We have two fireplaces to feed. Last winter it occurred to me that I might be better off simply burning the fuel that I use in my chainsaw rather than doing all the work of cutting, carting splitting and stacking firewood. The most common firewood here is Australian Wattle (Acacia) which as it happens has an excellent energy content. I made some measurements of what mass of wood I could cut with a tank full of fuel. I then did dome calculations and lo and behold ... the cut wood has 200 times the energy content of the fuel I use to cut it. Even allowing for poor fireplace efficiency I am many many times better off cutting the wood ... sigh!
Install solar or use off-peak tariffed mains electricity to run my pool?
I was feeling unfashionable living under a naked roof - no solar panels. Too slow to catch the now-defunct 60 cents per kWh feed-in tariff, I was struggling to make a case for a domestic solar system. But surely my energy-hungry swimming pool pump would be the key (it is the next biggest consumer after the hot water system). I could time it to use energy at the best time for solar and, if I were to generate any excess, I could earn something - around 6 cents per kWh these days. A call to my electricity utility company revealed that it's OK to run pool equipment from the off-peak supply. This is tariffed at around one third of the normal domestic supply rate. This changes everything! Allowing for an electrician to install the necessary timer and safety equipment, the payback is less than one year. The best I could calculate for solar (based on a 3 kW system) is a payback over five years. So for now, so long solar.
Epilogue: Suitable rearrangements were made to the switchboard (please email if you'd like the details) and Off-Peak supply made available to the pool equipment in January 2013. Close monitoring of the energy bills over the next twelve months confirmed my expectations of savings and before the year was out ... I was in the black! And, the pool never looked better!
How long before Small-scale Solar systems Break-Even?
There is no hard and fast answer to this question. It's a case by case thing. But, Energyfacts has done a couple of case studies.
The first involves a 1.5 kW domestic installation in Sydney for which highly detailed cost, generation and usage data was kindly made available via the web interface provided as part of the installation. Access to more than a year's worth of this data - measured down to 15 minute intervals - has enabled a comprehensive analysis which includes practical consideration of seasonality of both generation and demand. This particular installation is at a home with three phase power supply running, amongst other things, a ducted air conditioning system. The savvy owner took care to optimise the load across the three phases to obtain maximum benefit from the solar system which, in this as in most other situations, is connected to only one phase. This is a significant point because in such cases, unless the load is optimised, a significant amount of solar energy will not be used on site with consequential savings on energy costs, but will instead be returned to the grid earning a comparatively very small income. So what has been the bottom line? On a simple financial calculation basis, the owner must wait more than 7 years before his investment is recovered. If the more representative discounted cash flow method is used this stretches to over 9 years.
The second is a simpler set up north of Sydney. This one is a 3 kW system connected to the single phase house supply. Detailed data was not available for this specific case but the analysis has been enhanced by making use of the seasonality factors discovered in the analysis above. The bottom line here, on a simple financial calculation basis is that the owner will recover his investment in just over 6 years - longer of course if the more appropriate discounted cash flow analysis method were used.
Why, I hear you ask, does this bigger system have a shorter payback? There are two reasons. Principally, the bigger system was actually cheaper than the smaller which is a high quality, high functionality set up. Another is, being a single phase home, the second system doesn't miss any opportunity to substitute for grid energy.
Neither of these looks like a very good deal. Doubtless better examples can be found - particularly solar homes with pools. The bottom, bottom line is that buying small-scale solar in this post "mega-feed-in tariff" time is something to consider very carefully - perhaps with some unbiased professional help.
