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.

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.

Drizzly day

We visited our friend Dennis today and picked up 12 battery cores he donated from his defunct bank.  We also got to check out his latest project, repainting the dome exterior using this fancy 'Koolcoat' additive.  Supposedly it can add up to R2 insulating with these tiny foam beads (think fluffy grains of superfine sand).

In other news, we have been letting the chickens out to scratch and explore a few hours per day. But because of our tenacious coyote, these outings must be closely supervised!

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

San Angelo Battery Run

We are going to Hawkins Battery in San Angelo early tomorrow morning. We are stocking up on deep cycle Trojan T145s, a well trusted unit, though this will be our first time using this battery or this supplier.  We are hoping everything goes according to plans. 

Our previous supply of 100 lb, sealed, lead acid AGM blems is currently out. We were big fans of these sealed AGM batteries, as they held up great and were a lot lower-maintenance than a vented battery, but we are going to deal with the changes accordingly. 

Wish us luck.