How to determine how large of a system??

[Sean McFerran]

I am in the process of gathering information for putting together a power system for my home. I am already doing biodiesel and WVO for my vehicle and to me the initial choice would be to run a diesel generator off WVO since it seems to be the least amount of start up cost and most knowledge I currently have.

Is there an accurate way to judge how large of a system I will need?

I saw a 9kw system that seems affordable but am not sure of it is big enough for all my shop tools etc. I am presently quite the energy miser, but if I am generating my own electric I would like to induldge a little more. Also may go from oil hot water and heat to electric if I can generate it myself.

I have seen the method of adding up all of the appliances, etc, but this seems hardly accurate.

Is there a meter or info I can request from the power company etc.?

Thanks!
Sean

[Rob Beckers]

Hi Sean,

First, welcome to Green Power Talk!

If you're currently grid-tied (and it sounds like you are), the place to start would be with your electricity bills. Take a look at a reasonable length of time, say 1 year if you can, and you'll get a pretty accurate idea of the amount of energy you need to generate. It will also tell you if there is a seasonal effect (more in winter than summer or vice -versa).

Once you have that, next is to figure out what the largest loads are you will be using simultaneously. That will help set a number for your power needs (as in Watt, rather than kWh).

The method you mention, using a list of appliances and assigning a "percentage of use time" to each is another way to determine electricity needs. It works well if you start from scratch and don't have access to actual historic usage data.

-Rob-

[Sean McFerran]

Thanks for the info, I have some issues with determining size needed. I am grid tied at the moment, but my bills are pretty low due to my misering the power. Currently I am the only one living in the house which hopefully will change. Highest month's usage was August at 555kwh probably due mostly to dehumidification and air conditioning. I have a 400+ foot well and I have no idea how much energy draw that is. Also recently put in some shop tools including a 230V 5hp 160 gallon compressor and a a 230V welder, which have not seen too much use this winter. Other big draw units would be refrigerators, washer and dryer which are not used much now but would be if my girlfriend moves in. Also, if I am generating my own electricity I may as well put in some electric heaters and hot water heater instead of oil. I would really hate to purchase a system that is too small for my future applications. I could ask my girlfriend what her electricity bill average is currently and add the two I suppose, but she is not on a well or have any of the other factors either. Thanks for all the help! Sean

[Sean McFerran]

Maybe a better way to do this is see what the differnt units will provide and see if that would meet my potential needs?

I believe the systems I am looking at start at 9kw to whatever.

How do I determine how much power a 9kw system will put out in a residential situation?

This is a big investment and I really want to cover my self for expansion in the future.

Thanks Again!
Sean

[Jack Coats]

Just a thought, If you are wanting to stay grid tied or not, first reduce your load requirements.

Simple stuff, change incandescent bulbs to compact fluorescents. If you have 'instant on' appliances, determine how to really turn them off.

My wife and I did some simple things to help reduce our 'footprint' years ago.
1. do nothing. but turn off 'everything' (lights, TV's, but don't unplug things that are not normally unplugged) in the house. Read your power meter.
Go to a movie or whatever, and come back 2 or 3 hours later (it helps to do it in hour increments, but not required), and figure out how much your house uses while you are not there. Now do the math and figure out how many watt hours you are using per hour of idle time. ... This is your initial base line. Also, snag your last electric bill and figure out what you 'normally' use over a month. Now that you have numbers, normalize them (put them on the same basis so you can compare them) so you can tell what you are using versus your 'background' use.

2. Reduce background use - these are the little appliances you don't even think about that stay plugged in. Unplug them if you don't need them. You might be surprised as to how much they used. We were. And we didn't miss them.

We found we have lots of 'little' things. We made a 'recharging station' where we re-charged things, but didn't leave the chargers plugged in unless they were in use.

I read an article about one all solar house, where they had several power sockets along some planters near a large set of windows (for heat gain, but the plants made it look nice inside). Each of the sockets (10 of them if I remember right, a long wall) were GFI sockets. For safety they are required near areas with water. But each one drew 3W of power for the GFI sensor to work. He removed 8 of them (2 left for convenience), and put plane plates over the rest of the 'holes' (yes, terminated the wires correctly), and saved 24 watts of power ... that is 1720 watt hours each month. Only about 10 cents on the electric billl, but it was big to him. Especially given 1W of generation capacity is about $10 (I did a quick review of a commercial solution was really about $9 - $10 is good easy calculating number with some safety factor - in some areas rebates can reduce it to $3/w - really good).

for those interested. a 4420W system was $33,640 but after tax stuff it came out at $11,750 - this was a sample given at http://www.vibrantsolar.com/html/numbers.html that I randomly selected from the web. I have no ties to them.

3. Do you NEED alternating current? - some have gone all the way and gone off grid. Using DC appliances (and sizing the wiring in the house for it, and reducing length of wires) you can get away without the inefficiencies of doing a DC to AC conversion. There are DC appliances and motors available. (yes, there are high efficiency DC refrigerators available!) ... Do the math. Do what makes sense.

4. If your big button is reducing carbon footprint. Possibly a grid tie PV and wind system can reduce/eliminate your electric bill, without having a bunch of batteries to maintain (yes, they take regular maintenance and are not cheap). Don't think you will make real $$ by selling power back to the power company, but if you can come back with a net $0 electric bill, you will be generating quite a bit more than you use. Thus in that part of your life you can have a net negative carbon footprint!

5. Grid tie out of the box wind systems are available today. Some folks like wind mills, some hate them. If you are in a subdivision like I was in they hate anything that doesn't look like everyone else's. So that and solar panels were not an option and windmills were totally out of question.. ... to bad.

6. Consider your auto. Not all hybrids are good. Some that are coming out now are using the hybrid not to give better mileage, but to counteract putting in effectively bigger engines for performance. Not a good thing IMHO. The Prius is still good. If you could have a plug in option put on it that could really cut its pollution more. A 'topped off' battery is a good way to reduce the pollution generated on the first 30 miles or so the Prius uses each day, since about that much would come totally off the charged battery before needing to use the engine at all. -- there are 3rd party upgrades, but not Toyota OKed as far as I know. Most (even coal powered) power plants generate less pollution (with good scrubbers) than cars do for the applied amount of power from what I have read. Economically it would make the 1st 30 miles cost a lot less than the gasoline generated version of power anyway. (About 8 cents from what I read).

I hope this helps, but do your own research. Get info from RELIABLE sources that can back it up with verifiable scientific and economic data. Get it from multiple non-affiliated sources. (If the tree huggers and the power company and the oil/gas company and the government all tell you the same story, it is probably true. Otherwise question it HEAVILY.) The 'feel good' data from lots of places is often wrong or at least grossly misstated to help prove their point. (I guess I am just distrustful of everyone, given how much 'truth' I have been fed from many sources over the years.)

[Kathyann johnston]

Hi there, This is my first posting to Green Power what a great place I am just begining to put together a plan for living totally off the grid. I was reading your post from Feb and wondered if you ever came up with your system requirements.
Kathy:D