New Poster: Suggestions for 3kWH/Month Solar PV System

Re: New Poster: Suggestions for 3kWH/Month Solar PV System

Jedokahn,

Welcome to the forum--and I moved your post to its own thread so that you can discuss your installation without clutter of other conversations.

First, you are looking at a lot of power. Spending your money on conservation should be your first step. Insulation, double pane windows, CFL's, Energy Star Appliances, Most efficient A/C system you can justify, turning things off (unused computers, printers, entertainment centers, etc.), downsizing (use a laptop instead of a desktop computer when possible), etc... Many times, transferring loads like electric heat, hot water, cooking, to natural gas or propane is a big help.

Next, if you use a lot of hot water, look at solar thermal and/or a desuperheater hot water system (uses waste heat from A/C system to heat hot water). Perhaps, in your mild climate, a heat pump system would be more efficient than your current home heating system (if electric).

Next, sizing your system. We need the amount of electric power you will need (say 6x1,300+6x3,000=25,800kWhrs/year).

And, what kind of system it will be... Assuming Grid Tied, use a derating factor of 0.77 (solar panel watts*0.77=useful power) or 0.52 if off grid (batteries and extra inverter create more losses).

And use the PV Watts website to estimate how much power you will generate for your area. Using Austin Texas and 1kW of solar panels (nice round number):

"Station Identification"
"City:","Austin"
"State:","Texas"
"Lat (deg N):", 30.30
"Long (deg W):", 97.70
"Elev (m): ", 189
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 0.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 30.3"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.32, 99, 9.60
2, 4.96, 101, 9.80
3, 5.47, 122, 11.83
4, 5.52, 116, 11.25
5, 5.54, 118, 11.45
6, 5.93, 121, 11.74
7, 6.21, 129, 12.51
8, 6.22, 129, 12.51
9, 5.77, 119, 11.54
10, 5.65, 121, 11.74
11, 4.60, 98, 9.51
12, 3.96, 90, 8.73
"Year", 5.35, 1362, 132.11

And for off-grid (0.52 derating):

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.32, 65, 6.30
2, 4.96, 67, 6.50
3, 5.47, 81, 7.86
4, 5.52, 77, 7.47
5, 5.54, 78, 7.57
6, 5.93, 79, 7.66
7, 6.21, 85, 8.25
8, 6.22, 85, 8.25
9, 5.77, 78, 7.57
10, 5.65, 80, 7.76
11, 4.60, 65, 6.30
12, 3.96, 59, 5.72
"Year", 5.35, 900, 87.30

From the above, we see that a GT system will generate 1,362 kWhrs per year per 1,000 Watts of solar panels (estimated average over 20 years of data). And a Off Grid system will generate 900 kWhrs per year per 1,000 watts of solar panels.

And based on your current yearly power usage of 25,800 kWhrs per year:

• 25,800kWhr/yr * 1/1,362 kWhr per year per 1kW of panels = 18.9kW for GT System
• 25,800kWhr/yr * 1/900 kWhr per year per 1kW of panels = 28.7kW for Off-Grid System

For a turnkey GT Solar system, they cost (before rebates/tax credits) around $6,000 to $10,000 per kW of solar panels (installed, permits, etc.).

• 18.9 kW * $7,000 per kW of panels = $132,000 (aprox low end price)

For an off-grid system, you need more panels (because of more losses), extra hardware (battery charge controller, batteries), more labor to install (more hardware), and more maintenance costs (new batteries every 4-8-10 or so years). Pick a price of $15,000 per kW as a very rough price (-50% if you build it yourself, best pricing, etc.--or +50% if you contract the whole thing out and have other issues/expenses):

• 28.7 kW * $15,000 per kW of panels = $430,500 (very rough price)

Now, you should be able to get a 30% tax credit for the GT system from the federal government. Not sure if a "true" Off-Grid system is eligible. You can check www.dsireusa.org for current credits/rebates for your area.

There is a solar PV system that is a "Hybrid" of both the Grid Tied and Off-Grid system... Gives you the advantages of a Grid Tied system (using grid for Net Metering) and advantages of Off-Grid (emergency power when grid is down). You can build out a Hybrid system for a bit less than an Off Grid system (smaller battery bank for emergency power only, use grid/net metering for storage of energy across seasons, etc.). But, for Off Grid and Hybrid systems, you probably will need to add a generator if you are serious about emergency power. Solar does not work well in cloudy weather and batteries typically are sized to supply power for 3 days of bad weather.

To see a quick explanation of the three types of Solar PV system (GT, OG, and Hybrid)--take a look here.

For an Inverter/System that does a nice job of tying everything together, look at the Xantex XW system (4-6kW GT/OG/Hybrid inverter system).

Please feel free to ask questions--I threw a lot out there and it is a lot to take in from one post.

And, I would again suggest that you look at conservation and solar thermal/hot water first before you you look at solar PV systems. Generating electric power is not inexpensive. It is almost always cheaper to spend your money on conservation first. Very rough comparison of cost of electric power from various sources:

$0.08-$0.30 per kWhr for Utility Power
$0.10-$0.35 per kWhr for Grid Tied Solar with Net Metering
$0.35-$0.55 per kWhr for Hybrid Solar with Net Metering
$1.00-$2.00+ per kWhr for Off Grid Solar

-Bill

Re: New Poster: Suggestions for 3kWH/Month Solar PV System

You are very welcome... There are a lot of people here with good ideas and lots of experience.

jedokahn wrote: »

-Insulation, -recommendation ? I believe I have R13 in walls and R-30 in ceilings, is foam better?

If you can, more attic insulation would be better (from SG and others on the value of high R value insulation in attics who live in hot climates). R45-R60 range would be better. Also, see Stephen's link to home insulation discussion.

I will stay away from the foam/glass/blown newspaper arguments... I was a big believer in fiber glass... I mean, what could go wrong? I mean, it is just glass!

But, read about foam which seals against wind/air flow/moisture (all degrade fiber glass insulation)... And how blown (treated) newspaper may (or may not) be more fire resistant (fiber glass itself just melts, add plastic backing for fuel)... And New Paper may be more rodent resistant (fiber glass apparently makes OK bedding material).

I would be happy to hear more about the various insulation type recommendations.

Also as I intended on using a Hybrid system, I wanted to start with 4-5 Panels and continue to scale as they become cheaper and improved in technology.

Note, hybrid systems are expensive because of the initial battery costs, and replacements every once or twice a decade (and battery prices+electronics+wiring+labor are, typically, going upwards over time).

If you are looking at a large system (and I would suggest ~3kW as a minimum cost effective starting point)--adding a few panels over time is not a good way to go. The additional labor, high costs of small panel shipments/quantities (and applying for rebates/tax credits several times a year), probably need building permits/approvals each time you add new panels (should be a requirement for Net Metered/Utility Connected systems). And if you already have pre-installed the racks and the wiring for a 18kW system--the panel costs are not that much more ($3 per watt).

Just does not make sense to incrementally add small numbers of panels over time... 3+ kW at a time--maybe... But get your costs/issues all identified up front before using the incremental approach.

Solar panels are probably near their lowest costs at this time (and government subsidies are probably near their peak). Add to the fact that the current panels have 25 year warranties and 40+ year life--I am not sure I would delay on purely a cost basis at this time.

However, I am a big believer in not taking out loans for solar PV systems either... If you don't have most of the cash available now--I would wait until your savings supports the purchase (and you have other savings--typically 6-12+ months worth of cash for emergencies--note this is only my personal opinion). Solar PV is not a money making investment (at least at this time).

One question I did have was I have been researching Solar roofing and solar paint (which is not readily available yet).

If you are looking at the "NASA" designed solar paint (scroll down in this thread for a tiny bit about insulating paint) that adds RXX value to your walls just with a new paint job... I do not believe that the paint does anything for the average home. One poster here said they tried it at an industrial location and found near zero value.

...The question I pose with concerns to solar roofing is it as efficient as regular solar panels? I haven't found many spec data sheets on this and think it might still be an immature technology. Based on the 25,800kWh/yr estimate I don't think I have enough roof real estate to accommodate a 18kW array unless I use every inch available to me. Plus the estimated cost is roughly $7/W (which based on your estimate is about right $7,000/kW).

I believe this is the Uni-Solar Ovonic product you are looking at.

My 2 cents--Unless you have A) Home Owner Association problems that won't let you install standard solar panels and/or you have problems with vandal/rocks/panel thefts in your area--I would probably not bother using them (based on my limited understanding of product).

Generally, you would need more square footage/meterage per watt (vs standard glass covered crystalline solar panels--also check installed pricing)--as these panels are less efficient at collecting sunlight. And you are probably single/sole sourced for replacements down the road (if needed).

However, do your own research (and if anyone else comments here). I am not the expert here.

Lastly Tracker Systems, are they really 30% more efficient than fixed mounted systems?

Trackers made sense when solar panels were $10 per watt... Hardly when the panels are near $3 per watt.

Trackers are expensive and (usually, in my humble opinion) need lots of maintenance (failed actuators). If you are in a high wind area--they can be damaged.

Also, trackers need lots of land to work well (trackers should not shade each other in the mornings/evenings so they need to be spaced well apart). One nice thing is that trackers have good ventilation to keep panels cool. And cool panels generate more power than hot panels mounted near flush to a roof (5-6 inch minimum air gap behind roof mounted panels is ideal).

For a smaller system, they may make sense for some folks--otherwise, just add 30% more fixed panels and let it go.

If you wish, the PV Watts program does let you play with 1 and 2 axis trackers. Click on the help page for information on how more more "ground area" is required for fixed vs trackers is required.

-Bill