OFF
THE GRID
Thinking Alternatively... because we have
to...
Kathleen Jarschke-Schultze
System Sizing
Do the Math
So, now you have a good idea of what Renewable Energy potential your site has. The next step is to figure out just how big and what system components you’ll need to achieve your off-grid dream of electrical independence.
Info Plaques
What are you going to want to power up? Lights, TV, radio, blender, vacuum? Make a list of the appliances and power users you have or want. Look at each one. Search till you find the information plaque on each appliance.
On every appliance there is an info plaque that you need to be able to decipher. It will tell you the model number, the serial number, the motor amps, the heater amps and combined total amps, if applicable. The Volts and Hz are also listed, but it is usually 120v and 60Hz.
Formula for Success
You need to multiply the number of amperes by the volts to get the amount of watts used. I am using my Asko dishwasher as an example. So if the motor only uses 2.6 amps without using the water heater , this machine would use 312 watt/hr. (2.6A x120v). With the heater in use the combined 8 amps times 120 volts would equal 960 watts. Quite a difference between the two.
I use this appliance about 2 times a week. (A full dishwasher is an efficient one.) It takes one hour to do a load. If I keep the water heater on, my consumption numbers on the dishwasher would be 960 x 2 or 1920 watt/Hrs. This can also be expressed as 1.92 Kilowatt/Hrs. With this appliance alone I would need at least a 1000 watt inverter.
A 25 inch color TV draws about 100 watt/Hrs. If you watch it for three hours every day that would compute into 300 watt/Hours per day or 0.3 KWH.
One Person, One Light
Lights are easy. Wattage is clearly marked. Use compact fluorescents for best efficiency. We use what we call the ‘One person, One light rule’. This means that when you are in a room after dark you have the light on. When you leave that room turn out the light. You enter the next room and turn on that light. Your light follows you around your house. Do not leave your light alone. If no one is in a room the light should be off. This isn’t just a life style change, just a bit of re-education. If you can do it, your kids can. If you can’t, well….
Once you get your consumption estimate done you can begin planning. You have already figured out what Mama (Mother Nature) has given you for Renewable energy potential (See last issue of River Voice). Now you must combine this knowledge for sizing and buying components for your RE system.
Back to the Future
A lot of times our financial status does not jive with our plans. If you have the RE site potential but not the funds you can plan your system with an eye toward expansion in the future. You can get some photovoltaic modules (PVs) now and add more later. If you’ve sized the incoming wires with an eye towards expansion it is as easy as racking and stacking more modules of the same voltage as your existing array.
If you do plan on expanding your RE system later (I just want to point out here that most systems are expanded later) then your best bet is to get a bigger inverter than you need now. Resale on smaller used inverters is negligible. With the inverter technology today you can get full sine wave power that is cleaner than what comes off the utility grid. For example, there is a 2000W inverter that might meet your needs now and when you are ready you can tie in another 2000W inverter (of the same brand, of course) and have 4000W of inverting capability.
Talking ‘bout My Generation
Most, if not all, off-grid systems have a back up generator. We have one. It charges our battery bank. Our challenge to ourselves every year is to see how few hours we can away with not running it. The least amount of gen time for us has been about 18 hours or 6 gallons of gas in a full year.
The size of your battery bank will determine how long your household can go without some sort of electricity RE or genset) being put into your storage. Batteries are one part of the system that cannot easily be added onto later. It is always best to have batteries the same age. A good set of batteries will last seven to ten years, if properly maintained and not too deeply cycled.
We have talked about inverters, PVs and batteries. There are other components in an RE system. Some are necessary, some are good common sense to help you keep your system running at it’s highest efficiency. (Next issue-System Components)
Kathleen Jarschke-Schultze is trying
out “Beer Friend” Edamame soy beans in this year’s garden at her home
in Northernmost California.
kathleen@electronconnection.com