A Thorough Look at Solar Power

Today we have a guest article from someone who has spent 25 years in the solar power industry. This is going to be a fairly technical article, so get ready for some math. The prices involved may be more white collar than blue collar, for which the editor apologizes.

This article is an entrant in the 2nd Annual BCP Writing Contest.


Electric Power: Steps Toward Self Sufficiency
by Craig Wiles,  Renewable Energy Consultant


If you've ever thought "I want to be energy independent, but I don’t have the money to do it all at once," you'll need to answer a few questions.

Question 1: “How much energy do I need?”
The monthly utility bill we get right now has on it somewhere a number of Kilowatt Hours Used. These may well be expressed as KWH’s.

This is the amount of energy we use now, and what we would like to have available. We may be able to get by with less, but we don't, because we would be doing it now if we could Besides, our goal is to be able to live the way we live now.

Question 2: “What are the steps I should take to get to my goal?”

The easiest power backup is a generator, but it burns fossil fuel and you have to run it even if you want to power just one light bulb.

Adding an inverter/charger and a battery bank lets us charge the battery for four hours a day from the generator, and then run off batteries the other 20 hours of the day.

Every time we add a solar panel to the system we reduce generator run time.

Question 3: “How do I do this right the first time?"

The answer to this question will unfold as we detail each of these steps.

Step 1: Generator
This is what I call “The search of Goldilocks”as most people buy a generator that is too big, and then they end up burning more fuel than necessary because they aren't using all the power that generator provides.

Which Fuel? 

1. Propane is the best fuel for long term storage. A buried propane tank will always be my first choice. 
2. Diesel fuel is my second choice. With the right additives, diesel will last ten years. 
3. Gasoline is my last choice, although many people will start here because of the lower cost generator.

What else?

• Water-cooled engines tend to live longer than air-cooled ones, but the liquid-cooled models tend to be too big for the average homestead. 
• Electric start is a nice option because we can tie it to the renewable energy system to start automatically if the batteries get low. 
• The waveform, or how clean the output is, can be important if you are grid inter-tied and want to sell back to the grid.

Recommendation
My first place choice for best generator is the Honda EU7000.

Step 2: Batteries
Batteries are one area where it might be okay to plan on replacing them as we go along. Almost everyone kills a set of batteries as they learn about living with solar power; better to kill a cheap set and get your learning done with them, than to learn the same lessons from a very expensive set.

Battery Options

• T-105s, also called Golf Cart batteries ,are very good starter batteries with an expected life of 3-5 years. If you need more capacity you can add a second set of batteries, also known as a "string". Try and avoid more than two parallel strings; electricity is lazy and will take the path of least resistance (which is your best string) and the weaker strings will get neglected. If you have to have more than two strings, be sure and have some switches so that you can force charge any single string. T-105’s are six volt batteries. 
• L-16 is a battery size which is the same footprint as golf cart batteries but over twice as tall. This is the next step up in size and cost. These are also six volt batteries.
• L-16 - Two volt cells are another good step up. These will let you have a larger bank without having too many parallel strings. Although these are 2 volt batteries, they are really a conventional L-16 that has been paralleled internally. You really have three strings with these (2 volts times 3 parallels = 6 volts), which is the maximum number of strings you should have. Another down side to these is that you must still water each cell cap even though the plates are paralleled internally.
• Fork lift batteries are another step up in size, capacity and money. Now we are into taller cells which have a different routine of care than the shorter cells. You will need to charge them harder (they really like to boil) and will take more water as a result. Make sure you have enough power to charge your battery or it will sulfate faster, shortening its life.
• Top of the line are the big industrial cells like Hup Solar Ones, Surette and several others. These are also two volt cells in series, but are designed for off grid life. You can spend $20,000 on a set of these, but they can last 20 years.
• Sealed batteries are available, but they cost more and don’t live any longer, and so are not detailed in this discussion. If you are not going to be ACTIVELY involved with your system; get sealed batteries.
• Avoid used batteries!!!!! I can’t stress this enough. They were being gotten rid of for a reason, and it’s probably not the reason you were told. 

Recommendation

Start with a set of golf cart batteries and expect to replace them in three years with the best ones you can afford.

Step 3: Inverters
We have several dozen choices of utility inter-tie inverters, and almost as many choices in off-grid inverters. If we want the ability to sell electricity back to the power company (that's what "utility inter-tie" means) and the battery backup capability of the off-grid inverters -- and we do -- then we have just a few choices. The other thing we need with our inverter is a built in charger, which these have:

• First Choice for Sell back: Xantrex XW5548 (XW6848 for larger systems)
• First Choice for Off Grid: Magnum MS4448 PAE
• First Choice for small systems; (110V only) Outback VFX 3648 or GVFX3648

We need an inverter that will run our largest loads. These can all be “stacked” if we ever need to add more inverter power.

Step 4: Adding Solar Electric
Now that we have our generator, battery bank and inverters in place, we are freed from having to run the generator just to turn on a single light bulb. Running the generator from three to four hours per day gives us enough power to live off the batteries (through the inverters) for the rest of the day.

At this stage, every time we add another solar panel we will reduce generator run time. When considering solar panels we are looking for several things.

Price: Always price PV (photovoltaic) panels by the watt. Most “building block size” panels will be between 200 and 300 watts. We don’t worry much anymore about what voltage the panel is, because the Charge Controller will take the high voltage of the array and bring it down to battery voltage through a process utilizing MPPT (Maximum Power Point Tracking). Panels will be wired in series up to 150 volts or even more depending on the charge controller. Watch out for too many small panels, or you could spend more on interconnecting wires than necessary.

I usually try and include shipping in my final cost, i.e. “price per watt delivered on site.”

Reputation/Reliability/Warranty: There are, without exaggerating, hundreds of new solar manufacturing plants that have opened within the last few years. Dozens have gone out of business. Choosing a company that might be around in 25 years will be difficult (I can only name three still in business from 25 years ago.) Because PV panels are so reliable and trouble free, this is not as big a concern as it would be with some products. If it works for the first year, it should work for the rest of your life.

Efficiency: Solar panels are constructed in four different ways.

1. Mono Crystalline: An ingot of silicone is sliced into thin pieces to make solar cells. (these often appear black) Efficiency: The Best. 
2. Poly Crystalline: Leftover chips of silicone are compressed into a wafer and made into cells. (these often appear blue) Efficiency: Very good. 
3. Amorphous silicon or (thin film): Silicone is liquefied and sprayed on in layers. (these often have a reddish tint) Efficiency: Very Low. 
4. Ribbon string: Molten silicone is “drawn up” on two wires with surface tension forming a ribbon of silicone which can be sliced into cells. Efficiency: Very good.

Recommendation
Favorite charge controller: Outback FM80,


A word about system voltage
The national electric code has some voltage “breaks” that tend to have designers limited in what voltage is available. With a battery based system we have three usual choices: 12 volt, 24 volt, or 48 volt.

Higher is better. Unless there is a very good reason, always go with the higher voltage. Here is an example of why:

• An Outback FM 80 charge controller can handle, 12, 24 or 48 volts.
• Figuring on using 215 watt panels, we could fit 4 of them on one charge controller at 12 volts.
• At 24 volts we can fit nine 215 watt panels per charge controller;
• At 48 volts we can fit eighteen 215 watt panels per controller.
• At $750 per controller, this can make a bug difference in a large system.

How many panels?
At the beginning of this article we figured out how many Kilowatt hours per month we use from our electric bill. Take that number and divide it by 30; this will give you an idea of Kilowatt hours per day. That number is how many panels you are working toward to live like you do now.

We get between 4 and 5 hours of sun per day on an annual average (This will vary by where you live, but this is a general estimate) and your panels will likely be between 200 and 250 watts each so this is a pretty decent estimate:

250 watt panel times 4 hours of sun = 1 kilowatt hour.
200 watt panel times 5 hours of sun = 1 kilowatt hour.

Most likely you will need to add panels in strings of three.

Three 250 watt panels times $1 per watt = $750

This is the size “step” as you add more panels. There will also be racking and wire and a few other items as well, so figure $1000 “steps”. I don’t know of a more stable investment you could make at this time.

I already have grid-powered electricity. Are my steps the same? 
Because of some very nice legislation promoting “renewable energy” we may be able to take advantage of what is called “Net Metering” -- which means that the electric company will go back and forth with you at retail level till the end of the billing period. Check your state laws to ensure that this is an option for your location.

So while you're at work all day and the sun is shining, you can (in essence) run your meter backwards, and at night when you flip on all the lights you would run it forward. Every time you add another solar panel you reduce your electric bill until you are down to the monthly meter charge. With net metering we get to use the grid as if it were our battery at 100% efficiency rate (batteries are 80% at best).

Thanks to micro inverters we can grow a system like this in very incremental steps.

1. There will be a one-time installation of a breaker and a disconnect switch.
2. Each PV panel is $250. 
3. Each inverter costs $200.
4. Rack and mounts $100, labor $100. 

Our steps come out to be $650.

 Caveat: If the grid goes down, you go down. There are no batteries in this system.

However, there is one inverter, the Sunnyboy TL series, that provides one circuit of power when the grid is down and the sun is shining. It is becoming a very popular string inverter. We can add it to a battery-based system later on (AC Coupling) but there would be some redundancy of steps.

Expect a grid-tie system with no batteries to run about $3 per watt total cost.

How good an investment is solar electricity?

• A 250 watt solar panel costs $250.
• A 250 watt solar panel will average just over 1 Kilowatt hour per day. (4.3hr ave)
• At $.10 per KWH, this panel will generate $36.50 per year.
• $36.50 return on $250 equals a 15% return on investment. This does not factor in inverters and other pieces of equipment, just panels.

Best wishes in your quest for energy independence!