Neville Williams & Dak Bahadur Gurung in Nepal.They installed village-wide solar in 1995.

Off-grid energy supply is a task that has to be analyzed on three levels:

  • producing the energy from any off-grid source, preferably renewable
  • reducing energy use,
  • storing it for future when supply exceeds demand.

True off-grid life means using only free renewable (sometimes referred to as alternative) energy sources. But solar photovoltaic panels and wind turbines supply you with power only when the solar/wind power is available. There are only two ways to simple deal with this problem. But neither of them is a good one.

The first is to buy a conventional energy source, like a diesel genset, to produce enough electricity to satisfy your needs. It’s a very easy solution, but I don’t suggest it. Diesel genset is not environmentally friendly, as it uses crude-derivative diesel fuel. You might use biodiesel or straight vegetable oil, but whether those fuels are fully renewable, is a questionnable matter. Genset with internal combustion engine is a good way to supply enough power when you need it, as it’s relatively easy to increase the output of this machine when you need more electricity. So you don’t need to store energy or reduce energy use — you just buy larger genset with equivalent turndown ratio.

The second solution is to buy renewable energy source, such as photovoltaic panels or wind turbine, that’s able to supply enough power for your need at all times! So if you need up to 10 kilowatts (kW) of electricity, you buy a turbine that’s able to supply 10 kW at even very light winds. Oh, and despite that, you would also have to limit your apetite for energy to sunny daytime or windy hours/season… I must be honest — except for the places where you have constant winds it is not cost-efficient way to make your home off-grid…

That’s why we need to take into account all the three levels.

Save as much as you can!

The first thing you need to do is to think about how much electricity you can save. You take a look at all your electrical devices, like kitchen stove, microwave, washing mashine, dishwasher, power tools, electric heaters, air conditioners, computers, tvs, lightbulbs, etc, and to see if some of those devices may be replaced with more efficient ones.

Start with all the light fixtures, replace the incandescent light bulbs with compact fluorescent lightbulbs. They are the easiest to replace and will generate substantial savings — each CFL uses about 20% of the energy used by the incandescent bulb…

The next step would be to identify all the devices that use the most electricity. Getting a portable (plug-in) wattmeter would be great, as it not only shows the amount of power used by the measured device (in a given time), but also can calculate the amount of energy it used in a given period — within a day, a week, or so. You just plug the device via this wattmeter, wait for a week, use the device normally, and then read the wattmeter.

When you identified which devices are reponsible for the most significant energy use, think if you can replace the device with more energy-efficient one, or get rid of it at all! For example, check if you can sell your electric heater and replace it with wood-firing furnace. Can you replace the air conditioner with solar chimney connected to ground heat exchanger? Can you get a solar water heater instead of your electric water heater? Can you identify and kill all the phantom loads?

You must remember that in off-grid conditions it’s easier to save one watt of electricity than to make it on your own!

Produce enough to fulfill all your needs

When you can’t reduce your energy use any further, calculate the amount of electricity you need daily in summer and winter. You can assume that the amount you need on during any other season lies somewhere between those two, so one will be minimum and the other — maximum. Which is which would depend on your climate, life style, etc.

Then take a look in a good solar/wind database and see how much energy you can make with a given photovoltaic panel or wind turbine. You should probably find a map that shows the solar irradiation or wind speeds, use this data to see how big wind turbine you need to buy (or make), and how many PV panels you need to get. If you live in Europe, use this great PV potential estimation tool.

In most cases you can’t be sure that each day you will get the desired amount of electricity. So I suggest you to get two turbines of the calculated power and two sets of PV panels, so they can produce more energy when wind / sun is at its peak, to be stored in batteries. You might even increase the output of turbine / PV further, as you need to take into account the efficiency of storing electricity in batteries!

Think not about the power all your devices use and solar panels / turbine supplies. Think about how much energy you use daily / weekly, and how much energy can be supplied from your source in the average day or week. Remember about the seasonal changes of weather!

Store for a week or so

Depending on your local weather / climate conditions, you might need to store enough energy for a week without a wind / sun or so. If not, I believe that storage capacity for at least 2 days is a must. With anything less you might end up with going to sleep early in the evening when you use all your energy produced that day…

You can reduce the size (and cost!) of your battery bank easily. I think that this is the place where a small genset might become handy — and reasonable. In such a case you would not need to buy a large genset, able to supply all the energy you use, but a smaller one, that will be enough to charge your batteries in 10 hours of continuous work. If you like doing it yourself, try using the waste heat from this genset to heat your home. ;)

Photo source.

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7 Responses to “Off-grid electricity: produce, save and store”

  1. Jason

    The 600ah battery example is great but it would require 1200ah capacity battery bank at 50% depth of discharge.

  2. Krzysztof Lis

    @nikki: solar panels are very useful, if you have enough solar energy available. Storing that energy is not complicated at all, you just need to purchase enough batteries to make it work.

    For example, if you use 5 kWh (kilowatt-hours) of electricity daily and need to store your energy for, say, 4 days without sunlight, than your batteries must store 20 kWh of energy. If you have 48V system,than you would need batteries of total 20,000 Wh/ 48 V = 420 Ah (ampere-hours). Taking into account the efficiency of lead-acid batteries, you should buy about 600 Ah capacity batteries at 48 V voltage (if you buy standard 12 V batteries, than you have to connect them in series and multiply the number of require batteries by four).

  3. nikki

    What about solar generators?I have seen them online are these any good?
    I am a beginner and this is all very confusing.
    Storage seems complicated.I am in Maine and winters are dark. I am getting older as well,so in the words of the late Scott Nearing,I can’t be bothered with fuming machines.
    I have considered old fashion kerosine lamps,a root cellar for cold storage,and wood from my own lot for heat. Friends have a wood boiler which provides heat and hot water.Any thoughts on these?

  4. abhishek

    All the information provided here is really quite knowledge enhancing but other than this if you can provide me some data regarding how many personnel will be required, to produce solar pumps, solar light systems etc, in installation and operation and maintenance also then it will be very helpful to me.

  5. Krzysztof Lis

    elnav, thanks for your very detailed comments.

    Of course you can substitute a diesel engine with spark ignition engine that runs on gasoline. And you can replace that gasoline with homemade ethanol fuel.

    For both diesel and gasoline engines you can use the biogas you mentioned. It is a renewable fuel and a good way to utilise waste (using anaerobic digestion). Producing biogas is a good idea in warm climate, where you don’t need to heat the biodigester. But I am not sure if you can easily find it all over the world, except for landfills, marshes and sewage treatment facilities.

    I would recommend wood gas instead of biogas. It is also a renewable fuel (if you have renewable source of wood), but can be produced on demand, exactly when you need it. Too bad it can’t be easily stored.

    There are many ways to store electricity. On large scale compressed air is a solution, but not used frequently because of poor efficiency. Much better efficiency can be achieved with pumped water storage, but I can’t imagine a good way to store energy that way for a single autonomous house.

  6. elnav

    Energy storage: This is another area that needs more attention. Energy can be stored in more ways than in electrical batteries. At present power utility companies are storing energy in other ways. Compressed air is one way and water resevoir is another. The latter may be the most practical for small scale use. Even if you live on a perfectly flat lot you can store water in a raised tank.
    If you have a piece of property with elevation changes so much the better. Wind driven pumps can pump water into the resevoir and the a microturbine can generated power as you release the water through the turbine when you need it. You do not necessarily need to build a huge dam since your local power need is quite small . Dams and big rivers are only needed when the utility company is powering whole cities or towns at a time.

  7. elnav

    Most of these suggestions have already been implemented by someone , someplace in the world. The comment regarding diesel engines needs expanding upon. Methane is a viable fuel source but is for some reason ignored. Ordinary internal combustion engines can easily be converted to run on methane ( or natural gas) And these gasoline fuelled engines are often much cheaper than a diesel engine.
    conversion kits cost a couple of hundred dollars.
    There exist user group forums with members in Canada, the US, UK and Europe. You can find U tube videos showing methane powered generators from many olaces in the world.
    Methane is a naturally ocurring fuel that is renewable. Often free and available in most places in the world for the trouble to collect it. Despite this it receives almost no press or media attention so it goes largely ignored. Solar cells have a huge carbon foot print in the manufacturing process and at best is only about 20% efficient . Wind turbines also have a considerable carbon footprint during the manufacturing process. Battery storage of generated electricity has a few downsides beginning with the toxic chemicals and metals used to make batteries.
    Methane is a natural, organic originated fuel that is a by-product of food production. So why is this cheap renewable fuel being ignored?


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