Wednesday, November 08, 2017

Solar made easy

     How much solar do I need?
     Really that answer is easy but first you have to know how any batteries do I need. Wait, I thought we were talking about solar. A solar panel is just a battery charger that uses the sun instead of normal electricity to charge your battery. When the sun goes down no charge takes place.

     Normal deep cycle lead-acid batteries (the type everyone is familiar with) should not be drained more than 50% of their capacity to keep them healthy for maximum life. Less drain would be even better but we will use 50% because that is the known standard.

     Your batteries are like the gas tank in your car. If your car has a 10gallon gas tank and it gets 30 miles per gallon, you can drive 300 miles before you will run out of gas. You add gas before that happens and you drive as long as you keep adding gas. Just make sure you keep enough gas for the miles you need to drive.

     Your batteries are the same, you need enough power to last until you can add more. If you are using solar to charge your batteries, that means until the sun hits your solar panels again or sundown to sunrise. If your batteries are full at sundown you can use 50% of them by sunrise.

     Your batteries power capacity (gas in the tank) is measured in amp hours (ah). An amp hour means 1amp used for 1hour. If you have a 200AH battery, you can use 1amp for 100hours, or 10amp for 10hours, or 25ams for 4hours and so forth. Remember only 50% of your 200ah battery should be used, thus 100ah.

     Are you ever going to tell me how much solar I need?
     No, you are going to tell me!

     12volt appliances will be measured in 12volt amps,( example car radio, 2.5amp@12volt ), regular household appliances are measured in 120volt amps, example home radio, 2.5amp@120volt. Since 12volt amps are used at 12volts, they are easily measured, a 2.5amp appliance used 2.5 12volt amps an hour of usage.

     In order to use regular household 120volts from your 12volt batteries you need a 12volt-to-120volt inverter. Hook your inverter to 12volt battery and just lug in your 120volt appliance in and you have 120volts. Your inverter uses 10 12volt amps to make 1 120volt amp. So for every 1 120amp you are using 10amps from your battery. Now you see your home radio that uses 2.5amp @ 120volt will actually be using 25amps of 12volt battery power.

     Every appliance 12volt or 120volt will have its rated usage marked on it somewhere. Lets say it is marked 2.5amp@120volt. That means it could use up to 2.5amps so that is what we use. Remember that 2.5amp is for an hour, use if for 30 minutes and you use 1.25amp and so on.

     Wait cowboy, my appliance says 80watts@120volt. Some lower usage appliances are rated in watts. Watts, both 12volt and 120volt and be converted to amps by dividing the watts by the volts.
80watts@120volt: 80/120=6.66amps

     Now we can start to figure how many amp hours we will use when no battery charging is taking place. We will call that sundown.

     For example only, you must figure your own:

     1. rv 12volt lights 1.5amp@12volt                                                                      12volt amps
                                                                                     used 4 hours x 1.5amp  =      6.0   amps

     2. rv 12volt on demand water pump12amp@12volt
              ( 6 min is 1/10hour)                                        used 6 min x 12amp/10 =     1.2 amps

     3. laptop .5amp@120volt
              ( 120volts amps are x10 12volts amps )         use 2hours x 5amps =           10.0 amps

     4. cellphone charger  40watts@120volt
              (40watts/120=.33amps x10 for 120volt)         use 3hours x .33amps=           1.0 amps

     5. TV  2.5amp@120volt
               ( 120volt amps are x 10 12volt amps)            use 4 hour x 25amps=          100.0amps
                                                                                                 Total                        118.2 amp@12volt

     For this example we round up to 120amps used from our batteries. Since we can only safely use 50% of battery capacity, we know we need a bare minimum of 240ah batteries. Are we really going to use 118.2 amps. No, and here why, the light and the water pump will probably use their rated amps because their use is constant when in use. The cellphone and laptop will cycle on and off. The tv is really in constant cycle mode as the screen changes. Plus I have never measures a 12volt appliance that pulled current to its stated rate.   But 118.2 must be used as it represents what might be used.
     Now do your own totals for what you plan on using to determine your minimum battery capacity.

     Finally the reason you are here.................................
     Solar is the easy least a common consensus.
For every 1 amp hour of battery capacity you need 1 watt of solar power.   Our example was 240ah battery so we would need 240watts of solar power. That does not mean you can have less (you my not always fill your gas tank if money is short), this is just what is needed with adequate sunshine to have a full battery bank at sundown.

     Batteries are limited by weight, space, and money in that order. Solar is limited by space, money, and weight in that order.

     Add more batteries and you have more "reserve" for dark hours.(my choice)
     Add more solar and you have more "power" to use during charging hours and still have your full at sundown.
     Add more of both and you have the best of both worlds.

     To elaborate on our gas tank analogy a bit more. If you know your gas funds are limited then you only drive necessary miles like to work. Low on battery power, no tv tonight!

     I hope this simplifies things a little........thanks for stopping by.





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