Planning to survive off grid.
Over the years I've had visits from a number of folk who wish to "go off grid" the last being in August this year.
I have recently put together a few paragraphs of thoughts and ideas on the subject as an aid to my last visitor and it occurred to me that they might be of use to others so I post them here for general use. I make no claim to expertise except that in 20 years we've very rarely had a power cut and I've reduced my use of red diesel for the genny down from 2500 liters to 200 liters per annum.
Hope this is of some use to some one.
Principal points to consider.
1 Household power consumption. Actual average and peak.
2. Energy generation
3. Energy storage.
4 Control and integration
Before considering the various elements in an off grid power system you need to consider your own (and families) abilities. Assume that there is NO BACKUP and if something goes wrong how are you going to cope? Forget about warranties as they will not turn out in the rain, in a gale and mend things. Buy the very best kit you can afford with the best reputation for reliability.
Keep your system as simple as possible and where possible have spares in store or other backups planned. Keep a record of the system design so some other competent person can understand it. Try to ensure you understand the set up and ideally be able to repair or replace stuff yourself. Most trade’s men (electricians) will run a mile from any DC power set up.
1 Every book will tell you to measure your electrical consumption for a year then plan accordingly. But for a new off grid this is difficult.
Although if you plan to install low energy devices i.e. LED lights etc, then you can plan to reduce consumption. Also plan for life style changes i.e. most off grid set ups will have an upper limit for capacity so (e.g.) you may have to run the washing machine AFTER you have done the vacuum cleaning. Insulate to a high degree to reduce heating consumption. Turn off kit at the wall if not in use, standby still eats power.
When you have teenage children they will ignore all your guidelines and burn energy so plan for this too.
I’d suggest that for a family home living a “normal” life you may need to allow for 10kWh daily consumption.
2. The sexy bit!! PV panels are the base line now in 2020. Various models exist and I have no view on brands or types all have pros and cons.
For a Welsh mountain side I’d go for ground mounted and fit as much as you can afford. In mid-winter a 4.5kW array may only produce 1.5kWh in a day, so if your house needs 10kWh per day you are short by 8.5kWh. In midsummer the same array will probably be capable of producing 20kWh. Of course if you fit 8 times as much PV you will have more power in winter but have 16 times more power than your daily needs in summer.
PV power is easy to control and very reliable.
SO you are seeking a balance. More winter electric generation can be obtained by using a wind turbine (WT). Small WT i.e. under 1kW are generally toys made using car alternators and plastic blades. AVOID them. Under 3kW there are very few products on the market. There are Chinese products of varying provenance and likely no back up or support. There are also a couple of European brands to research.
NB A 1000W WT may only produce 100W to 200W per hour on an average to quiet day. It will only produce 1000W when the wind is over 20mph so you may well still have a short fall. A 3kW WT is probably required for full self sufficiency. Obviously costs rise with size. A small WT may well mean more run time on the genny. As I say there is a balance to be struck and every individual is different.
6kW WT exist (Proven) but the cost is high with a suitable tower and control gear probably in excess of £20,000 unless second hand gear is obtained.
The key with a WT is location and the WT tower. Most WT failures come from tower failures. A location with “clean air” is desirable. If the site has a definite prevailing wind it can work even on a hillside that shadows the site, but you’ll only get power on some days.
The other issue with a WT is control. Domestic scale WT have no “off button” so if a gale is blowing you need to be able to use the power generated. A WT running with no load, can or will run over speed and destroy itself.
Ignore vertical axis WT they are toys and don’t mount the WT on a building.
You can plan to dump or waste power from the WT by using resistors OR plan to use the surplus by heating either water or “space”. Or you can lower or disable the WT before the wind blows.
I have chosen to build a WT using plans by Hugh Piggot. The designs are sound and if you are unskilled the components can be made by others.
As a backup and/or an alternative to a WT a generator (genny) will be required. There are many brands on the market ALL will need some love and maintenance. If your genny is the backup it’s got to work when needed so look after it.
For ultimate long term reliability a genuine Lister is the tops. For the 10kW daily house demand envisaged an 8kW alternator will be sufficient. This will be enough to power the house if required and charge the batteries.
Diesel gennys need to have diesel fuel which can be brought in bulk and stored if a lorry can make it to you. Petrol gennys will need to be refilled frequently with petrol although similar machines are available which can use LPG gas which is cleaner and large gas bottles are available. Modern diesel gennys are often quieter than the traditional air cooled Lister.
3. Energy storage. An off grid system requires an energy store so surplus can be kept for later use. Batteries are the usual system and in my opinion traditional flooded lead acid “fork lift” type cannot be beaten. They are relatively cheap and very reliable and will work for years even if abused. The drawback is they are large and heavy and need to be stored away from the main house and some regular maintenance is required. Water caps can be fitted to reduce the weekly topping up usually required.
The battery stores Direct Current power and will be charged from the various items I.e. PV, WT or the genny. The general guidance is to charge a battery at around 10% of its capacity. So a 1000Ahr battery can be charged at 100 Amps per hr. Therefore if you have a 2000Ahr battery you need to have the means of charging it at 200 Amps per hr.
The house will be supplied by drawing power from the battery which is then converted to Vac current for use in normal household appliances. The component that does this conversion is known as an Inverter and it uses some power in the process.
An off grid system is a balance of components to try to give power when needed for the house, either directly from the energy source e.g. PV or from that stored in the battery. If the battery falls below a set point (Vdc) the genny will be needed to run to make up the short fall.
There are differing schools of thought about how much to discharge a lead acid battery. I suggest asking the manufacturer. Personally I will allow my 24Vdc battery to drop to 22.2Vdc but some will say never drop below 23.5Vdc. Proper fork lift batteries are designed to be heavily discharged and can take the punishment that fork lift drivers give them every day. Shop around as prices vary enormously and haggle. At end of life a set of batteries has a good scrap value so don’t give them away!
4 System control and integration.
To the greatest extent it is wise to follow the KISS principal. Keep it simple, stupid!
Each element (PV etc.) will have its own control box which ideally will be able to communicate with the rest of the system.
PV panels will produce Vdc which can be used to charge the battery, to avoid over charging the battery the PV array(s) will need charge controller(s).
The house will need an inverter to take Vdc power from the battery and change it to Vac. Normally a combined inverter/charger is used. This is capable of monitoring the battery (voltage) and can auto start the genny if required and control the battery charging.
WT; in the simplest systems a WT which produces Wild (variable ) Vac current is connected to a rectifier. This converts the wild Vac to Vdc current which is then fed into the battery. This can be direct or via a charge controller. Either way if the WT brings the battery voltage above a set point a switch (relay) is used to start sending surplus power to the dump load.
More complex WT systems can be Vac coupled. In this set up the wild Vac is first converted to Vdc and then reconverted to Vac and synchronised with the “house grid” using a grid tie inverter. Although more expensive initially this set up allows the use of Vac in the power cables which can be a significant cost saving in a remote set up.
In addition to the components listed, most items will require suitable fuses and isolators. It is generally easier to connect the Vdc elements using a + and – “bus bar” to avoid having multiple connections on the battery.
It is probably wise to use kit from one brand although not strictly necessary. Using one brand makes it harder for a supplier to blame someone else in the event of equipment failure. I favour Outback but other good kit exists. Some brands offer greater levels of monitoring and no doubt it could be useful to know how much PV you’ve produced whilst sunning yourself in foreign climes using blue tooth or something but it is one more thing to go wrong.
All of the house loads will be connected in the normal way using consumer units with MCB’s or RCD’s as appropriate.
Although not directly part of the electrical energy system, take a view on the whole house energy consumption i.e. space heating and water heating. Modern systems with lots of pumps are all using power which you may not have budgeted for. An instant over sink water heater may be great but if it makes the genny come on every time you use it, it’s not so good. So the traditional indirect water system may suit you better and can have an immersion heater(s) fitted to use surplus electricity.
Costs. October 2020.
How long is piece of string?
PV panels budget for 5 KW PV system (panels only)- £4000
2 Nos Outback PV charge controller FM80- £1100
1000 Amp Hr C5 lead acid battery 24V- £2000
Outback 24V 3 Kw invertor charger- £1600
Wind Turbine (future energy)- £ 800
WT Tower guess- £1000
Balance of system fuses cables etc- £ 500
S/H lister 3 cylinder genny- £1500
PV ground mountings estimate DIY- £ 500
Guestimate to set up off grid system no labour- £13,000