In case you hadn’t realised it, I’m a big fan of renewable energy systems. In the article A Solar Powered Life – Part I I gave an introduction to both grid connected solar power systems and off-grid (or standalone) solar power systems and described some of the differences between the two.
In this article I will cover some of the common questions that I am asked by people and look at how the off-grid solar power system at PRI’s Zaytuna Farm conforms with the three ethics of permaculture.
One of the questions I am often asked by people is:
How many solar panels do I need to buy and install in order to cover my daily electricity usage?
This depends on how much electricity the household uses on average every day. In Australia, as I covered in my last article, various sources state that the average electricity used per household varies from around 15kWh (kilowatt hours) per day to about 20kWh per day (Wikipedia gives a figure of 24kWh per day for US average daily household consumption (1)).
This is the equivalent of a household having 10 x 100W (Watt) incandescent light bulbs switched on for between 15 and 20 hours per day every day of the year.
Being an optimist, I’ll use the best case average electricity usage of 15kWh per day, to determine the number of solar panels that you would require.
With solar power, the system generates power only when there is sunlight. This means that the system is limited by the amount of sunlight received each day. The further south you are in the Southern hemisphere or north in the Northern hemisphere then the greater the extremes will be between the available winter and summer sunlight.
For example: My house is located at about 37 ½ degrees latitude south of the equator. If you were in the US, according to Wikipedia the equivalent distance north from the equator would be the southernmost borders of Utah, Colorado and Kansas, and the northernmost borders of Arizona, New Mexico and Oklahoma.
The Rainbow Power Company in Nimbin, Australia provides an excellent calculator for peak sun in Australia (2). According to the calculator, during summer my house would receive at best about 6.5 hours of peak sun and during winter at best about 3.13 hours of peak sun.
If you want to generate enough solar power to cover the daily electricity usage for an average household over a year, you could probably calculate an average of the Summer and Winter amounts of daily peak sun that you receive. At my house this would be around 4.8 hours of peak sunlight per day (3).
Given that solar panels only really produce power when strong sunlight is available, you can divide the 15kWh per day by the average amount of peak sun available at 4.8 hours to determine the capacity system that you require being 3.125kWh.
This means that if you had a house at my location and you wanted to use 15kWh per day of solar generated electricity you would need to have a system that could generate 3.125kWh to cover your total electricity usage over an annual period. Note that there would be periods with greater generation and other periods with lesser generation.
Using the same calculation shown above, if you wanted to go feral and use an average of 40kWh per day of electricity (this would be the equivalent of having 20 x 100 watt incandescent light globes switched on for 20 hours per day every day), you would require a system that generated 8.33kWh at my location in order to cover your total annual electricity usage.
So how many solar panels does it take to produce 3.125kWh?
Solar panels are commercially available that can generate anywhere between less than 1Wh and 260Wh. If we assume that I wanted to buy a system based on 260Wh solar panels you would require about 12 x 260Wh solar panels (to produce 3.12kWh). You could get onto eBay and have a look at how much these size solar panels will cost (as well as other size solar panels too).
With a grid connected solar power system you need an appropriate generation capacity for your usage!
You can quickly see that it takes quite a lot of expensive solar panels to produce a large amount of solar electricity. You can also see that if a household has a 1kWh grid tied solar panel system installed at my longitude, yet they use 15kWh per day, then they are never going to cover their total electricity usage in any given year. At best, they will cover about a third of the annual electricity consumption. Not to get discouraged though as it is great that the particular household is doing something and it is to be respected, however it would be far better if that household could reduce it’s average daily electricity usage.
You may recall that if a household is not generating electricity through the installed solar panels, then any excess required is drawn from the electricity grid. In Australia this is a bit of a disaster because most electricity is generated from the burning of either black or brown coal and not only are they non renewable resources, they also produce huge quantities of carbon dioxide unless that household opts with their supplier for electricity sourced from renewable sources.
With an off-grid solar power system you need an appropriate generation capacity for your usage based on a worst case scenario!
With an off-grid (or standalone) solar power system, you have to have generating capacity based on a worst case scenario which is the available Winter sunlight. The reason for this is because if you continually use more energy than you generate, the off grid solar power system will eventually fail and you may even permanently damage the batteries.
Many off grid solar power systems try to get around this limitation by including other methods of generating electricity. These include: Wind turbine generators, hydro turbine generators, petrol and diesel generators, steam engine generators — and some may even have a battery charger connected to the electricity grid.
With a standalone system you need to be committed to being conscious about your levels of electricity consumption, rather than the typical mindless consumption of electricity by households that are connected to the electricity grid. I have had to change the way that I consume electricity, by understanding what appliances use large quantities of electricity and using them when I know the solar system is generating large amounts of power, rather than just when it’s convenient. Using solar makes you think about your energy usage and consider ways to to reduce it.
How does an off grid-solar power system align itself with the three permaculture ethics if the surplus electricity is not shared with the mainstream electricity grid?
The article Advanced Solar, and Independence, at PRI’s Zaytuna Farm received several comments, and the gist of one of them was "how can an off-grid solar power system comply with the three permaculture ethics?" I thought that this was a fair concern that required addressing.
The three permaculture ethics are People Care, Earth Care, and Return of Surplus to the first two ethics.
The concern of the commenter was really based on the third ethic, which focuses on the return of surplus — in this case surplus electricity for the benefit of both other people and the Earth.
The answer to this is that the system installed at PRI’s Zaytuna Farm is unlikely to have much surplus electricity. If you have a second look at the example above about covering average daily electricity usage and how many solar panels are required to do so, you will notice that it takes a very large solar power system to generate an average households electricity needs. In addition to this, with an off grid solar power system you have to change the way that you use electricity (ie: reduce and minimise your usage). This can be as simple as running the washing machine at noon rather than at night, or holding off a welding job until the next sunny day. It’s not dissimilar from obtaining your heating needs from a wood stove where you have to plan your fuel requirements years in advance as trees need to be planted and cut firewood needs to be seasoned for up to 2 years before use. Contrast this concept to simply switching on a 2,400 watt fan heater!
The other thing to consider is that in a rural situation the electricity grid may be 100s of metres away from your household. To connect up to the electricity grid via underground cables may cost upwards of AU$10,000 per 100 metres. The resources spent on achieving this may be better spent elsewhere.
Finally, disconnecting an inhabited property from the electricity grid has the benefit of making the electricity available to other households. If you’ve ever looked at a housing development, you’ll see lots of new houses being built and occupied. Well, each of those households will consume electricity, so over time electricity consumption rises, of course. What we are not doing as a society in Australia, is increasing our generating capacity in any meaningful way (and I am not advocating that we should do so). With rising electricity consumption and a finite supply, we end up in a situation where (in Australia) on hot days, sections of the electricity grid are shut off until the conditions creating the huge demand change.
What happens with an off-grid solar power system when the electricity grid fails and your household still has power?
Another commenter from the Advanced Solar, and Independence, at PRI’s Zaytuna Farm article suggested that if the electricity grid failed for a period of time and your household, having an off grid electricity system still had power, you may be in trouble. This is what I call the zombie argument. It’s a false argument, because I have been in this situation where the electricity grid has failed for just under a day and although I have good relations with the neighbours who are also lovely people and I had previously offered help in these circumstances, they did not take up the offer. They preferred to tough it out on their own.
In the next Article I’ll look at how solar panels operate in the real world.
- https://en.wikipedia.org/wiki/Watt#Kilowatt – There is a reference to the average daily consumption of electricity for a US household as being 8,900 kilowatt-hours. Divide this amount by 365 days to get an average daily usage of 24.38kWh per day.
- https://www.rpc.com.au/products/services/faq-info/calc/calculator.html – The site provides a calculator for Australian Solar Radiation Figures originally sourced from the Australian Solar Radiation Handbook, April 1995 (Energy Research and Development Corporation)
- You get an average of 4.815 hours of sunlight per day by adding summer peak sun hours 6.5 + winter peak sun hours 3.13 and dividing it by 2.