6-25-10

Let's talk about battery banks, their size (capacity) and how to actually use the off grid deal without going through a ton of batteries during the couple of years.

PART ONE, PLAN THE PLAN

Our first stop has to be the planning phase. When you get done planning, plan some more. I'm serious about that. There are a number of issues related to using off grid power like under sizing the charging source (solar panels, wind turbine, generator). Here is an excellent free tool to help you plan your system. It's called HOMER and is made by the NREL (The National Renewable Energy Laboratory). Go here to get it. 

Using HOMER, we can plug in all aspects of our alternative energy system and it will break down the entire system right down to the cost associated with it. Use it and play with the numbers, run the simulations and most importantly, think about what you are doing!

A small system like the one we use can cost a lot. But some simple "look ahead" planning will save headaches later on. Let's take a look at the three areas that I've are in aN off grid system. You'll find a lot of web sites that discuss this but I haven't found any that break it down like this.

The three areas are power generation, electronics and power storage. The most important of the three is the electronics. I know what you're saying to yourself: Bill, how can you say that? Look at it this way - design your system to grow with your needs. Okay. You can add solar panels pretty easily. Same with the battery bank. But once you buy the electronics you are done. Your only choice is to buy new. Take a look at solar charger choices. You go out and buy a solar panel that puts out 10 amps at 12 volts. Sweet, you think to yourself we'll just cut some costs and buy a 10 amp solar charger and we are done. Next year you find an awsome deal on another solar panel so now you have 15 amps of power from solar. Oops, now you need a new solar charger. Bummer, you spent $50 on the first one and now you have to spend another $75 dollars on a new one which brings your total cost to $125 insead of the $75 you should have spent in the first place.

The same holds true for an inverter. Inverters come in so many flavors and sizes it's hard to get your brain wrapped around it all. From modified sine wave, true sine wave, 150 watts (1 amp) to 2,000 watts (20 amps) to GFI equipped to the effeciency, it all swirls around you like a tornado of decisions.

Well, the same thing holds true here. If you decide to stick to the low voltage appliance choices (there are many, many low voltage appliances) your inverter decision suddenly becomes much easier. You can literally cut your 110 AC needs to almost nothing by choosing low voltage appliances like coffee makers, toaster ovens, and even lighting (do a google on LED 12 volt lighting). So lets say you've made the calculations and bought a true sine wave GFI 300 watt inverter for $250 dollars. In a few months, that 300 watts seems like a distant memory because you found a great deal on a combo LCD/DVD television that uses 200 watts and your fridge takes 250 watts.

What I'm saying in the end is overbuy on the electronics, you won't be sorry.

PART TWO, BECOME A POWER RANGER!

What I mean by that is using HOMER to designing your system, you'll get a pretty good idea about what you need to do to get the power that you need. Here's the deal: you will by human nature underestimate your needs. Look around you. Time and time again the city that you live in, our military, everyone underestimates. The people that are truly successful are the ones that overestimate what they need. My first attempt at working with our off grid system was just that - a vast underestimation. I first bought too small of a generator, too small of a charger and half of the solar panels that I needed to do the job. My next phase was to overestimate what our needs were and from there we never looked back.

Overestimating of course has it's own drawback; costs. Say you're looking at building your first off grid system. Figure $100 for each battery. You buy two which it turns out is not enough. Using overestimating, buy three instead and your cost is $300. Of course, you'll need additional cables, more solar panels (eventually but sooner rather than later) and a larger solar charger to handle the increase in solar panels. So, overestimate the whole system right from the start and plan on expansion of the system. 

This, of course, is easier said than done.
PART THREE, THE SEA OF BLACK PANELS

So, grasshopper, what do you want; more or less of those black glass panels laying around your yard? Well, less of course. With less, you get higher output panels. But due to the great keeping the cost high (no, there's no collusion involved, after all BP, Shell and other oil companies make solar panels and they'd NEVER all conspire to keep their costs high....would they?) efforts of the solar panel industry, the cost per watt just never seems to go down much. At any rate, there are deals out there, namely the Harbor Freight kits. But the drawback is 3 panels equaling 45 watts and you can get 45 watt single panels all day long for about $400 dollars. The HF kits cost $250 when they're not on sale. 3 instead of 1. However, the HF kits come with the frame for mounting them and two 12 volt CFL lights to boot. So the tradeoff from 3 panels to 1 is a matter of cost. If you have the room, go with the deals that you can find - used panels, discontinued items, the HF kits. The idea is to generate power for the least number of dollars per watt. If you can get below $3.50 per watt, you are doing great.
PART FOUR, WHADDYA MEAN BIGGER MEANS LESS?