THE "OFF GRID" SOLUTION
Most people interested in solar usually would like an "Off-Grid" solution. "OFF-GRID" Now there's a term we hear often, but just how feasible is an off-grid solution? How much will it cost and is it ever truly off-grid?. Yes off-grid is possible but one needs a tremendous amount of money or make some serious life style changes if you want to go "off-grid". Operating electrical ovens, stoves, hot plates, geysers or any other high load household items will increase the total cost by minimum 300%. Changing these to gas or any alternative will bring the total "off-grid" cost down quite significantly. The term solar assisted should rather be used. Here we use as much as possible (or what our budget allows) solar energy and revert back to the grid when needed. To follow is an example of a very moderate "Off-Grid" solution for the low to mid energy consumer. In reality it is still a solar assisted system for larger homes whereby most energy is generated from solar.
First we need to calculate our total power requirements:
I) Take an Eskom electricity meter reading every morning at 09:00 and again at 16:00. Do this for a whole week (7 days). Day - 09:00 - 16:00 - TOTAL Tuesday - Day = 8KW / Night = 12KW (20KW/H) Wednesdays - Day = 8KW / Night = 12KW (20KW/H) Thursday - Day = 8KW / Night = 12KW (20KW/H) Friday - Day = 8KW / Night = 15KW (20KW/H) Saturday - Day = 11Kw / Night = 12KW (23KW/H) Sunday - Day = 10KW / Night = 12KW (22KW/H) Monday - Day = 8KW / Night = 12KW (20KW/H)
From the example above we can see that the average usages per day is around 20KW/H but we will work with the maximum usage 23KW/H
II) Calculate your needs: Day = 11KW/H (This will determine our solar panels) Night = 15KW/H (This will determine our batteries and solar panels) As a rule of thumb we do NOT use the average power consumption but rather the highest day time and night time figures. In the above example we will be using Day=11KW and Night=15KW. This is our benchmark that we start our calculations from.
III)Locate the most power hungry devices in your home and calculate the time of day they are used and how many of them are used at the same time. The idea here is not to calculate the total power consumed but rather to estimate the highest power load at any given time. Equipment - KW/H - Day/Night Kettle / Coffee Machine - 3KW - Day/Night Clothes Iron - 1.5KW - Day Clothes Washer - 2KW - Day Tumble Dryer - 3KW - Day Dish Washer - 2KW - Day Hair Dryer - 1KW - Day/Night from the example above we will choose a combination of devices that consume the most power when turned on together. During the day we may use the Kettle, Clothes Iron and Hair Dryer together. At night we may use the kettle and dishwasher together. Day = 3KW(Kettle) + 1.5KW(Iron) + 1KW(Hair Dryer) = 5.5KW - This equates to the maximum power consumed at any one point during day time. Night = 3KW(Kettle) + 2KW(Dish Washer) = 5KW - This equates to the maximum power consumed at any one point during night time. These totals we can calculate the size of the inverter and the maximum drain that the batteries need to withstand.
IV) INVERTER SIZE & TYPE: For Off-Grid solutions it is essential that a TRANSFORMER based inverter must be used. These are the only inverters that can withstand the immense in-rush current required by electrical motors and inductive loads (Fridges, Freezers, Hair Dryers, Toasters, Water Pumps, etc.). When working with solar we use a "magic" number, 1.2 to calculate our needs. From the above example we need a 5.5KW inverter. 5.5KW x 1.2 = 6.6KW, closest available inverter is 8KW. We now know that an 8KW inverter will be ideal for our installation. Choosing a larger inverter will have many implications on costs, battery size and conversion efficiencies. Choosing a 5KW inverter means some life style changes (which is easily achievable with the correct mind set). Inverter Size = 8KW
V) BATERY SIZE: NB! When it comes to solar there is no such thing as too much stored power. We need to compensate for weeks of rain and cloudy weather during rainy seasons. We know from the above that we need at least 15KW/H for our batteries at night. But what happens when it's over cast or heavy rains? There will be no sun to charge our batteries so we need to compensate for that as well. Max/Day 11KW/H + Max/Night 15KW/H x 1.2 = 31.2KW. This is the size of the battery bank that we need. Battery Bank Size = 31.2KW
VI) SOLAR PANELS: We need to charge the battery bank at between C0.25 and C0.5 (25% to 50%). Meaning we need at minimum 31.2KW / 4 = 7.8KW Solar Panels or ideally 31.2KW / 2 = 15.6KW Solar Panels x 1.2 = 18.72KW Solar Panels = 18.72KW OR 40x 465W Panels
VII) MPPT CHARGE CONTROLLER: Since it will be nearly impossible to place all 40 panels in exactly the same location we will break them up in separate strings. For this we will need MPPT Solar charge controllers. Charge controllers = 4x 100A (5KW) MPPT = 20KW
COSTS - HOW MUCH CAN ONE EXPECT TO PAY? (NB! 2022/2023 Prices - This is not a quotation) 8KW TRANFORMER BASED INVERTER (VICTRON or MICROCARE) = R38,000.00 to R78,000.00 35KW Lithium batteries = R220,000.00 to R300,000.00 4x 100A MPPT Charge Controller = R45,000.00 to R 55,000.00 40x 465 Panels = R110,000.00 to R150,000.00
This system (Victron or Microcare TRANSFORMER inverter), fully installed to PV GREEN CARD specification R650,000.00 to R1,000,000.00 (site dependent).
NB!! SHOULD THERE BE THUNDERSHOWERS FOR A WEEK THEN THE "THEORETICAL" SYSTEM IN THE ABOVE EXAMPLE WILL NOT GENERATE SUFICIENT ENERGY TO POWER THE HOME DURING THAT TIME UNLESS A GENERATOR IS ADDED OR SIGNIFICANT POWER USAGE MANAGEMENT IS APPLIED.
In reality there are numerous options, much cheaper and smaller, to choose from, please contact us for a custom designed system that will suite your home's needs.
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