FAQs

The following is intended to cover some of the most common questions we hear about off-grid solar systems. Please post your questions in the comments for a Part Two!

What is the most important component in an off-grid system?

The charge controller.

This is actually a hard question to answer, but if you consider that your battery bank is usually about 1/3 of the total cost of your system, it makes sense that you should do your best to protect that investment. Buy the best charge controller you can afford, and avoid controllers that don't have a reputable manufacturer's warranty to back them up. Warranties are generally 2-5 years for the good equipment. Even the smallest micro-solar systems should at least have a Low Voltage Disconnect built in so that you cannot discharge your batteries to the point of damaging them.

Why don't I have enough power in the summer?

Because you didn't size your system for the summer.

The most common problem we come across in the summer months is that people don't realize that they are using more electricity when the weather gets hot. Summer is when most homes in the Big Bend use the most electricity, and the same applies to solar-powered homes. In the summer you are likely running fans all day and into the night, and also your refrigerator has to work harder to maintain its temperature. This is why solar systems should be sized for a Worst Case Scenario.

A system that is adequate in the winter may struggle to provide enough electricity in the summer. Big electric companies often have the same problem, which is why brownouts are more common in the summer (when everyone's air conditioner is running at the same time).

I want more power. Should I buy more batteries?

No.

While adding to your battery bank may seem like an easy way to enlarge your system, what you are actually doing is upsetting the balance of your system. If you make your battery bank bigger, your solar array may not be able to charge it adequately. If this happens your system will stop working once the batteries are drained, and if you cannot keep the batteries charged, they will quickly become junk.

Also, it is not advisable to mix new batteries with old batteries because it will shorten the lifespan of your new batteries.

I want more power. Should I buy a wind turbine?

Probably not.

Wind turbines are a great renewable energy technology, but it is both difficult and expensive to make them work on the residential scale. Per Watt, wind turbines are much more expensive than solar panels. Plus, you have to build or buy a very tall tower and install the whole shebang. This can get extremely expensive if you are paying a professional installer, and it's not a ton of fun to do it yourself either.

If you have your heart set on a wind turbine, you should adhere to the following guidelines:

Choose your site wisely. Being near a hillside or structures will cause the winds to swirl unpredictably and not get you a good electrical output. You want your turbine to be either on the top of a hill or in the valley. A wide open expanse with a strong prevailing wind is best.

Buy a reputable brand with a good warranty. Anything with moving parts is prone to problems. Buying from a well-known and respected company can help you avoid those problems, and a good warranty will save you a lot of headache if issues do arise.

Get your turbine as high up as you can. At least 20 feet off the ground is recommended, and the higher you go, the better the wind conditions are.

Brake your turbine. In powerful storms, it is best to stop your turbine spinning. Otherwise it could over-spin and get damaged. You will also want to brake your turbine if your batteries are fully charged and you don't have a dump load ready to accept the extra power from the turbine.

Ground the turbine well. Wind towers are lightning rods and if your system is not adequately grounded with over-current protection, a lightning event could destroy your system in part or in whole. Not to mention the possibility of setting your house on fire (rare, but certainly possible). It doesn't even have to be a direct hit to do severe damage, so you're definitely better safe than sorry when it comes to lightning protection.

I want more power. What should I buy?

More solar panels.

Even if you don't have enough batteries to store the extra juice that additional panels will make, you can still use the extra power if you are mindful about when you run your heavy loads. If you use your energy-intensive appliances (washing machine, vacuum cleaner, etc) when the sun is high in the sky, you will probably be running them directly off the solar array and not dipping into your batteries at all. This is very good for the batteries, and allows you to have more power at night. You can always increase your battery capacity later, when finances allow or (better yet) when your battery bank is due to be totally replaced.

Scene of Green

April 6th was the 5th annual Green Scene, and we got to power the event for the third year running.  We built a SunStation just for the job, our smallest and most cost-effective model ever. Version 3.0 has 570 rated watts of PV modules, four deep-cycle flooded batteries, a digital PWM charge controller, and a 2300W 24V modified sine wave inverter.

We always have so much fun, and this year was the best ever. We gave a demonstration explaining the basic principles of solar power and living Off Grid. Our friends and neighbors Tim McKenna and Kevin Elmore teamed up on a very informative demonstration on reclaiming the desert land using simple techniques and proven principles.

There was so much else, I can't even begin to cover everything.  Between the stand-up comedy and belly-dancing, there were lots of great demonstrations and educational materials. And as always, tons of great, fresh food.

Delivery

We just received a shipment of Suntech modules. We will take these to the site and unpack them tomorrow.

They look really well packaged. 

Snow Day

Can't even see the Christmas Mountains today.

A very gray day here in Terlingua, with thick snow clouds weighing heavily around us.  It is always exciting to get snow in the desert, since it only happens once or twice each year. If the sun comes out, the snow will not melt, but sublimate, meaning it skips the liquid phase and go straight to water vapor because of the incredible dryness of the desert.

But there is no sign of the sun and little hope it will show itself at all today (check out our local forecast here).  Bad news for photovoltaics, but if we are conservative with our power, our battery reserves can last for days.

When we began studying photovoltaics back in New York, the standard was to design the systems with enough reserve to supply at least a week of power with no input.  This means everything has to be oversized, not just the battery bank but the array size that pumps in the juice, and therefore all the components that handle the current as well.  This is one of the main reasons that solar power is so much more expensive in cold, cloudy New York State.

2008 NREL insolation map of US

Here in the American Southwest, we get some of the strongest insolation in the nation, and very few cloudy days.  This allows us to size systems smaller, usually preparing for a maximum of three days without sun. But sometimes, even here in the Chihuahuan Desert, we exceed our reserves and have to have a backup plan.  So once in a blue moon, we have to run a generator to keep our batteries charged. It is so important to keep the batteries above 50% charged, or else we risk damaging the batteries, which are the most expensive and weakest link in the system.

In the future, we hope to use a renewable fuel like biodiesel or woodgas to power the generator.  But right now we don't have a diesel genny, and the woodgas apparatus is too big and cumbersome to run alongside our house on the hill (moreover, the desert sun has really taken a toll on the plastic components!).

But so far, so good. We haven't used all our power yet, and we plan on being very careful with what we have got until the sun comes back out.

Solar sign

It's always great to see renewable energy making inroads toward becoming the norm. When we were in New Jersey visiting family, it was exciting to see that PV arrays and solar hot water panels had cropped up all over the state. 

Just the other day in Alpine, we drove past the new library and were very glad to see that their beautiful new sign is illuminated by solar power.  In fact, the Terlingua Ranch Lodge had made plans with us to do the same thing, but they backed out at the last minute.  

On a new installation like the Library's, solar is an easy choice because the installation costs of grid power are so high.  By comparison, the initial investment to install a small solar system is minuscule.

Perhaps an entirely solar-powered library is in the not-too-distant future, but for now we are really happy just to have the sign.

Lightning Strike

Lightning behind Paisano Peak

We occasionally see off-grid power systems get damaged by lightning, and the other day one of our good friends had her system go down during an electrical storm. She was inside when she heard a very loud, very close lightning strike, and simultaneously lost all power in her home. She rode out the storm, then came and got us the next day.

The first thing we did was do a visual inspection and found all the batteries intact (and reading 12.7 V), the solar charge controller dead with frayed wires, the household inverter dead with the output wires charred, and a wind generator charge controller dead with evidence of smoke.

Back outside, we found one of the wind generators had been unconventionally wired, and was connected to the battery room via a long extension cord on the ground. Where the turbine wiring met the extension cord, out in the yard, the two ends of the connection had been blown apart, and were now five feet away from each other.

Inside the home, a surge protector had been blown apart, but lucky hadn't caught anything on fire, and managed to protect all the appliances and whatnot inside the home.

What should we learn from this? 

First, lightning is noted as being upwards of 120 million volts, which allows it to arc across great distances. Really, that's all a bolt of lightning is: a buildup of electricity which then arcs through the air, trying to find its opposite charge (in this case the ground, but there is also ground-to-cloud lightning).

Second, it likes tall objects, especially those with wiring, which may offer an easier path to ground (like wind turbine towers).

And third, it will search for the path of least electrical resistance to a suitable earth ground. In this case, the lightning eventually found its ground through the telephone line. As a result, the phone in the house was destroyed and the telephone company's service in the area was affected.

These acts of nature have to be considered when we design and build any power system. A few things done differently could have greatly changed the outcome of this lightning strike.  

First of all, the wind tower could have been grounded much better with such simple components as a copper clad grounding rod and a solid copper grounding wire.  

Each wind generator should also be equipped with a lightning/surge arrestor, which will ground all the wiring when lightning strikes, typically self destructing in the process, but saving other components.  

The inverter needed a much better ground than it had, and another lightning/surge arrestor on the 120VAC output side of the inverter would have protected the loads  from lightning strikes on the house or the turbines.

Our friend was lucky. Her batteries, solar panels, and household appliances were all fine, thanks to the telephone line's ground. With proper safety measures, she could have taken the lightning strike much better. Her new system will have all the above protections in place, ready for the next time an electrical storm rolls in.

Rain and Sun Station

It's been raining today and yesterday, with no sign of stopping. The rain has been a double edged sword.  We're enjoying the cooler temperatures and catching some rain in our tank.  But a lightning strike wiped out most of our friend and neighbor's power system.

We've gotten over a half of an inch so far, which translates to potentially  70 gallons or so from our one little roof. When we have all our roofs on the property guttered, that half an inch of rain will mean some 425 gallons of water to our storage tanks.

There's been no sun for a couple days, but it is easier to be thrifty with power when you don't need every fan on to fight the heat.

The new SunStation uses the same 85W poly panels as our household PV array.

We have just started building another SunStation for an off-gridder way out in the desert past the ghost town. This new one will be smaller than the first, with just over 400 rated watts of PV. We're using the same kind of panels that we use in our own power system, so we can definitely vouch for the durability.

Solar Racecar

We're so happy to see that our former Renewable Energy professor from SUNY New Paltz finally achieved his dream of racing a solar car! He started out as a garbage truck driver and worked to become an engineer; we were lucky to have such an inspiring, passionate, and hardworking instructor. Congratulations, Mr. Otis!

Getaway

We're back from a long weekend spent relaxing and adventuring at the Chinati Hot Springs, five hours away in Ruidosa, Texas.  We'll be posting an album of photos from the trip on our Facebook Page, if you want to see more of this gorgeous area.

We had a great time and met so many wonderful new friends. Strong and sassy West Texas gals Maddie and Sierra kept the whole operation running like clockwork while the full-time managers took a vacation of their own. We look forward to seeing Maddie around Alpine, where she has just bought the old Richie Hotel next to Murphy St. Raspa Co. and La Yarda.

Geologist lovebirds David and Stephanie found their way to Chinati all they way from Fort Worth, and seemed to be loving the every minute of their stay in the Big Bend.

David and Stephanie promised to come visit us in Terlingua soon, and were curious about acquiring property in the region.  They already have the smarts, the skills, and the passion to thrive out here ... just need to work out some details!






While in Presidio, we stopped to check out the High School's very large PV array. We wanted to see the famous Big Ol' Battery (BOB) which is supposed to supplement the overextended power grid in the Big Bend, but it wasn't as easy to find as we had thought.

The Presidio rocketry team also recently had the great distinction of being selected to have their project sent to the International Space Station via the Dragon spacecraft in September:

Presidio High School Student Project Will Fly To NASA’s International Space Station

The rocketry team participated in a NASA launch of a different kind back in 2010:

We also made our first trip to Mexico (I know, we should be ashamed that we've been here three years and this was our first trip) where there was much to see -- including lots of flags, fliers, posters, and other political ads for the recent federal elections.

It is a little disappointing to see the PRI back in power, but we can hope that their strong-arm political tactics are behind them.  In any event, the people have spoken.  Democracy can be messy, but that's kind of the point.

Keeping busy

Ron's pre-fab buildings make moving in easier.

Cleverly concealed and incredibly effective battery storage.

 We spent Thursday running around the county, stopping first at Ron's new storefront on 118.  He's selling premade wood buildings for folks who want their shed or cabin to be delivered on-site.

Of course, Ron is also our Terlingua solar supplier, so we loaded up with lead for our friend and customer Zoey who has lived off-grid for over a decade now.

A couple of eco-nerds in new digs.

Shot Time's official greeters.

After swapping the new AGMs for the leaky lead acids, we headed farther south to town and Tonia's fleet of vehicles.  We also noted the damage around town after the hailstorm. One person with a weather station logged a 93 mph sustained wind gust, and you should check out our facebook page to see Dan & Jess's video of the flooding and hail.

Old Terlingua EMS building post-storm

Solar as usual

We recently helped our friends expand their solar power system. They added 1,400 watts of PV to their array, which doubled their power input.

Their new panels are mounted to the roof using a prefabricated IronRidge aluminum mounting system.

The SunTech PV modules come with a 20 year output warranty and are well matched to the battery bank voltage, which means the OutBack Power MPPT charge controller can operate at peak efficiency.

Our friends are happy to now have more electricity than they need, even during times of heavy electrical usage.




The 1.8 kilowatt SunStation was recently delivered to its new owners on the Terlingua Ranch.  The couple is pleased with the performance so far, and are able to run their Airstream travel trailer, including a hefty, roof-mounted air conditioner. 

Surprisingly, the brand new, modern AC (13k BTU) consumes 1.9 kilowatts per hour.  That's about 600 watts more than the similarly sized window unit at my parents' home, which dates to about 1980.


We received a large delivery of concrete blocks for some upcoming homestead improvements. 380 8x8x16" blocks, 20 bags of mortar and 20 bags of Portland cement.

We are adding a back wall on the shop in blocks up to 7' high, the remainder is framed in steel and covered by steel panels.

The floor of the chicken coop was also excavated and poured with homemade concrete this past week.  Just a little bit of ferro-cement work on the remaining wall, and our last surviving chicken Foxy Lady (who is doing really well, by the way) will be moving back in.

Maximum Power Point Tracking (MPPT)

Solar charge controllers that come with maximum power point tracking (MPPT) are becoming widespread and less expensive. But many people don't know much about charge controllers in general, and even less about electronics and MPPT specifically. So we thought we would share our knowledge and experience on the subject.

Maximum power point tracking is not related to solar tracking.

Solar trackers move your array to point at the sun wherever it is in the sky, which can increase it's power output by a few percentage points, and help your system make power during dawn and dusk.

Maximum power point tracking has nothing to do with physical tracking, and has everything to do with the laws governing electricity. Specifically, Ohm's Law and Joule's Law.

The following may seem boring and/or confusing to some of you, but understanding these laws and the behavior of electricity is crucial to understanding how solar power works (and how it can be made more efficient).

Ohm's Law states that current, voltage, and resistance are measured proportionally. This law can be distilled into the following mathematical formula:

V = I x R

Where V = voltage, I = current, and R = resistance.

And knowing what we do about algebra, this formula can be rearranged to find a value for any one of the three elements. For example, to find current:

I = V / R

And to find resistance:

R = V / I

Joule's law states that power (P, which he measured as heat dissipated) is proportional to the current value squared and the resistance in the circuit. The law is distilled into the following equation:

P = I² x R

Thanks to Joule's Law and Ohm's Law, we know that power also has a special mathematical relationship to voltage and current.
 

P = I x V

Manipulating one value in the equation directly affects and changes the values of the others. And this very wordy explanation is leading to how MPPT charge controllers work, I promise.

So now that we know how the values relate to one another, we can manipulate the input value to optimize the power output.  This is usually illustrated with a PIV curve

So what a MPPT charge controller does is this:

The charge controller's electronics evaluate all the data it is receiving from the batteries and the solar panels, and adjusts the values for P, I, and V to the best possible benefit of your battery bank.

In doing so, the MPPT charge controllers increases your system's overall efficiency by a significant percentage.  Using an MPPT charge controller on our homestead's system has given us added power equivalent to an entire extra solar panel in the array. 

An added benefit of using an MPPT charge controller is that you do not have to match your array output voltage to your battery bank voltage.  Not only does it make the rules about sizing your system a whole lot less strict, this allows you to set up an array at high DC voltage and transmit the power farther, and on lighter gauge wire.

So you see, MPPT is a technology that opens up many doors to users of PV power.  It increases the efficiency of your array, netting you more useable power; it allows arrays and battery banks to be mismatched; and it allows us to use high voltage DC transmission lines from array to power center.

Parallel Inverters