this attached map interesting and want to be sure I am understanding this all correctly.

If we look at an average area for the east coast of 4kWh/m^2/Day and divide that by 24 hours we get 166 W/M^2 right?

And the panels I looked at that claim to be some of the most advanced for residentail usage have ratings of around 150W @ 800W/M^2. Is that correct?

So if we have an average W/M^2 rate of 166 W/M^2 in a area (I assume this average is night and day, acoss a year) we can estimate the output of this panel to be a little over 31 watts over the course of a year. And if I put 6 of these panels on my roof I would produce an average of 186 watts, and 4.46kWh per day?

I am really trying to learn here so please correct me if I am wrong. This is interesting stuff, I get that there are peak production times, which just so happens to be peak usuage times for residential systems, and looking at that solar seems to be a better future replacement for gas fired peaker plants than base load plants. But for now I just want to make sure I am looking at the average output of a typical panel correctly.

 

[ggunn]

View attachment 5697

Hey guys, been trying to educate myself on residential solar systems on "that other forum" but can't seem to get any technical answers (Just insults). So I find this attached map interesting and want to be sure I am understanding this all correctly.

If we look at an average area for the east coast of 4kWh/m^2/Day and divide that by 24 hours we get 166 W/M^2 right?

And the panels I looked at that claim to be some of the most advanced for residentail usage have ratings of around 150W @ 800W/M^2. Is that correct?

So if we have an average W/M^2 rate of 166 W/M^2 in a area (I assume this average is night and day, acoss a year) we can estimate the output of this panel to be a little over 31 watts over the course of a year. And if I put 6 of these panels on my roof I would produce an average of 186 watts, and 4.46kWh per day?

A better (and easier) way to predict what a given system will produce in a given orientation at a given location is to use PVWatts (http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/). It takes into account local weather/climate data and some system specific input to generate yearly and monthly (and even hourly if you want to dig that deeply) output numbers.

It's pretty good. I had a chance to analyze a system that had been in place and monitored for three years and compare PVWatts projections with the real system output. The numbers agreed to within a couple percent.

 

[zog]

A better (and easier) way to predict what a given system will produce in a given orientation at a given location is to use PVWatts (http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/). It takes into account local weather/climate data and some system specific input to generate yearly and monthly (and even hourly if you want to dig that deeply) output numbers.

It's pretty good. I had a chance to analyze a system that had been in place and monitored for three years and compare PVWatts projections with the real system output. The numbers agreed to within a couple percent.

That is a really neat tool (Bookmarked), so looking at a 150W rated panel (About $500/each) I would need 27 of these for a 4kW (DC rated on the calculator) system? Is that correct?

While this is a really cool program, just as I don't let my new techs use our fancy automated test equipment until they learn how to use old school equipment that requires understanding of the basic principles in play, I would still like to know if my calculations and thinking in my first post are correct so I can really understand the basic principles.

 

[iwire]

If you go here http://www.fatspaniel.com/fat-spaniel-in-action/live-sites/ you can see actual power production from systems all over the place. The also tell you the system size ......... compare the system sizes to the actual output, I think it is very telling.

 

[iwire]

I would still like to know if my calculations and thinking in my first post are correct so I can really understand the basic principles.

I can recommend this book for all the fundamental formulas used for the calculations.


http://www.amazon.com/Photovoltaic-...3083/ref=sr_1_1?ie=UTF8&qid=1314283842&sr=8-1

 

[iwire]

Here are some good links


College of Engineering Southwest Technology Development Institute

College of Engineering Southwest Technology Development Institute Codes & Standards

Photovoltaic Power Systems and the National Electrical Code: Suggested Practices

The North American Board of Certified Energy Practitioners (NABCEP)

Whenever you see something from John Wiles it is worth paying attention too, he has written a lot of the NEC proposals for PV

 

[K8MHZ]

If we look at an average area for the east coast of 4kWh/m^2/Day and divide that by 24 hours we get 166 W/M^2 right?

An easier way to understand this is to use capacity factor.

Here, in Michigan, we have a capacity factor of about 16 percent, or 3.8 useable hours of sunlight.

So, if we are using 150 watt panels, each panel would produce 570 watt-hours per day, before factoring in shading.

Also, prices of high quality panels are coming down. I think Sanyo's 3'x5' panels now produce 230 watts and are around 500 to 600 dollars. They are very well made, and I think they are made in the US.

And, don't forget to factor in inverter efficiency. Typically that will be 85 to 90 percent.

For your area, the capacity factor about a half a percent higher which works out to 4 hours of useable sunlight per day, an easier figure to work with.

So, in your area, each 150 panel would produce 600 watt-hours per day.

Six panels would produce 3600 watt-hours per day. To estimate how much energy that is, using 13 cents per kWh, a little math shows an average of 108 kWh, or $14.04 per month.

As far as I have heard, Sanyo, Sony and Evergreen make the best panels. They are all over 200 watts per 3'x5' panel. If you are only getting 150 watts out of a 3'x5' panel it is likely amorphous and should cost you half of what you mentioned.

For panel efficiency, the best have about 15 percent, or 150 watts per square meter in direct sunlight. I have heard that a company in Britain has reached the 40 percent mark.

Does this make better sense for you?

 

[jumper]

Nice info guys. I have been curious about PV systems also.

 

[K8MHZ]

And the panels I looked at that claim to be some of the most advanced for residentail usage have ratings of around 150W @ 800W/M^2. Is that correct?

Why are you using 800 watts per meter, instead of 1000?

STC for solar panels is 1000 watts per square meter.

 

[K8MHZ]

Nice info guys. I have been curious about PV systems also.

I just finished a 13 week long college course on solar design and installation. I went from curious to fascinated.

To me, it's amazing we can use sand as a raw material and turn it into a thing with no moving parts that makes electricity.

 

[iwire]

To me, it's amazing we can use sand as a raw material and turn it into a thing with no moving parts that makes electricity.

I agree, amazing.


I just think we have a long way to go before it becomes a real option ....... of course if fossil fuel prices continue to climb PV may become much more viable on it's own without incentives.

 

[ggunn]

That is a really neat tool (Bookmarked), so looking at a 150W rated panel (About $500/each) I would need 27 of these for a 4kW (DC rated on the calculator) system? Is that correct?

While this is a really cool program, just as I don't let my new techs use our fancy automated test equipment until they learn how to use old school equipment that requires understanding of the basic principles in play, I would still like to know if my calculations and thinking in my first post are correct so I can really understand the basic principles.

Your first post does not take into account system location (climate data, latitude) and orientation, which PVWatts does. Your calculations assume a constant average insolation 24/7/365 normal to your array and ignores the fact the the sun is always moving. Are you going to track the sun with your array? If not, what tilt and azimuth will you use? Is where you are usually cloudy in the morning and sunny in the afternoon during the month of April? Is November mostly overcast? What is the location in the sky of the sun at noon on February 22nd at your location? At 4PM on May 31st? PVWatts takes all that into account by accessing years of very granular and site specific data from NREL.

Your calculations are OK, I guess, as far as they go, which isn't very far. I don't believe that with a hand calculator and application of first principles you will be able to duplicate PVWatts' results. It's not like a string calculator whose results you can check with a few hand calculations.

 

[zog]

Why are you using 800 watts per meter, instead of 1000?

STC for solar panels is 1000 watts per square meter.

That was the STC I found on some of the first specs I looked at, since then I have found most to have STC of 1000.

 

[Chamuit]

I just think we have a long way to go before it becomes a real option ....... of course if fossil fuel prices continue to climb PV may become much more viable on it's own without incentives.

I agree. Took some intro type classes a few years ago. The ROI here was 7 - 10 years using the numbers available. Imagine it would be longer without the fed, state and other incentives.

 

[zog]

Your first post does not take into account system location (climate data, latitude) and orientation, which PVWatts does. Your calculations assume a constant average insolation 24/7/365 normal to your array and ignores the fact the the sun is always moving. Are you going to track the sun with your array? If not, what tilt and azimuth will you use? Is where you are usually cloudy in the morning and sunny in the afternoon during the month of April? Is November mostly overcast? What is the location in the sky of the sun at noon on February 22nd at your location? At 4PM on May 31st? PVWatts takes all that into account by accessing years of very granular and site specific data from NREL.

Your calculations are OK, I guess, as far as they go, which isn't very far. I don't believe that with a hand calculator and application of first principles you will be able to duplicate PVWatts' results. It's not like a string calculator whose results you can check with a few hand calculations.

I understand what you are saying with all the factors I did not account for, I just wanted to verify I was doing the math right. I want to play around with these numbers to look at some other things I want to figure out, little pet project, and everything I will do will be based of the basic concepts in my OP being correct, I just wanted to be sure i had the concepts right, and it sounds like I do.

 

[zog]

Don't want to stop this thread, this is getting interesting and I don't want to get it off track with my little project, so lets keep it rolling.

Thank you guys for all the great info, I find this stuff very interesting to discuss with people who actually know what they are talking about and not what they read in some biased magazine or article. We are smart enough to figure out how effective PV systems really are, and where they really need to be a viable solution that can stand on its own without incentives.

 

[K8MHZ]

Don't want to stop this thread, this is getting interesting and I don't want to get it off track with my little project, so lets keep it rolling.

Thank you guys for all the great info, I find this stuff very interesting to discuss with people who actually know what they are talking about and not what they read in some biased magazine or article. We are smart enough to figure out how effective PV systems really are, and where they really need to be a viable solution that can stand on its own without incentives.

In Michigan there are no incentives other than the general energy tax credit, same as one would get for insulation.

Also, once the POCOs get to their 'goal', for instance it's one percent for Consumers Energy, they will no longer allow grid ties and net metering. At this time, the 'goal' is 70MW for solar and wind combined, and in about 18-24 months a large wind turbine facility near my house will be built to provide for 29 of those 70MW.

We must realize that the POCOs are being forced to allow and / or provide renewable energy. It certainly isn't in the best financial interest of the POCOs to promote any reduction in the amount of energy they sell.

I figure all my systems without any sort of incentive or credit. If such exists at the time of sale, that is the time to figure it as changes abound and are not predictable.

Another thing to consider in both our areas is snow cover. The winter's colder temps provide for a higher output so it's important to keep snow off the panels. There are already companies making tools for this. They are basically snow rakes with foam heads. The foam heads have been available for cars, but they are small. The one's for panels are a couple feet wide.

If you know you will have snow on the panels and will not, for some reason, be adamant about removing it, your yearly output will be less than anticipated. Bear in mind that 5 percent shading presents a 40 percent loss, and the reduction of output on a single panel in a string will impede the current flow from all the rest of the panels.

 

[zog]

In Michigan there are no incentives other than the general energy tax credit, same as one would get for insulation.

Also, once the POCOs get to their 'goal', for instance it's one percent for Consumers Energy, they will no longer allow grid ties and net metering. At this time, the 'goal' is 70MW for solar and wind combined, and in about 18-24 months a large wind turbine facility near my house will be built to provide for 29 of those 70MW.

Several years ago I did commisioning on the Ubly wind farm, don't recall the output but is was a big one. there are some real concerns with safety of these wind turbines, tossing ice chunks over long distances is one of them so I hope you don;t live too close.

Another thing to consider in both our areas is snow cover. The winter's colder temps provide for a higher output so it's important to keep snow off the panels. There are already companies making tools for this. They are basically snow rakes with foam heads. The foam heads have been available for cars, but they are small. The one's for panels are a couple feet wide.

If you know you will have snow on the panels and will not, for some reason, be adamant about removing it, your yearly output will be less than anticipated. Bear in mind that 5 percent shading presents a 40 percent loss, and the reduction of output on a single panel in a string will impede the current flow from all the rest of the panels.

Might be a crazy idea but can't they put little heating wires like the rear window of your car on them for snow removal? Mayeb have a "de-ice" button on your inverter?

 

[K8MHZ]

Zog,

Here is something you need to consider in order to put your investment in the proper perspective.

In class, we were encouraged to use Kill-a-watt meters to see where our energy was going. There were two in class we could check out. I just bought one.

I found that by keeping my desktop computer on 24/7, that added $12.02 cents to my bill.

I also found that by keeping the florescent light over the stove on as a night light was adding 4 bucks to my bill.

I now turn the computer off when I am not using it. I also got some LED night lights that draw so little power that it won't even register on the Kill-a-watt. I put some in the bathroom, too, so it isn't even necessary to turn the light on for a quick visit at night.

I also found a few other areas of waste. I won't know until my next bill, but I am pretty sure I scrubbed off 14 bucks of energy costs off my monthly bill just by changing light types and turning off stuff that isn't being used.

Total investment, about 40 bucks and that includes the meter and the LED's.

An off the cuff estimate of a solar installation that would provide 14 bucks a month is in the 5,000 range. Less, of course, if you do your own installation.

The Kill-a-watt taught me the importance of targeting continuous loads. My next check will be the outside lighting. I have a 175 watt MV or halide that is on all night. I also have a 300 watt set of floods that come on with a sensor. Not a continuous load, but the 300 watts is worth looking into. I am thinking there is another 10 bucks a month there I can scrub off.

I'm not saying this to take the wind out of your sails. All I am doing is trying to temper your enthusiasm with reality. One thing I really liked about the class I took was that it was real world and taught by a real world instructor. He was an electrical engineer that installed solar systems. He knew how to use tools, and everything. When it came time to use the Solar Pathfinder and put up some racks, he was on the roof doing it along with the class. We actually installed two panels on a garage on college property as part of the class.

Iwire has mentioned on more that one occasion that PV is not, at this time, 'viable'. I am not so sure he is 100 percent correct, but his real world experiences need to be considered.

I think that there are some areas right now that it would be viable to install solar systems on their own merit. I also think that viability takes some effort on the designer's part. Energy costs, types of loads and times of loading, array orientation and material costs all affect the viability of a PV system.

But, there are also many more places where PV would not be viable now or in the near future.

This will change. Almost every time I check, panels and inverters are getting cheaper and more efficient. Companies that make mounting systems are now competing against Uni-Rac and the other high priced mounting and racking systems, bringing the cost down.

That's the good news. The bad news is that another factor of viability is energy costs. As they rise, they make PV systems more viable. That's bad news for people that have shady locations.

I know someday I will see people cutting down trees that shade their homes in order to run their air conditioners. Stupid, I know, but that is what will happen when the sheeple all 'go solar'.

I won't be there to cut down the trees, or even watch. I like trees. But I will be available to design the systems.

 

[K8MHZ]

Several years ago I did commisioning on the Ubly wind farm, don't recall the output but is was a big one. there are some real concerns with safety of these wind turbines, tossing ice chunks over long distances is one of them so I hope you don;t live too close.



Might be a crazy idea but can't they put little heating wires like the rear window of your car on them for snow removal? Mayeb have a "de-ice" button on your inverter?

Our wind turbines are going on an 11,000 acre sewage reclamation site. They won't even be visible from the nearest road.

I have read that getting only a portion of snow off the panels is needed as once they start producing, they heat up and the snow just slides off. I don't know that for a fact.

De-icing would be very costly, using up more energy than you would be producing. That rear window de-icer is probably the biggest electrical energy hog in your vehicle. When I was working for Chrysler, alternators were designed around de-icers. If the vehicle had a de-icer, the alternator had to be larger, like 100 amps vs. 60.