Solar Power – Photovoltaic’s
As we all know, Solar Power is the creation of electricity from the sun using solar panels to harvest the sunlight and turn it into electricity.
The are two main categories of Solar Panels
Standard Rigid Panels used in the conventional solar systems we see on house rooftops, and Building Integrated Solar Panels (BIPVs) that are integrated into the building materials such as windows and roof structures.
With the standard rigid panels, there are two main types;
Mono crystalline and Poly crystalline.
Mono Crystalline panels use groups of single cell silicon crystal which have very little electrical resistance within the cell due to the configuration of the cell to make up a solar panel.
Poly Crystalline panels use groups of multi crystal silicon cells. In multi crystal cells the silicon is many pieces all formed together in different directions which causes a higher resistance and therefore less efficiency.
This is why Mono crystalline cells have a few percent higher efficiency than the Poly Crystalline panels.
There is a trade off, as Mono crystalline cells are black which heat up more than the blue Poly Crystalline cells and therefore lose electricity in the form of heat.
Price wise, Mono Crystalline panels are a little more expensive than Poly crystalline.
The trend today seems to favour the use of the slightly cheaper Poly Crystalline panels.
An inverter is required to transform and regulate the DC current coming in from the panels and to step up the voltage to transform it to household 240v AC.
Inverters also have what is known as MPPTs (Maximum Power Point Tracking). MPPTs track the suns power and maximise the amount of power the solar panels can deliver.
A MPPT will only track the power from one angle of the sun, so if the solar panels need to be installed on two roof faces with different orientations, then an inverter will need to have 2 MPPTs
An inverter usually has one or two MPPTs.
Inverters are best run overloaded than under-loaded. It is quite safe to run a good quality inverter at 30% above its rated operating size; for example a 3kw inverter could run an extra 0.9kw, provided the panels combined voltage matched with the inverters total voltage input.
If the inverter is overloaded and the panels all face due North; then during the peak of the day the power input may exceed what is expected, this is the main reason to choose a good quality inverter so that it de-rates if the load becomes too much, such as a Fronius inverter.
There are four main different types of inverters used for household and commercial solar power systems; Grid Tied, Hybrid, Stand Alone and the smaller 12, 24 and 48 volt portable type of inverters as used in camping
Grid tied, means the inverter needs the power grid to work, when the grid goes down the system stops working.
Hybrid inverters also known as battery ready, are equipped to charge up batteries but they are also reliant on the power grid to work.
Stand Alone Inverters are used in Battery Storage systems not affected when the power grid fails and can still deliver power.
How much power does a system deliver
This is worked out on the size and amount of panels and the amount of sun and the orientation of the panels.
Traditionally it is best to align the solar panels due North so they get the maximum amount of sun during the best part of the day.
But there is a growing trend and with good reason to align the panels North east and North West as well as North
The reasoning is that the North East orientation will get more sun during the morning and winter months and the North West will get more sun during the later part of the day.
To calculate the amount of power a system will deliver, multiply the average amount of hours per day by the size of the solar system to get the amount of kwhs produced by the system per day.
In Perth there is an average of about 7.5 – 8 hours a day.
A 3kw system would deliver 3 kws an hour or about 23 kws a day, about the same amount as the daily average household power consumption
Sizing up a system for your household needs
To size up a system for your house, look at the power bill to see how many kwh units you use daily. This will tell you you how many kwh a day you need your system to produce.
In most case a 3 -4 kw system is more than enough for most families, bearing in mind at night the grid is being used, or a 5kw system for a larger household.
Without doing some exacting calculations and referring to the household power bills, it is difficult to give a correct account of the pay back period, but an average estimate would be somewhere between 3 to 5 years, which is very good when you consider the system will last a good 20 years.
Future Proofing your Electricity Bill
If thinking about battery storage, then a slightly larger system would be needed to make sure there is enough power for daytime use and enough to charge up the batteries for night time use.