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Choosing your back-up/off-grid power source

A guest post by Skvez.

This article is the first in a series by SKvez on power. This one is on choosing which type of back-up/off-grid power source you want. I want to do another article on *sizing* this power source but this article is on the pros and cons of selecting what source to use.

I’m going to consider petrol generator, diesel generator, steam generator, hydro generator, wind power and solar (Photo Voltaic) power.

Cost:

Cost of Petrol is about £500 for a 1kW generator.

Cost of Diesel is similar to Petrol however you won’t get a diesel generator as small as 1kW. Diesel engines aren’t made this small (the smallest I could find was over 5kW).

Cost of Steam is about £1700 for a 1kW generator.

I have been unable to locate typical costs of hydro-electric, the cost varies too much based on what sort of dam is required. I’m going to guestimate about £1000 to £2000 for 1kW.

Cost of a 1kW Wind Turbine is about £800 + £300 for a suitable tower, £1100 total. (Do not think of mounting your turbine to your house roof, your roof was not designed to handle the vibration, I’ve seen many pictures of shattered turbines and chimneys lying in people drives, or worse yet on-top of their neighbours car!).

Installed cost of 1kW of solar is about £3500.

Duty Cycle:

Petrol, diesel and steam are available whenever you want it, up to the full rating of the unit.

These units should come with some form of Voltage regulator (to keep the Voltage relatively constant as load changes).

Hydro is only an option if you have access to a reliable flow of water (and have permission to compromise the flow by damming it up). Provided the flow of water is strong enough year round you have power whenever you want it up to the full rating if the unit.

Wind is obviously only available when the wind blows, and although it will generate some power 75% to 80% of the time, it won’t be anywhere close to the full rated power of the turbine. The energy in the wind is proportional to the cube of the wind speed so a 2m turbine rated at 1kW in 30mph winds will produce about 125W at 15mph (the average wind speed) and a paltry 65W at 12mph (the most common wind speed), the turbine will probably stall and produce no power at wind speeds below about 10mph.

You can expect on average about 20% of the ‘full rating’ from your wind turbine.

If you’re in a sheltered area wind power is probably not for you.

You will almost certainly (but not definitely) want some means to store the power between when it’s generated and when you want to use it (battery bank). This cost is not included and varies depending on just how much storage you want.

You will also need some form of Voltage regulator as the output Voltage will vary somewhat with wind speed and load. Most loads require a stable supply.

Solar is obviously only available during the day. However people often don’t appreciate that daylight has only a tiny fraction of the solar energy available that sunlight has. Also panels are rated in equatorial conditions with the sun overhead and the panel at 25°C. This never happens, anywhere, ever. Even if you were on the equator at noon it would be so hot the panel would be well above 25°C and so not as efficient. However it’s these ‘standard conditions’ panels are rated at.

Here in the UK we are far from ideal conditions. In winter I’ve had truly appalling power from a solar panel, approx 1% of its ‘standard conditions’ rating.

Similar to wind you will probably need storage and you will need some form of Voltage regulator as the Voltage varies with sunlight and load.

Fuel and Maintenance:

The Petrol generator obviously needs fed petrol and like any other engine needs oil, oil filters and air filters and spark plugs and bearings replaced periodically.

Storage of Petrol has legal restrictions in the UK due to its flammable nature, and petrol has a limited shelf life.

A Diesel generator again needs fed diesel although diesel has a longer storage period than petrol. Owing to diesels higher compression ratio diesels need starting batteries where small petrol engines can be hand cranked, diesel can become syrupy in sub-zero temperatures making the generator hard to start. Maintenance is again required on oil, oil and fuel filters, air filters, and bearings (but no spark plugs). While older diesel engines were tolerant of a wide range of diesel-like fuels (such as home heating oil) newer emissions legislations have driven changes to the injector design of newer engines that make them very fussy about the quality of their fuel.

Steam generators can be run on coal, or wood or pretty much anything that burns. Steam engines also require a considerable supply of *water*. They require replacement seals and oil. Steam generators are something of a novelty item and may not be designed with continuous heavy use in mind.

Petrol, Diesel and particularly steam also product useful amounts of waste heat that can be put to use in heating your home (something called ‘combined heat and power’).

Hydro need some maintenance on the moving parts and will periodically require sticks and other debris removed from the water intake. If your stream totally freezes in winter (i.e. freeze right to the bottom, not just a surface freeze) the expansion of the ice can destroy your hydro-generator.

For Wind turbines, the wind is plentiful and free. They have bearings that need maintenance and the blades tend to need cleaned from time to time to keep them efficient (which doesn’t sound like a big task until you remember it’s up a tower, you either have to go up there or lower the tower, You won’t have power for a power winch, a manual winch can be used but you can’t winch yourself up the tower). Blades also wear away slowly. Wind turbines should have some form of furling mechanism (that points them progressively out of the wind as it gets very stormy) but even so damage in storms is common.

Sunlight is free. Solar benefits from a wipe down from time to time but otherwise needs no maintenance.

OPSEC:

Petrol, diesel and steam are loud and produce fumes that make them hard to hide (can’t run it inside).

Hydro have few OPSEC issues.

Wind turbines need to sit up above surrounding obstacles (ideally 10m above the nearest obstacle for 100m) and are therefore very obvious.

Solar needs to be outside (actually you could run a small panel from inside a window but generally we’ll assume it’s outside on a south-facing roof) they are not overly obvious, especially if your south facing roof points towards a ‘private’ side of your property.

The second part of the series is Power 2 – Overview of Terms.

5 comments to Choosing your back-up/off-grid power source

  • Justin

    I’d have to agree with most of the above, especially the choice of hydro and solar as the most viable. A hydro power source could be created with the right skills and knowledge using an alternator and manufactured wheel. Takes knowledge of various areas including gearing systems and wheel types (go back shot if possible) but is doable by someone handy with their mind and hands. All I need now is a river in the garden to go with my 20 acres of woodland, underground fortress and my good friend Ray Mears… (Joke, not being facetious!)

    All the above would obviously power electrical products, and I realise that that is the point of this post, but I think that gas and fuel oil need to be discussed at some point. A fuel oil tank or gas tank in the garden would give you the ability to heat in both cases and cook in the latter case. You could rig a steam generator to run off gas if necessary and skills allowed.

    • Skvez

      Thanks Justin, I should have included those.
      Gas gensets can be considered similar to Petrol gensets except for the storage issues where Gas has fewer storage issues (keeps ‘good’ much longer).
      I’m not as familiar with fuel_oil but I expect it’s similar to diesel.

  • Skean Dhude

    Justin,

    Good points. I was thinking along the lines of after the gas and oil runs out.

    Personally for most of us I see wind for power generation with solar, in the form of solar ovens being used for cooking and heating. Most don’t have access to power with any viable potential energy and wind will not be powerful enough except for the basics. Running all day will charge the batteries for the radio and computer when required whilst a solaroven will do the cooking and heat the water for washing etc.

  • moosedog

    Almost a quarter of a century ago I moved onto my narrowboat where I spent 5 very pleasant years living off-grid. I found a 12 volt system to be perfectly adequate for most things in life and that was before LED lighting and LCD televisions: nowadays a very comfortable standard of living could be maintained running 12 volts. That would mean much lighter duty wind generators, needing nothing more than a scaffold pole & guy ropes for mounting so easier to set up, maintain and, if necessary, relocate. Adding a few solar panels suitable for motorhomes would keep the batteries topped up when it’s not windy. From memory I think a 40 watt solar panel will run a 12 volt compressor fridge for a week off one (previously charged) battery. For the odd times 240 volts is needed a generator could last many years. That’s if we adapt to not needing mains electricity. Just because it’s the norm now doesn’t mean we have to rely on it forever. Adaptation is the key to long term survival WITH a good quality of life.

  • Skean Dhude

    Moosedog,

    A 12v system will be better in many ways. First of all all vehicles use 12v as their base. Most portable items have the facility to use 12v. If you have the odd item that needs 240v then you can always use an invertor. 12v seems the best way to go.

    It may be worthwhile ensuring that the bulk of your purchases use 12v as a default.

    Adaptation is what the human race is good at. Or was good at anyway.

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