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Estimating Your Solar Needs!

My charming husband is the brains of the solar part of our project because when it comes to calculating how much solar energy a cell phone or light bulb uses, my light bulb is burnt out! So, on this post I will be writing, the information comes from his brain and research.

Currently, we are apartment dwellers and are using this time to research and plan our build. One of the things in our plan is to be off the grid with solar energy. So, the first thing we did to estimate how many solar panels we would need or how much energy our home will consume, we made a list of what uses energy and how much it uses in a day, like our lights and devices.

Here is what we will have powered in our 16'x20' cabin:

Bathroom Light (2 LED bulbs)
Kitchen Light (3 LED bulbs)
Loft Light (1 LED bulb)
Living Room Light (3 LED bulbs)
Outdoor Lighting (3 LED bulbs)


Each of our LED light bulbs uses 3 watts or less (we already have them and are using them in our apartment to save on our electric bill, they are to replace halogen bulbs with two prongs) so if we assume all 12 lights run for 9 hours a day, we would require 324 watts of energy per day (12 bulbs x 3 watts x 9 hours). We realize that we will not have all our lights on for 9 hours everyday, especially in summer when the sun doesn't set until 9 pm but in the winter the sun sets closer to 4:30 pm.. You can see why we averaged this out.

2 Cell Phones charged once daily 12 watts
2 Tablets charged once daily 60 watts
Laptop charged once daily 80 watts


To estimate what our devices use in a day, we are going to assume we charge everything once a day. Now, we don't own a television, a DVD player, have home internet or a game console and we are doubtful we will have to charge everything, everyday, but we want to over estimate and have extra power rather than the alternative. We found this article, which with some fancy math, René came up with 152 watts per day to charge each device. According to the Forbes article, the iPhone has a 1440 mAh battery or about 6 watts. So if an iPad's battery is 6930 mAh, it would require just under 30 watts. Ta-dah!

1500W Induction Cook Top used once a day for no more than 20 minutes on highest setting 500W


We plan to do the majority of our cooking on a hot wood stove during winter, or a BBQ and solar over during the summer. Occasionally, like on summer rainy days when we don't dare to BBQ, we will have a one burner induction portable cooktop. If the cook top uses 1500 watts on high in an hour and we only use it for 20 minutes, we can estimate it would use 500W once a day.

Refrigerator 269kWh

We found a small under the counter fridge, 4.4 cubic feet, that the Energy Guide claims uses 269kWh a year. So 269 divided by 365 is 0.74 kWh per day. Mulitply that by 1000 and we get 740 watts per day.


The final tally!

324 watts a day for Lights
152 watts for electronic Devices
1240 watts for Food 

1716 watts of energy will be used each day in our cabin. So, if we have a 500W solar panel system, here in New Brunswick, we would require 3.5 hours of full sun for optimal power generation each day. We found a great deal on a 400W Solar Panel Kit to get us started and we can add more panels as we need them

Clearly this is all an estimation and we are not mathematicians or solar gurus but this is how we calculated it all. Of course, we will want to ensure we have enough battery storage to get us through a couple cloudy days in a row or maybe even add a small windmill! Let us know your thoughts!

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2 comments:

  1. We're in Nova Scotia and have a 750 watt system. On a good, sunny day (like today), we make +/- 2kWh of electricity. We run two laptops, the modem and router, two cell phones, and the cell phone booster on the roof. We don't use a fridge or electric stove/oven because it is such an awful draw on power - as you saw in your calculations. Our battery system is a series of 8 deep cycle marine batteries.

    The problem is December. Or rather, mid-October through mid-February, peaking in December. We ration our power carefully in December because we seem to average about 2 sun hours a day.

    I should say, though, that our first year here, we had a 160 watt system! We ran lights and charged one old flip phone! :) So you can manage without very much, but you will probably be seriously rationing your power during the dark months.

    Marie

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    1. Marie, you are such an inspiration! We worry about the long winter months as well and intend to do our cooking on the woodstove. It will be a lot to get used to, so we are practising in our apartment!

      Thanks for reading!

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