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Grid Tie Battery Backup, On or Off Grid Solar |
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| Grid Tie Solar Energy System with Battery Backup Power, Information How To |
| Part 1. Battery Backup / Off Grid Solar 1 Find the wattage of every item that can or will be ran at the same time. Remember battery power in a backup system is normally limited so do this with survival mode in mind. Just what you have to have to keep on going for 24 hours. Maybe things like the fridge, alarm clock, a light, coffeepot, the hot water tanks thermostat and the energy monster, the hair drier. 2 Total all the wattage and you have your inverter size. 3 Next you need to know how many hours or minutes each item will be ran in 24 hours. 4 Based on the information from line 3 you will size your battery bank. If line 3 tells you that you require 5,000 watts of power per day. You already know what inverter you have chose so the battery bank voltage will be 12v DC, 24v DC or 48 volts DC. Divide the wattage by the DC volts of your inverter to get your battery bank AH rating, 5000 watts / 48 volts = 104 Amp- hours in battery power at 48 volts. Double this to 208 AH because you never want to run your battery bank lower then 50% discharge. Part 2. Grid Tie Backup 1 Gather up your last 12 months electric bills. 2 Total the kWh from all 12 electric bills and divide it by 365 days for your average daily usage. (kWh equals 1000 watts.) 3 Look on our worse case solar isolation map and find the average peak sun hours for your area. 4 Divide the average daily usage from line 2 by the average peak sun hours number from line 3. 5 To allow for heat losses in the solar modules, voltage loss in long wire runs, energy loss in the inverter and charge controllers, add 15%. If you use larger wires and the most efficient equipment you can get this 15% tare loss down a little. See our Voltage Drop Calculator in excel format. 6 Get a site shading survey, This will track the sun’s path and give the effect a tree or house might have. Add this percentage to the above. (normally a dealer only item) Example: A 12 months electric bill shows a total of 6,600 kWh. Add three zeros to the end to get total watts (6,600,000 watts). 6,600,000 / 365 = 18,082 watts per day For Northwest Arkansas the average Peak Sun Hours are from 4 to 5 hours. 18,082 / 5 = 3,616 watts in solar modules. Now lets add back in the heat, equipment and wiring loss of 15%. 3,616 * 1.15 = 4,158 watts in solar modules To completely wipe out your energy bill you will require 4,158 watts in solar modules as long as there is no problem with the shading survey. Look for a Solar kit system with battery backup in this list by looking at the array size. All you need next is to find a contractor in your area to install it. Or you can do it your self and hire an Electrician to get the permit and twist the wires. You will want a solar grid inverter that will be able to back feed all of the solar energy produced. No need for any larger unless it is a battery backup system. If by chance you have a large starting surge from an air compressor in your shop and it requires more power then your inverter can produce. The system will get the extra power required from the utility grid. In the above example we ended up with 4,158 watts in solar modules. Now to make sure this is enough energy to charge your battery bank. Divide the wattage of the solar array output by the battery bank voltage, (4158 watts / 48 volts = 86.6 amps output). You need a minimum of 5% rate of charge to get the watter to bubble in the battery bank (86amps / .05 = 1720Ah at largest), However, It is better to have a 10% rate of charge (86amps / .1 = 860Ah). You can have smaller battery banks because a good charge controller such as the Xantrex MPPT60-150 or Outback FM60 will control the charge and not over charge the battery or warp the lead plates. Plus using a good MPPT controller will down convert the voltage while increasing the amp output. You have less loss then using a standard controller. |
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