ISO input on a system

Boburk · May 2014

First off...I gotta admit that I am not in Arizona. I am in North Central Texas. Not a small town (by my standards) but limited in companies that offer solar power.

I don't know why...but I have an itch to get a system installed. That said, I am looking for input on the first quote I got.

Info:

Annual usage is 20744 kWh
High usage was Jul at 2900.
Low usage was Feb at 1100.

I have a shop that has a south facing roof. They are looking at putting 42 ReneSola 230 panels on the roof, connected to SMA 8000 inverter.

From what I can figure, this adds about 1600 lbs to the roof...should I worry?

Cost, after power company incentives, tax rebate, cash discount, etc...it about $10k installed. This is no batteries, I believe it is called a grid tie system. Do I need to keep looking?

So this is a 9.66 kWh system (or something like that). The roof will get very little, if any shade (early morning it might get some from a pine tree). What kind of power production should I expect?

Anything I need to know? I have been doing some reading here, but the use of abbreviations is overwhelming...so anything I need to understand would be appreciated.

Sean

Boburk · May 2014

Re: ISO input on a system

Another question I have is how having a system installed effects home value. Everything I find with Google is from the web site of companies that sell solar...so I fear it is biased.

Sean

AuricTech · May 2014

Re: ISO input on a system

I can think of two things off the top of my head:

1. What can you do to conserve more energy before you build your photovoltaic (PV) system? Less power needed = smaller PV system needed = less money spent

2. What are your local utility's policies concerning how to credit you for any power you feed into the grid? There are a variety of metering methods, some of which are more advantageous to the consumer than others. Those with experience with grid-tie systems can help you sort through the various methods.

solar_dave · May 2014

Re: ISO input on a system

This all depends on your net metering plan with the utility. Have you looked at the terms for that agreement?

BB. · May 2014

Re: ISO input on a system

Some answers to your other questions:

Boburk wrote: »

First off...I gotta admit that I am not in Arizona. I am in North Central Texas. Not a small town (by my standards) but limited in companies that offer solar power.

Our host NAWS is in Flagstaff Arizona--But the forum is free for all to use and pretty much everything is run by volunteers. Northern Arizona Wind & Sun kindly pays the hosting fees and keeps the forum software running.

I don't know why...but I have an itch to get a system installed. That said, I am looking for input on the first quote I got.

Info:

Annual usage is 20744 kWh
High usage was Jul at 2900.
Low usage was Feb at 1100.

I have a shop that has a south facing roof. They are looking at putting 42 ReneSola 230 panels on the roof, connected to SMA 8000 inverter.

Using PV Watts for Lubbock Texas, fixed installation titled to 34 degrees from horizontal, Grid Tied system, 9,660 Watt array, defaults:

Month
Solar Radiation
(kWh/m²/day)
AC Energy
(kWh)
Energy Value
($)

1
4.78
1110
107.67

2
5.48
1133
109.90

3
6.29
1394
135.22

4
6.40
1317
127.75

5
6.43
1360
131.92

6
6.45
1273
123.48

7
6.00
1220
118.34

8
6.13
1231
119.41

9
5.87
1185
114.94

10
6.27
1338
129.79

11
5.35
1161
112.62

12
4.80
1087
105.44

Year
5.86
14807
1436.28

It will cover you base load--But those summer days are still a killer (A/C I would guess).

As others have said, how your utility calculates its bills can have a big infulance on your actual return on investment.

For me, summer afternoons, I get "paid" $0.30 per kWH and buy (off peak) at $0.09 per kWH (roughly, our rates are way more complex if I had an A/C system and used more power). So--during sunny summer afternoons, my array looks almost 3x larger because of peak power rates (I buy/sell power at retail rates).

That is a good "net metering" plan. There are other plans where you would not come out near as well.

Also, if you are on Co-op power--Many smaller co-ops will not allow net metered solar, or sometimes no GT solar at all.

Your two thing to look at are 1) conservation and 2) your utility's GT solar rate plans. If you are going to have a professional installer, they should be able to answer question #2 pretty easily.

From what I can figure, this adds about 1600 lbs to the roof...should I worry?

Many building departments will require a structural engineer to sign off on the weight calculations. Usually it is not a big issue, but it is good to check (especially if this is an older home).

Also, if this is an older home, a bunch of insulation in the ceiling, check the walls for insulation, look at windows (double pane, shaded against summer sun, etc.). all helps.

Cost, after power company incentives, tax rebate, cash discount, etc...it about $10k installed. This is no batteries, I believe it is called a grid tie system. Do I need to keep looking?

Typical installed prices for GT solar is "around" $3-$5 per watt, before rebates. Double check with them regarding how the system would impact your utility bill.

Get several quotes, check references.

Also, see what the "largest" GT residential system would be allowed (and fit) on your home. In many locations, 10kW (roughly 13kW of solar panels) is the maximum, or the maximum before you have to jump through more hoops.

So this is a 9.66 kWh system (or something like that). The roof will get very little, if any shade (early morning it might get some from a pine tree). What kind of power production should I expect?

See above.

Anything I need to know? I have been doing some reading here, but the use of abbreviations is overwhelming...so anything I need to understand would be appreciated.

Learn more about your loads and your utility's policies regarding GT Solar. We are close to entering a phase where GT solar is being pushed back by utilities (and sometimes governments). In California, there is a 20 year grandfathering that is just about to be implemeted... After 20 years (or possibly 10 more years in my home's case), there is a very good chance that we will lose the "good" 1 year net metering plan we have. What will replace it is anyone's guess right now.

Also--Check with a real-estate agent in your area and ask them how GT Solar may affect your home's price. I am not sure that all potential buyers down the road see GT solar as a positive.

The average American moves around every 7 years--If you do not plan on staying in the home long term (kids move out) or your energy profile changes (kids move out, electric car moves in)--You are making a long term commitment.

Personally, I would highly suggest that you install solar with "extra money"--Don't take out a loan that you may have trouble paying back if the economy crashes (more). GT Solar is not an "investment" in my humble opinion.

Also check with your local property/taxing authority... Some places will up the property tax on your home... And a few places actually may charge utility taxes on what you generate (even income taxes). Pay back on solar is not that high, extra expenses/taxes can take your "investment" negative.

-Bill

Boburk · May 2014

Re: ISO input on a system

Conservation...thought of adding more insulation to the attic. Not sure how much that will help. It has batts with blow in on top of it now.

I have gable end vents and a ridge vent (that I had added) in the attic. Thought of adding soffit vents too. Again, I think this will help, but I don't think it will be much.

Did replace my metal framed dual pane windows that did not shut very well with energy compliant (tax credit worthy) windows a couple years ago...truthfully, didn't see much of a difference in my bill.

Changed out most bulbs in the house for CFLs when we moved in. Changed the most used ones for LEDs now. I don't think this will save more than a couple bucks a month.

Thought of changing out my barely big enough (when it is 105 outside, set on 78, my house is 80sh) 3.5 ton 10 Seer AC unit for a higher rated 4 ton unit...but was given a quote of $8k for it. I can see where this would help in the summer, during the hottest couple months. But don't think it will help much, or not at all, the rest of the year. House is heated using my gas hot water heater...and only costs $70 for the worst winter month.

Other larger cost appliances...pool...I don't know what I can do about the pool to lower costs. During the winter, if it gets below 38 degrees, the pump turns on to keep the pipes from freezing. This was a rough winter...

Only other way I can think to conserve is to bump off the daughters and burry them in the back yard, but I think they have laws against that... 8-P

I have tried to ask the wife and kids to NOT run the drier midday during the hottest part of the day, but it goes in one ear and out the other. Of course for every cubic foot of my air conditioned air that the drier pushes outside, the house sucks in a cubic foot of 100 degree air.

Anyhow, you can see that I have put some thought into this...and wound up here. As I told the guy that gave me the estimate, I am not looking at getting rid of my electric bill, just lowering it.

Local policies...we are deregulated in Texas. So I pay less than 9 cents a kWh most of the time. There are three companies that are solar friendly, and they all treat it differently. The one I have just happens to be one of them (green mountain...100% renewable). From what the salesman said, green mountain kind of does net metering (but I have read that Texas does NOT actually do net metering). Anyhow, during the day when I produce more than I use I bank the kWhs up. Then during the night, or on an overcast day, I would use power from my bank. On January 1, it resets to zero, and I would have to start banking them up again.

Another of the three has a free off peak plan. No idea how that works under normal conditions, I am guessing that the on-peak power is very expensive...but with the solar, I would be making most if not all my power during the peak hours, then at night I would get power for free (would help if I could get the family to do laundry in the off peak hours). The salesman referred to it as double dipping.

The PV watts chart. I have seen it before, but don't 100% understand it. Is the first column hours per day I generate power each month? Why is it lower in July than it June or August? On that chart, I would not bank up much, but it would wipe out, or nearly wipe out some of the bills.

What is GT? Grid tied?

The shop is about 15 years old. It is a metal building, with a metal roof. They would work around the skylights I have in it. (Point I guess is that it is NOT an old house I would be putting them on). The shop was here before the house, so it has the meter and main power CB panel on/in it.

Real Estate agent. I called one company and got an older lady that said it adds no value and she would not do it. I am guessing a 60-70 YO agent might be basing her input on not liking/understanding solar power. I will need to do some more research on this. I guess the other option is that if a buyer does not value it, remove it and take it with me to the new house. I have a 17 YO and a 14 YO still in the house...both girls, so not sure how long we will have them here. But won't need all this space when they leave (unless I can get the bills down, then might as well keep it).

Taxes...they passed a bill in Texas so that they can NOT increase the tax value of your home if you put a renewable energy system on it.

I just got the written estimate from the installer. I guess the SMA 8000 can't handle all the panels, so they would use micro inverters for 6 of them. Not sure what this will do to the overall efficiency of the system. Also, they figured out 5 of the panels would NOT fit on the roof of my shop, so they are looking at putting them on the carport, which is pretty much flat (has a slight angle for rain runoff). I am thinking it might just be better to not have these 6 panels installed (the ones with the micro inverters). My understanding is that optimum angle is 30 degrees here...so the 5 panels laying flat would take a loss in generation (not sure how much), or they would cost more to install because they would have to put them on a frame that angles them at 30 degrees. Minus the 6 panels I am looking at about 8.8 kWh system.

I don't think I would make payments on the system, but that is still up in the air. I have the money to pay for it up front...but it is invested. Right now that is not doing so good. I have read numbers that are 15sh-20sh percent return on solar investment. Not sure how that factors in, but it is better than I am getting on my money right now.

Sorry about the VERY long post...but still interested in inputs.

Sean

BB. · May 2014

Re: ISO input on a system

Boburk wrote: »

I have gable end vents and a ridge vent (that I had added) in the attic. Thought of adding soffit vents too. Again, I think this will help, but I don't think it will be much.

Actually putting solar panels on my roof really cooled my attic--Not sure it made the house that much cooler or not (we moved in around the same time we added the panels (after we insulated the walls, 1930's construction).

Did replace my metal framed dual pane windows that did not shut very well with energy compliant (tax credit worthy) windows a couple years ago...truthfully, didn't see much of a difference in my bill.

I was happy i replaced my my old wood double hung windows with low E/double panel vinyl. Made my west facing bedrooms much cooler (old house).

Changed out most bulbs in the house for CFLs when we moved in. Changed the most used ones for LEDs now. I don't think this will save more than a couple bucks a month.

Changing to CFL/LED is a big help--More efficient lighting and less heat dumped inside the house for the A/C to remove (my area, few people have A/C--So my experience is limited).

Thought of changing out my barely big enough (when it is 105 outside, set on 78, my house is 80sh) 3.5 ton 10 Seer AC unit for a higher rated 4 ton unit...but was given a quote of $8k for it. I can see where this would help in the summer, during the hottest couple months. But don't think it will help much, or not at all, the rest of the year. House is heated using my gas hot water heater...and only costs $70 for the worst winter month.

If I understand correctly a 20+ SEER unit should use 1/2 the amount of power (not A/C guy either). Can be a big help. Some folks have gone with mini-splits. Ducting can be a huge heat gain/loss for HVAC. Ability to "zone" can be a big help too.

Other larger cost appliances...pool...I don't know what I can do about the pool to lower costs. During the winter, if it gets below 38 degrees, the pump turns on to keep the pipes from freezing. This was a rough winter...

Changing to two speed motors, possibly pumping at low speed for only 1/2 the day can help a lot to reduce energy usage. As I understand, most pool circulation systems are way over-sized.

There are other changes that can reduce power usage (more efficient PM motors, more efficient pumps that have inlets below pool's water level vs suction capable pumps, etc.).

Hopefully some folks here with more experience can help.

Only other way I can think to conserve is to bump off the daughters and burry them in the back yard, but I think they have laws against that... 8-P

Yea--There are limits. My two teenagers leave a trail of lights on where ever they go... All those lights are now CFL/LED. And their computers are laptops.

I have tried to ask the wife and kids to NOT run the drier midday during the hottest part of the day, but it goes in one ear and out the other. Of course for every cubic foot of my air conditioned air that the drier pushes outside, the house sucks in a cubic foot of 100 degree air.

Few good solutions for driers that don't increase fire hazards/problems with humidity/combustion gasses.

At times, utilities have offered cost reduces or even free energy evaluations--Of course, some are probably better than others.

Regarding your A/C, it may be time to get a quote from different vendors with a couple different solutions (mini-spit, high seer central, etc.).

Anyhow, you can see that I have put some thought into this...and wound up here. As I told the guy that gave me the estimate, I am not looking at getting rid of my electric bill, just lowering it.

Local policies...we are deregulated in Texas. So I pay less than 9 cents a kWh most of the time. There are three companies that are solar friendly, and they all treat it differently. The one I have just happens to be one of them (green mountain...100% renewable). From what the salesman said, green mountain kind of does net metering (but I have read that Texas does NOT actually do net metering). Anyhow, during the day when I produce more than I use I bank the kWhs up. Then during the night, or on an overcast day, I would use power from my bank. On January 1, it resets to zero, and I would have to start banking them up again.

Another of the three has a free off peak plan. No idea how that works under normal conditions, I am guessing that the on-peak power is very expensive...but with the solar, I would be making most if not all my power during the peak hours, then at night I would get power for free (would help if I could get the family to do laundry in the off peak hours). The salesman referred to it as double dipping.

Things change--If things go as planned--What would you do with $0.30 to $0.50 per kWH power bills. That is were California folks are in the central valley/commercial customers.

The PV watts chart. I have seen it before, but don't 100% understand it. Is the first column hours per day I generate power each month? Why is it lower in July than it June or August? On that chart, I would not bank up much, but it would wipe out, or nearly wipe out some of the bills.

The first column is average (based on season, weather, etc.) full noon time hours of sun per day (not length of day) at ~1,000 Watts/sq meter.

The lower months are (probably) afternoon summer storms, any monsoons you may get, etc. that reduce average available sunlight (could include humid/hazy weather).

9,660 Watt array * 6.2 hours of average sun per day * 0.77 average panel+controller derating = 46,116.84 WH ~ 46 kWH for that average day

What is GT? Grid tied?

Us, Grid Tie, or Utility Interactive solar installation. Basically solar panels to GT Inverter to Main Breaker panel. Not batteries (which an "Off Grid" inverter would need). Note that GT Inverters do not provide backup power if the utility power fails (in general--there is one exception).

The shop is about 15 years old. It is a metal building, with a metal roof. They would work around the skylights I have in it. (Point I guess is that it is NOT an old house I would be putting them on). The shop was here before the house, so it has the meter and main power CB panel on/in it.

You the best you can.

Real Estate agent. I called one company and got an older lady that said it adds no value and she would not do it. I am guessing a 60-70 YO agent might be basing her input on not liking/understanding solar power. I will need to do some more research on this. I guess the other option is that if a buyer does not value it, remove it and take it with me to the new house. I have a 17 YO and a 14 YO still in the house...both girls, so not sure how long we will have them here. But won't need all this space when they leave (unless I can get the bills down, then might as well keep it).

Pretty much close to my family.

Again, I would not count on your spending on increasing the value of the home by much--In some cases, buyers have requested solar arrays to be removed (don't know if this is a common request or the exception to the rule).

I just got the written estimate from the installer. I guess the SMA 8000 can't handle all the panels, so they would use micro inverters for 6 of them. Not sure what this will do to the overall efficiency of the system. Also, they figured out 5 of the panels would NOT fit on the roof of my shop, so they are looking at putting them on the carport, which is pretty much flat (has a slight angle for rain runoff). I am thinking it might just be better to not have these 6 panels installed (the ones with the micro inverters).

I would wonder about mixing Central and Micro Inverters. Central inverters usually have an LCD readout so you monitor the output directly. Many/most/all have optional remote logging options.

Micro Inverters pretty much need a central communications box to download real time data from the micro inverters. One comm box can handle 1-XX micro inverters. Why not run micro inverters on the whole system and just one data collection system (may need internet access for full data access).

There would be no efficiency or odd configuration/connection issues with mixed central/micro inverter systems.

For central inverter systems, usually the have a single (sometime dual) MPPT input. All panels on an MPPT input should have all the solar panels on the same plan/orientation--If the panels are mixed, you will get less than optimum output.

My understanding is that optimum angle is 30 degrees here...so the 5 panels laying flat would take a loss in generation (not sure how much), or they would cost more to install because they would have to put them on a frame that angles them at 30 degrees. Minus the 6 panels I am looking at about 8.8 kWh system.

You can plug in zero degree tilt into PV Watts and see the changes. You will probably have higher summer output and lower winter output.

Note that laying panels flat can cause issues--Panels with ~5 degree tilt or more tend to be self cleaning. Flat panels tend to accumulate debris.

I don't think I would make payments on the system, but that is still up in the air. I have the money to pay for it up front...but it is invested. Right now that is not doing so good. I have read numbers that are 15sh-20sh percent return on solar investment. Not sure how that factors in, but it is better than I am getting on my money right now.

At $0.30-$0.50 per kWH hour, solar power systems can really save money. If your power is (current) $0.09 per Watt, you are pretty close to break even or even a bit of a loss (remember that central inverters usually have a 10 year warranty... It is very likely you will have to replace the inverter before 20 years).

Also, if you have heavy hail in the area, make sure your insurance will cover solar panels (and if there will be a rate adjustment). There was a person here that loss something like 1/2 the panels in a hail storm (insurance paid, as I recall).

Solar panel damage from hail storm

-Bill

Cariboocoot · May 2014

Re: ISO input on a system

I have gable end vents and a ridge vent (that I had added) in the attic. Thought of adding soffit vents too. Again, I think this will help, but I don't think it will be much.

This venting is wrong. The air can blow around the top of the attic and never move air through the attic. Take the gable end vents out and put the soffit vents in. That way air will flow from eaves up and out the ridge vent.

Boburk · May 2014

Re: ISO input on a system

I noticed the estimate showed an SMA 7000 (and six micro inverters) on it instead of the 8000. I asked them about this change and was told the 7000 comes on at a lower threshold....allowing the system to come on sooner. So ...I asked for a price without those 6 panels and micro inverters ...it was $1k less.

BB. · May 2014

Re: ISO input on a system

In general, larger inverters have higher losses... But, the differences between a 7k and an 8k inverter should not be that different (i.e., 15% difference, not 50% difference).

Solar panels do not produce much power unless in direct sun. Once in direct sun, they produce a goodly amount of power and the minimum losses are not giong to be very large (GT inverters run around 95 to 98% efficient).

Saving ~25-50 watts on a 10,000 Watt array is not enough to worry about.

Do not get a piecemeal system.

However, if your roof space for the array is only large enough for a 7kW inverter, and the second 6 panel array is not on the save roof plane/orientation, then mixing it with the main array is usually not a good idea.

In that case, you are looking at "independent" GT inverters (whether two central inverters or multiple micro-inverters--you have to look at the details).

My concern about the big central inverter and a hand full of micro-inverters is the monitoring hardware (and sometimes charges for monitoring). You need the monitoring of micro inverters because there is no way to know if anything failed. And the the monitoring system for micro-inverters is not "cheap" (usually).

For the Enphase system, somewhere around:

Enphase Envoy - Energy Management Unit (EMU) $534.00

-Bill

Boburk · May 2014

Re: ISO input on a system

I get the feeling that the salesman I am talking to, though knowledgeable, does not know it all. I am betting that the smaller main inverter and six panels with micro inverters is because of the two different planes. At least that makes more sense.

Are there any brands of micro inverters that can be monitored without test equipment? He told me the brand, but I can't remember what it was...

Sean

BB. · May 2014

Re: ISO input on a system

I am sorry Sean,

Not really my area of knowledge--I am not in the solar business... But I would bet that the typical micro inverter uses power line communications and a network interface box to extract the data. Most are probably proprietary networking solutions at this point.

In general, there is not (from what little I know) a big difference between a central vs micro inverter installation. If you are going to need multiple "planes" for the array, I would seriously consider a micro inverter system.

There is another discussion, the issue of micro vs central inverters over time / reliability / having to go up on the roof to replace any failed modules.

One can argue that micro inverters could be less reliable/more difficult to Remove and Replace if there is a failure. However, we may not know for 10-20 years if micro inverters will last (hot roof top environment). However, central inverters probably have a 10 year + life...

I think you would probably be happy with either solution (with good quality vendors).

-Bill

SkiDoo55 · May 2014

Re: ISO input on a system

If they are mounted on two differs facing roof sections then they should be split. 6 Standard GT style panels will not have high enough voltage to bring most string inverter online and hold it. Most string inverters require around 195 + VDC to start.

Boburk · May 2014

Re: ISO input on a system

I have a second guy coming tomorrow to see what he says.

Sean

ISO input on a system

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