Using Roof Shingles instead of panels

ken, thanks for the post, have been busy in preparation for going to costa rica.  I'll be working from our office down there for a couple weeks. 

lori,

as per usual, ken is on the money.  I'm not sure how you got the numbers you did, but I would try again.  remember, watts is a rate, like miles per hour. 

if somebody asked you how far you drove, you would not reply 50 miles per hour.  That is the same as saying we use 1750 watts. 

to do it right, take each load and note its RATE of energy usage in WATTS.  take that number and multiply it by the number of hours you use that thing in a day.  that will give you watt-hours - a quantity of energy used.

do that with everything that uses electricity.  sum up the total in watt-hours and multiply by 30 to get watt hours per month.

post again and i am sure you will get more help, or call the sales staff here.

good luck,

james - Alt-E staff

James:

I hope you will be able to find some time for the board while in Costa Rica.
I think your presence as a resident staffer has added to the quality of the board.  I remember a time when there was very little, if any, staff presence.

While playing with some numbers for the roofing products, I realized that your cost per watt figures are not a real valid comparison for the unschooled.  You are dividing the panel cost by the panel wattage, regardless of the panel voltage.

The 64W, 12V Roofing laminate is listed at 5.44 a watt.
The 136W 24V is listed at 5.39 a watt. 
If you are building a 24V system and intend on using the 64W, it will cost 10.88 a watt.

Perhaps in addition, you could list a WV (watt volt) price for comparison purposes. Panel cost divided by watts times nominal volts.
I will also throw in the Sharp 170W PV panel at 4.95 a watt.

The  64W,12V becomes $0.9545 per WV
The 136W,24V becomes $0.2246 per WV.
The 170W,24V becomes $0.2063 per WV.
Simple, which one is the best value ?

(for fun, you could use VoltWatts. That way it would be a VW price) :-)

The same comparison error can creep into a watt per square foot figure.
The 64W 12V  is  5.48 w/ft2 and becomes  65.83 wv/ft2.
The 136W 24V is  6.04 w/ft2 and becomes 145.07 wv/ft2
The 170W 24V is 12.34 w/ft2 and becomes 296.13 wv/ft2
Again, it makes it real clear which panel gives the most energy density per square foot.
(I used the gross dimensions of the roof panels in this example, not exposed area. I didn’t take the time to research the overlap)

I know you guys have probably wrestled with this internally. Hope the suggestion might be of use.

Have fun in Costa Rica.

Ken

Lori:

The answers the calculator gave you are correct, if you are trying to take your current home off grid and maintain your current electrical consumption. 

That is not a good approach to build a house off grid. And 1000 kWh a month is still a tremendous amount of power for an off grid system. The 17.2kw system to support the 1000kwh per month will cost a bundle, approximately $225,000.   

You have listed (in your initial post) many factors that should lower your power requirements in the new house.  If you want to estimate an approximate monthly kWh  figure now, use the room by room inventory/estimate method that James and I talked about in our earlier posts. See what that number comes up to.

A word of warning, the first number you come up with, will most likely be too low. It is generally a re-iterative process of going back through and saying how many hours will this light burn? What else electrical is in this room? What did I miss?  You massage the number to something you are comfortable with.  The inventory will also point out things to you that are an opportunity for further savings. This is area lighting, it can be a compact florescent, 13 watts instead of 100w. This refrigerator that I wanted burns to much energy, what models are more efficient ?. A new washer will save money, etc.
By putting a tubular skylight in, I can cut down on using this light during daylight hours.
 
After you firm up the size (kWh per month), then you can talk system voltage, size and number of panels, batteries, etc.  The Monthly kWh figure drives everything else.

Are you using an architect for this new house ? (If not, who did the design or where did you get the design from?)  He/she could probably help with the room by room electrical loads estimate, and they may have completed parts of one already.

Energy efficiency (or conservation) is ALWAYS cheaper than generation. Since you are designing the new house, you have the best opportunity to save (energy and money) by putting the right features in the house, selecting the right lighting and appliances, etc, before it is constructed. The less electricity the house needs, the lower the cost of your system.

Ken