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One of the most frequent questions I am asked is “How big a system do I need or how big can I go?”  Without providing any other detail that really is like saying how long is a piece of string and is all part of the system design.  System sizing is dependent on a lot of factors such as motivation for getting a PV System, budget, roof area and believe it or not advertising.  Generally, we can get a guide from your electricity billing more so from the daily kWhr figure (Kilowatt-hour- the amount of energy used) that is on the bill rather than the dollar amount. The dollar amount is used later in the design for working out the payback periods and economic returns on the system.

But to really design a good system we need to work out WHY what motivates you to get solar? This can vary from the need for power supply in the event of a grid failure if you are looking to reduce the amount on your electricity bills or you could just have a desire to reduce your impact on the environment.  Once we know the WHY then we work out the POSSIBLE, how much space (ground or roof) is available for mounting the system, factors that will limit solar production such as shade or the direction the system will face.  Then there is the electrical supply authority to contend with (in regional NSW that is essential energy as opposed to your retailer who you pay your bill to), they can impose an export limit on your system.  

This basically means you can have a system as large as you like, but if you can’t use the power, it is just wasted like rain going into a full water tank.  For example, if you have a system that can produce 10kW, essential energy may impose an export limit of 5kW on your system, if you are only using 2kW within your house only 5kW can be sold into the electricity network which leaves 3kW just being wasted away. In this scenario, the system is just too big.

Then comes the BUDGET which can have a little EXPECTATION mixed in, this can put a damper on the POSSIBLE. There is little point in designing a system that can have you self-sufficient for days without power with controllers for your pool and hot water system, a car charger for the new electric vehicle you plan to buy in a couple of years (you think I jest). What we can do, however, is make sure the system we design for now and the components we use to give you the best chance at expanding the system and adding onto it in the future with minimal fuss.  But if there is a need for everything now or have the need for a system that’s a little over your budget then finance can be a viable option.

There are a variety of options these days including a no-cost system with guaranteed lower electricity bills of 30% or more, personal loans or, if available, redrawing on your mortgage. Most solar systems designed for a budget can have a payback period under 5yrs with savings outweighing the cost of finance. “Hang on Scott, did you say I can have a system without spending money AND I get cheaper power bills?”, well yes, I did but there can be a lot of options for finance so you may have to tune into a future blog where I will cost out some of the options and list the benefits and pitfalls.

So now we have the WHY, the POSSIBLE and the BUDGET, we need to manage the EXPECTATION. This can be the hardest part. Most people start their journey into solar that have very limited knowledge, most of which is gained from a google search, reading the paper or seeing big exciting ads on TV advertising massive 6.6kW systems. This is hard because how do you argue with big advertising.  Honestly, a 6.6kW isn’t that massive anymore, it is an average system and may suit some households but not all, with household electricity loads increasing with air conditioning units and pools you may find this system is undersized for your needs now and won’t give you further options for the future in a couple of years when you have your electric vehicle.

So how big a system do you need? It is a balancing act that I am more than happy to help you with and provide a variety of options that can meet your needs now and in the future. I hope I have answered a few questions and make you start you thinking about your solar journey.

Guest Blogger – Scott McAllister

www.precision-solar.net