[Pundyburn Lynn]

Hello folks,


My off-grid plan was coming together last year, but we lost out on the land we were hoping for and everything fell through.


We're now onto our next potential site, and I have forgotten EVERYTHING I had learned last year about power!


Sooo, who can remind me how to calculate energy??  Our current on-grid house (larger) uses around 13 'units' of electricity per day, with no attempt whatsoever to conserve energy.  I've forgotten whether this is kw or kwh?  The site we're looking for has a fast flowing downhill burn and is south facing, so let's assume that we can generate enough power to meet our needs in a slightly smaller off-grid house, say 10 units per day.  We could also reduce this somewhat if necessary.  What I want to know is how to calculate the energy input required to achieve that level of power, and what size of battery bank would be required to cover most daily tasks?  (We don't expect to use every appliance at once.). Is there an easy formula that I could learn to use, rather than having to ask you all for help??


Thanks,
Lynn

[regen]

No easy formula!

 You need to write down all the appliances etc which will use power and how much and when. This will give you an approximate maximum usage and also a total daily usage. eg fridge max= 0.8kw daily usage 1.2kwh. Once you have done this then decide how little you could manage with ! Only you know your lifestyle and how much you are prepared to sacrifice to go off grid.

Once you have a projected usage pattern then you can decide how you are going to generate that power and how much you will need to store and for how long.

A fast flowing stream may be next to useless if for 6 months it is a trickle or you have a very low head. If you are thinking hydro the then you need flow figures which represent a full year. If you have a head of say 50m and a minimum usable flowrate of say 3 lpm then you could generate around 1kwh which would cover lights and fridge freezer 24/7 but not cookers without serious battery storage. (although there would be plenty to spare for water heating) Hydro and solar pv dovetail to gether fairly well but for a legal system think about 15 to 20 grand!

Its a huge and fairly complicated subject and i would suggest a lot of reading so you know enough about the basics to ask the right specific questions relative to your situation.

Regen

[Creagan]

First step is to take any heating and cooking away from electricity and use bottled gas, wood, etc.
That should leave a managable electrical requirement for everything else. LED lighting is fantastic, you will probably find your main consumer of electricity is the freezer, especially if you are producing and storing your own food. Worth buying the most efficient fridge and freezer you can find.

The units that electricity is measured in are kilowatt hours (kwh), i.e. one unit equals a load of 1000w for an hour.

Are you willing to consider running a generator to meet some of your needs? Thinking more out of the box, you could consider combined heating and power generation, e.g. a wood fuelled steam engine running a generator.

A combination of solar and hydro is a good bet, as the two should balance out through the year. Solar has become very affordable and IMHO more cost effective than wind for small installations. Hydro is extremely site specific but can be very reliable.

Batteries are expensive, environmentally not very friendly, and need regular replacement. You want to avoid or minimise their use, if you can.