Green Oversite



Photovoltaic System

Bruce Barbour - June 2019

I have recently (at the start of March 2019) installed a photovoltaic (PV) system on my roof for the generation of solar electricity. The system is a nominal 4.3 kW system comprising 14 310 Watt Trina Honey Plus Monocrystalline Solar PV Panels and Enphase IQ7+ Microinverters. The panels are on three orientations. The system is grid connected with no batteries. You can view the electricity production and other details at this link. The PV system was a lot more expensive than many of the advertised systems I saw. By paying the additional amount I am hoping that I am buying quality - a system that will last at least 20 years without significant issues. Time will tell whether that decision pays off.

I have been satisfied with the operations of the system thus far. Although it is now (June 2019) at the start of winter on the majority of days it generates more electricity (kilowatt hour - kWh) than I use. My energy usage is fairly modest averaging about 6 to 8 kWh per day at the start of winter (less during the "shoulder" season when no space heating or cooling is needed). There is no gas connected to the property so electricity is used for all heating, cooking, lighting and other functions. Not having gas connected to the house means lower carbon dioxide production and also a cost saving to me in that I don't have to pay for gas usage nor the quarterly gas property service charge for the house - at around $320 per year, depending on the distributor chosen. The low electricity consumption is assisted by having the hot water heated by a heat pump system (Sanden) and the space heating provided by a reverse cycle air conditioning system (Daikin Inverter split system - 0.9 kW input power) and a new refrigerator (LG - 300L) that uses about 0.66 kWh per day. The lighting in the most used areas is LED (batten fix). CFL lighting is used in other lower use rooms and will be changed to LED over time.

Update December 2019: I installed pelmets and lined curtains on the double glazed windows in the main (heated) living area in December 2019. I hope that these may further assist with the energy efficiency of the house. I installed another 4 LED globes, replacing CFLs. This leaves about 6 CFL light globes on the house - most of them for outside lights which have low use.

The hot water system is set to commence heating at 11 am (Australian Eastern Standard Time) in the morning and can continue until 4 pm. I chose this time as by then the PV is approaching (at 88% of) its peak production, which is typically at around 12:30 pm on a cloudless day. Usually the system commences heating at 11 am winter (12 Noon in summer) and has switched off by 12:30 pm (1:30 pm summer). The Sanden heat pump hot water system uses approximately 1.2 - 1.3 kW when on. It was rated at 1 kW so I don't know what is happening there - may be because in the colder weather it uses more power? Even in winter on sunny days and days with some light cloud cover the PV system is generating more than a kilowatt during that time - and I try to avoid other large power loads during that period. In summer the system is often generating over 3kW during that period, easily covering the heat pump's 1.1 kW demand. Usually the water is being heated with electricity from the PV system, though on overcast days it draws some electricity from the grid. The system works well and I recommend this approach to hot water heating for people with a grid connected PV system (>4 kW). (There are other hot water heat pump systems around that draw less power - less than 0.6 kW - which may be suitable for use with smaller PV systems.)

Refer to the My House page for further details.

Western Panel Energy Production

It is interesting that the production from the panel on the West side (actually oriented 20 degrees off West at 250 degrees) is a lot less than the North facing and also the East facing - at this time of year - July. I was expecting some lower production from these panels but on many days it less than 50% of the North panel production and less than the East panel production. I anticipate that the difference between North and West energy production will be a lot less during summer when the sun is higher in the sky and will shine more onto the West panels. The figures from March 2019 - the time when the system was turned on - show this trend. However the North panels will still generate more.

I should have investigated getting more panels onto the North face instead of just accepting the recommendation for that face from the installer. I think the number of panels on that face could have been doubled to six if the panels had been laid horizontally instead of vertically.

December 2019 update: On 22 December, which was a largely cloudless day and happened to be the summer solstice - the longest day of the year, the system generated 31.5 kWh, which is the highest daily total generation for the system. Being the longest day of the year I expect that this may be the highest peak that I will get. The panels on the North and the West generated an average of 2.28 kWh each. The panels on the East face generated an average of 2.14 kWh.

Maximum PV Output
                December 2019

My expectation was largely correct - except that the statement that the North will still generate more than panels on the West in summer is not correct - at this time of year they are roughly equivalent. Having the panels on the three faces increases the amount of generation in the morning and in the afternoon meaning solar is available over a longer period of time during the day, which is advantageous.

Incidentally if I had not been connected to the grid approximately 28.5kWh of the 31.5kWh would have been wasted. Also on the graph note the rather small "bite" taken out of the PV production by the heat pump hot water system.


I had to decide whether I wanted batteries. This was fairly easy at the time as most experts were saying (in March 2019) that batteries for domestic installation in areas with grid electricity available could still not be justified economically. Simple back of the envelop calculations showed that this was a correct assessment.

Update - December 2019: However, on reflection, perhaps economics should not be the primary consideration - there are benefits to the grid and to decreasing greenhouse emissions from installing batteries that make them worthwhile considering, especially if they are part of a scheme that allow the electricity distributors to obtain power from domestic batteries and pay the home owner for it. And if Government is not doing enough it is one way to increase Australia's action, despite Government. I will reconsider installing batteries in the future once a scheme to allow distributors to use the excess domestic battery capacity, with payment to the batteries owner at premium rates, is available. Without that type of scheme it is likely that batteries that I purchased would be under utilised (except if I purchased a small battery pack). There also might be some kind of Government subsidy for batteries in the future that may make them more attractive. Some reportage suggests that as battery powered cars became more prevalent the batteries in the car may be able to be used to power the home when the sun is not shining.

Update - November 2019: I would not consider purchasing an electric car at this time firstly because they are still expensive but secondly they would not lead to much saving in greenhouse gas (GHG) emissions, while the country's level of renewable energy is still way below energy consumption. Even if I was charging primarily from my PV system, this may mean my personal green house gas production is less and my costs would be less, but my PV electricity would then not be available to the grid meaning that more fossil fuel energy would need to be produced. So overall there may be little GHG saving. Though I will say this - someone needs to be buying electric cars at this time, as the design and production of the cars, and construction of the infrastructure necessary for total fleet conversion cannot happen overnight. It has to start rolling out before there is the excess of renewable energy that will be necessary in the future. The primary requirement is to decarbonise our electricity grid as quickly as possible. With a decarbonised grid there is going to be times, primarily in the middle of the day, when there is excess electricity which would be available for electric car recharging.

A couple of more points about batteries. If I do elect to install batteries in the future I would probably install a small capacity battery pack, say 4 kWh, and still remain connected to the grid. This amount of batteries would allow me to draw no power from the grid for, say, 95% of the days. Remaining connected to the grid also allows me to sell my excess back to the grid. If I wanted to disconnect from the grid I would probably need to at least double the amount of batteries, to 8 kWh - though many experts recommend a battery capacity of 4 times the daily usage for off grid. I may also have to increase the number of panels. For this large increase - 2 to 4 times - in cost, I would save the electricity imported from the grid on those 5% of days and I would save the electricity distributor's property service charge, approximately $360 per annum (June 2019). However I would lose the opportunity to sell my excess electricity back to the grid, which in summer would be well over 20 kWh per day (for over $2.40) on clear days. I will know more precisely when I have run the system over a summer. I am hoping the amount that I sell back will cover the cost of the electricity property service charge, plus some more to cover the cost of the grid electricity that I use. The other aspect of this is that it would not just be a loss to me, but a loss to the whole grid. If I was not connected to the grid the excess PV power generation (20 kWh per day in summer and more) would be wasted. My PV infrastructure, and its embedded energy, would be partially wasted. Additional infrastructure may have to be built in the grid to cover for the admittedly small loss of my PV system to the grid. It is a waste that should be avoided.

Update January 2020: - In December 2019 the system produced 757 kWh - an average of 24 kWh per day. In the same month I consumed 134 kWh - 4.3 kWh per day. This means that the net export to the grid was 623 kWh (worth $74). If I was not connected to the grid this energy would not have been produced and therefore wasted. 
For comparison, six months earlier, in June 2019 the system produced 241 kWh - 8 kWh per day - and I consumed 207 kWh - 7 kWh per day. The greater usage in June, compared to December, reflects the use of the reverse cycle air conditioner for heating during winter.
This comparison with my small system indicates an issue and an opportunity with renewable energy. The issue is that in order to meet winter demand we are going to have to install a lot of renewable energy which means that there will be a surfeit of power available in summer. This is an opportunity. This power will be cheap and plentiful. It can be used for, say, the generation of hydrogen. Generation of hydrogen may need to be turned off in winter to make the power available to other less flexible industries. There may be a number of these type of industries that only work part of the year.

The point of this is that I want to discourage people with PV systems that are currently on the grid from exiting the grid when the cost of batteries falls to a point that allows it to occur economically. Hopefully systems will be in place that will make it more economically advantageous to stay connected, such as where the distributor can access power from the householder's PV system, including the battery storage, at times of high demand and low supply, and pays the householder a premium rate for the privilege. Or a payment system might be developed where the householder can remain connected to the grid so they can still sell their excess PV electricity to the grid, but pay a heavily discounted property service charge as most of the electricity is leaving the property. Under this arrangement if the householder wanted to take electricity from the grid, to cover an electricity shortfall from their PV system in a period of low solar, they would have to pay for it at a premium rate per kWh.


April 2021 Update:

As of April 2021 I have had the PV system for just over 2 years - 25 months or 760 days. During that time the system generated 11.4 MWh. This calculates out at 15 kWh per day. As I have 4.3 kW of panels installed this calculates as 3.5 kWh/day/kW of panels. Your Home Manual suggests that Melbourne gets an average of 4.5 hours of peak sun per day on average which should mean given perfect conditions a kW of panels should generate 4.5 kWh. However the panels on my system are not orientated in the ideal direction (True North), being on three different orientations due to the roof configuration. The lower generation is partially offset by the benefit of PV electricity being generated over a longer part of the day.

During the 25 months of operation my electricity consumption was 4.1 MWh. This means I was generating 2.8 times more electricity than I was consuming. This will at least partially offset the embodied energy / carbon in the house construction and my carbon footprint from other activities.

Financially I still get a small electricity bill. (And of course no gas bill.) Last year I paid a total of approximately $100 for the whole year. While I was getting credit for the extra electricity I was feeding into the grid this was insufficient to fully cover the cost of the grid electricity I still needed to import after dark and on overcast days, and the annual service charge for electricity.


I will update this page if I have further observations to report.

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