The following article has been contributed by a fellow prepper named Mike. It has been published with permission of the author. It does not necessarily represent the views of PreppingToSurvive.com.
This article is the second in a three-part series on off-grid survival using solar power. In the first installment, I talked about how solar power works and the types of solar panels available. In this article, I’ll share with you how to calculate how much energy you’ll need to support your home or boat. In the third and final post, I’ll share how to mount and wire your new panels.
How Much Power Do Solar Cells Make?
Generally, we measure solar panels by wattage and that is how we buy them. You can buy solar panels for boats as small as 10 watts to as large as 200 watts or even larger. But it is easier to understand when we convert watts to amperage.
We arrive at these values by multiplying the number of hours the panel spends in full sun (usually defined as 8 per day in Florida) times the panel’s wattage.
For a 195 watt solar panel the output would be 195 x 8 hrs = 1,560 watts/day. Taking it step further, 1,560 watts/12 volts = 130 amps per day.
Keep in mind that solar panels produce DC power which means that you will need a deep cycle battery bank to hold the charge. Batteries are rated by the amp hours they hold.
So what is Needed in a Solar Panel Setup?
Obviously one or more solar panels are necessary to make the system work. In addition, you will need:
- a large bank of deep cycle batteries, the bigger the bank the better
- an inverter, choose between pure sin or modified (to be discussed in another article)
- a controller and
- proper wiring and fuses to wire the parts together.
Energy Consumption – A
My guiding principle on how many panels to buy is simple; buy as many panels as your budget and mounting location will allow. You cannot have too many. But you should complete an energy audit to make sure you are buying enough for your needs.
Example, if you have 3 interior lights that draw 2 amps each and you leave them on for 24 hours per day, your consumption would be 3 x 2 x 4 = 24 AH/Day.
You can generally find the amp load for appliances on a label inside a door etc.
Electrical Loads
|
Amps |
Hours |
AH/Day |
|
| House Lighting | |||
| Refrigeration | |||
| Freezer | |||
| Stereo | |||
| Other | |||
| Total Amp Hours |
Inverter Loads – B
An inverter is a device that coverts battery DC power to household AC power; without an inverter, unlike on a yacht, your solar panel will have little value if used at a home. But with an inverter you can use your hair dryer.
Inverter loads use DC power but they are powering AC appliances and equipment. If you need to convert watts to amps use (12watts/12 volts = 1amp).
|
Amps |
Hours |
AH/Day |
||
| Computer | ||||
| Microwave | ||||
| Refrigeration | ||||
| Freezer | ||||
| Heater | ||||
| Hair Dryer | ||||
| TV | ||||
| Other | ||||
| Total Amp Hours | ||||
| Calculate your total daily energy consumption AH/per day | ||||
Solar Energy Production – C
Alternative sources of power such as solar panels can replace the amp/hrs drawn from the batteries. But like the energy budget that calculated your usage you will also need to calculate your re-supply of amp hours. Remember the formula – (12 watts/12 volts = 1 amp). But keep in mind, the formula is only a gage; absolute accuracy can only be where the panel output is constant and a solar panel may at times operate inefficiently due to shading by clouds.
|
Watts |
Amps |
X – Hours Sun Exposure |
= – AH/Day |
||
| Solar Panel 1 | |||||
| Solar Panel 2 | |||||
|
Total Amp Hours Production |
|||||
Solar Panel Needs
Compare the daily energy consumption in AH/Day to the solar energy production. Your solar energy production ( C ) should be greater than the consumption ( A, B ). If not, select a larger wattage panel and recalculate. Always purchase more solar panel output than you will think you will need; some planners recommend at least 30% in excess.
We bought our panel from Sun Electronics in Miami, www.sunelec.com as they had the best pricing I could find anywhere online. But remember, panels must be shipped via freight as they are heavily packed to reduce the chance of damage so be sure to calculate those costs in your purchase.
Next Up
In the next post, I’ll talk about mounting and wiring your solar panels.
Fair winds,
Mike
PreppingToSurvive.com 
August 7, 2012 at 9:45 am
If you do get solar panels, within a few days you will realized that only those devices that draw 220 watts are responsible for almost all of your power consumption. This will be one of your first eye openers and will lead you to start thinking about how a smart meter connected to smart plugs could change everything during a time of emergency..
November 5, 2012 at 8:10 am
This is the best layman friendly explanation of the technical aspects of solar power I have been able to find. I have looked everywhere. Many thanks!
November 5, 2012 at 11:19 am
Thanks, Swampox. I agree; Mike did a great job explaining a pretty complex topic.
November 6, 2012 at 10:22 pm
Question – my electrical knowledge is not much above knowing how to flip the switch to control the lights, so if anyone can tell me if these little solar panels connected to a 12Volt battery I see connected to a neighbors gate to open and close it, are powerful enough to operate an electric pump to keep water coming from my 200? ft deep well,
I sure would appreciate it.
November 8, 2012 at 10:58 pm
The answer to your question is yes because you will be running off the battery. The gate motor is likely 12 volt and you will need a inverter. The more battery capacity you have the more water you can pump All the panel does is recharge the battery. However if your water pump is 220 volt you are getting into a lot higher priced inverter and should have a bigger solar array and battery bank to match it. You can put a ton of money into a system and still dim the lights to make toast. My personal opinion is to spend the money on a high end inverter and high capacity battery bank. Then buy a sized diesel generator to automatically charge the battery bank. Then as money allows add a small wind turbin a 1000 watts to start with and then add the solar panels. In the end you should burn 5- 10 gal. of fuel a month. To step right out and pay 30-40 grand for a solar system you will never get your money back from makes no sense.
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February 20, 2016 at 6:56 pm
“Example, if you have 3 interior lights that draw 2 amps each and you leave them on for 24 hours per day, your consumption would be 3 x 2 x 4 = 24 AH”
Is the 4 in your equation the number of hours per day? If so should it be 24? Or is 24 a typo and it should be 4 in the text?
August 7, 2018 at 1:27 pm
3 x 2 x 24 = 144 AH, so i think he means leave them on 4 hours a day.