If you are considering going off-grid, you have probably already considered a solar system. When planning my off-grid home, one of the things I struggled to find and desperately wanted to read, was particular specifications of other peoples systems, therefore I’m posting mine here. People also often ask about what it’s like living off grid with solar, how we chose the size of the system, the hardware etc. so that’s here too. I am by no means a solar expert or electrician and I neither designed our system nor fitted it. I can’t offer any advice on the inner workings of your system or how to build a system from scratch, if I did I’m pretty sure it would end very badly. I’ve had my fair share of bad experiences with amateur set ups, which is why I decided the best choice for us was to go with a good local solar company that took care of everything. I’m just a woman who likes to do a lot of research, (my husband would say too much…), before making any decisions and this was some of the information that was useful to me, I hope the information here will give others more confidence to make the decisions that will help them follow their dream to go off-grid.
I apologise if this is extremely basic and obvious, but I had to look it up when I first started planning to go off-grid and therefore I thought it would be useful for those like me who had never encountered any of this before. At its simplest (without the wiring, racks etc.), a solar system is made up of 4 main components:
- A Solar array – Solar panels, also known as photovoltaic systems (PV) use the sun to generate electricity. A set of panels is called a solar array
- Regulator/Charge Controller- A charge controller or regulator is only needed if your system has a battery bank. It regulates the voltage of the current going into and out of the battery to prevent them from overcharging or over-draining
- Battery Bank – Batteries store the energy that is not being used and provide a supply when the sun is not shining or is not generating much power (i.e. at night and on cloudy days). The bigger the battery bank, the longer you are able to go until the next charge.
- Inverter – An inverter changes the current coming from the battery bank from direct current (DC) to alternating current (AC)
Such systems also generally incorporate some kind of back-up energy for when the solar is not providing sufficient energy e.g. from a generator, wind or water turbine.
The domestic mains voltage and household appliances here in Australia are designed to operate on 230 volts AC (alternating current). Solar cells and batteries produce DC (direct current), typically at a lower voltage. This needs to be converted, to AC and at a higher voltage (230 volts AC). The name of the process is inversion hence the Inverter (it is the reverse process of converting AC to DC used in battery chargers and to give the alternative option of powering portable electronic equipment from the mains at home to save the batteries).
A battery is a collection of basic low voltage cells wired together (the nominal value for a lead acid type cell is 2 volts). These can be wired in configurations to give multiples of the cell voltage e.g. 12 volts (typical lead acid car battery), 24 volts, 48 volts etc.
The choice for solar power is a balance of convenience and expense.
Electrical power in Watts is a product of volts and amps (Watts =volts x amps).
1 kilo Watt or 1kW = 1000 Watts.
The same number of Watts would be produced by doubling the voltage and halving the amps or visa versa. (Current flow is measured in amps or Amperes).
However large current flow requires more expensive thicker cable and bulkier control gear. Leading to a preference for higher battery voltages and lower DC current operation in medium (24 volts (1kW-5kW)) and higher power systems (48 volts (2 kW-15kW).
Specifications of our system
3.75 KW solar array (15 x 250 REC panels)
2 x 80 amp Midnite classic solar charge controller (allows for more panels to be added to system in future)
SP Pro interactive inverter charger 3kw cont 9kw surge
24 volt 1330 a/h @C100 Exide flooded tubular plate battery bank
2.8KW ATG Vegetable oil generator for backup power
This was chosen from suppliers tables to give us 6.5kWh a day and 2 days of stored backup power.
The unit of electrical energy use is the kilo Watt hour or kWh.
1kWh is equivalent to 1 kW of energy used for 1 hour.
It is a product of power x hours. The same product would result from 2 kW x ½ hour
or from ½ kW x 2 hours.
Electrical Watts themselves are a product of volts x amps so that there is a connection between Watt hours and the Ampere hours associated with stored energy in a battery.
Our choice of Hardware
The supplier specified the charge controller, inverter and panels as per our usage specifications.
We decided, although a little more expensive, to go with an SP Pro interactive inverter charger (orange unit shown above) so that we would be able to monitor usage, switch on the generator and be aware of any problems from the house. The screenshot below shows the SP pro panel shown on our computer at the house.
The systems backup is a 2.8KW 230V/50 Htz ATG diesel and vegetable oil generator (more details here). It can be operated with diesel, heating oil, vegetable oil (canola oil, sunflower oil, corn oil, soy bean oil etc.) or cleaned waste vegetable oil. We are able to buy recycled vegetable oil in large quantities very cheaply locally. One current disadvantage of the system is that the generator does not have an automatic transfer switch and has to be started manually when the power is low. We hope to rectify this so that it comes on automatically (just for peace of mind if we are not home) sometime this year.
We considered the choice of batteries long and hard. Batteries store the energy that is not being used and provide a supply when the sun is not shining or is not generating much power (i.e. at night and on cloudy days). The solar portion of the power being used at any time depends upon the state of charge of the battery i.e. when the battery is fully charged then the domestic power being used is all from the solar panels. Consideration of the required portion of backup power compared to direct power will determine the relative ratings of the solar panel output capability versus the battery energy storage rating. In general it is less expensive to add more solar panels for direct use and arrange for the major use of power during those hours than to add more battery storage.
There are three main types of batteries used in PV systems, flooded lead-acid, gel cell and absorbed glass matte (AGM) and each has its own advantages and disadvantages:
Wet-cell – Liquid electrolyte in the form of dilute sulphuric acid. They are less expensive than the alternatives, but require maintenance in the form of topping up the liquid level of each cell with distilled water.
Gel – Gel batteries are sealed, valve regulated lead-acid (VRLA) batteries, meaning that they cannot be (and do not need to be) opened for maintenance. They are very similar chemically to the flooded lead acid batteries but the acid is stored in gel rather than liquid form. They are more efficient and lower maintenance but have the same life-span as flooded lead and the same capacity, their charge rate needs to be more carefully controlled or the Gel cracks. They can be stored closer together and require less ventilation than Flooded-lead acid. No access to terminals is needed as they do not require maintenance.
AGM– AGM are the most expensive batteries. In this case the sulphuric acid is absorbed in fibre glass mats. They are maintenance free, efficient and less susceptible to over-charging problems than gel cells. They don’t require as much ventilation as flooded cells and can be stored closer together with no access to the terminals. The major downside is cost.
In the end we went with flooded lead-acid. These batteries have a shorter shelf life than the other components of the system (generally lasting 3-7 years) and we figured that we would be in a better financial position by then and could reassess when they needed to be replaced. I also have first-hand experience of how easy it can be to damage gel cell batteries so was nervous to invest in those. Generally batteries fail due to lack of maintenance, running them too low, or insufficient charging. Maintenance aside, going for a system that is too small for your needs can therefore be a false economy as it can significantly reduce the life of the batteries.
Do you have enough Sun?
The effectiveness of your panels will depend on the climate as well as the position of the panels (see below). Having had solar systems and solar gadgets in rainforest conditions in the past, (none of which had worked very well), I was very sceptical that our often cloud covered site would provide much in the way of electricity. As a result I looked into wind power and water turbines first, both of which proved not to be all that suitable for our site. I discussed my fears with the supplier and he calculated the amount of sun our site would provide and eased my concerns somewhat, although even a year into living of grid with the system I was still waiting for it all to go wrong. The best option is to speak to people who have systems near you and find out their experiences. Alternatively, there are a range of smart phone apps that you can use such for this purpose such as solar meter for android and PV Solar Calculator , Solar Sizer PV and SolarChecker for iphone.
Positioning the system
When positioning the system you must choose a spot with no trees or other objects shading it (we had to cut down a few trees to position ours, but this was no hardship considering we live in a rainforest full of them). The angle of the panels is also very important and will determine how much power you receive. Obviously the most effective means of harvesting energy from the sun would be to have the panels constantly track its movements. It is possible to do this with automated trackers, but the cost is prohibitive and it works out better to just get extra panels instead. You can however, opt to mount the panels on frames that tilt to make better use of the sun at different times of the year. We went for static frames, on our North facing (best facing for panels in Australia) shed roof. But your choices, as with ours will depend on your site, location, system and of course how much you want to spend. There is a great web calculator that helps you work out the angle that will work best in your country and city to harvest power here. According to the calculator this is the best tilt for our site
When trying to decide where to locate your battery bank, temperature, ventilation and space are the main factors to consider. Our battery bank is also located in the shed. This works well as the system can be quite noisy at times and on very hot days (when very close to full) the batteries give off a rotten egg smell. This smell, called ‘Gassing’ is apparently perfectly normal, but pretty gross and I certainly wouldn’t fancy it in my house. The first time I experienced the smell I assumed the whole system was about to explode and contacted the installer in a complete panic. I was understandably relieved to learn our electricity supply wasn’t about to go up in smoke and I’m sure I gave the guy a laugh.
Here are some factors to take into considerations when planning the location of a battery bank:
– Batteries can lose over half of their charge when exposed to extreme temperature swings, so ensure they are located out of direct sunlight and off the ground to minimise temperature fluctuations.
– The batteries should be protected from rain, insects and rodents
– As you may spill some acid when refilling the batteries it is best they are on a concrete floor or somewhere that will not be damaged by a spill
– Batteries require ventilation, wet -cell batteries when gassing can explode if exposed to a naked flame or a spark. Gel or absorbed glass matte (AGM) batteries do not create explosive gasses to the same extent, so ventilation is not as important.
– You must be able to gain access to wet-cell battery terminals and caps each month for maintenance. AGM and Gel cells don’t require such maintenance
– Batteries are generally stored in large insulated pressure treated plywood box with pipes to vent the gas outside. The lid must lift to allow access to the batteries for maintenance etc.
Running power to the house
The disadvantage of placing the panels and batteries on the shed rather than the house was that there was an extra cost to run the power cables to the house in underground armoured tubing. This turned out to be a substantial extra expense. Make sure you take this into consideration if it applies to your site when working out the size of system you can afford. We also have a data cable fitting that passes information about the system to the house and this is fed thorough the armour casing (more on the data feed later).
How did we select the size of the system?
Collecting the basic information needed when working out the size of your solar system.
kilowatts = 1,000 watts of electrical power. A unit of energy [Watts = Volts x Amps]
1kWh = unit of measurement equal to 1,000 Watts of energy (a kilowatt) used over a period of one hour
Amp or Ampere = is the rate of flow of current
Amp hours or Ampere hours = the number of amps flowing x number of hours
1Ah = 1 amp flowing for 1hour
Batteries have Ampere hour ratings where Amps times hours is a product such that a 50Ah car battery could theoretically supply roughly 5Amps for 10 hours or 10 Amps for 5 hours etc.
When calculating how much solar you need, the key is to work out how many kilowatt hours you will use in a day. So with our system I can use 6.5 kilowatt hours in a day from the storage apart from a direct amount from sunlight. (Suppliers can and will provide more carefully worked out values before you buy).
The 24 volt, 1330Ah battery can store 24v x 13300Ah Watts of energy this gives 31920 Watt hours or 31.920 kWh of stored energy. Unfortunately as lead acid batteries discharge, their voltage falls and they can be damaged if it falls too low. A typical compromise to ensure reasonable battery life is to use no more than ½ the total storage capacity which here is about 16 kWh. This would give about 6.5 kWh for two days without sun and a contribution to the amount collected from solar panels on the previous day.
The solar panels can supply a nominal 3.75 kW in good sunlight giving a potential 3.75 kW for each hour i.e. 3.75kWh/hour. The same level of light for 2 hours leads to a potential 2 hours x 3.75 kW = 7.5 kWh. However the light level is not always constant or predictable. In addition the battery size limits the amount of this that can be stored.
The average home in Australia uses about 18 kWh (Kilo-watt hours) of power a day, the price of such a solar system would be astronomical and is totally unnecessary. We were lucky, or unlucky depending on your perspective, in that when we bought our place, neither of us had much in the way of electrical goods (or anything else for that matter) as we had both been living abroad. That meant that we were able to choose our electrical goods/fittings and our solar system together and focused completely on energy efficiency. I spent months planning, researching and reading reviews before we went ahead and bought anything. If you are hiring a professional outfit to fit the system, their first step will be to give you a table to complete that will help you calculate what size system you need. We wanted room to expand over the years and we wanted to live comfortably without constant fear of losing the power, whilst relying on the generator as little as possible. We were also worried that during the winter months our place is covered with mist and fog a lot of the time, so we incorporated considerable redundancy into the system for such times.
I have attached a spreadsheet form (link below) for you to calculate your usage, with some examples. I found that some electrical goods were labelled with watts and some with amps (To convert amps to watts multiply the amps by the voltage eg watts = amps x volts.
Here’s what we generally use now (we were much more frugal in the beginning)
|Fridge||75watts||Controlled on/off over 24 hours||0.01kWh|
|Freezer||75watts||“ “ “ “ “||0.047kWh|
|Satellite Internet||6 watts||24 hour/day||0.144kWh|
|Netgear router||15 Watts||24 hours/day||0.36kWh|
|Water pump||450watts working, 1-2 watts on standby.||10 mins a day working normal use||0.075kWh|
|Washing machine||432 watts||4.5 hours/week||0.278kWh|
|TV||160 w||2 hours/day||0.320kWh|
|Led Lights||1w 240volt B15 ecoglow bulb2 Phillips 9.5 watts||3 hours at night two in morning,4 hours/day||0.005kWh0.076kWh|
|Smart phones||2 x 6 w||2-4 hours a day||0.036kWh|
|Laptops||65 watts||14 hours a day||0.910kWh|
|Blender||2238||4 mins a day||0.150kWh|
|Microwave||1100w||12 mins a day||0.220kWh|
|Battery charger (AA and AAA batteries)||6W||14 h0urs/month||0.003kWh|
|Vacuum cleaner||1200w||2 hours/week||0.343kWhif surplus power|
|Water pump for watering plants||450 watts||1/2 hour watering/day||0.225kWh if surplus power|
Experience after over two years with the system
I am very happy with our solar set-up. If you were to stay at my house and didn’t know better, you would think we were on mains power. For the first year I was extremely strict, no blender, vacuum or microwave. When we checked over the year’s usage statistics however, we found that we were generally using only about half of the power available! After that I became less militant and a few high power items began to creep in, but I’m still careful.
I changed a few of the very low wattage light bulbs we had throughout the house for higher ones in some key spots (kitchen, lamp where I sit and read, lamp next to dining table) as the others were a bit dark for cooking and reading, but are fine for sitting watching the TV, bathrooms etc. The blender and microwave are high wattage and seem like a real splurge, but as we use them for seconds or a few minutes they actually don’t use a lot of power at all. I drink a lot of tea and it doesn’t make environmental or monetary sense to have the Rayburn on if we are not heating water or cooking just to have the odd cup of tea. Three minutes in the microwave makes two cups of tea and depending upon power rating, uses say 1100watts for 3 minutes or 1/20 of an hour is 55watt hours or 0.055 kWh, which is very little power and saves a lot of resources. The vacuum is more of a splurge, so it’s banned during cloudy rainy winter days, but I use it the rest of the time with no problems. If we didn’t have so many animals we could probably continue to live without, but sweeping takes up time I would rather spend cooking or in the garden so I think it’s worth it
For most of the year, we have an abundance of power. As you can see from the AC history usage tab screenshot shown below, we used 3.3Kwh hours yesterday and our average daily usage for the last seven days in 3.70kWh. The year to date average is 4.62 kWh, but this includes using power tools for building projects, movie watching marathons on rainy days etc. In bad weather, when we have two weeks of rain and fog straight and the batteries are charged at a significantly lower rate we run our generator, but this is generally only a couple of times a year.
This is the maintenance schedule for our system to give you an idea of the work of a wet cell system:
|Action||1 monthly||3monthly||12 monthly|
|Check for leaky cells||X|
|Check inter cell connections||X|
|Top up cells with electrolyte||X|
|Check overall battery voltage||X|
|Check cell voltage on float charge||X|
|Check pilot cells for electrolyte density||X|
|Check electrolyte density of all cells||X|
|Test alarms, check charge voltmeter||X|
|Check electrolyte temperatures||X|
|Clean solar panels||X|
How we minimise our power usage
– I use high power appliances at times of day when we have excess energy. On hot summer days from about 11am-2 pm the system is generating way more energy than we are using. It’s those times I break out the vacuum, fill the water barrels in the garden with a hose etc. [hose powered by an electric motor]
– The average fridge uses 1-2 kWh a day which makes a major dent in energy consumption. I bought two super-efficient Vestfrost SE255 freezers that run on only 0.47 kWh of power a day. I then converted one to act as a fridge with a cheap 17.99 thermostat and it uses 0.01kwh a day. That’s less than 1/2 a kWh for both the fridge and the freezer! To find out how to do this read my blog here
– I avoided the use of electricity for heating water or cooking by installing a Rayburn wood burning stove and evacuated solar water heater (more on this and our water system in a separate blog).
– I bought ridiculously energy efficient 1W led light bulbs from Ecoglow and placed them through the house (these are no longer available but they have 4W versions here). Three years on, I have replaced a few in strategic spots with slightly brighter higher wattage bulbs (Phillips 9Watt) , but the majority in our home still run on 1Watt.
– The house was designed to encourage cross-ventilation so that we would not need air conditioning. I installed energy efficient ceiling fans in the kitchen and above each bed in the bedrooms, but as we only switch them on a couple of times a year we could probably live without them.
– I chose a water pump that was energy efficient to pump water up to the house (Grundfos CMB 3-4 pump it has a P2 of 0.5kW and 3.1 Amp draw). I initially thought to use gravity, but the nature of our site and the fact we are in a cyclone area made this prohibitively costly so after a lot of research I abandoned the idea. I also preferred placing the tanks under the deck for aesthetic reasons so we would not have to look out onto the tanks
– We chose an energy efficient LED TV and rely on energy efficient laptop computers rather than desktop computers. We have energy saver sockets in all plugs allowing everything to be easily switched off rather than being left on standby.
– I used a sweeping brush and dustpan on the floors rather than a vacuum cleaner for the first couple of years (we have hardwood floors), now I vacuum only when its sunny. I initally used an Airtec (Bisell) G-ram environmentally friendly vacuum that uses only 100 watts, but it broke twice in a matter of months and performance in my home was very poor.
– We line dry our washing or place in front of the fire to dry rather than using an electric dryer
– I avoid using an iron for most clothes by hanging the clothes and allowing them to dry.
– We purchased energy efficient led outdoor lights and a 10w security light
If you have any questions on anything in this post, just leave a comment and I will get back to you as soon as I can!