My Solar Panel Power Project

[Loren49]

Rob - my panels are about 5 feet higher on my homemade mount. I would have problems with snow depth with your height - mine are hinged near the top and are set at an angle except for during the winter. I'm at 43.8 north latitude.

Loren

 

[Kyle_in_Tex]

Great thread! Real systems and real data from real users. I'm on a COOP with no incentives but I'm still looking at falling prices for systems. It gets really hot here and I'm looking at replacing my shingle roof to a reflective galvalume metal roof. I wonder how much the initial heat plus reflective heat from a metal roof would effect efficiency. Say the air temp is 100 deg F. and add reflective heat from metal roof (maybe 40 more degrees?) what would the effiency drop to? Or would it be even hotter than that? Does total heat exposure lower lifetime?

 

[Rob-D]

Great thread! Real systems and real data from real users. I'm on a COOP with no incentives but I'm still looking at falling prices for systems. It gets really hot here and I'm looking at replacing my shingle roof to a reflective galvalume metal roof. I wonder how much the initial heat plus reflective heat from a metal roof would effect efficiency. Say the air temp is 100 deg F. and add reflective heat from metal roof (maybe 40 more degrees?) what would the effiency drop to? Or would it be even hotter than that? Does total heat exposure lower lifetime?

Hi Kyle,
Heat is always the enemy of electronics.
With that said you should look at a few panels in your price and wattage range and then get the specs on them from the manufacturer. (All panels have readily available specs)
Can you pick a color for your roof? Up here you can get an array of colors and if you pick a light color it will be cooler. Years ago when I did photography we did an experiment and found that sticking your head under a white cloth was 25F cooler than a black one. Also if you're handy you can make you own mounts on the ground. I like ground mounts much better than roof mounts, cooler too.

Incentives are nice but I'd do PV even if there weren't any.

Rob

 

[varmint]

Kyle- I just happened on this thread, and will have to go back and read it! I installed solar panels on our little barn's roof last fall (well, we had it done) but before hand, I cleaned and painted the old aluminum corrugated metal roof. I got an Energy Star rated white elastomeric roof coating (that means certain areas where heat is an issue have tested and approved it, like Miami-Dade) that we sprayed on. Man, what a difference it made! On hot and sunny days, the roof is now cool to the touch, and the barn's loft is a lot cooler. Hopefully, I will see increased output from the PV system this summer, since they are over a cooler surface. Spraying it was easy, once I found an airless sprayer that could handle the viscosity. Water based, and should last a long time. Uniflex is the source, if anyone is interested, and I got it thru Sherwin Williams.

 

[Kyle241]

This is a great thread. :thumbsup: Pete, I am envious and have been looking at alternatives (including MicroFit in Ontario) and am still on the fence on what to do. Hopefully one day in the near future I will make a decision to help reduce/eliminate hydro bills as they are going up, up and up!

 

[Rob-D]

I think we're seeing an interesting phenomena. Oil prices are a spiking and PV is dropping and becoming easier to install.
Rob

 

[varmint]

Having read the whole thread, I am very impressed by the explanations and care that has gone into Pete's installation. When we installed our little system last fall, we sized it to fit the barn's roof, our "budget comfort zone" and, most importantly, our annual usage- down to around 4KWH a year and not easy to take it any lower. We may achieve about 90+ % of our annual usage from PV- so far, I think we are exceding design output a bit). We had extra costs, since we opted for the mirco inverters from Enphase, (shading issues from trees) the best panels, to maximise output and service life, and we had to have our main electrical panel replaced since it was old, full, and I mean full. Pete is obviously an electrical engineer, and knows what he's doing, which makes projects like his sooo much more interesting to read about. I'm just a handyman, do it all sort of guy, who tries to stay out of trouble and do it right, but with very limited exposure and knowledge, you have a handicap going into projects. I thought about doing it myself, but with the required permits, it didn't make any sense. I did recoat the roof after reinforcing the rafters and leveling them across the roof... this is a farmer built barn, and 40+ years old to start with.
So far, after a little over 6 months, we show a net meter reading of around 100 KWH total used from the grid- and it's been a cloudy and rainy spring. Summer, with better sunshine, better panel angles, and more usage from the AC will be very interesting to watch. I know climate change, subsidies and the like are not good issues for this forum, so let me just say we did it because we felt it was a good thing to do, and if we can save money over 10 or 15 years, that's just icing on the cake.

 

[Rob-D]

Having read the whole thread, I am very impressed by the explanations and care that has gone into Pete's installation. When we installed our little system last fall, we sized it to fit the barn's roof, our "budget comfort zone" and, most importantly, our annual usage- down to around 4KWH a year and not easy to take it any lower. We may achieve about 90+ % of our annual usage from PV- so far, I think we are exceding design output a bit). We had extra costs, since we opted for the mirco inverters from Enphase, (shading issues from trees) the best panels, to maximise output and service life, and we had to have our main electrical panel replaced since it was old, full, and I mean full. Pete is obviously an electrical engineer, and knows what he's doing, which makes projects like his sooo much more interesting to read about. I'm just a handyman, do it all sort of guy, who tries to stay out of trouble and do it right, but with very limited exposure and knowledge, you have a handicap going into projects. I thought about doing it myself, but with the required permits, it didn't make any sense. I did recoat the roof after reinforcing the rafters and leveling them across the roof... this is a farmer built barn, and 40+ years old to start with.
So far, after a little over 6 months, we show a net meter reading of around 100 KWH total used from the grid- and it's been a cloudy and rainy spring. Summer, with better sunshine, better panel angles, and more usage from the AC will be very interesting to watch. I know climate change, subsidies and the like are not good issues for this forum, so let me just say we did it because we felt it was a good thing to do, and if we can save money over 10 or 15 years, that's just icing on the cake.

Varmint,
How do you like the Enphase? I'm going with them on my intertie. They just came out with a new inverter that will be avalable the beginning of June.
My roof is east/west so it is actually cheaper to run the Enphase as opposed to say two Sunny Boys.

I'm not crazy about the fact that they keep dropping their MTBF though.

Rob

 

[eepete]

Looking back on the article, it looks like I never posted the logging of the panel's performance. So here it is. You can see a bit of a day where it was variable cloudy. The next full day was no clouds at all. The other day I saw a peak power out of 9200 watts! The brown trace on the graph labled "Light" is just a relative indication of the amount of sunlight there is. There are no units associated with this graph. You can see that at "3 days ago" we had very cloudy skies.

I've had a half a year to reflect on all this. It's looking like the panels will provide about 50% of the power I use, and my bill is about 1/3 what it was. It's averaging out to about 2 cents per square foot per month. Can't wait to have a years worth of data....

As for the cost of solar going down, the mounting stands for the panels need a lot of work. Probably due to low volume, they are extruded and drilled pieces. A little design work here and the install time would go down quite a bit. It also doesn't help that each manufacturer is different. Generic panel sizes and mounting would be nice for the consumer, not so nice for the manufacture. Think "Flat Screen Mounting" where there is a sort-of standard that lets there be one bracket that works with all TVs. Need the same thing with panels.

The inverter cost is way to high. Volume and competition will help that. I can see the micro-inverters driving that too. It's easier to make a box that outputs 250W of AC than a box that outputs 10KW. Between that, eliminating shading penalties and eliminating single point failures that take down the entire system I see a lot of promise there if the "big" inverter prices don't come down.

During the next year, I'll be bringing more automation and logging on line, and should be able to do a better job of explaining where all that energy goes...

Pete

 

[Rob-D]

Looking back on the article, it looks like I never posted the logging of the panel's performance. So here it is. You can see a bit of a day where it was variable cloudy. The next full day was no clouds at all. The other day I saw a peak power out of 9200 watts! The brown trace on the graph labled "Light" is just a relative indication of the amount of sunlight there is. There are no units associated with this graph. You can see that at "3 days ago" we had very cloudy skies.

I've had a half a year to reflect on all this. It's looking like the panels will provide about 50% of the power I use, and my bill is about 1/3 what it was. It's averaging out to about 2 cents per square foot per month. Can't wait to have a years worth of data....

As for the cost of solar going down, the mounting stands for the panels need a lot of work. Probably due to low volume, they are extruded and drilled pieces. A little design work here and the install time would go down quite a bit. It also doesn't help that each manufacturer is different. Generic panel sizes and mounting would be nice for the consumer, not so nice for the manufacture. Think "Flat Screen Mounting" where there is a sort-of standard that lets there be one bracket that works with all TVs. Need the same thing with panels.

The inverter cost is way to high. Volume and competition will help that. I can see the micro-inverters driving that too. It's easier to make a box that outputs 250W of AC than a box that outputs 10KW. Between that, eliminating shading penalties and eliminating single point failures that take down the entire system I see a lot of promise there if the "big" inverter prices don't come down.

During the next year, I'll be bringing more automation and logging on line, and should be able to do a better job of explaining where all that energy goes...

Pete

Pete,
Great software!

I have the same issues with mounting systems. The Unirac (?) is 69 cents a watt. Now that you can get watts for 2 bucks that stinks! It will add about $5k to my intertie so I'm looking into the "Quick Mount PV" system where you just buy the plates and materials to attach to your roof and then you can use any system you want. It also saves the cost of shipping long rails.
I'm going to my steel mill and getting aluminum angle. I'll MIG weld it into channels if I cant's get extruded aluminum in the shape I want.
Anyway you look at it saving several grand on the mounting is a big deal. I understand installers can't take the time to do this but they just transfer the cost to the buyer so it's nothing to them, for us it's a big saving.

Rob

 

[eepete]

The Unirac has you attaching to one side for the rail, and another side for the post mounts. So the holes in the ground don't quite line up. I didn't catch this, so I have a little off-angle tilt to the posts. Fortunately, I got a bunch of neoprene washers that I used to give the system some slop tolerance and to separate the face of the stainless steel washer from the extruded aluminum angle (long term galvanic concerns).

If I could have found a good source of aluminum C channel here, I would have put 6 holes per 12 panels. The channel would be held up with 1/2" stainless threaded rod. Instead, I have 18 holes per 12 panels and used 3/8" stainless threaded rod. You can see where the install time would go down, leveling would be easier, and the whole array would be more symmetric. I had problems with the 3/8 rod bending as I mounted things. All the usual first-time discoveries and like most project only when you are done do you really know how to do it.

The software is part of the automation stuff I'm working on. For the solar, I'm going to have to make a new current sense board. The inverter has about an amp of imaginary power you can see at night, presumably from the EMI filters in the unit. So I'll be taking a chip made for power company residential meters and making the equivalent of a meter. Then I'll have real power, power factor, and harmonic distortion. The cheaper current transformer only sensor is OK for lots of stuff, but with the PV you're talking big power and big money so there is more accuracy needed. Of course, since the PV array cost so much, the extra cost of an accurate reading system is not too bad.

All the inverter manufactures are trying to make money selling you the ability to see what your system is doing. But it's not an open system, there are no standards. So it's yet another stand alone hack like the weather stations and HVAC systems- no integration possible. The extra cost they charge for the inverter add-on is on the order of $400 and up, which is more than enough to cover whatever I end up building. There are also some interesting isolation problems since the panels are outside, have area, and can be hit by lightning. For battery current, I've got a nice instrumentation differential amplifier that can take 4mV and make it 4V (that's at max gain- gain is jumper programable) so a small 1 milliohm shunt on the low side where the batteries connect to ground would work. There are some high side current monitoring systems out there, but the single chip ones don't like big voltages- problem for another day. But what fun problems!

Pete

 

[Rob-D]

Pete,
I remember running into the high side current sensing, high voltage issue on a design once but it was awhile ago and I'm having a 'senior moment' so i can't remember how I solved it or where the circuit is but I don't think I went to the low side sensing. Advantek makes some nice current sensing chips you might want to check out. I think some manufacturer solved the high voltage issue (Zetex maybe?), they have several sensing chips that I've used with good success.
Mostly I'm interfacing to Atmel's uC's these days for low current apps. I'm playing with energy harvesting and Atmel's chips are giving me currents in the low nanoamps. Actually there's a nice little chip from TI, the INA209 that gives you voltage, current or watts out that is great for watching what's going on with small solar apps.
Right now I'm lost somewhere in a 2's compliment algorithm in assembler that I'm determined not to go to C to resolve, I'm sure it will all work out.
Like you said, lots of fun!

ps: Stainless to aluminum, I haven't seen real problems with it unless you're talking a lot of current moving directly through the connection.

 

[varmint]

I haven't looked into the Enphase website since we got our system installed. Not good that MTBF is going down! I recall that it was a high number to begin with... I got a spare inverter as part of the package, just in case I need one in 10 years and they are gone. As early adaptors, we run certain risks. I sold solar heating systems 30 years ago, and the big names back then are only memories now. I salvaged a system a few years ago, and put together a system to heat my shop, but finding an expansion tank with a bladder that compatible with the sythetic oil has proven impossible! I have an original tank, but it's borrowed from a friend who got half of the equipment we salvaged, and when and if he needs it, I'm screwed. I am not an expert, but I can tell you that we had no issues with galvanic corrosion between stainless steel and aluminum, maybe because the SS componets were small and the aluminum items were big, relatively? I did use neoprene isolaters where my alum. mounting pads touched my steel metal roofing, just in case.
I would think that racking should come down a lot in cost, once it becomes more of a commodity product in demand. All very interesting.

 

[tcartwri]

My little project that I'm just finishing up. There are two arrays like the one pictured. Total panel capacity is 11.75 kW. I'm over powering the inverters to boost output over the course of the day in contrast to installing trackers. Excess power will be discipated as heat. ( we are only allowed to push 10kW into the grid )

Gratuitous tractor pic included.

 

[eepete]

tcartwri - Very nice :thumbsup: and tnx for the tractor pix! I got a kick out of the "If I make too much power, I just dissipate it as heat".

On the stainless-aluminum, it was on the edge looking at the various tables for galvanic corrosion. I was concerned about the large surface contact areas so played it safe with the neoprene. Good to hear that no one has seen any problems in the real world. The neoprene also helped in case there were problems with metal expanding/contracting with temperature, and again that is a long term issue I have no direct experience with. The big surface area contract was a mix of more contact area and the ability of a large surface area to hold water longer.

About every 6 months I plan to take 15 minutes and WD-40 all the hardware just in case.

The obsolescence problem is real now. These are Sharp 216 watt panels, and now they don't make them any more. In that same size, it's a 225 watt panel. Since there are three groups of 12 panels, if I have to replace one I may have to replace 3- problem for the future I suspect....

Pete

 

[Rob-D]

Tcartwri,
Thanks for the photos, great job!

Pete,
What I did to compensate for any expansion problems was to mount all the panels off the aluminum rails with angle brackets. Since each panel only spans 30 to 40 inches between anchors I did not have any problems.

Varmint,
You make a good point about obsolescence, I think this a plus for the Enphase inverters. You just stack them on for each panel. Just as long as they are compatible with the rest of the inverters you're OK. My thinking is that we'll all be changing parts around in 5 or 10 years as things get cheaper and better. Let's hope so anyway!

Rob

 

[andrewstone81]

I am thinking about getting a 1-2kW solar panel setup for my house. I'd like to hear if anyone has any direct experience with this that might be able to help me. Thanks a lot.

solar panels maryland

 

[Rob-D]

I am thinking about getting a 1-2kW solar panel setup for my house. I'd like to hear if anyone has any direct experience with this that might be able to help me. Thanks a lot.

solar panels maryland

First you have to decide if you want to run an off grid or an intertie. An intertie runs with no batteries and all the power you generate gets fed to the grid with your total consumption being reduced by that amount.

An off grid system runs with batteries and all the power you generate is used at your location. Both systems have distinct benefits.

You also have to determine to a great extent how much energy you need. You might want to get a "Kill A Watt" meter to determine your usage on different appliances. Do a web search for "P3 kill a watt", they're about $25.00 and will give you exact power usage of your different appliances.

Where are you putting the panels? Do you have south facing roof with good sun exposure?
You can get a certified in installer to come over and monitor your site to tell you these things. Figure the price of installation from them at $5 to 7.50 a watt. It's a lot cheaper to do it yourself but you will need experts to help you. It can be done but you have to be very handy. Maybe you have a neighbor with a background who can advise you and you can do the labor end.

Rob

 

[crbr]

Good thread.... thank you

 

[EHR]

I have a 1.2 kilowatt array grid tied with battery backup. Additionally I have solar dhw as well. What ?? do you have?