To get the most out of a solar power system (performance/payback on your investment) solar installers can make a recommendation for a system size that will best suit your needs. Ultimately, the choice is up to you.
When filling in the My Solar Quotes request for 3 free quotes form, you can choose the option from the drop-down list that states 'I don't know - please suggest the best system size for me' (in the section that asks what system size you would like). Once your quote request has been received from solar installers they will take into account how much power you currently consume and the time of day you consume it, to determine a suitable system. Roof size and your personal budget are other factors to consider when making your decision.
When discussing solar power system sizing, industry folk tend to refer to sizes as kW's. Before purchasing a solar power system, it's important to know the difference between kW and kWh's. In the short video below we discuss kW and kWh's, and why they are key components in solar power systems.
Solar power systems are available in a range of sizes, but the smallest system a solar panel installation company will (generally) offers is 1.5kW. Solar power systems for households rarely go above 10kW in size.
A 6kW solar panel system produces enough electricity to match the average New Zealand household's consumption of grid produced electricity (which is 7,000kWh a year). However, matching a system size to your power demands won't eliminate your power bill. When exporting a percentage of power to the grid, power companies don't pay as much for your exported power as what they charge for power. See buy-back rates here>
If the aim is to eliminate your electricity bill, then you will need to increase your solar power self-consumption, and/or include battery storage.
A 3kW grid connected solar power system has proved to be a popular system size in New Zealand, due to the fact that it will make a significant change to your power bill and is relatively affordable (around $8,000).
A 3kW system in Auckland generates approximately 3740kWh/year. For the average New Zealand home, eliminating your power bill with a 3kW system is unlikely. However, a slightly smaller system (3kW size) will ensure that a large portion of the power from the system is used by your household with less power being exported to the grid, maximising your return on investment.
Above: A 3kW solar power system in Tauranga
The different system sizes can be confusing - 1.5kW, 2.3kW, 4.5kW. What's really important is to find out how much power a system will actually provide over a year and what your return on investment will be.
For the sake of simplicity: having a 1.5kW system means that at any given time on a clear summer's day the system will produce up to 1.5 kilowatts.
This graph is provided only to help reinforce the point above; the data is not precise.
A 1.5kW system in Auckland will produce an estimated 2,000 kWh annually.
If you would like to start with a smaller system it is possible to scale the system size up after a year or two. Scalability can be achieved with all micro-inverter systems, and selected string inverter systems.
Considerations when installing a string inverter;
Initially you will need to install a larger inverter. You could have a 3kW system with a 5kW inverter, for example, and add extra panels in the future to build up to a 5kW system. However not all large inverters are compatible with smaller solar power system sizes. Ask your solar power installer which large inverters will be compatible with a smaller system (to start off with).
Secondly, you will need to make sure you can get the same sized panel in a few years' time. If you initially go for standard 250W panels, then you should be able to order these panels again in the future. This is important; if you purchase panels that are a different size your solar power systems overall performance might decline.
You need to be sure you have enough roof space to add extra solar panels to the system at a later date.
Being modular, a micro-inverter system can have one panel added at a time. However, you would need to consider the cost of getting an installer out to your house every time a panel needed to be installed. There is no need to match new solar panels to existing panels should you wish to install more in the future.