Thursday, October 1, 2015

Starter Solar System

A typical solar power system has several main components as shown below:

  1. Solar Panel - converts sunlight to electricity. Price starts at about $200.
  2. Charge Controller - controls battery charging (included with panel)
  3. Battery - stores electricity.  Price starts at $65 - $75 for a 12 VDC 35 Ah Deep Cycle battery
  4. DC to AC Inverter - converts DC battery power to 120 VAC.  Prices start at $80
Total cost for a low cost DIY starter solar system is about $350 in 2015. Compare this with an equivalent cost generator.
Generator - a good low cost generator (~$350 - $400) that in theory produces 3,500 watts per hour (as long as you have gasoline) is the DuroMax XP4400E from Amazon:
 It has a 4 gallon gas tank that reportedly lasts about 8 hours. A model hooked to your propane tank or natural gas might be a good option too.  Either way, this generator is a good deal, For a few hours it is very practical as it produces more than 10X the power of an equivalent costing solar system. But its worthless when there is no gasoline.  I would figure on having three 5 gallon cans of gas per day which costs 30 to $45 per day at $2 - $3 per gallon.  This equates to about $1,125 per month at $2.50/gallon. This is very expensive, and gasoline with ethanol has a short shelf life (6-12 months) so you can't store too much with out rotating it.  Propane on the other hand has an indefinite shelf life.

After buying one of these generators and several cans of gasoline to cover my short term needs, I would get the solar panels below.

 Solar Panel - Here is a sample 100 watt solar panel below.  A 100 watt solar panel can in theory run a 100 watt bulb while the sun is shining directly on it.  The charge controller is included with this unit and shown in the upper left hand corner of the picture below.  This controller will handle 3 - 100 watt solar panels allowing for expanding your power generation. 

Battery - A 12 volt 35 Amp hour (Ah) battery will provide 12 X 35 = 420 watt-hours of power.  This in theory will power a power a 100 watt bulb for 4.2 hours or take 4.2 hours for one 100 watt solar panel to charge it.  To preserve the life of the battery, you only want to use a maximum of 50% or 210 watt-hours.  So to recharge your half discharged battery would only take about 2.1 hours of sunshine and your 100 watt light would only run for 2.1 hours.

Often the battery cannot hold all the power the solar cell can generate.  If you don't use this extra power, it goes to waste.  So the remaining power from the solar cells after the battery is charged could be used to power other things during the day.  Only the battery is used to power things at night.  Note that such systems are only about 70% efficient. 

A 12 volt AGM Deep Cycle rated in 100 Ah battery costing about $250 will store 1200 watts-hours of electricity (12 volts X 100 amp hours).  Recharging a half discharged battery would only take about 6 hours of sunshine for 600 watt-hours to use each night.  Two (2), 100 watt Solar panels would recharge this 50% spent battery with 3 hours of sunshine leaving several hours of power while the sun is still shining to run other things.
Ideally, you should get the largest battery you can afford.  A 12 VDC, 250 Ah battery costing $550 will provide 12 x 250 = 3,000 watt-hours.  To recharge your half discharged battery (1500 watt-hours) would take about 15 hours of sunshine.  You can add 2 more solar panels (3 total) to charge it in 5 hours of sunshine and have an hour or more per day of additional power. 

DC - AC Inverter - takes your 12 volts of Direct Current (VDC) power from the battery and converts it to 120 volts Alternating Current (VAC) like you use in your home.  Below is a 1,000 watt 12 VDC - 120 VAC Inverter.  It is inexpensive and has battery cables that can be connected to your solar battery OR your car battery, which is why this would be my first purchase.  This will power about 8 amps of 120 VAC electrical devices.  This will work for a starter system, but it is what limits how much you can run at one time so you may want to get 1,500 to 2,000 watts later on, especially when you have more than 2 - 3 solar panels.

Now what can you run with this?  Lights, a refrigerator or a freezer OR a small water pump can each be ran off this system (not at the same time) for as long as your battery can support it. Any lighting should be 25 to 40 watt LED bulbs.  Do not use incandescent bulbs, heaters, A/C's or microwaves as they use too much power.

To be safe, figure on about 6 hours of sunlight per day.  If it takes 2 hours to recharge your batteries each day, then you have 4 hours of additional solar power you can use for other things.  Each 100 watt solar panel will in theory generate 100 watts per hour of direct sunshine or 100 watt-hours.  Keeping your panels pointed directly toward the sun will increase your output.

Here are some typical things that we need to run on solar power during power outages:

A new modern small refrigerator uses about 800 watt-hours per day.  An old large refrigerator or freezer will use up to 1500 watt-hours per day.

So with the 35 Ah battery, you could keep your small refrigerator running for about 6 hours each night and about 4 hours during the day. The large refrigerator would run about 3 hours each night and about 4 hours during the day. This would cover you for a short power outage which might save your food for several days.  If my power was going to be out for an extended period, I would also turn my refrigerator temperature setting up (45F) to use less electricity and keep things cool longer. 

With the 100 Ah battery, you could keep your small refrigerator running for about 20  hours each day. The large refrigerator would run about 9 hours each day.

With the 250 Ah battery, you could keep either refrigerator running all day as long as you have 3 solar panels (300 watts) to charge them each sunlight hour of the day.  This will deliver about 38 kwh (kilowatt hours) per month on average and more in the summer.  So let's look at some other things.
  1. A 1/3 HP well pump uses 500 - 1500 watt-hours per day, depending on how much you use it.  For drinking water only, you could figure 300 watt-hours per day.  Add  one tub of water per week for laundry, bathing, etc. and you should figure 400 watt-hours per day.
  2. A ceiling fan, portable fan or can opener would use about 100 watts while running.  So if we run a fan for 8 hours per day, it uses 800 watt-hours per day.
  3. Charging a radio or cell phone for an hour uses about 4 watt-hours and running a clock radio uses about 7 watts while running.
  4. Lighting has a lot of variation:  a 60 watt incandescent bulb uses 60 watts; a 60 watt florescent bulb uses 18 watts.  Even better, down size your bulbs to a 40 watt LED bulb that uses 4 to 7 watts.
Here is a good link to show you the power requirements for most items in your home:

Let's look at some electricity consumption for the following items:
  1.  Running a small efficient refrigerator at a low temp setting - 800 watt-hours per day;
  2.  Drinking well water at 300 watt-hours per day
  3.  Using 4 - 40 watt LED light bulbs for 4 hours at night or  80 watt-hours;
  4.  Radio at 7 watt-hours per day. 
The above items require 1187 watt hours per day and 12 (11.87) hours of sun for one 100 watt solar panel or 6 hours of sun for two 100 watt solar panels.  Considering the system is about 70% efficient, we should figure on having three (3) 100 watt solar panels.  With 6 hours of sun per day and 70% efficiency, this would deliver about 1,260 watt-hours of usable electricity to meet the above.

The 250 Ah battery above delivered 1,500 watt-hours of power, which meets the above needs. The cost is as follows:
  1. First 100 watt solar panel and charge controller - $200
  2. Two additional 100 watt solar panels - $300
  3. 250 Ah 12 VDC AGM Deep Cycle Battery - $550
  4. DC - AC Inverter - $150
     Total: $1,200, and you can start with $900 and add the additional 2 solar panels later.

You can get this full 300 watt system, or you can start with the initial 100 watt system at the top for $350 and easily expand it. You can add 2 more solar panels and add additional batteries (in parallel) as you can afford it.  The only thing you might need to replace would be the inverter, and I wouldn't do that unless I had some things that it would not support running.  If you do replace your 1,000 watt inverter with a larger one, you can still use this one with your car battery.

You may be able to use the solar panels to run some of your small household appliances and save on your electric bill to help pay for this.  However, it is not practical and you should NOT attempt to wire it in to your house wiring.  Also, your battery life is limited and should be saved for emergency outages only; not routine use.

Note it is a good idea to keep an extra solar panel and charge controller in a Faraday cage in case of an EMP.  Good luck with your solar system, and post comments to let us know how it is working!!

Please note that I'm NOT affiliated with nor endorsing any of these Solar products and list these brands only as examples that were easy to find and readily available at the time.  I will say that Amazon ratings are generally reliable and usually anything that is rated 4 starts or higher by 10 or more reviewers and has less than 10% rated as 1 star is usually a good product.

For additional information see the following links: