One of the biggest decisions for any engineer when designing a system is reliability. However, you don’t have to be an engineer to design your own Solar Energy Panel system. Well, not after you read about these system design tips!
The graph above is a visual example of the “80/20 or 20/80” design rule. In short it means that when you design a system you can design 80% of it for 20% of the cost but to pursue the rest of the 20% of the reliability it will cost more than an additional 80%.
So what does that mean when you decide to look at your system design criteria:
1) How much do you want, or what loads do you want to run?
Washing Machines, Dryers, Dish Washer, Fridge, Toaster, Coffee Machine, Ceiling Fan, Television (HD or Standard) and lights, all have different rates of consumption. Nonetheless a solar energy system can be designed to run most if not all of these appliances simultaneously. However, to optimize the design you must understand the energy intensity of your habits.
Do you use the washing machine and the dryer at the same time?
Do you use the Toaster, Coffee Machine and the TV at the same time?
Do you use the Lights, Ceiling fan and Dishwasher at the same time?
After answering questions like these you can narrow down the activities that you do on a day to day basis and find out what the largest amount of electricity that you consume at any given point in the day is. This will give you guidance on a soft upper limit on your design.
2) Site Constraints?
Space on roof, shading caused by surrounding objects like buildings or trees or billboards, cloudy days, and local insolation data will all play crucial roles in determining the site-specific efficiency of your system.
Thus having found out your most energy intensive habits and the amount of sunlight available (site-specific efficiency) to you on your roof you have almost come close to an optimal system size.
3) How far does your wallet get you?
Once you’ve found out the upper limit of your consumption habits and your homes lower limit of solar energy available, you can reach a number in Kilowatts that describes the size of a system that would give you, according to the “80/20” rule, a system reliability of 80%. This value could be higher depending on the lower limit of the solar energy that can be captured on the roof of your house.
A common next step, in a non-grid-connected home, would be to consider storage, to increase system reliability, and a common misconception during this step is that buying more batteries/inverters and running them hard will allow you to get greater returns on your investment. However, one must remember that modules last longer than batteries/inverters do and even though it might seem economically beneficial to buy more inverters you can only store based on how much you generate and use during the day.
Written by Prateek Chourdia
MEngSc – Photovoltaics and Solar Energy, UNSW
Solar Energy Analyst
© 2010 Solar Choice Pty Ltd