SOLAR SYSTEM AND OFF GRID ADVICE

Getting it wrong can waste resources

From my own experience and expertise I can guide you better to get it right.

With my training and experience I can help you to start on the path of providing home energy to keep your lights on, run your central heating boiler (even wood boilers often use electricity) and solar water heating water pumps. At present, no grid, nothing works. People who I have advised often do much more than this, running fridges, freezers, washing machines, kettles and toasters . . . and one lady even is planning on running a boat engine . . .

I am a physicist with experience of my own system, trying out various products and finding the best. Hopefully you can save as a result of that experience. I can guide you to products that I have tested and work well and avoid expensive items that don't work so well at all. I sell inverters and other equipment on ebay from time to time and questions about these inevitably lead to questions of design and decisions at the heart of people's systems. (Please note, I can guide you to assist you to design and implement your own system to the best of my research and expertise but I cannot be held responsible for what you actually do.)

If you want to discuss your installation with me or ask me for design advice, please can you Buy Now a timeslot and phone me on 01342 850594 asking if I can speak then or later to mutual convenience telling me how much time you have bought. Common questions include:
What voltage should I use? 12V 24V 48V?
Will these panels be compatible with my other equipment?
What sort of solar controller do I need? Is an MPPT controller worth the extra expense beyond an ordinary PWM controller (I have tested 1kW of panels on both . . . )
What type of batteries should I use?
How many batteries do I need for this application?
How many solar panels do I need?
These flexible thin film panels are great - can I use them? How can I use them? Can I split them into smaller sizes?
Can I use cheap inverters? Are modified sine inverters useful? Why can't I use a 3000W inverter to run a 3kW electric kettle? What goes wrong with the cheaper inverters? What should I look for? Why are there so many faulty inverters for sale on ebay "for spares or repair"? Can you repair my inverter? What sort of inverter is best for my house? Or boat? Why are the more expensive inverters worth investing in?
How do I switch between battery/inverter power and mains when I want to?
What sort of cable is good to use?
How can I incorporate safety features in case of a fault?

Of course there are lots more questions that I can help with . . . .

I have been consulted about off-grid solar systems asking these sort of questions in Spain, West Africa and the Caribbean and increasingly people in Britain are looking towards being more self sufficient and independant of oil and gas. I'm happy to help. But many people don't really appreciate how valuable energy is and think that they can live an off-grid existence entirely cocooned in 20th century energy consumption styles. Unless one has the sun actually shining on panels, one does not want to waste expensively stored energy merely on low grade water and space heating unnecessarily. One has to re-think lifestyle choices and actually run the washing machine when the sun is shining. Meanwhile it's important to get as much solar installation capacity on our roofs - we have enough built environment with wasted roofspace facing east and west to give us power from morning to evening without covering our virgin countryside necessary for food growing and wildlife with solar farms. Grid-tie installations need to be east and west facing to achieve this without a hump of production just in the middle of the day driving supply voltages up uselessly.

You'll pick up lots of tips from my videos

but there is more than this. IF YOU FIND THESE VIDEOS USEFUL PLEASE CAN YOU Buy Now a £10 video donation on this page? Then I might be encouraged to do updates to these . . .

A basic knowledge of electricity is helpful. W=IV Watts = Amps x Volts. Series and parallel connections. Voltages add in series. Putting things in parallel increases current.

People often ask me about designing off grid systems. The requirements of powering a boat for a limited number of outings per year, or a trailer, are different from those of a long term project. The life of deep cycle batteries is often 400-500 cycles - so on a daily basis this is only around 18 months to two years. For a lifespan of 10 or 20 years one has to use only 5%-10% of the capacity per day. So for a long term installation one needs 10-20 times as many batteries as one does on a trailer or boat. Below is a response to a lady buying equipment for Jamaica.

I would go for a 24 volt system (although see lower regarding 48V which is better still) - that is made of pairs of batteries connected with pairs in series with each of these pairs in parallel - so that's 12V + 12V to make 24. I use solder wire between the batteries which blows at 7 amps and this provides safety - and for a start I'd have 20 to 40 batteries - so that would be 20 x2 to make the 24 volts. The 90 amp hour batteries would then be 90 amps x 24 volts - so one pair of batteries at 24V would be (amps x volts = watts) just over 2000W hours - in other words 2000W for one hour or 100 watts for 20 hours. But you only want to use 10% of this per day so that is 10 watts for 20 hours per pair of batteries. So 20 pairs of batteries - that is 40 batteries, will give you an ability to use say 200 watts - possibly 200-300 watts for 20 hours.

Your fridge might be 400 watts and might run for 12 hours out of 24. So this capacity is necessary for a fridge. What you want to run on top needs more but will be more here and there.

The reality is that your two 250W solar panels won't be enough. 250W times 2 is 500W and you will probably get say 250 watts averaged over the day unless your panels are on a tracking frame and track the sun. In Jamaica you get a constant average of 7 hours sun per day. So you will have a total energy of just under 2kW hours per day to put into batteries and use. Batteries are not 100% efficent so you will probably have only 1.2 kWh to use every day. That is 400 watts for 3 hours. So that is the fridge running for 3 hours. You want it running for perhaps 12. If it is more efficient or a smaller fridge, great, you'll have power for other things. But we want 12 hours not 3 hours so you want 4 times as many panels - you need 8 panels.

Because you are away from technological expertise I would go for the largest inverter possible to maximise reliability and minimise the chance of a piece of equipment blowing it - either 5000W or 8000W of the pure sine sort so that a computer or microwave won't object to the type of power supplied.

But of this capacity, you are probably going to use 1000W or 2000W peak - so you should limit the current coming into it to whatever size of cables you're using for connecting up the batteries together and to the inverter. 1000W at 25V is 40 amps, 2000W is 80amps. Your cable should be 12mm squared - 12mm2 for 40amps and 24mm squared for 80 amps and larger pro rata.

http://www.ebay.co.uk/itm/280608627568 are good circuit breakers that you can order at the level at which your cables are limited.

Pure sine Inverters with output transformers - 5000W £540-560 8000W £880-920. If you have four 12V batteries in series instead of 2 to make 48V rather than 24V then you can use thinner interconnecting cables, or double the current for the same size, double the power.

The normal cheaper inverters are not guaranteed for use on fridges of above 200-300W

For more complex loads, so more reliable, are Low Frequency inverters. These are more expensive so you can expect to pay around £560 for a 48V 5000W low frequency inverter. Ranges up to 15kW are possible although heavier and more costly, £900 for a 8000W unit.

The CM6024 solar controller comes in a 48V version - the CM6048. http://www.ebay.co.uk/itm/60A-Solar-Charge-Controller-12V-24V-48V-lighting-timer-Controller-LCD-display-/151057326448 comes in a 48V version.

> 1 Fridge (Small / medium)
200 watts. 12hours a day or more?
> 8 Low energy lights
LEDs - flourescents more difficult to power - say 4w LED x 8 = 50
watts + one 60W normal lightbulb total 5 hours
> 2 Fans
How long? Assume 50 watts each but are they more? Assume ?18 hours?
> 1 Tv
To be used as wallpaper? Or for serious watching? 50 watts for say 3 hours?
> 1 Video recorder
Say 50 watts. 3 hours
> How many panels would I require, how many batteries (110 amp hour)and size of inverter.

200W x 12 2400Wh
50W x5 250Wh
60W x5 300Wh
100W x18 1800Wh
50W x3 150Wh
50W x3 150Wh

so this is 5050Wh - say 5kWh per day.

Sierra Leone http://www.weather2travel.com/climate-guides/sierra-leone/ say 7 hours of sunshine per day but in the rainy season you need to store 2 days sun. In the rainy season you'll need more power with more lights and TVs. What about fans? You'll need to advise me.

But say 7 hours per day and we aim to store for two days without sun.

Our maximum draw at any one time with fans and fridges and lights (by
the way, possibly use one normal filament light bulb as this will
resist surges within the system) is about 500W or so.

To cope with peaks, whilst a 3kW inverter might suffice a 5000W inverter should be better in the long run.

So assume 2 panels of 250W coping with powering all demands during sunshine and we need more to charge the batteries. I'm going to over estimate a shade. 7 hours of sun in which to collect 5000Wh for the day. To store for two days in the rains, then assume 2.5 hours of sun per day. 5000 / 2.5 is 2 kW of panels so we need around 8 panels of 250W.

We need to store 2 days' electricity - 10,000Wh

Let's use 48V because it's more efficient in terms of cable current carrying capacity. Say 50V Watts/Volts=Amps so 10,000/50 = 200Ah

So that is say two rows of four 110Ah batteries. Four batteries in series gives 40V at 110Ah and your two rows gives 220Ah. So this is 8 batteries.

But the batteries have a lifecycle of only 300 to 600 cycles. That is only between one year and two years. Many people for events and trailers in the UK in a more expendable setup can manage with 8 batteries. To last 10-15 years it's important to cycle only 10%, so this means having 10 times the number of batteries.

This would be 80 batteries. But this is an over estimate because we are only going to deep cycle them for four months of the year during the rainy season when we might need to store two or three days electricity at a time and use it.

But I'm told by a friend with experience in Congo that batteries are the weak link in the system and variable quality can let them down significantly. So it's a good idea not to economise.

It's a good idea to arrange each bank of 8 batteries perhaps so that all 10 banks are switchable, rotating daily one bank turned off every day to monitor how fast the voltage falls so that in the course or time any set with a low battery can be isolated.

You might get away with 40 batteries as I deliberately over estimate rather than under.

But more is better.

Have a look at www.bimblesolar.com for the different types of batteries. You might go for 2V traction batteries perhaps. Some can be shipped dry and you add acid on site. In the course of time, this type can perhaps even be restored and refurbished, but I don't know about that. Worth investigating. Otherwise AGM batteries or Valve Regulated are the most civilised. Cheap leisure batteries might be fine, but they might be cheap for a reason.

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Useful tips & innovative ideas leading me to more research. A good start!

You have probably got to this page simply seeking to be independent from rising bills, overcome problems of power cuts, or simply getting power to places beyond the reach of a cable . . . and I can help with guidance on those issues but the real reason is urgently more important. I don't run a business doing this: there is a more important reason than making a profit. By 2020, just 7 years away, it will be within everyone's consciousness that we are on the last drop of oil. https://sites.google.com/site/architecturearticles/home/article-007---britain-future-climate-and-architecture We have just 7 years of comparative plenty in which to prepare for fuel famine - and everything else that follows. By preparing as individuals, neighbours, communities, the problems are not insurmountable, but those who leave it till late in the day will find it increasingly difficult. Only people who work together will survive.