| When you are considering installing a solar | | | | Add up all the items power usage in Watts for |
| electrical system, you need to think about what | | | | your daily usage. |
| your needs are and how much power does that | | | | Just to give you an idea of what you are looking |
| involve. One solar panel putting out 18Volts is | | | | at : |
| not going to get you very far when you need to | | | | - 5 x 15W Compact Florescent Globes = 75W per |
| supply a cabin on the farm or supplement your | | | | hour. Run for 5 hours = 375Watts/Day |
| home power supply. To put it into perspective, | | | | - 1 x 75Watt TV for 3 hours day = 225Watts |
| 5 Compact Florescent Globes (CFL) of 15W, will | | | | Day |
| draw 75W per hour, run them for 5 hours and | | | | - 1 x 50 Watt Laptop, 3 hours/Day = 150 Watts |
| that means 375Watts you need to provide either | | | | Day |
| directly or from batteries. If you are on the | | | | - Total Daily usage = 750 Watts/Day. |
| Grid, no problem, flick the switch. But, if you are | | | | ADD THEM ALL UP |
| on Stand-Alone, then you need to design your | | | | - Using over 3 days = 2250 Watt Hours (with |
| system to provide your power. | | | | no recharging) |
| The main place to start is your batteries. When | | | | Now also remember that you should not |
| the sun is shining, your solar panels convert light | | | | discharge you batteries any lower than 40% |
| into electricity and charge your batteries. At | | | | capacity or you will begin to damage them, we will |
| night or when the sun does not shine (cloudy | | | | work on a 50% discharge to keep them safe. |
| days), you draw from your batteries. The size | | | | - We need 2250 Watt Hours at 50% discharge = |
| of your battery array depends on two things : | | | | 4500 Watt hours. |
| 1. How much power you use when everything is | | | | So you will need batteries that will supply |
| on. | | | | 4500Watt Hours for you. |
| 2. How long you run your appliances on your | | | | To work out you batter rank, or how many and |
| batteries. | | | | how big your batteries we need to work on what |
| Now, there is a couple of other details that you | | | | is termed Amp Hours. Batteries are usually |
| may not come across so often. Batteries do | | | | quoted in Amp-Hours, so we need to do a small |
| not discharge in a "linear" way. To explain, a | | | | calculation. the formula is easy, AMPS = |
| 200Amp Hour battery should theoretically provide | | | | WATTS divided by VOLTS |
| say 50Amps over 20 Hours, but this is not so | | | | OK, lets say you are buying 6Volt batteries rated |
| due to its non-linear discharge. Add to the fact | | | | at 225Amp/Hours, how many do we need? |
| that batteries are affected by cold, so if you live | | | | - Each 6Volt battery at 225Amps provides |
| in snowy climates, make sure you factor in bigger | | | | 1350Watt Hours. |
| battery arrays. The more slowly energy is taken | | | | - Our usage of 4500Watts divided by 1350Watt |
| from a battery, the longer it will last. | | | | Hours = 3.3, so we need 4 Batteries. |
| Ok then, lets do some calculations to work out | | | | - That means you would have have a |
| how many batteries you need. | | | | “bank” of 4500 watts of power in your |
| Make a list of all the electrical appliances you | | | | four batteries. |
| intend to use | | | | Something else you would need to consider is |
| Get the wattage of each item from the items | | | | how to connect them to match your inverter. |
| product label | | | | You could now connect your batteries in series to |
| (If the label shows only Volts & Amps, Then, | | | | get a 24 Volt output or 2 x 2 in parallel to push |
| Volts x Amps = Wattage (per hour of usage). | | | | out 12 Volts. So you can see that when |
| For each item, calculate the number of Watts it | | | | designing a DIY solar system there are many |
| uses (per hour) | | | | details to consider. You really are advised to get |
| Estimate the number of hours you will use that | | | | hold of a comprehensive guide to explain all the |
| item | | | | details in putting together your solar panel and |
| Multiply by the hours of usage with the hourly | | | | supply system. |
| Wattage for its consumption (per day) | | | | |