Harnessing the Sun

Readers if you can remember back to 2017 you may recall I fitted an electrical usage monitor to the house switchboard and started to collect data on our electrical consumption.  After a year of collecting data we have had a solar array fitted to the roof.  However before this could be done I needed to remove the old solar hot water system off the north facing side of the roof.  This was accomplished several months ago and I then started researching specific solar panels, inverters and installers.

Things started to accelerate when the current Federal government started making noises about removing the government rebate on residential solar installations.  At the time the government was subsidising almost 50% of the cost of a solar system with a rebate.  These “rebate credits” then have to be purchased by dirty polluters (ie, industries with harmful emissions).  Initially this was a good idea as solar systems were expensive and the subsidy (rebate) was a way of encouraging home owners to invest in “green energy”.  Of course there were other benefits to the nation such as it deferred the need for more major investment in power stations because surplus residential solar electricity was fed back into the network.

However the cost of solar systems has dropped rather dramatically during the last decade which has resulted in a rapid acceleration of residential solar system installations.  We have almost reached the situation where residential solar power generation will be a major contributor to the national demand. 

One problem is the cost of energy (eg, electricity) has risen.  Mostly caused by the failure to construct new power stations in the last two decades.  Moreover numerous old power stations have been decommissioned because they are heavy polluters which requires their commercial owners to pay an emissions tax.  Then you have the elderly, renters, and those with insufficient funds to pay for the installation of a solar system on their house.  Consequentially the government has been considering removing the rebate for residential solar installations and transferring the money as a discount/rebate to the “needy” who have to purchase expensive power from the large electrical utility companies (ie, those who don’t have solar). 

We decided to take advantage of the solar rebate before it disappeared.  We also decided to fit the largest possible array to the roof.  In Australia, by law the maximum size array you can fit to a grid linked house is 6.5kW.  So we had a 6.5kW array installed.

The installers completed the work over two days.  On the first day they fitted the panel mounting rails to the north and west sides of the house along with all the cabling

You can see the original red roof tiles in the next photo.  These were underneath the solar hot water system and didn’t get painted when the roof was repainted in 2016.

On the second day the panels were installed along with the inverter.

13 panels on the west facing side and 11 on the north.  Each panel has a maximum output of 275 Watts.  The north side gets sunlight all day and the west from 11am to dusk.

The inverter has two MPPT controllers and a maximum output of 5kWh

  

There isn’t a display on the inverter.  Instead you have to use a smartphone or Windows app.  Neither of which is particularly good.  More on that later.

The solar inverter works like any other converting the DC electricity produced by the panels to AC.  It also produces the electricity at a slightly higher voltage than the grid.  This is what forces the surplus electricity we produce back into the grid (against the flow) where it gets used by others.

As mentioned earlier, the inverter data monitoring system isn’t very good.  I’ve ordered a second Efergy clamp and transmitter which will enable me to have an independent and more detailed monitoring system for the solar array.  This will enable me to accurately measure consumption and production.

Currently it appears we consume an average of 10kWh daily and we are producing an average of 25kWh’s daily.  So we are selling 15kWh’s of surplus electricity back to our electrical utility company.  However some of our electrical consumption occurs when there is no sunlight.  When this occurs we have to purchase electricity at 30 cents per kWh from the utility company.  Our surplus is sold to the utility company at 7 cents per kWh.  Additionally the electrical utility company charges us a daily connection fee of 97 cents irrespective whether or not we use their electricity.

Two things have quickly become apparent.

1. Our 6.5kW solar system isn’t producing 6.5kW.  Actually the 5kW inverter has never reached 5kW.  Occasionally we get a spike in production of 4.2kW.  I’m discussing this with the supplier.
2. With a 6.5kW system we will never produce sufficient surplus electricity to be cost neutral or get a credit back from the utility company.

The obvious solution is to store our surplus electricity using it when there is no sunlight.  That means installing a battery and at the moment the cost of purchasing a battery system isn’t cost effective.  However I have this idea (project) of building a suitably sized lithium battery. 

But even this won’t solve our problem.   Regulations require residential homes to be connected to the “grid”.  So if we were to fit a battery and be self sufficient we would still have to pay the daily 97 cent connection charge to the utility company and I can only see that figure increasing.  At 7 cents per kWh it would take all our surplus electricity to pay the daily connection fee, leaving us with no surplus electricity to recharge the battery.

There will be a solution…. I just have to find it!