Getting The Most From Your Solar PV Investment

You want to save the planet right?  So you buy a solar PV system and install it on your roof.  But how do you get it to pay itself back quickly and still receive the lowest electricity bill possible? 

Glad you all asked because I received this email today from a reader who asked exactly that.  She wanted to know why her power bills were still very high when she received a feed-in tariff, and followed the recommendations of her Solar installer.  Over to Pam.

Hi Gavin,
Quickly caught your segment on ABC Local Radion yesterday, and felt you may be able to help answer a couple of solar/grid questions that have perplexed me of late.
We are in a rural area in northern NSW, with three electric pumps to deliver water from tanks and for us in swimming pool, plus fridge, freezer and usual domestic appliances including electric oven and gas cooktop.Country Energy is our grid supplier.  Our annual electricity bill hovered around $2000 per year. 
Our household consists of three people, plus a fair amount of hosing etc is done outside as we have quite a few domestic animals.  (While we do also have livestock we use a petrol pump to draw water from a creek, which is then gravity fed to their water trough.)
We installed a 1kw solar photovoltaic system, grid connected, in September 2009 (2 ks inverter).  Following installation, and advice that daylight power usage will be through the solar panels, we changed our methods so that all washing, ironing, vacuuming and other household activites would be done during daytime while nightime use is restricted to electric oven and water consumption, plus the frige/freezer burbling away at night.  Hubby switched the running of the swimming pool pump to daytime only.  Naturally I turn off standby lights as much possible in the evening, very Gavin-like!  Lower energy light bulbs are used, however I do find that the resultant loss of brightness is irksome, especially in winter. 
Due to a mix-up with electricity bills for the first six months it was difficult to ascertain actual grid cost-savings, although summer did appear to be slightly less than usual.  I understand our solar panels generate 9 kWh per day, while our bills suggest our consumption is 21 kWh per day.   (Although their graph states 24.9 kWh)  Very disappointingly, our recent bill, for three quite wet months, was $630.  (Credit for Solar Bonus Scheme Net was $13.20)
I have thought of utilising some water containers besides the sink and hand basins to avoid pump usage at night (family not too keen on idea, however). 
We have been quoted around $4000 to increase our system to 1.5 kw
So, if you Would be so kind, I hope you can answer some of my questions:
a) Is is true that (on sunny days) all power usage should be from the panels?
b) Can our fridge and freezer really then use all of the remaining 12 kwh overnight, whilst we sleep?   Wouldn’t this be off-peak, if that term still exists?
Other than building gravity fed tanks, at great expense, I can’t think of any other ways to save energy, without greater minds than mine stepping in! 

Thanks for the email Pam.  Here are the answers to your two questions
Q1.  This all depends if you get paid a premium for the power you feed back into the grid.  As I live in Victoria, we have a Premium Solar Feed-in Tariff of 66c per kWh.  So I do quite the opposite of you, and I think you were given very dodgy advice by your installer.  This advice has cost you a lot of money!
Most of our electricity usage is during the night after sunset, because I want every single watt I generate to be fed back into the grid during the day, so that I get paid the premium.  You indicated that you are part of the NSW Government Solar bonus Scheme, which from my understanding pays you 60c per kWh.  To maximise your return on investment you need to use the least amount of electricity during the day so that the excess is fed back into the grid.  Here is a more detailed explanation.
My pool pump only runs at night, as does the washing machine, dishwasher, and dryer if it has been raining for a week and I am running out of jocks :-).  All the heavy energy demanding appliances and pumps.  We buy 100% Green Power from the grid which only costs me 25c per kWh, and we try not to use the day time power generated by my Solar PV system which is worth 66c to me.  
So for instance, if it was a sunny day and I generated 10 kWh, and I used 10 kWh during daylight hours I would mostly be drawing that electricity straight from the solar PV system.  Therefore, I would be ripping myself off by 41c per kWh utilised.  If I did this every day it adds up to a loss of $4.10 a day or over a 90 day billing period that adds up to a whopping $369.  A massive difference as you can see.  The way I see it by using you electricity during the night when I am not generating electricity, I am still carbon neutral and am just using the system to my advantage!  Certainly no crime against that.  Use your power at night and maximise your Solar PV investment.

Q2  Yes, the fridge and freezer could use that much electricity, as my old pair used to draw 10kWh per day.  Also if they are old models they tend to be heavy power users, with newer models being at least 4 times as efficient.  My new fridge (2 years old) only uses 2 kWh a day and it is a large model split fridge freezer.  Maybe check if the seals are in good condition, because a lot of energy can be wasted via leaky seals.  If you have a co-gen meter or smart meter installed by your energy wholesaler, then it is more than likely that you will be paying the same tariff from the grid all day long.

I hope that answered you questions, and has helped all those people who own or are thinking of installing a grid tied Solar PV system.

May the Sun shine on your panels for eternity!


  1. says

    Just another idea. Swap electrical companies. Some companies offer more than 60 cents. AGL ofer 66cents per kilowatt and Orign Energy Offer 68cents. They are NSW companies.

  2. says

    A couple of comments:

    – The NSW solar feed-in tariff is a gross tariff, so it doesn’t matter what time of day you use electricity. You’ll be paid for everything you generate.

    – There’s no way a 1 kW system would generate 9 kWh/day. It would be more like 4-5 kWh/day.

    – Most inverters have a way to read how much power you generate each day. Check your manual, and then keep track of the numbers over a few weeks. If the reading is significantly less than the 4-5 kWh/day on sunny days, you may have a problem with the panels (wiring, alignment, dirt buildup, shade, faulty panel, etc).

    – Check if you’re on time-of-day metering (probably not, in rural NSW, but check anyway). If you are, you’ve moved all your consumption into the most expensive time of day! Electricity would be cheaper at night. If you don’t have time-of-day metering, then electricity costs the same whether it’s day or night.

    – Investigate more energy-efficient swimming pool systems. The standard systems use a lot of electricity, but there are systems that use much less. Also have a read of this booklet:

    – Off peak power is only used by appliances plugged into the off-peak circuit of your house. This is typically only a hot water system. As far as I know, it’s not legal to plug other things into this circuit (check with your supplier).

    – In all this, remember that it’s much, much cheaper to save 1 kWh of electricity than to generate 1 kWh. You’re doing the right thing to cut back your consumption wherever you can before spending money to generate more. Expanding your system by another 0.5 kW (generating 2.5-3.0 kWh/day) will cost you around $4000 (according to your quote) – you might find you could spend a similar amount of money on more efficient appliances, a new pool pump, insulation, or whatever and save much more electricity per day.

  3. says

    NSW has a gross feed in tarrif. It doesn’t matter how much energy you use, you get paid 60c per kilowatt hour for everything your system generates.

    Having said that, our power usage is similar, around $2000 per year (on Green power at 20c per kwh) and we needed a 3.2kw system to offset our bill completely.

  4. says

    I have another comment on the fridge – check where you have it positioned in your kitchen. We had ours in a spot where it didn’t get much air circulating around it, so if wasn’t operating efficiently. We moved it to another spot where it is open on most sides, & the drop in our electricity usage was amazing.

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