How to “solar” – Part II: Doing The Math

Hi, solar energy fans. Thanks to everyone who read my Location, Location, Location blog post.

Now that you’ve had a chance to consider whether you have a good place to put solar panels, I wanted to begin to answer the questions all of you have on your minds: How much money can I save?

I’m going to express my “savings” answer like a banker or an investment advisor: as an annualized rate of return on investment (ROI). I do this not just because I’m an accountant, but because going solar is a long-term investment. Defining money savings in terms of ROI lets you compare your solar savings apples-to-apples against all other long-term investment options. It also helps you determine how big a system would be right for you. Furthermore, there are a number of ways to finance your solar electric project, and your ROI number will help you distinguish the good from the bad.

ROI and interest rate are not the same thing. For instance, at the time of my writing, you could buy a 30-year US government bond and receive a 4.69% interest rate. So, for every $1000 invested, you’d get $46.90 in interest per year. If you’re in the 15% Federal Tax bracket and your state income tax rate is 3%, your governments will take away about $8.45, leaving you $38.45 and an ROI of 3.845%.

Return On Investment: A Sample Solar Electric System

Suppose you were able to buy the following solar electric system under the following terms (the system we purchase was slightly larger and at a lower overall price, but at a time when local utility incentives were about 10% higher than they are now):

· Rated capacity: 6000 watts DC

· Out of pocket cost after all tax breaks and utility incentives: $12000

· Warranty on solar panels: 25 years

While your solar panels usually will have a 25 year warranty (some have just 20 years), a key component will NOT. The inverter (the device that converts DC energy from the solar panels into AC electricity you can use in your home or, if/when you produce more than you use, put to the grid) usually will carry a 10-year or 15-year warranty. Out of the desire to be conservative, I’m going to assume you’ll need to replace this during the 13^th year of your solar array for $5000 (in year 2023 dollars).

Also, one negative feature of solar panels is that each year they’re less-effective than the last. The solar panels’ 20/25-year warranty usually provides for the panel to be producing at least 80% of the power on the last day of the warranty as it did on the day it was installed.

The ROI on this system depends upon 3 other things:

1. the current all-inclusive price of electricity during daylight hours,

2. your “noon-equivalent cloud-free sunshine” (also known as your Solar Resource)

3. the expected rate of electricity inflation.

In order to simplify things, my calculations are going to assume a 3.5% electricity inflation rate over the next 25 years. Relative to US electricity inflation since the 1980s, this inflation figure is moderately conservative. Actual inflation has varied from state to state; Arizona’s has been lower & the northeast US has been higher (as they say on CNBC: past performance is not an indicator of future results).

So that leaves two variables, electricity prices and Solar Resource.

In my bullet point above, I expressed the price variable as “all-inclusive daytime” price of electricity. Electricity is often subject to sales tax. In Phoenix, state and city sales taxes (plus fees that act like sales taxes) apply, totaling more than 12.5%. Under this scheme, daytime electricity nominally priced at about 14.5 cents per kWh actually costs me about 16.3 cents per kWh at the bottom line of my electric bill.

In my previous blog post, I gave you a link to a map that would help you determine your Solar Resource. Below is a listing of select cities and their approximate Solar Resource values (+/- 0.1).

City	Solar Resource		City	Solar Resource
Milwaukee WI	4.2		Dallas TX	5.2
Cleveland OH			Miami FL
Boston MA			San Francisco CA
Washington DC	4.7		Salt Lake City UT
Louisville KY			Boise ID
Chicago IL			Las Vegas NV	6.2
Minneapolis MN			Phoenix AZ
			El Paso TX
			Palm Springs CA

Below is a chart showing the estimated 25-year ROI at various Solar Resource points (corresponding to the cities above) and various electricity rates that might be in effect at the installation date.

Solar Resource	Price of Daytime Electricity (US cents per kWh)
(kWh/m2/avg. day)	8	10	12	14	16
4.2			5.8%	7.9%	9.8%
4.7			7.3%	9.5%	11.6%
5.2		6.2%	8.7%	11.1%	13.4%
6.2	5.6%	8.6%	11.4%	14.2%	16.9%

The table above has some conservative assumptions built into it. Your actual ROI would go up if:

1. The out-of-pocket cost of the system was lower either due to

a. Lower pre-incentive prices OR

b. More-generous tax or utility incentives.

2. The solar panels last longer than the warranty.

3. The solar panels perform better over time than indicated by the warranty.

4. The initial inverter lasts significantly longer than warranty.

5. Electricity inflation is higher than estimated.

Implications of Solar Power ROI

Investment Implications

First, let’s compare solar energy to the 30-year bond example I gave earlier.

· Where sunshine, electricity prices, and financial incentives are ample, solar energy’s ROI can be substantially higher than the ROI for government bonds.

· You pay taxes on bond interest, but not on your lower electric bill.

· The investment risk is comparable. Since the USA has existed, (a) the government has paid its debts every day and (b) the sun has risen in the east every day. Reputable manufacturers generally put out products to a quality level that vastly exceeds their warranties, and in the rare cases when the products fail, they make good on their warranty claims.

The fact that solar energy often pays a higher return than government bonds isn’t reason enough to go forward unless you have absolutely no debt and want a relatively risk-free place to put your money. Most of us have debt and many of us couldn’t fund a solar energy project without some debt. The values in the ROI table will help us determine whether solar power makes enough sense to go into debt (or to stay in debt).

If you plan to get a home equity loan, it makes sense if the term of the loan is less than or equal to the warranty life of your solar panels AND in the following scenarios:

1. Your interest rate is lower than your Solar ROI AND

a. The loan is a fixed rate loan OR a variable rate loan capped at or under your Solar ROI.

b. Every dollar of interest is tax deductible (consult your tax advisor)

2. Your interest rate is more than 3% lower than your Solar ROI AND either

a. The loan is a fixed rate loan

b. The loan is a variable rate loan capped at or under 3% less than your Solar ROI.

As for credit cards… in a word: DON’T. Your ROI is almost never as big as your credit card interest rate. The only exception to my credit card rule: it would be OK to use a credit card a bridge to a tax refund. And then, I only condone using a credit card for the portion of the cost you will recover within the next 15 months from credits on your federal or state tax returns (consult your tax advisor for more information).

In fact, if you have more than $2500 in outstanding credit card debt, don’t buy a solar power system now. Instead, pay your credit card debt down THEN go solar. That goes for any other debt over $2500 where the interest rate is higher than the ROI.

“Buy or Lease” Implications

So far, my post has focused on the purchase of a solar electric system. There are companies that will lease systems to you. Most leasing companies will charge you little or no up-front cost (especially if your credit is good). You won’t get any tax credits or utility assistance (because it wouldn’t be YOUR system).

The reasons I chose a purchase over a lease when I opted for solar power were

· the initial monthly lease payment quoted me were as high as 90% of the cost of the electricity the system would replace (where’s the ROI?)

· the lease also included an “escalator” clause, which would have increased my payment 5% or 6% per year (remember, in Arizona, electricity inflation has been about 2.5% in the past 20+ years).

· I would need to concern myself with replacing the leased system (or renewing the lease) in 15 years

· a purchased system has the possible upside of lasting much longer than the warranty and I wanted to capture that upside.

Sizing Implications

It isn’t worth it to build a system that will produce substantially more electricity than you use long-term.

Right-sizing one’s solar array is a topic unto itself, so I’ll reserve that for my next post.

Thanks for sticking with me.

 

You can read How to “solar” – Part I here.

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Making Real Bavarian Pretzels (Laugen Brezen)

To a Bavarian like me who lives a Brezen-less life outside of Bavaria, this is a sight for sore eyes.

Actually, I’m quite lucky that I took this photo. It’s a little fuzzy, and I wanted to take another, but the phone rang. When I came back from my phone call there were no Pretzels left to photograph!! My 5-year-old ate them all!! And yes, I do feed the boy LOL

He did leave us the Laugensemmeln (lye rolls) and the Domspatzen (little birds made from this dough) – but all the Pretzels were gone. Except for the one I snagged fresh out of the oven for myself! YUM!!

His father then finished off the rest LOL

Both my men, but especially the boy just love, love, love fresh bread of any kind and the Bavarian Brezen rank right up there with his most favorite. He had been camping out in front of the oven when he realized what I was baking!

Anyway, here is how I made them.

First let me say that the dough itself is nothing terribly special. The huge difference to other recipes and what makes this as delectable as it is, is the lye bath. And it is the lye bath that will never compare  Bavarian Brezen to other soft pretzels. Even the hot baking soda bath methods used in American recipes don’t quite compare. They make nice Pretzels, don’t get me wrong, but they are NOT like these! This is the real deal!

It’s not just the difference in color. The lye bath imparts a subtle, very thin crunch and a very particular cracking of the crust, as well as a subtle but very distinctive taste. As well as a slight sheen.

 

So, first of all, get yourself some Food Grade Sodium Hydroxide Lye. I got this one – it works well and it will last me a good long time!

Now let’s get down to it!

This recipe makes about 8 Pretzels.

For the dough:

1 cup whole milk 

1 tbsp sugar 

1/4 oz granulated yeast 

2 tsp salt 

1 tbsp shortening (I use Spectrum Organic Shortening)  

2.5 - 3 cups flour (I use King Arthur Bread Flour) 

Pretzel or kosher salt for sprinkling

For the lye bath:

2 quarts of water

2 tbsp  Food Grade Sodium Hydroxide Lye 

To prepare it, get a sealable container, a thick tupperware type bowl like mine for example, and fill it with 1/2 a gallon of cold water. Do NOT use a metal bowl! Glass is ok though!  You need it to be wider than it’s deep so you can easily and quickly dip the dough.

Wearing latex gloves and protective eye gear, add the pellets, stirring carefully with a metal spoon until the pellets are dissolved.



They have a tendency to form this crystalized structure at the bottom. Break it up and keep stirring until it is all dissolved.



Careful, the contents can get HOT!
Seal the container until you are ready to use it. 



BEWARE: 

This stuff is not only poisonous, it is very caustic. 

So, please be extra careful and take precautions! PLEASE keep it far away from children!  Flush any unintentional contact with plenty of water.

You soap makers and olive picklers out there know the drill, but it can never be said enough – be careful around this stuff!

Now let’s get started:

1.  Warm the milk a little (30-40 seconds in the microwave usually does the job) and dissolve the sugar and yeast into it. Allow it to sit for a few minutes and see if bubbles form. It confirms that your yeast is active.

2. Add the liquids to a mixer with a kneading hook if you have one.  Or add to a big bowl with a wooden spoon and give it some elbow grease.

Add salt, shortening and 2 cups of flour. Start the mixer and let it all knead together. Add enough flour to form a dough that doesn’t stick to the sides anymore and is nice, uniform and elastic. It can take a total of anywhere from 2.5  cups to 3 cups.

3. In the microwave, boil a small bowl of water. Or if you prefer, boil some water on the stove top, place a lid on your boiling pot until the lid is nice and hot and wet on the underside. Remove the mixer bowl from the mix and place the hot, wet lid on top. Let the dough rest for a few minutes.

Or, back to the microwave method. Quickly open the microwave, place the bowl of dough in and shut the door. Again, let the dough rest for a few minutes in the warm, moist environment. It relaxes the gluten and will make forming the pretzels much easier.

4. Remove the dough, knead through one more time by hand. The dough shouldn’t stick to your counter top. Divide into 8 equal pieces.

5. Roll a long snake, thicker in the middle than on the ends. This needs to be MUCH longer though before you form the pretzel shape.

I forgot to take a photo of the shape and length of dough , so here’s a photo from a bakery, courtesy of google images It gives you an idea where you need to be :



Then form a Pretzel shape.

If you’d like to make some little lye birds, here is how.

Roll a snake, like before, even though this time you’re keeping the thick part more towards the front. Like so:

This one doesn’t actually have to be very long. Just long enough so you can make a knot in the dough and have a little bit left for the head and the tail.
Then you make an actual knot in the dough.



Now pinch the head part into a beak and make a cut in the tail and separate it a little.

6. Let the Pretzels rise for about 1/2 hr in a warm, moist place. I usually turn on the oven to it’s lowest setting, turn it off and place a bowl of water in there with the Pretzels.

7. If you haven’t made your lye bath yet, do it now!

8. When the half hour is up, remove the Pretzels from the oven and preheat to 400 F.

9. Make sure your baking sheets are either lined with silicon or baking parchment. Once the dough is dipped, it wants to stick to anything and everything! Put on your safety gear, especially the gloves!

10. Dip your risen dough shapes quickly but carefully into the lye bath. I find that it works best to never quite let go of them. Dip them top down first, let them be for about 2 seconds, turn them around briefly and scoop them out, placing them immediately on the baking tray. These are going to be REALLY fragile, so  be gentle.

11. Sprinkle them all with pretzel salt. 

12. Bake for 12 – 15 minutes or until you get that deep brown color.

Remove  from oven, place on cooling rack, wait as long as you possibly can and until you basically you don’t burn your mouth anymore eating them.

  Enjoy with fresh,cold butter! Yum!
Let the feeding commence:


That’s Max on #4 … he slowed down some I guess

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Easiest, creamiest, low-cal rice pudding ever!

Just put it in your crock pot and forget about it until the last 10 min or so.

Ingredients:
32 fl oz fat free half and half (or fat free milk, even though it doesn’t get quite as creamy)
32 fl oz fat free or 1% milk
3/4 cup sugar or sugar substitute of choice ( I use truvia)
1 pinch of salt
1 tsp vanilla extract, or the scrapings of a vanilla bean,  or  Vanilla Bean Paste
1 cup white long-grain rice (I prefer brown these days, which works well too!)
2 eggs, set out at room temp when cooking begins, then  lightly beaten just before use

Preparation:
Add half and half, milk, sugar, salt, vanilla and rice to your crock pot.
Set to cook on high for about 3  hrs. You might want to go and stir it once or twice during that cooking time. If your crock pot runs a little hot, reduce the heat to low after 2 hrs.

Once your cooking time is done, temper your eggs. This means that you add about 1/4 of a cup of your hot rice pudding to the beaten eggs, and mix thoroughly. Then you add another 1/4 c, mix, then another. This ensures that the eggs are being cooked slowly and you won’t get scrambled eggs when you add them to your rice pudding.

Now add the tempered egg mix to your pot of rice pudding and stir well for about 2-3 minutes, to distribute and cook the eggs evenly. Give it a few minutes more in the pot, then check for consistency. Your rice pudding will thicken up quite a bit more with the eggs.

This rice pudding doesn’t thicken significantly in the refrigerator. What you see in thickness in the crock pot is where it will stay, so make sure you cook it long enough to the thickness you desire!

And that’s it! 

If you like your rice pudding hot, go for it. If not, transfer the pudding into a covered container/dish and let it cool, making sure that the lid has at least a corner open for steam to escape. You could also cover the dish with plastic wrap, folding over the corners. Once cooled down some, cover fully and refrigerate!

Serve as is or with a sprinkle of cinnamon, or some fresh fruit, or fruit compote, or jam, or whatever your heart desires!

Note: When using fat free milk and half & half, no calorie sugar substitute, a 3/4 cup serving of this rice pudding is around 100 calories!

This makes about 15 servings or so.

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Happy Valentine’s Day!

Happy Valentine’s Day everyone! I hope you’re having a great and loving day with all your big and little loves!

This year is the first year that I actually “got” my children something for Valentine’s day!

Usually I just do cards and little love notes all over the place, heart shaped sandwiches and some love/heart type of dessert.

But this year I wanted to do one of those Hallmark Recordable Books for each of them. I just love the idea that they can hear me read to them even when I’m not there, or when they wake up at night or when they need a bit of extra comfort, or or or

And even though Max can read perfectly fine for himself, it’s still different when Mommy or Mommy’s voice does it!

So I got them a book each. “Guess how much I love you” for Anna and “All the ways I love you” for Max.

 

 

They were rather pricey and I was kind of shocked, but I had my heart set on it, so I went for it anyway.

The recording went fine, even though I find that the volume is a little high and you can’t adjust it. Even speaking quietly, produces a pretty loud end result. But ok, it’s not like my kids mind loud things It’s probably just a little loud by Mommy’s standards.

 

Anyway, so this morning they got their books … and they absolutely LOVED them. Well they loved the idea once they got to a page that would actually play it back to them.

 

Seriously guys, even though every single page played back to me perfectly well when I was recording the book, it just wouldn’t do it once the kids opened them.

I opened it for them, turned the pages this way and that way etc … Max thought that maybe one had to push on the page to make it work, Anna kept on pressing the buttons (disabled by the lock position) etc and hardly anything would work. So I thought it was the batteries. Changed all 6 batteries – no change!

 

LONG story short … I figured out that the book works on light sensors. And apparently it needs a fair bit of light to figure out that it’s supposed to play something. A dimly lit room at 6 AM isn’t going to do it! At least not unless you sit right beside that bedside lamp and hold the book half under it.

 

I was recording them during the daytime – in front of a window, ergo, bright light … instant great playback. *sigh*

 

So, dear Hallmark, don’t you think it would be helpful if that was stated somewhere? It never even occurred to me that light sensors would be involved!

It does somewhat defeat the purpose for us, because the last thing I want the children to do in the middle of the night, is to get up, turn on every light in the room, so they can hear mommy’s voice read them a story to go back to sleep. Yeah, that’s going to work really well!

The kids love it, so it’s not an entire waste of money, but I feel like I got duped somehow, especially for the price! It’s not like they need a mechanical device to have a story read during the day time while everyone is awake!

I guess it may be different when an absent parent or grandparent reads the book, then it doesn’t matter so much if it’s day or night, but for my intended purpose … not so much!

I don’t entirely remember the commercials for these books, but don’t they show kids at bedtime too? I would hazard a guess that the chances of both of our books, from two different stores, being defective are pretty slim!

 

I still love the idea of those books though … not so much the execution in our case!

Anyway, I just thought I’d let you know of  our experiences there!

 

Now I better get back to the kitchen! I’m making greek Moussaka for dinner …  the real from-scratch kind that is totally to-die for, even though a little work intensive! And then I think I’ll make some Valentine’s day brownies as a treat for dessert!

Have a great day everyone!

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How to “solar!” - Part 1

So, as many of you are aware, we recently went “solar.” I talked about it a little in this post. I don’t think we showed you the finished result up on the roof though! So here it is.

Prior to the installation, but after our addition and extended roof line:

And here we are after the panels went up:

{Please ignore the dead plants … that’s what several nights of  hard frosts in the dessert do to new-ish landscaping!}

  

I had visions of ugly huge panels, sticking out like a sore thumb! To be honest I was quite surprised how little we notice them. In fact, they don’t seem to “stick” out at all!

Of course it helped to have the roof built pretty much to specification angle and size wise, so no “scaffolding” was necessary, but more about that later. Suffice it to say that it sure helps the aesthetics that they are as flat to the roof as possible!

We are two months into it now and whenever my husband or I randomly post how much we generated this month/week/day and what that means for our electricity bill, we have an onslaught of questions in our inboxes from folks interested in this.

Since the majority of the research and the process was done by Ian, my husband, I finally twisted his arm enough to write a blog post about our process, what steps we had to take when, what the important things to watch out for are, where the pitfalls were and how we ended up where we are now.

Where are you now, you ask?

In the last 30 days we generated 921 kwh of solar power. Bear in mind that this is winter and the days are shorter and often overcast, even here in Phoenix!

Our latest electric bill was $32 ($1.23/day) plus credits for ~$35 future electrical use. So essentially the electric company is at this point paying US!

Same electric bill last year: $147 ($4.35/day) – and it was warmer too last year which means we used less electricity then as the heating barely had to kick in, but this year we had several hard frosts, which means that the heating did come on a fair bit!

Not too shabby, right?

Well, without further ado … here is Ian with the details!

Hi everyone!

I'm amazed… amazed that a repost of my 3 line Facebook post would command so much interest and attention. 

Perhaps I shouldn’t be amazed. I suppose if I knew very little about solar power and if an acquaintance was saving serious money with it, I’d want to know how he did it too.

At any rate, I’m flattered and humbled by your interest.

I’d like to show my thanks for your interest by embarking on a series of blog posts about my experience with solar power and other home energy topics.

Starting a series of blog posts about home energy with the topic of solar electricity is sort of like how George Lucas must have felt when he began producing the Star Wars movie series… the first film in the theaters was the fourth story in his saga.

Installing solar panels was only my most recent home energy project. I can’t promise you my words will be nearly as exciting as seeing Luke Skywalker blow up the Death Star, but maybe they’ll help you blow a hole in your electric bills.

Before I proceed, let me first warn you that I am from the United States. My terminology, units of measure and cultural references likely will be USA-centric. I hope people in other countries will find some of the concepts useful too.

Let me start my blog post in earnest with the 3 most important planning considerations for a cost-effective solar electric system.

They are:  Location, Location, Location

I say this because there are 3 elements of location that play a huge role in the determining the costs and benefits of a solar electric system, also known as a photovoltaic system.

The most-important location element is geography. The dot on Google Earth (or for middle-aged guys like me, the dot on “the map”) that represents your house is significant for several reasons.

• It indicates how much sun you get. Sunlight is your fuel source in this equation. To see how much sunlight would hit your solar panels, view this map at the National Renewable Energy Laboratories (NREL) solar map site.  
  The units on the map are best understood as the average daily hours of “noon-equivalent cloud-free sunshine” received in a location. Most of the continental USA gets between 4 hours (olive green) and 6. 5 hours (reddish-brown). 
  
  
• It indicates what state you live in. The Federal Government offers a 30% tax credit to most taxpayers who install a solar electric system. This credit, unto itself, is not yet beneficial enough to make solar power economical to most homeowners. Some states offer a tax credit in addition to the federal tax credit. Some states also waive their Sales Tax on purchases of renewable energy systems. 
  
  
• It also indicates (roughly) how much you pay for electricity and to whom. If your electricity is relatively expensive, you’ll get payback sooner. Also, individual utilities (typically under pressure from State & Federal regulators) also provide financial incentives to install solar power systems. In my experience, my electric utility’s contribution to the construction of my system was larger than my Federal Tax Credit. The Database of State Incentives for Renewables & Efficiency (DSIRE) is a good resource for indicating State-sponsored and utility-sponsored programs, as well as links to the relevant state agencies and the utilities’ renewable-energy program websites. 
  
  
• Your location also indicates your place in the solar-power supply-and-demand scheme. Locations where solar installations are rare might suffer from a relative scarcity of contractors qualified to install photovoltaic systems (a licensed contractor must install your solar system in order to ensure you’re getting the same quality of electricity as you would from your electric utility {the grid} AND in order that you qualify for all tax credits and utility incentives). 
  
  
  Also, you might be stuck far from a facility that makes solar panels. The manufacturers will charge higher shipping costs to your contractor, who WILL pass along the shipping cost to you. 
  
  
• No one geographic consideration trumps the others. For instance, if you looked at the NREL map alone, there doesn’t appear to be much cause for a photovoltaic system in Connecticut, but electricity rates in Connecticut are among the highest in the USA, and according to the DSIRE site, the state-sponsored incentives are decent. So, take heart; it still might be worthwhile to put the sun to work for you!

The second location consideration is a suitable place on your property for the solar panels. The ideal place for a photovoltaic system is your own home’s roof IF

(a) part of the roof faces south or nearly south 

(b) the slope of that roof is about equal to or a bit less than your location’s latitude (for Phoenix: 20-35 degrees is best; 35-50 degrees for New York City).

Building an additional structure specifically for your solar panels probably isn’t worthwhile. You’ll lose the use of the land underneath the structure. You’ll need to build the structure strong enough to withstand the same wind, rain, snow and earthquakes for which the roof on your main house already has been built. Most importantly, it adds to the total cost of the system… and you cannot get a tax credit or a utility subsidy for building a structure to support your solar panels.

Stationary solar panels will capture sunlight the best when facing south and when tilted at your latitude’s angle. Panels that face due east or due west will generate 20-25% less energy than if they face south. A tilt of +/- 15 degrees from your latitude costs you 3-6% in power output. However, there are a few strategic reasons you might intentionally stray from the highest absolute power output.

1.) Time of use electrical pricing.

If you pay substantially more for electricity in the afternoon than in the morning, southwest- or west-facing panels are much more favorable than east-facing panels… and may prove a bigger cost-saver than south-facing panels.

2.) Seasonal differences in electrical usage or price.

If you use a lot more electricity in the summer than in the winter and/or the price of electricity is higher in the summer than the winter (a la Phoenix AZ), panels with a tilt of 10-to-15 degrees less than latitude {tilting toward the summer sun} is financially favorable to an “at latitude” tilt.

There are mounting systems that let your solar panels track the sun, but they add at least 50% to the cost of the system and only allow you to collect, at most, 40% more power. Also, you can’t attach them to the roof of your house (ground mount only) and sun-tracking systems, because of their moving parts, are more expensive to maintain than fixed systems.

I’ll describe the cost structure of a solar electric system in a later post, but for now, I’ll say there are fixed costs (like the building permit) and costs that vary according to the size of the system (like the solar panels).

Because of the fixed costs of the system, it is almost never worth building a rooftop system unless you have at least 300 square feet (27 m²) of usable roof space... and I don’t think you’ll get attractive returns on a system of less than 400 sq. ft. (36 m²).

What constitutes usable roof space?

That brings me to my third location consideration: where are your sources and potential sources of shade?

Shade is a killer for solar panels, partially because of the way they’re engineered. A solar panel is made up of 30+ individual cells. Due to the way they’re wired together, if any one of the individual cells is in full shade, the productivity of the whole panel goes to zero. If half of a cell is in full shade, and the rest of the panel is in full sun, the panel will produce only half of its potential energy (thus half of its potential payback).

Not all shade is equal. Full shade or hard shade is cast by solid, opaque objects, like your neighbor’s house, block wall, or any protrusion of earth (embankment, hill, cliff). The hardness of their shadows does not vary with the distance of the object. Avoid hard shade at all costs. Soft shade is cast by things like tree trunks and power poles, and less so by tree branches, wires and flags. The hardness of these objects’ shadows varies with their distance. Also, branches of deciduous trees cast harder shadows than branches of conifers.

That said, any part of your roof that’s in hard shade when it’s 2 hours after sunrise or 2 hours before sunset on Christmas should not be considered usable. Following this rule would give a system a minimum of 6 hours of potential sun exposure in Phoenix (or 5 hours on Long Island, NY) on even the shortest day of the year.

As for soft shade, it’s a little harder to generalize, but I’d avoid any area where there is a source of soft shade (excluding power lines or other wires) less than 15 feet (4.5m) away from your prospective panel space. If it’s especially tall shade or dense shade, you’ll need to put even more distance between it and your panels.

Also consider potential shade from the neighbor to the south. Does your neighbor plan to plant an oak tree or build a second story? If you live next to commercial property (especially vacant commercial property) or land that sits on fuel or mineral wealth, what could be built there and how high?

Particularly in the wetter parts of the country, some homeowners will be presented with the conflict of choosing between their 100 year old Oak Tree and their ideal solar site. If that old Oak has sentimental value for you, it will be a very tough decision no doubt. 

However, if your only obstacle is the thought of "I don't want to reduce my carbon footprint with solar panels only to raise it by chopping down some trees," consider this: you can donate $200 to the Arbor Day foundation for them to protect more than an acre (50000 sq. ft. or 4650 m2) of tropical rainforest.

That'll do more for the planet's carbon profile than any dozen trees in the temperate zone... and a cost-effective solar electric system would pay you back that $200 and then some.

To be continued …

Part II - Doing The Math

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