As already sprayed around on twitter, I have a system installed within my solar domain from a startup called Reposit Power. When I first discussed the install with Natural Solar this was one of the key points in the install; a smart way to use battery power, as well as help reduce my costs.

If you didn’t watch the video, in a nutshell:

Reposit Power provides controller software that adds smarts to the system I have, as well as offering the ability to sell battery power to the grid during peak events (GridCredits).

The SolarEdge inverter with StorEdge Battery interface is quite happy playing with the Powerwall. When the sun is out, it powers the house, directs any leftover to the Powerwall, and exports the rest. Battery is called on when solar is not available. Simples.

Reposit Power takes this ecosystem and adds a layer of predictive analysis, including my usage patterns, type of energy tariffs, and weather patterns, to decide on the best way to manage this power on my behalf.

This is the kind of technology that other companies are selling out of the box, but Reposit are making it applicable to multiple systems. This device-agnostic approach is very important as we move deeper into the IoT (Internet of Things), particularly with connected energy systems.

Reposit Power also provide a sexy, sexy web interface for looking at power usage. Here is a sample from 13th May:

It has a level of granularity slightly better than the SolarEdge web interface, which is really useful to understand house consumption in particular.

My favourite thing about the image above is the Solar generated – almost a perfect curve, gracefully rising from 0720 hours to 3.6kW through midday, and then falling to zero again just before 1700. Beautiful…

Fine… but what does it mean?

At the moment, I’m probably not taking full advantage of the Reposit setup, because I am trying to be the smarts in the system. And while I’m a control freak, there are factors beyond my control.

The guiding philosophy is to use devices when the sun is out, and get the battery to run the house when its not. Life sometimes gets in the way of that, though more often its cloud cover getting in the way of that.

A couple of days in a row of decent cloud cover, or rain, and the battery is going to roll over and go to sleep until the sun comes out again. As we head into winter here in Australia, daylight hours will shorten somewhat.

_{(I’m still cranking 20+ kWh on a clear day in which is doing alright for a latitude of 33.7S).}

If I’m importing power from the grid once the battery gets low, I’m paying a bit over 20c / kWh for it. That means I might spend $3 on power on a day where I have cloud cover, looking at the average consumption.

Winter will require more power consumed on heating, so that cost will go up on a cloudy day. Single rate electricity tariff gives me a level of surety with my consumption, but perhaps to maximise the benefit, we need to shift our thinking and take a bit of a risk.

Reposit Power to the rescue?

In discussions with the guys at Reposit, I’m considering moving to a TOU (Time Of Use) tariff with Diamond Energy. Let’s look at the costs involved in TOU before any discounts apply:

Rate Description	Time Period	Cost inc GST
Daily Supply Charge	–	101.20c / day
Peak Rate	1300-2000 business days	32.84c / kWh
Shoulder Rate	0700-1300 business days0700-2200 weekends 0700-2200 public holidays	25.30c / kWh
Off-peak Rate	2200-0700 every day	12.27c / kWh

Compared to the current single-rate of 82.45c / day for supply charge, and the 21.29c / kWh for usage, this could be either terrifying or awesome.

The connection fee increase to go TOU from single-rate is nearly 23%. Over a billing period (quarterly) is a difference of just over $17, or $68.25 in a year. Not huge, but I’m trying to get as close to zero as possible; the related benefits have to stack up.

Peak rates are going to be the killer – 54% higher than single-rate. Ouch.

Shoulder power rates are nearly 19% more expensive than single-rate, which is where quite a bit of our usage probably sits, based on my quick API-based calculations. That is something to put a red line under in considering the switch.

Off-peak power is while off-peak is 42% cheaper than single-rate, so can it help?

Certainly – running the dishwasher overnight is an obvious one, as it has water heating requirements. Water has the highest specific heat of any regular household substance (unless you’re heating Helium or Hydrogen* gases), and therefore needs a lot of power to do it, if only in peaks.

_{*Author’s note: if you’re thinking about heating Hydrogen gas in your home, just don’t.}

What about other devices? Washing machine run before 0700? Perhaps, but ours draws gas-fired hot water so its not a big deal. Hanging washing on a cold winter’s morning doesn’t sound like fun, either.

Oven? Generally not cooking anything between 10PM and 7AM at night. We tend to be asleep or generally less active (and hungry) at those times.

Air conditioner springs to mind as something that needs to operate off-peak as much as possible, particularly in winter where we are warming up the house before getting out of bed. We have a reverse cycle ducted system which sucks a lot of power to cool, so probably a similar amount to heat.

If we had off-peak power, we could time our heating and cooling to maximise use of off-peak power, though that is less useful in summer when the heat is coming in the afternoon i.e. during peak.

However, if we’re talking about the ability to effectively use off-peak power, we need to consider the most useful device on the premises.

If Sydney is going through a cloudy period, and I’m not able to generate enough solar power to both run the house and fill the Powerwall, why not use off-peak power to do it?

Even though its one of the stated benefits of the Powerwall (time-shifting solar and off-peak power) I wasn’t really considering how to do it until Reposit Power came along.

The Reposit Power box is capable of analysing my usage patterns, and understanding that I get up around 0700 every day, flick on a few devices (not simultaneously if I can help it) and make breakfast. Over time it gains an understanding of how much electricity I require for breakfast.

So, if I moved to off-peak power, Reposit could pull that off-peak power in, and reduce my breakfast costs by 42% on days where I don’t have the battery to boil the kettle, compared to what I have today.

What if its a wet week? At the moment I’d trickle a bit of solar into the house, maybe the battery, but my import costs would climb at a set rate of 21.29c / kWh.

If I move to off-peak, Reposit could pull in 6kWh at 42% lower cost, and deploy that power at peak time to avoid the higher rate. I’d take a bit of a hit on the shoulder time, but would be better off overall if the figures work out.

My next step is to look into the exact numbers, and discuss some points of interest with the guys at Reposit Power. Scientifically speaking, I’d like to just let this single-rate billing period finish, then switch over to TOU for the next quarter and look at the results.

Yes, it would be an Autumn compared to Winter comparison, but in theory Winter should be even better for this strategy.

Whether I stop being lazy and look at the figures might be irrelevant in light of another factor introduced by Reposit Power…

GridCredits FTW!

At the moment, I get 8c / kWh for exporting power off my solar generation. Not crash hot, but not bad either compared to some in the Australian market.

One of the reasons for the low rate compared to what I pay for electricity is that solar generation is not a guaranteed resource. It peaks and troughs with available sunlight, and of course doesn’t run at night.

If you go back to the table on power pricing with Diamond Energy, you’ll see “peak” runs from 1300-2000 hours business days. This is generally when most power is required, so companies can sell power for a higher rate as they crank up the hamster wheels.

Even though my solar may be exporting during peak times, the environment today is such that the pricing is not adaptive. Firstly the technology doesn’t really exist at a network level, and secondly the power companies are keen to maximise their projected profit.

This is where GridCredits step in, and home storage steps up.

Anything I have stored in the Powerwall is guaranteed power. Besides a minor amount of efficiency lost in transmission, if I have a full Powerwall, I have about 6kWh available that could go into the grid to help smooth a demand surge peak.

Of course, given this is now a guaranteed source of power, and isn’t subject to interruption from the sun disappearing, I’m going to want decent compensation for it. That compensation works out to a figure state as “up to $1 / kWh”. Yep, a whole, tasty dollar.

And if its a bright day, I can keep pushing power into the battery from the solar panels, or exporting at 8c /kWh. Bonus!

Financially, that is a major windfall for the Pfitzner household, as the first exported kWh will pay for my supply fee that day, and any subsequent kWh exported will cover other days.

With around 77 peak events per year in Australia, with the right conditions I could get that power bill well below zero, and even pick up some beer money.

Beyond my selfish personal gain, systems like Reposit Power are a game changer for the electricity network. Long range power distribution seems a little odd when we’re capable of generating it on our rooftop.

The Rise of the Microgrid

There are a few projects around Australia at the moment that are looking at microgrids, or discrete systems that don’t require the main power grid as we know it.

Think about it like peer-to-peer power sharing. Its basically the bit torrent of electricity.

The concept of a nation- or state-wide grid will probably fade over time. Connected energy systems at the current scale are only 50 or 60 years old, and the concept of connected electricity grids just over a century to date.

I see the grid as something like the automobile, powered flight, or telecommunications. They are all recent innovations in human history, and as such are subject to more rapid change in their short life cycle.

People are naturally resistant to change, and only like a change that introduces convenience, financial benefit, or exceptionally pleasing aesthetics.

Renew Economy ran an article relating to the thought process of microgrids in Western Australia. Asset Manager for Western Power, Seàn McGoldrick, gave a talk on the peculiar set of circumstances in the west. As mentioned in the article from Giles Parkinson and Sophie Vorrath:

… when you have a service area equal in size to the entire United Kingdom, but with just one million customers (as opposed to 73 million), it’s a big challenge – economically and logistically.

The profitability of Western Power is almost nonexistent, but it is an essential service, subsidised by the West Australian State Government to the tune of half a billion dollars per annum.

What if that money could be shifted to communities, to reduce the long-term costs of network maintenance? Provide customers with reliable power, while not having to manage the poles and wires across the wide brown land?

McGoldrick presented four general approaches, and bucked for option 3 below (Modular Network).

 

If you take some of the maintenance budget out of the equation, Governments could save money, or put it into development of newer, more efficient technologies.

You create a snowball effect, that can allow low-carbon generation, electric vehicles, and storage technologies to leverage off each other.

I remember having a PC back in the day and moving to Windows. This change forced the need for better components. As CPUs got better, memory had to advance, along with graphics cards, and the motherboard technologies that tied it all together. Something similar can happen with renewables.

There are still issues around reliability for microgrids, but a combination of efficiency measures, storage, and generation diversity (e.g. wind and solar PV together, along with solar thermal) can contribute to advances across the board.

Further, it can remove the issues of the grid going down at some distant location, leaving consumers stranded.

With smarter devices, smarter management, and more efficient housing, domestic microgrid implementations can lead the way. Once the base is established, and more research money flows in, light industry can also benefit as the technology advances in leaps and bounds.

From there, we won’t just be talking about decentralising our power needs, we can start talking about decentralising our population.

If only the government would hurry up and get us a first-world internet. In an election year, anything could happen…

In my last post I alluded to having some thoughts on whether my house was making the most of solar power, particularly in regard to how I was using it. Knowledge is power, and the knowledge I’ve gained in the past few of weeks of my solar power usage has been very interesting.

Understanding which appliances burn the most power, what the usage patterns are, and the effect of weather, are all critical to getting the most out of the investment. This ensures that I can achieve the ROI I want, and that I’m a responsible user of any fossil fuel energy I’m required to draw from the grid.

In all my analyses, the ducted air conditioner keeps cropping up as the villain (and at some point I’ll reconcile myself to that).

Its a difficult issue to address, as ripping it out of the roof space and replacing it with something else would just cost a load of money, and may not practically address the issue of solar power for cooling on a bang-for-buck basis. I need to ensure I’ve investigated other ways to either offset its use, or reduce my reliance on it.

Air conditioning comes down to a simple premise: comfort. You use it because you have too much outdoors in your indoors, so to speak.

That’s not a bad thing in the world of modern convenience, where our cars, offices, and houses are all air conditioned. However, have you ever thought that air conditioning is just treating a symptom of the main problem, and not the root cause?

The root cause – intrusive heat in this case – is going unaddressed. Even if you have a really efficient unit with all the bells and whistles, you may be able to do even better through other, more practical means.

Beyond “don’t leave the door open!”, there are many factors affecting your use of air conditioning or heating, often reflected in the design and quality of your building. Do you have adequate insulation of suitable quality? When was the last time you had it checked? Gaps around the doors? What about covering the windows?

Windows are a general weak point for heat transfer into or out of a building, particularly in large parts of Australia, where we don’t suffer the kind of harsh winters that require central heating or double glazing.

As a design point, a lot of modern houses here open up windows far more, which often results in more energy usage. One design element I need to deal with in my house are the large, west-facing windows.

Both windows are in the same room at the front of the house, are 1800mm (6 feet) high, with the one on the left nearly square and the other about 2700mm (9 feet) wide, getting hit by sun all afternoon. The internal venetian blinds, while slowing the direct heat down a little, aren’t stopping it from advancing into the room in the first place.

Simple science: the sun hits the glass, which heats up, subsequently transferring its heat to the cooler air inside that is right up against the glass. That air rises (because heat) and more cool air is drawn against the glass. Rinse and repeat for 4-5 hours on a hot Aussie summer day!

Some people also look at tinting their windows or installing double-glazing to assist with this, but I remain unconvinced about either option in terms of value-for-money in most parts of Australia.

Tinting provides an extremely thin buffer, so it is only going to slow things to a certain degree – better than nothing of course, and relatively cheap compared to other methods. The downside is that in winter its going to perform the same function, stopping heat from entering the house via those windows. As a side note, the privacy aspect of tinting is lost when the lights inside are brighter than the lights outside i.e. at night when you are using that space.

Double (or triple) glazing is the architectural method of choice for sound proofing and insulation of glass. While its overall effectiveness year-round as an insulator cannot be questioned, the expense often makes the average home owner hesitate. Double-glazing in summer is best used where you can keep the internal temperature cool, and therefore stabilise the buffer between glass panes at a temperature somewhere between the outside and the inside. Generally speaking, if you’re not keeping the room cool through e.g. air con, the buffer will heat up, and start transferring that heat into the room.

In my opinion, and that of several electricity companies, the best way to stop this kind of heat transfer is to stop the heat hitting the glass in the first place. In essence, you create an external buffer zone where the sun’s heat and UV rays can’t get to the glass in the first place.

There are several options available, from adjustable fabric awnings, metal shutters, louvres, window shades or fixed awnings.

Rather than run out and spend a pile of money on anything custom-made for those windows, I decided to experiment first on our north-facing garage window. In the garage I have a network cabinet* in which I have my network backbone with appropriate patch panel for all the points around the house. I don’t want that equipment to overheat, and shielding that window should help prevent that.

_{* on reflection, probably a mistake to put it there, but it wasn’t going anywhere inside the house, according to my wife. Its called “compromise” I think…}

Window coverings

I went to Bunnings Warehouse and, for the princely sum of $297, bought a fabric awning (1800mm wide, 2100mm drop) to cover the garage window from the worst of the heat. That’s it on the right, and I put it up myself in about an hour.

The awning can quickly be retracted in case a storm blows up, or in winter when I want the sun to warm up that side of the house. Sydney winters may not be harsh with snow and such, but we tend to have low tolerance for cold as a result ?

I’m going to keep an eye on this for the next couple of weeks, as we move into cooler months, and see how it performs as the sun moves back north and puts more sun on this window.

Some (including my wife) may say that these kinds of awnings are a bit daggy, and yes you can buy them in stripy patterns if you want to be reminded of your grandparents’ post-war bungalow. However, if they do the job then I think for next summer I’ll be pushing to cover the rest of the problem glass on the north and west sides of the house.

It will be a battle royale between her Better Homes and Gardens and my New Scientist approach to this whole thing.

In the meantime, the best we can do is shut the problem room off during the heat of the day and let it become the buffer zone. My issue with that longer term is the electronic equipment in that room is under strain during that time from heat. And its the rumpus room for the kids, so now I have them in the main room watching my TV!

Garage door

The double garage door also faces west, and therefore gets a lot of heat in the afternoon. That was an issue from the day we moved in (late 2013), so after a bit of research I bought a roll of Green Insulation Reflecta-GDI which looks a bit like this once fitted.

It definitely works – I can’t touch the bare metal of the door for more than a few seconds on a hot day like today (35^oC / 95^oF in the sun), while the insulation is merely warm , slowing the heat transfer into the space.

Measure your door panels before you order and, once fitted, you may need to recalibrate the garage door lifter to account for any weight change (it isn’t much but some units are sensitive). No adhesive required as it designed to fit most modern panel garage doors in Australia by sliding into the space at the correct width. That is actually a shot of it overhead – no issues whatsoever with staying in place in over two years.

While we’re on the topic of garage heat, DON’T close your garage door immediately in summer after you park the car in there. The heat you trap will radiate into the house through plasterboard before it will escape through brick or wall insulation. Leave the door up and get some air flowing through the place for at least half an hour.

Not so bad to trap that car heat in winter, but make sure the engine is off!

Solar Power Design – more than panels

If you’re in the process of building or renovating, you may have already made a lot of decisions around how you wants things to look. Some of those things may focus on solar power, while many more are about the right fittings, colours, and facade for your home.

Those with solar power aspirations will already know how important aspect is, though after discovering what I have about my own house, I believe it should be more than how many panels your roof can hold.

If you haven’t adequately considered the thermal efficiency of your home, you may not be capitalising on your investment properly.

Even if you’re not considering solar power for your house at this point, you might think about getting the place pre-wired while the build is occurring, as Jennian Homes in New Zealand is doing with all new builds.

Consider the design factors around your insulation (wall and ceiling) as well as windows and cooling or heating options. Sometimes these things can be lost when you’re focus is on the right marble bench top, or the right tapware.

The builder may promise the latest, you-beaut ducted AC, but it may end up costing you more over the longer term. Look instead at smaller, more efficient air conditioners (like split systems) to cool or heat the space you need. In either case, make sure you understand the energy requirements of these add-on extras and how they will affect your power usage.

A few little decisions now can save you hundreds or thousands in the future, particularly as prices rise (and they will) and governments feel pressure to adopt renewables standards across the world.