Solar roof system. Pros and cons of buy as I go? Is this ok?

C_Heath · April 2013

I'm looking at a 2 year window to have my rooftop system up. Maybe less. For instance, is like to do 20 panel (sharp 235w) and a battery bank. I don't have the funds to do it all and I don't want to finance. My question is, can I buy a piece here and there and not have to worry about incompatibility issues. I get little bonuses at work from time to time. Currently, I have $1100 to make a purchase and I'd like to pick up some panels. There are a few smokin deals on the ones I want ($175 each less ship) and Id like to stack them up in the corner of the basement until I get more funds, IE: batteries, rails, inverter etc. is there a drawback to this approach?

Thanks!!!

C_Heath · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

Sorry. Didn't give enough info. Ill be on grid, 2000 sq foot brick home. I'm using anywhere from 1000 min to 2000 max (winter) kwh. Just looking to have a backup plan on power outages. Though I'm not hardcore, I am a prepper and want to be ready if something happens but most importantly at age 40, I want to be financially ready to retire with very little expenses (like power bills) when I retire. I'm so new at this I'm still oblivious but I am learning fast. I live just walking distance from our community college and I found that they have a 2 year course on renewable energy. I went out behind the building and found an awesome panel setup. Ill post pics if I can.

BB. · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

It is really hard (and can be expensive) to slowly grow a solar powered system over time.

There are the issues of permits (if required in your area), and as you have seen, solar panel models/specifications/pricing varies wildly over time. And if you cannot find "compatible" inexpensive panels a year from now--You may be stuck getting a second charge controller or other solution.

Part of this depends on why are you building the system. If your place is already off-grid, you are left with burning lots of fuel for much of your power (starting with a small system).

If you are on grid, looking for emergency backup and/or eventually going off grid (for whatever reason), you might start this way:

Measure/estimate your loads
Do a paper design (or three) and see what makes sense now and in the future
Install a backup genset (sized to loads and to your ideal battery bank size)
Install a battery bank + Off Grid Inverter or Inverter/Charger (use grid/backup genset for now)
Install solar panels (either in bulk, or try your distributed approach)

Anyways--Lots of ways to address the problem and some have a bit more uncertainty in the future (mostly solar panel combinations, and questions about expanding battery bank capacity).

-Bill

BB. · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

1,000 to 2,000 kWH per month in winter--That is a pretty large system for Grid Tied, and getting close to huge for a full off grid system.

To give you some ideas (in my humble opinion). A 3.3 kWH per day (100 kWH per month) is about the smallest off grid system that will run a refrigerator full time plus lights, small well pump, washing machine, and laptop computer).

10 kWH per day system (300 kWH per month) will run a home pretty well if you have alternative fuels for cooking/heating/hot water.

A 33 kWH per day (1,000 kWH per month) system--That is pretty large and will not be cheap...

Just to give you an idea with a 3.3 kWH per day system assuming 4 hours of sun minimum (usually less in dead of winter):

Battery battery 1-3 days of storage, assume 2 days as a balanced design with 50% maximum discharge (for long life). That means 4x your daily power usage for a battery bank:

3,300 WH * 1/24 volt bank * 1/0.85 inverter eff * 2 days * 1/0.50 max discharge = 647 AH @ 24 volt bank

That is ~12x 6 volt @ 220 AH golf cart batteries in series/parallel connection.

Assuming 4 hours minimum of sun per day, a 3.3 kWH system would need:

3,300WH * 1/0.52 system eff * 1/4 hours noon time equivalent sun per day = 1,587 Watt array minimum

And a battery bank should be charged at 5-13% rate of charge:

647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "cost effective maximum"

So, you would be looking at, roughly a 1,587 watt to 3,168 watt array for a 3.3 kWH per day system on 4 hours of sun (or better) harvest.

Note that each of the break points (3.3/10/33 kWH per day) systems are about 3x larger than the previous step... So, you can start by multiplying out the above by 3x or 9x to see what a "rule of thumbs" system design would look like for larger power outputs.

Obviously, I would be suggesting a 48 volt battery bank for the larger systems. And you can certainly use larger batteries vs golf cart batteries for better wiring/battery bank life--Just trying to give you an idea of the physical sizes/costs for off grid power systems.

-Bill

C_Heath · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

BB. wrote: »

It is really hard (and can be expensive) to slowly grow a solar powered system over time.

There are the issues of permits (if required in your area), and as you have seen, solar panel models/specifications/pricing varies wildly over time. And if you cannot find "compatible" inexpensive panels a year from now--You may be stuck getting a second charge controller or other solution.

Part of this depends on why are you building the system. If your place is already off-grid, you are left with burning lots of fuel for much of your power (starting with a small system).

If you are on grid, looking for emergency backup and/or eventually going off grid (for whatever reason), you might start this way:
Measure/estimate your loads

Do a paper design (or three) and see what makes sense now and in the future

Install a backup genset (sized to loads and to your ideal battery bank size)

Install a battery bank + Off Grid Inverter or Inverter/Charger (use grid/backup genset for now)

Install solar panels (either in bulk, or try your distributed approach)

Anyways--Lots of ways to address the problem and some have a bit more uncertainty in the future (mostly solar panel combinations, and questions about expanding battery bank capacity).

-Bill

Thanks Bill, you have helped me a lot. In this thread as well as others.

Photowhit · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

Conservation is the start to much of the "prepper" scenarios, see how little you can live on...

A wood stove is carbon neutral, and will reduce your winter bills significantly. If allowed in your urban setting.

Grid tied systems offer the best bang for the buck in the current economy, depending where you are in the country they are even likely to be cost effective. If you want to 'grow' a grid tied system, I would suggest learning about the permitting required in your area and see if starting with the proper branch circuit and adding a few panels with micro inverters each year. In this way you can get started, perhaps give the community college a project, to help with your labor expenses, and not have a compatibility problem, though you may find you have somewhat mismatched panels. If your in the states, you could plan on 4 years to have your system complete, taking the 30% tax credit each year and using that money to help you expand your system.

The tax credit is scheduled to end in 2016, though it may be extended, in my opinion it has worked where other forms of solar incentives and backing have not, or ran in direct opposition to the greater demand the tax credit created. Backing more expensive technologies.

Off grid is least cost effective, unless you have a very unusual situation. If the SHTF you could plan to have an cheap PWM charge controller and inverter and a couple 6 volt golf cart batteries on a good charger to offer some lighting and a fan, radio for a nominal additional expense. If things get crazy you could attach a couple panels and have a back up in an emergency. Trying to have enough off grid system to run a large house would be very expensive.

On availability... Someone else, who is trying to expand their system, was asking about those panels and discovered they are sold out...Good deals will go fast! Panel sizing is often very close, I have 4 Ningbo, and 2 Shingarah(?) panels and even though they have different frame material, they are the same size and the only obvious difference is a 1/8th inch cross in the center of the Ningbo panels cells. Doubt you can get that close, but likely close to the same size...

Sparkletron · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

BB. wrote: »

If you are on grid, looking for emergency backup and/or eventually going off grid (for whatever reason), you might start this way:
Measure/estimate your loads

Do a paper design (or three) and see what makes sense now and in the future

Install a backup genset (sized to loads and to your ideal battery bank size)

Install a battery bank + Off Grid Inverter or Inverter/Charger (use grid/backup genset for now)

Install solar panels (either in bulk, or try your distributed approach)

I agree with this approach. Set up the battery bank first (charged from the grid or genset). Get the panels last--after you've lived with the bank for a while and have either adjusted it or accepted it as is. It also makes sense from an "incremental" perspective since the batteries can be used without the panels, but the panels aren't much use without the batteries.

BB. · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

I should add that Fed Tax credit(s) and other utility rebates have all sorts of rules. The Fed tax credit is going away in a couple years (who knows what will really happen with the rivers of red ink most of our governments are gushing) are typically not eligible until the entire solar system is turned on--So, my multi-step implementation will leave 30% on the table until the entire system has been installed turned on (installing 1 solar panel may allow the Fed credit on the system installed to date, although it would be hard to justify in an audit).

-Bill

C_Heath · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

tried to send you a pm bill. I think I may be too new to send one yet lol. anyhow, here tis.

thanks alot. finally a forum that hasnt blasted the new guy for being unknowing. Im in NC, have a larger brick home, on grid and staying that way. Id like to have backup and yet its more expensive, id like to have a battery bank. Now, Im still learning. I dont even know whats what much past the inverter when it comes to what Ill need inside the home. Also,

Id do have another question and sorry to bother but.......per your reply yesterday.

If you are on grid, looking for emergency backup and/or eventually going off grid (for whatever reason), you might start this way:
1.Measure/estimate your loads
2.Do a paper design (or three) and see what makes sense now and in the future
3.Install a backup genset (sized to loads and to your ideal battery bank size)what is a Genset? A generator?
4.Install a battery bank + Off Grid Inverter or Inverter/Charger (use grid/backup genset for now) how would I charge the batteries without panels?
5.Install solar panels (either in bulk, or try your distributed approach)

thanks and sorry!

my next question is how effective would panels be mounted towards the ease or even north east. My home runs kinda northeast/southwest. Mounting the panels on the front of the house (facing southwest) is totally out of the question

BB. · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

Our pleasure--We moderators and posters never tell a newbie to, for example, use search to find their answer... Many times, if you know enough to use the correct search terms, you already know enough to not be a newbie.

A Genset is Generator Set... Technically, AC "generators" are really AC alternators. A generator is really a DC device (remember the old cars that have a generator with brushes and a voltage regulator box). But, over the years, generator and genset have become the generic term for any large device that creates electrical energy (there are even ads out there now for Solar Generators--almost aways run away from those companies--they are over priced and will not perform to a customer's expectations).

Plus, these days, AC vs DC systems, and the electronics have blurred the distinctions (i.e., cars today have alternators, but they contain internal rectifiers and voltage regulators--functioning like a DC generator).

How to charge without solar panels--It depends on your needs. You said emergency backup power. If you have a "full sized" battery bank with 2 days of storage and 50% maximum discharge (i.e., your battery is 4x larger than your daily loads), you would have 2 days of blackout coverage without needing a genset. And if your outage goes longer, you would just run the generator 4-6 hours per day until the power is restored. And use the grid power to recharge your battery bank (a battery bank takes around 0.5 to 2% of its capacity as "float current" so there is a cost for a large off grid/backup battery bank (and you have to replace the batteries every ~5-15+ years--depending).

Note that generators are most efficient in the 50% to 100% of rated output... So instead of running a generator 24 hours per day (many times at 1/4 load or less), you use the battery bank for low power times and run the generator >50% load to recharge the bank during the day (this is being done in Africa now--"hybrid" power systems. Batteries for "low power times", and generator for high power times (evening when people want to cook/have lights/TVs/Computers and recharge the battery bank). Such a system can use 1/2 the fuel or less.

PV Watts will allow you to "test" your array settings. Use 0.52 derating for an off grid system. Just plug in 1 kWatt array (or larger) and see what pops out (kWH per month by month is its default output).

Using PV Watts for Greensboro NC with a 2.4 kW solar array, using 0.52 system derating (off grid) and one facing south (180 degrees true) and one facing east (90 degrees true):

"Station Identification"
"City:","Greensboro"
"State:","North_Carolina"
"Lat (deg N):", 36.08
"Long (deg W):", 79.95
"Elev (m): ", 270
"PV System Specifications"
"DC Rating:"," 2.4 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 1.2 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 36.1"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.97, 153, 13.01
2, 4.52, 153, 13.01
3, 5.44, 198, 16.83
4, 5.67, 192, 16.32
5, 5.68, 197, 16.75
6, 5.84, 188, 15.98
7, 5.59, 185, 15.72
8, 5.61, 187, 15.89
9, 5.31, 174, 14.79
10, 5.04, 178, 15.13
11, 4.13, 145, 12.33
12, 3.45, 128, 10.88
"Year", 5.02, 2077, 176.55

And East:

"Station Identification"
"City:","Greensboro"
"State:","North_Carolina"
"Lat (deg N):", 36.08
"Long (deg W):", 79.95
"Elev (m): ", 270
"PV System Specifications"
"DC Rating:"," 2.4 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 1.2 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 36.1"
"Array Azimuth:"," 90.0"

"Energy Specifications"
"Cost of Electricity:"," 8.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 2.45, 87, 7.40
2, 3.02, 98, 8.33
3, 4.12, 147, 12.50
4, 4.86, 162, 13.77
5, 5.44, 187, 15.89
6, 5.86, 189, 16.07
7, 5.49, 181, 15.38
8, 4.85, 159, 13.52
9, 4.20, 135, 11.47
10, 3.37, 114, 9.69
11, 2.49, 81, 6.88
12, 1.90, 62, 5.27
"Year", 4.01, 1603, 136.25

That is why we do the paper design first--To see how everything plays together before laying out money.

Such a setup would cost you about 1/2 your winter month production...

Solar panels need lots of sun, if you do not have lots of unobstructed sun, you already have two to three strikes against you. We need to talk more about this.

-Bill

Photowhit · April 2013

Re: Solar roof system. Pros and cons of buy as I go? Is this ok?

BB. wrote: »

...are typically not eligible until the entire solar system is turned on--So, my multi-step implementation will leave 30% on the table until the entire system has been installed turned on ...

In my research I found that adding to an existing system is perfectly acceptable, I've done so 5 of the last 6 years, hasn't been flagged yet.

Yes, the system must be installed to code, and you can only take the credit the year the equipment is put into service, so the panels I purchased in 2011, were credited last year when I put them in service. This would be a good thing for the community college to answer for you!

It has been discussed here that if you have a generator and batteries for a backup and add solar in a later year, the batteries can not be considered part of your solar credit.

Solar roof system. Pros and cons of buy as I go? Is this ok?

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