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Let’s go camping with solar

March 17, 2010

Let us consider a possible scenario. You want to go camping and want to use solar power to charge a 12V battery connected to a 120VAC inverter to power your stuff. Calculating battery size and solar panel power is important if you don’t want to be left without power. Amp hours (Ah) work much the same way as watt hours (Wh). Multiply battery voltage times the Ah rating and you get Wh (more or less), but there are also other things to consider.

Let’s setup a possible scenario

Let’s say you would like to take a primitive camping trip. You want to make sure you have enough power to occasionally run your laptop and charge batteries for your camera. You would like to run your laptop for 4 hours a day and charge 4 AA NiMH batteries a day. Let’s also assume you’ll be gone for 5 days.

As we go through this scenario, keep in mind that this same deductive reasoning can be applied to many different scenarios. Maybe you want to power:

something during an outage
your RV’s appliances
your laptop through a 14 hour flight using a few parallel sets of 16 NiMH batteries in series
a remote pond water pump

Also keep in mind that this is only a general guide. It does not consider discharge rate, temperature, or various other factors. For details, check out the following:

How much power am I using?

To know how much power you need, you first need to know how much you’re using. If you can’t measure the current your laptop uses, check the power supply rating. Also, your NiMH batteries will need to have at least as many watt hours as they store. Don’t forget to compensate for conversion efficiency.

Estimating Laptop Power Usage

Let’s say your laptop power supply puts out 19V at 4A – that’s 19V * 4A = 76W. However, it may only use that much power powering your laptop and charging its battery. If the battery is charged, assume 76 watts anyway. If your laptop actually used 60 watts, given a conversion efficiency of 85%, the actual power consumed would be (100% / 85%) * 60W = 70.6W. Running for 4 hours, that would be 76W * 4hrs = 304Wh.

Estimating Battery Charger Power Usage

If you have 4 AA NiMH batteries with a capacity of 2500mAh (2.5Ah), then 1.2V x 2.5Ah x 4 = 12Wh needs to go into those batteries. Again assuming a conversion efficiency of 85% for the battery charger, let’s say we need (100% / 85%) * 12Wh = 14Wh.

Total Usage

So, all together you’ll be using about 304 + 14 = ~320Wh a day. To err on the side of caution, let’s say 350Wh.

Where will I get my power?

It’s unlikely that you’ll have a MPPT solar power converter that will work directly for your laptop or batteries. (Although you might be able to charge 10 AA NiMH batteries in series with a 12V charge controller.) So you’ll likely need a 12V SLA (sealed lead acid) battery and a 120VAC inverter. If you bring a big enough battery, you won’t even need a solar panel, but that would be quite a heavy battery.

Estimating Battery Size

Assuming you’re using a 12V battery and your inverter has a conversion efficiency of 85%. To have enough power for one day the battery would need a capacity of (350Wh / 12V) * (100% / 85%) = 34Ah. For five days you would need 5 of these batteries or one 170Ah battery (34Ah * 5 day). But that’s about 140lbs of weight and it doesn’t take advantage of the sun, so let’s use only one with a solar panel.

Estimating Solar Panel Needed

The battery we chose can store about 34Ah * 12V = 408Wh. Assuming a charge controller efficiency of 90%, we need about (100% / 90%) * 408Wh = ~450Wh from the sun. Let’s also assume the sun will shine adequately for about 6 hours (or a fourth of the day). You’d need a 450Wh / 6hrs = 75W solar panel, or an 80W panel which is more common.

It’s not rocket science

March 14, 2010

It’s true that the necessary parts to have a usable solar/wind system are fairly expensive, but the skill required to make it work isn’t rocket science. In fact, it’s probably easier than auto repair. Probably more often than not, contractors will simply follow the available instructions. At worst, they might cut corners. If you do it yourself, you could probably save quite a bit of money while knowing exactly what you did and how well it was done.

Do the Research and Planning

Chances are you’re reading this blog because you want to know how renewable energy works and how you can use it. If you don’t know how to do something, you research it and find out from those who do. I didn’t know a thing about Tesla coils until a couple of years ago. Since then I’ve made a few.

Once you’ve developed a better understanding about how the parts work together and what they’re called, you can begin to plan. Here’s some good things to remember:

Do your homework.
Failure to plan is planning to fail.
Plan your work and work your plan.
Know your limits, (then reduce them).
Make long term plans in short term intervals.

Consider Economic Efficiency

In some instances, it might be more economically efficient for someone else to do the work. What costs more? How much is your time worth? Let’s assume the following scenario as an example:

You normally get paid $15 an hour.
You estimate it would take you ~20 hours to install your renewable energy system.
That would cost 20 * $15 = $300 of your time.
Unless someone else can do it for less than $300, you might want to do it yourself.

The above example of course doesn’t factor in intangibles. Even if you you could find someone to do it for a little less, perhaps you would still want to do it to know how it was done. Therefore the knowledge would be worth the extra hours spent as well as the peace of mind knowing it was done properly.

Consider Electrical Codes and “Qualified Personnel”

Perhaps you watched the Enphase Micro-inverter System Installation video I mentioned in my last article. Don’t let the phrases about electrical codes and “qualified personnel” scare you. Electrical codes are good to consider, but you can find and research this information on your own.

What if I miss something?

Realize that people just like you already install their own light fixtures, ceiling fans, switches, and sockets. Be honest and ask yourself if you really think anyone has studied all the electrical codes. More than likely they simply follow the instructions. Realize also that even some of the jobs done by some “professionals” could be questionable if not disturbing.

Common sense should always be used. Always turn the electricity off before servicing something electrical. By using common sense we also understand that like colored wires are usually connected together, you need larger wire for more current or power, and they shouldn’t be hanging out in the open. If there’s something you’re not sure about, ask someone or look it up.

What if I’m not “qualified personnel?”

What makes a person “qualified?” Do you think I’m qualified even though I’ve had no formal training? Does reading blogs, watching videos, and researching what you want to do, doing it, and then gaining experience make someone qualified? You must crawl before you can walk, but you won’t get anywhere if you don’t ever crawl.

Notice the video says “all work should,” not “must,” but this is all according to who? The contractors, understandably, want to get paid. They’re licensed. The reason why they need a license is because they are in the business of installing systems for other people and therefore are liable. It’s unlikely that you will sue yourself if you screw up.

Some Personal Experience with Supposed Professionals

Preparing for a Hot Tub

At some point my dad decided we would get a hot tub. The people that delivered it would connect it, but we had to supply the wire and conduit they would use to connect it to the breaker box. (We also ran the required wiring from the main breaker box and installed the dedicated external breaker box. Understandably, they would only wire it to an available box.)

Everything sounded good, but there was something fishy. They would not connect it to a GFI (ground fault interrupter) breaker in the breaker box because the hot tub already had an internal GFI circuit breaker. (Don’t we also want to protect the people outside the tub from electrocution?) When asked why, they said because a GFI breaker in a box would always trip without reason. But what they didn’t know, I researched on the web to learn about GFIs.

Learning about GFIs

A GFI is designed to detected differences in current in both the neutral and hot wires. If a GFI circuit breaker is far from the device it’s connected to, a delay in current causes the breaker to trip when it should not. However, our breaker box would be right next to the hot tub.

Had the GFI been far away, at the main breaker box, then what they claimed would probably have been true. Needless to say, when the installers went through the trouble to bypass our GFI breaker, we connected it back like it should be and haven’t had any problems since.

Hearing From a Friend

One of my best friends used to work with a general contractor. He told me about some interesting things they did and did not do. Then there’s the issues with government and insurance contractors. If you plan to find a real good contractor, you may have to do as much research to find one as you would learning to do the work yourself.

Using microinverters for solar power

March 13, 2010

If you only plan to sell the electricity you produce back to the electric company and not go off the electrical utility grid, then the microinverter may be the most elegant solution. You use a single one of these inverters with every solar panel in the system. Simply connect the solar panel to the inverter and connect the inverter to your electrical box–only two sets of connections.

What are the benefits?

If you use a microinverter, expansion is easy. You can start with a single solar panel and inverter to have a complete grid tie system. Adding to it is almost like adding a set of Christmas lights to an existing set. The plugs and sockets are different because they’re made to withstand weather.

In addition, microinverters give the advantage of maximum power point tracking (MPPT) for every individual panel. This means shadows or performance issues with one panel won’t affect the others. If you opt for Enphase’s microinverter, you also have the ability to get detailed day-to-day, hour-to-hour statistics for every panel! Watch the How It Works video for a video representation.

Where can I get one?

Microinverters are still somewhat new and haven’t really made it to mainstream as far as solar power is concerned. The Affordable Solar Group and EcoDirect have some pretty good prices, (but their solar panels are a bit pricey). There are many places on the web to get microinverters.

The only microinverter that is currently available is from Enphase. Another is in development from SolarBridge.

How do I connect it?

Don’t be intimidated with wiring this device. If you can install a household socket or light switch, you can install this. If you can match colors and put up Christmas lights, you can install this. The instructions alone should make it very easy to understand.

If you watch the Enphase Micro-inverter System Installation video, they make it sound simple, because it is simple. But, it does take some time. Don’t let the phrases about electrical code and “qualified personnel” scare you. I’ll discuss this in more detail in another article. Check out this New Jersey Solar Installation video for some good details.

Choosing a Solar Panel

All you really need to focus on is buying a compatible solar panel for the microinverter, (unless you’re comfortable with splicing and soldering the wires of an incompatible panel). You should be able to find a compatibility list in the support section of the company’s website. Enphase, for instance, has a download section.

Connecting the Microinverter

First you generally need your inverter in place before you connect your solar panel. Run conduit up to your roof (or your panels’ location) to a junction box. Enphase prefers you to buy an AC branch “Install Kit” for $60, but you could easily get your own parts separately. Or, you could just run the inverter wires to a box and run conduit to an inside switch which would probably be cheaper, maybe $20. From there, just run wires into your electrical box to a circuit breaker. Check out Installing Electrical Conduit Systems for more details.

Connecting a Solar Panel

The inverter and solar panel will likely have special connectors. These connectors are designed to be fool proof. But if you’re an electronic hobbyist you may want to get less expensive solar panels that aren’t on the compatibility list. If that’s the case, make sure you have the correct voltage, (you might need two panels in series or parallel). To connect a panel, just:

Cut off the connectors from the solar panel and inverter (this may void the warranty)
Prepare heat shrink tubing to cover your connections by placing them over the wires (available locally at Radio Shack or online)
Solder positive to positive, negative to negative
Cover your connections with the heat shrink tubing and shrink it

Living on DC

March 8, 2010

Most of our everyday appliances and electronic devices operate using AC (alternating current), right? … It might surprise you that most appliances we use today are using DC (direct current) rather than AC. Internally they convert the AC to DC. If you’re an electronic hobbyist, you probably already know that. If you’re using a solar system with batteries, you could save by using DC directly.

Reaping the Benefits

The benefits of running things off DC directly is that you have no conversion loss. Inverters and power supplies alike have a conversion efficiency. Most conversion efficiencies lie somewhere between 80-95%. If you can reduce the number of conversions, you will come out ahead. However, it may require you to have ten 12V batteries wired in series to obtain between 110-130 volts DC. You could use a DC-DC converter, but that would defeat the purpose.

Distinguishing What Uses AC

First you need to know what you can and can’t operate with DC. You cannot use DC on anything that has a transformer on its power input. You can use these steps as a guideline to determine what can be operated using DC, but the only way to really know is to look inside:

If the appliance has a mechanical switch, turn it on unplugged.
Use a multimeter to measure ohms (Ω) across the prongs of the plug.
If the meter reads about 500 ohms or less, it likely uses a transformer.

Here are some things that typically require AC to operate:

Air conditioning and heating systems
General purpose fans and ceiling fans
Washing machines/dryers
Refrigerators/freezers
Microwave ovens
Garage door openers
Fluorescent lights with ballast transformers
Cell phone chargers (which are usually small wall mount transformers)
Anything with an AC motor

Distinguishing What Uses DC

You can use DC on anything that has a bridge rectifier on its input. A bridge rectifier is something that converts AC to DC using four diodes. If you can measure around 1 meg ohm (MΩ) or more across the prongs of the plug using a multimeter, it most likely uses a bridge rectifier. Again, the only way to really know is to look inside. Most of the following items use a bridge rectifier or can use AC or DC:

Any lengthwise oriented or switching power supply (doesn’t mount on the wall)
Computer/Laptop power supplies
Incandescent, CLF, and LED light bulbs or Christmas lights
DVD players and newer VCRs
Game consoles

AC wall transformers and DC switching power supplies

Replacing Wall Transformers

One of the most pesky things to deal with are those big black and inefficient wall transformers. The output of most of these are DC because they use a bridge rectifier on the output of the transformer. If you can find a switching power supply at the same DC output voltage to take it’s place, then replace it.

Solar panel wiring

February 28, 2010

Some may think there’s a lot to know about wiring a solar system, but the truth is the basics are pretty much the same as they were 20 years ago. Wiring solar panels is like wiring Christmas lights. There are several sites out there that show you the basics. However, it’s important to know when to use the methods discussed.

What’s your input device?

Before you buy solar panels, you need to know what you’re going to use to convert the solar power. Are you using a charge controller and/or a grid tie inverter? Here’s a couple of different things you could use (click on their description tab for details):

Wiring

First, it’s important to know the basics. There are two basic ways to wire solar panels, series and parallel. Series arrangements increase the voltage of an array. Parallel arrangements increase the current of an array. Let’s use an 80 Watt, 12 Vpm, 6.6 Ipm solar panel for examples. (See my article about choosing solar panels to learn what Vpm and Ipm means.) Wiring panels in series:

+/plus/red to –/minus/black, +/red to –/black, + to –, etc.
Three panels in series equals 36V at 6.6 Amps.

Wiring in parallel:

+/plus/red to +/red to +, –/minus/black to –/black to –, etc.
Three panels in parallel equals 12V at 19.8 Amps.

For more examples and pictures, check out these sites. Keep in mind that you will likely have to use both series and parallel connections within the same array:

Series vs. Parallel

These wiring arrangements, though different, generally achieve the same result in terms of power. But there are differences you should consider:

	Series	Parallel
Electrical focus	voltage	current (amps)
Wire diameter	smaller	larger
Physical handling	easier	harder
Cost per foot	less	more
If one panel is in the shade:	the whole string produces less power	the other panels are unaffected

The device you use to convert your panels’ power will determine your wiring arrangement, or vice versa.

Direct Solar-to-Grid Inverters

Most high power grid tie inverters (for solar systems) will require many series connections of solar panels. If you look at the input specifications for the first two devices listed at the top, they require 120-400 VDC.

You’d need 25 * 12 Vpm solar panels in series to make 300V. Or, 5 * 60 Vpm panels. Notice how much current these inverters can handle, about 20A. They generally don’t need a lot of current at that high of a voltage.

Charge Controllers

Most high power charge controllers will require more parallel connections of solar panels. If you look at the input specifications of the last two devices listed at the top, they’re good for 45 or 80 Amps DC.

You’d need 6 * 10 Ipm solar panels in parallel to make 60 Amps. Or, 2 * 30 Ipm panels. These charge controllers can still handle up to 150 Voc, but they’re designed to work with higher current. They generally don’t need higher voltage like solar-to-grid tie inverters. But keep in mind that the voltage should be higher than the voltage of your battery bank.

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