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Off Grid Systems
Components of an Off Grid Solar Electric System:
- Solar Panels - Turn sunlight into 12, 24 or 48 volt DC electricity.
- Combiner Box - Combines the Solar Panel wiring into one circuit.
- PV Disconnect - Isolates the Solar Panels (can be in the Combiner Box).
- Charge Controller - Regulates the DC current going to the Battery Bank.
- Battery Bank - Stores the DC Electricity for later conversion to AC by the Inverter.
See Below.
- DC Disconnect - Isolates the Battery Bank and protects from surges.
- Inverter/Charger - Converts the DC power from the Solar Panels and Battery Bank
into 120/240 volt AC power. Also can automatically start a Generator if
the Batteries need charging during long cloudy periods.
- Generator - Charges the Batteries through the Inverter when there is no sunlight
and runs large loads when required.
- Main Service Panel - Distributes the Inverter Power to different circuits
in the home and elsewhere. Each circuit requires an appropriate Circuit Breaker.
- Transfer Switch - Isolates the Inverter Power from the Generator Power.
- Ground Block - Grounds the DC side thru a Ground Rod.
Sample Off Grid System Schematic
About Storing Electricity in Batteries
- Batteries have a capacity measured in Amp Hours rated on a 20 hour full discharge.
So an L-16 rated at 350 Amp Hours would fully discharge in 20 hours at 17.5 amps.
- Do not discharge Batteries more than 20% of their rated capacity (50% for
Deep Cycle) To preserve their lifespan do not leave them discharged for a long periods.
- Deep Cycle Batteries require regular maintenance including refilling with
distilled water, cleaning the terminals and Equalizing the cells. Equalizing
involves charging them until they reach 15 volts for a 12 volt system, 30v for
24 volt system, or 60v for a 48 volt system and continuing for 2 hours. This boils
the liquid inside which makes it homogeneous and it also cleans deposits on the metal plates.
Do not charge at a rate above 5% of the rated Amp Hour capacity during Equalization. It is
recommended that Batteries be equalized monthly.
- Batteries can be combined in series (+ to -)which doubles the combined voltage (but does not increase the
capacity)or in parallel(+ to +)which doubles the amperage(and capacity)or in a combination of the two. So a 24 volt system would need 1 or more parallel sets of 4 6-volt Batteries in series.
- Do not mix new batteries with old ones in parallel banks. The new ones will try to charge the old ones
resulting in a looping circuit that wastes power.
- Battery Banks should be well ventilated and kept away from electrical components.
- L-16 Deep Cycle Batteries should last 8-10 years or 1280 discharge cycles to 50% capacity.
How to Size Your Solar Power System
- The system sizing calculator you can link to below will give you a rough idea of the number of solar panels and batteries your system requires to power the loads you put in.
- List all the things that you will need power for along with the hours per day they will be used. (To make the system as small and cheap as possible, I suggest combining items like toasters and microwaves into one entry and
planning not to use them simultaneously)
- Enter the rated watts for each item. (There is a link to a power usage table at the top of the calculator)
- You may change the default values for the batteries and pv array to customize the calculations for your components. The default for Days of Storage is 1. If you want longer storage, change the days to what you want. Longer storage requires more batteries and that can get expensive.
- Read the Solar Script Help Page for more tips.
- Click here to visit the Solar Off Grid System Calculator.
Sample Results
from
Off Grid Calculator
For more information call (707) 462-2427 or E-mail Collins By Design
Cal Contractors Lic #B557124
Pictures compliments of Advance Power and Zapsucker.com
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