The partnership with Reposit is a chance to launch some new tech initiatives (micro-grids) in the renewables area. So a lot of boxes are being ticked.
I was even more happy when I saw their rates – here’s a comparison to my old provider:
| Item ex GST ex Discount | Diamond | Old Provider | Difference |
| Price (cents) / kWh | 19.35 | 23.61 | -18.0% |
| Connection (cents) / day | 74.95 | 77.63 | -3.5% |
| Feed in tariff (cents) | 8.0 | 5.1 | 157% |
Not bad, eh? Of course, the rates will vary with usage, as each provider has set bands for pricing, sometimes calculated against a daily average amount. The old provider dropped their price per kWh slightly at each band, while Diamond go up slightly, and use a monthly band.
It reinforces that we need to use less power, and more thoughtfully. The bands for Diamond are: first 100 kWh per calendar month priced as above, next 240kWh per calendar month (19.95c), remaining (21.6c).
Based on known use since install, I should not use import much more than 70kWh per calendar month (about 2 per day), so should always price against the lowest band. Famous last words?
I also receive a discount for paying on time and by direct debit with Diamond, and even though that percentage is smaller than the ~12% I received with the old provider, the lower base cost is winning the race.
The Balancing Act
Import versus export is another key stat from the table above. The feed in tariff for Diamond is a lot higher, as a percentage, than I’d otherwise get from a lot of companies, and combined with the lower pricing, has a lot more impact.
If I get 8 cents for every kWh I export, and pay around 20 cents for every kWh I import (once GST and discounts are applied), then my ratio for being cost neutral on usage is almost exactly 2.5 export to 1 import. Under my old provider it would be almost 4.5 due to their higher purchase cost and lower FiT.
Of course, there is still the connection fee charged every day, with any provider. To cancel THAT out with Diamond, I’d need to export 10.3kWh per day in addition to keeping my 2.5 ratio above!
Unlikely, but every little bit helps to get that ROI under 10 years. If, by some miracle (or more likely, Reposit Power), the connection fees are also wiped out, then ROI drops to less than 7.5 years.
A Moving Target
Diamond’s cheaper energy prices change my ROI calculation. I accept that, but at the time I bought the system, I was calculating off the old provider, so that is still the basis for everything I look at, moving forward.
This all assumes I keep using power at the rate of 2015. Several things have changed in that area, which tip the balance in my favour.
Firstly, my pool equipment got replaced in January. It was older than the house I’m sitting in, purchased through eBay according to the neighbours. As a result, it wasn’t terribly efficient, and I’ve since discovered plenty of issues with the pump itself after pulling it apart out of curiosity.
The new equipment will lower power bills due to smarter controller options and newer pump components, allowing it to run less hours per day, at a more efficient rate.
Note that I wasn’t planning it as part of the Powerwall install, and wouldn’t mind that money back in the ol’ skyrocket. C’est la vie, which is French for “I’ll take the good with the bad” I think. Language is not my strong suit…
The house has been fully fitted with LED lighting, which was only completely part way through 2015. Timers are now on the AV and computer equipment to help reduce overnight use, and get the Powerwall through to morning, hale and hearty.
The crimes of the ducted air conditioner are now on display for all to see. As a result we’re dealing with our ventilation with a bit more thought, and using other resources (love our Dyson fans) to regulate air flow.
I’ve been clear on communicating with the kids about leaving things running (TV, lights, PlayStations) when they don’t need them. Every little bit counts, and “Less waste = more holidays” is the mantra. They are on board and excited about it… or the holidays, maybe.
In Summary
We still have lives to lead. We’re still going to want to do things that involve carbon fuels, directly or indirectly (at least until I get my Model 3). Nobody has a good plan for commercial electric flight, though they’re having a red-hot go at it.
As a family, we’re just going to do it a little smarter with the things we can control. More consideration for the budget, the planet, and the grandchildren I hope to have some day, in a functioning and more enlightened society.
That sounds a little disingenuous, when I just spent the last 4000 words talking about money, but this is one of the major things critics miss about renewables:
It isn’t about growing your own kale in a mountain retreat, seeking purification away from the evils of the rat race, while aligning your shakras. I’m not knocking anyone who wants to do that, mind.
Its a balancing act, because we can’t all just jump off the grid and leave a few users with the burden. Some of us will seek independence, or be forced into it to live where we want. Some need to live in suburbia because of our commitments. Many won’t even be able to afford solar hybrid in any case, until the price drops after the early adopters get the ball rolling.
The point is, we have options, and we should use them.
We can all contribute – in fact we’d bloody better! If we don’t start moving in the same direction on this, from the policy makers right through to the average citizen, we’re not going to have an environment or society left to worry about.
Long-term, with energy companies acting the way they are, and regulators supporting them, it will be up to us to take back control, and make sure we can improve things for our generation, and the ones to come.
I’d encourage anyone who can raise the capital to get into solar at the least, and look at battery storage as well. There are plenty of options hitting the market – check out the new gear from LG Chem, Redflow, Panasonic, and Enphase, just to name a few.
Oh yeah, and Tesla Powerwall! Can’t forget those guys…
Hopefully this information has helped you look at your own situation, in terms of considering a system, or you just find it an interesting perspective.
Moreso, I hope the motivation for buying a system – which ever option you go for – is beyond purely financial.
As always, if you’ve got any questions, ping me on Twitter.
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That 21.9kWh/day is an AVERAGE figure. In the southern states at least, most of that energy will be needed for Nick's electric heating during the three winter months. This means that for these three months there will be much more energy used than the PV can provide and this energy will have to come from the grid. The result is that Nick will not be saving much of his $1920 electricity bill.
There are only three ways to avoid this problem. [1] Heat only a couple of rooms and wear lots of jumpers and Ugg boots. This is what most of us do. [2] Radically improve the house thermal insulation. [3] Install much more storage. Average daily energy of 21.9kWh would indicate that the winter daily usage might be about 40kWh. To allow for those long cold wet spells, one could justify perhaps two days worth of storage before one has to draw power from the grid. This means 80kWh of battery storage at $2000/kWh or an investment of $110,000!
What to do? Since Nick needs low grade heat, why not store the energy as heat? Water stores the most heat at about 55kWh/cubic meter, heated to 90 Celcius. The hot water is fed through a tempering valve into hydronic wall radiators at perhaps 45 Celcius. Water costs only 22 cents/cubic meter so the only extra cost is the insulated water tank which need not be pressurised so can be home made.
Other requirements are a low pressure pump, an air scoop to remove air bubbles from the flow, Variable-Voltage off-grid PV inverter and some sort of temperature sensing controller for the pump. With this system the amount of storage can be increased with little financial penalty to whatever size Nick desires.
If Nick likes he can start off by just feeding his PV energy into an (electric) hot water service for domestic hot water. A second heater element can be fed from off-peak when necessary in wet weather. This is what a lot of people will do when the 60c/kWh tariff finishes at the end of the year.
Some interesting thoughts there. Not sure on the practicalities of running hot water pipes around the house - we had a small flood when the fridge plumbing gave way in 2014, so the less wet areas, the better. My wife would agree, as living without carpet for several weeks in winter was not an experience I'd care to repeat.
Without knowing the costs, it looks like another capital spend designed to save a couple of dollars per day. Not going to do much for my payback time :)
I didn't get the system to avoid the grid altogether, because I'm in suburbia and the advantages of keeping the grid are obvious. I accept that there will be good days and bad days, and most modern consumers I think would fall into a similar category.
I definitely don't like paying bills, but under my current plan with Diamond, I have no issue trying to "beat the bank" with those rates.
BTW, the bill for mid-June to mid-July last year shows usage of 27.01kWh/day on average. Its remarkably similar to the bill cycle that covers summer. In both cases, I'm pointing the finger at the ducted air con.
Higher than the average, but should be offset to a degree by the power I can sell in Spring and Autumn.
Please do not use ROI or return on investment to describe payback time. I know many solar 'specialists' are using this terminology, but this does not make it any better.
ROI or return on investment gives a result in % and not in years. As can be seen from this Wikipedia report ( https://en.wikipedia.org/wiki/Return_on_investment ) even the correct ROI is not a very good descriptor for investments.
I prefer to use the 'comparison rate' which is defined by the government for home loans. In case of a solar system the solar owner is the bank. The comparison rate can be calculated very easily using the IRR() function in Excel.
Another option is to calculate the net present value (NPV). But that is harder to understand for most people, especially because a discount rate has to be estimated.
Nick, your calculation is a good start and a brave move. The problem is that there are so many variations in energy production and consumption during the day and the seasons of the year that calculating with averages will result in a very high error.
One way around is to use a calculation which takes the half hourly consumption and production data for electrical energy into account. That is the same time interval retailers use for calculating your electricity bill. These data are hard to get from your retailer. But you may be lucky or you can actually install some system to measure it. For industrial applications customers can get these data from their power company without any problem.
Once these data are available they can be used with a solar calculator from the Alternative Technology Association. It is called 'Sunulator' and in its newest version it can also calculate the financial situation when using batteries with solar.
One final point: Please do not use return on investment or ROI when you talk about payback time. I know may solar guys do that, but that does not make it any better. ROI is a financial term and gives a result in % not in years. You can google it if you don't believe me.
Thanks for the advice Jo. I'm more conscious of usage than ever, with a serious financial goal: get to cost neutral. Maybe that can't happen, but its something to aim for.
I've got a few ways of measuring my power, going forward:
1) The SolarEdge inverter feeds their monitoring portal, which is accessed via their website. That provides some decent graphs and summary information to give a reasonable level of detail. If you look at this article you'll see some samples: https://stepoffthegrid.wpengine.com/my-tesla-powerwall-tales-of-an-early-adopter/
2) I can access this same SolarEdge data via an API. I've built some basic retrieval for which I display simple charts on my own website, here: http://unleashthepowerwall.com/statistics/
I'm storing that API data so I can slice and dice at a later date. I've already done some calculations based on usage to date - my bill is roughly 55 cents per day since 18th February, when the latest version of the SolarEdge firmware. That includes connection fee, which is presently being discounted by a fairly healthy import:export ratio as mentioned above.
3) I've just had the Reposit Power meters installed, alongside their software, which will allow an even more detailed look at the physical meter data via another API. On a side note: this data is also being supplied to Endeavour Energy, because they want to understand the effect of battery storage in more detail, with the spotlight that Tesla have brought into the arena.
I'm working with the guys at Reposit on this and hope to have a writeup done on how that works shortly.
Good advice, Jo.
Daily, let alone seasonal, variation in solar generation and household consumption, severely erode calculations based upon averages. Storing energy in a battery only partly solves
solar's problem of generation and demand mismatch.
Also, the limited output power of the battery (3.3kW) means that larger demands must be supported by the grid. Those peak power demands can be quite large when washing machines, dryers and air conditioners are operating. It's not an easy task to find all of these data, nor use them in calculation, but energeia have done a lot of the work for the prospective purchaser. NPV and 'bill savings' are displayed graphically. For all but a few housholds having high energy consumption, payback is described as 'infinite'.
http://energeia.com.au/wp-content/uploads/2014/02/Australian-Residential-Solar-Storage-Analysis-Part-1-An-Enthusiasts-Market.pdf
We all know that making your own electrons at home using solar panels is cheaper than buying electrons from the grid.
We only need to know the cost of storing electrons in the Powerwall.
Better yet, Choice should put the Powerwall through cycle life testing to see how many cycles it can do.
Nice article thanks. :) It amazes me how solar is looked at in payback years or ROI. So we are buying a system for say $6,000 that will generate clean energy from the sun, pay for it self in 5 to 10 years and then provide FREE energy for another 10 plus years.
But we easily spend money on a new car costing $30,000 plus that depreciates at around $4,000 / year for the first 3 or 4 years and we don't have to justify that as an investment...