This little post is about generating cheap solar energy and reveals all the nitty gritty that took ages to find on the internet.
Why I want Solar Power
I want to put up some solar panels and reduce my electricity bills and do my bit for the environment. I live in a north facing house (in the northern hemisphere, UK) and so for 3 quarters of the year the house is naturally colder that outside which is really annoying when the summer sun is shining bright and the house is chilly. None of my roof sides are south facing south but I have a one story garage at the end of the garden that has a 6 x 2.5m roof facing south - a perfect sun catcher.
So - options of getting solar power :
1. Buy a system from a supplier and get it fitted and registered for FIT - and a 4kw system will cost £7000 odd and pay for itself in 10 years.
2. Buy a system - perhaps a lot smaller - with second hand panels - say 0.6kw which can cost about £450, fit it myself, don't apply for the feed In Tariff (FIT) and pay for itself in about 4 years.
Why DIY and not get the Feed In Tariff?
Cost - installers are expensive and the FIT for my property is not going to be much since it's a pre-1900's house with many conversions which can't be insulated to modern standards and the amount you get for FIT depends upon the energy band of your house.
How cheap is a DIY system?
I have been looking at the packages from Bimble Solar. They have (at the time of writing - (Sept 2014) have some second hand panels and various kits at really quite cheap cost - around £400 for a 660 Watt system.
The small scale systems they advertise use micro-inverters which are clever devices that take the DC power from a panel and convert it into AC power - you simply plug one end into your panels and the other into any old mains socket and hey presto, your house is powered by the panel. The invertor's are designed so that when turned on, they synchronise the voltage they produce to the mains voltage they detect. They also produce a voltage slightly higher than the mains so that when a device in the house is turned on - say a television - it will extract power from the invertor before extracting it from the mains.
I have seen small portable plug in systems being sold which use this technology which state in their advertising that their systems can be used without telling the power companies. Just plug and forget. However, even though I have tried to confirm the legality of using these systems, so far I have not been able to do so. These are discussed here and one example is here.
The ones I have seen are incredibly expensive for the power they produce and so not worth considering in my opinion.
How Easy to Install?
Looking at the bimble system - 3 panels, one micro-inverter, cables and connector - the fitting of the system should be pretty easy.
Step one - Mount the panels on the roof
If I was fitting the panels to my house roof, then I would be much more timid to DIY this. The danger of working at height and the thought of damaging my roof tiles puts me off a little. However, since I want to fit to a garage in my garden then my worried are greatly reduced.
Fitting panels does not normally require any planning permission - unless you live in a listed building, conservation area, etc, etc. Panels must not raise more than 200mm from the roof. This prevents you from changing the angle of the panels to get a more advantageous sun aspect, but also helps to prevent excessive wind loads etc.
Trying to find a supplier of a mounting kit is still ongoing.... The only site so far that might supply is mountsolar.co.uk. They have a wind load calculator which can help you design your mounting system and give you a list of items you need - but unfortunately no way to order stuff. Have emailed them (yesterday) and am awaiting a reply.
The most important aspect of fitting the panels to a tiled roof is the roof hooks. Basically you lift out a tile, screw a roof hook to a rafter and then replace the tile. The hook must be the correct dimensions for the tile. If I could make these hooks then it would make the task easier - but it is important that these are strong enough to secure the panel (it can be very expensive and dangerous if the panels come off in high winds) and so unless you are a dab hand at forging, I wouldn't try it.
Step two - Wire Up
The kits supplied by bimble provide the basics you need. However, I think that these kits should really contain additional equipment to make them safer. The G83 standards (for small systems with micro-inverters) indicate that there should be an isolator switch between the panels and the invertor and the inverter and the mains. I think that if the inverter is plugged into the mains by a socket - then as long as the socket has a switch on it - it probably meets the criteria as the mains isolator. However a heavy duty DC switch should be between the invertor and the panels.
What if the inverter should go faulty and overheat? You could turn off the mains but the invertor will still be getting power from the panels. Without a switch you wont be able to remove this power and so the invertor could burst into flames while you stand and watch or perhaps burn or electrocute yourself by trying to disconnect the wiring.
Looking at DC switches rated for around 30Amps (700Watt panels at 25V), they cost around £50. This is quite a lot when compared to the £400 system sold - but it would be foolish not to have this in - not only emergencies, but also for maintenance.
The micro-inverters that bimble sell are also quite cheap - £80 - £130 is - and are for internal use only. Many large systems mount micro-inverters on the underside of the panels - normally one per panel. The cheap bimble system uses larger rated micro-inverters to which you wire up many panels to one inverter. This is much more cost effective but perhaps slightly less efficient in terms of electricity generation. the larger inverters have an efficiency around 85% whereas smaller ones might be nearer 95%.
So for the bimble system I would wire the panels on the roof together - using the set of straight and 'Y' connectors they offer and pass the last set of wires looping under a tile to inside the garage and down to the garage wall where I would mount a wooden insulator board with DC isolator. The invertor would be mounted on the same board and the AC to a plug socket.
I would then be able to switch on and hey presto free (well not really free) power!
Next problem - the meter running backwards
The next problem I might have is that on a sunny day when I'm not using any power, the panel will generate more power than I need and push it through my meter into the grid. Looking at a list of meters that may run backwards in this circumstances, it looks like my meter may run backwards.
Great! I here you say... well yes and no. It would mean that my bill will be reduced but it also means the my power provider may get annoyed. The way I would see it is that since I'm not using a feed in tariff, then I am giving power back to the grid an therefore should be recompensed by paying a lower bill. From looking about the internet, I think that they will state that the meter - the import meter - is there to register how much energy they supply. They charge for how much they supply - but have no agreement with me to buy energy back from me. Therefore they don't care if I put energy back - they want to know how much they supplied and if I turn back the meter then I am tampering with it - e.g. stealing. So if the meter doesn't spin backwards then they have no problem. If it does then I should report it to them and then either me or they will have to pay for a new meter.
It would seem that some MCS registered installers don't realise that backwards meters is a problem. I have seen web advertising and comments from people who were proudly shown the backward meter by their installers that for a long time made me think backwards running meters was OK. It really is stealing if you are on a FIT - you get paid for the electricity make, they assume you use 50% of that - so you get a discount of the electricity bill for that 50%. If your meter is also running backwards then that will reduce your bill even more.
So if I install the system - and the meter runs backwards, I may have a run in with my supplier which could be costly. Meter fitting or them billing me for energy they'll estimate used. Since the 600W system I was thinking of would probably only reduce my bill by at most £100 a year, the supplier might not twig. However If the meter reader came along on a sunny day - he might well notice it running backwards and then that would be that.... do I take the risk? do I report If it runs backwards?
What if the meter doesn't run backwards?
If I got my meter changed or it happens to be ok with reverse current, then where would that leave me.
Well during a normal sunny day whilst I work from home on my computer - the house stays under about 250W. This means with a 660W system - assuming losses and non perfect sun - I could get a peak PV energy input of about 500W. This means I'd be using 250W from the panels and pumping 250W into the mains and not getting any benefit from it what's so ever. Not good for the cost benefit of the system.
What I'd like to do is store that power for use later on. Using batteries and stuff would greatly increase the complexity and cost of the system. The best use of that power would be to heat water or the house.
So whens the suns shining I could just flip on the emersion heater - wrong. The emersion would draw 2.5kw (at least) and thus I'd be drawing more than a 2Kw from the mains again. Since I heat the house and water with gas which is 1/4 the cost of electricity, using 2.5 kw of power would be a waste even if .25kw were "free". The efficient way to heat the water would be to have a low power heater - which could be tailored to the amount of free power available. This means a heater that could operate at say, 150W, 100W and 50W depending upon the excess power at the time.
The simplest and cheapest (and most Heath-Robinson) way to do that that I can think of would be to put three 50W old incandescent light bulbs in a tin and mount them under my hot water tank so that the heat would conduct into the tank. A timer would turn it on during daytime hours and two switches would allow me to turn on/off bulbs to keep the energy usage of the house as close to zero as possible. The tank is well insulated so I would imagine that in general the heat put in by the bulbs would at least equal the heat normally lost.
However, the time spent putting all this together and for me to monitor and adjust is of course stupid to consider. An automatic system might be possible, but again would cost a considerable amount to put together (when compared with the resulting cost savings)
In summary, and as a result of writing this article, I think it is fair to say that I am in love with the idea of getting energy from the sun. As I sit here writing this with my fingers getting numb from the cold whilst the sun beats down outside... I would love to capture that energy and bring it inside.
I have had my head turned by Bimble Solar and their cheap offers of power but have come to realise that the effort and cost involved in setting up a solar power system - which is safe and does not put me in danger of prosecution, electrocution or house fires - which at first seemed so easy is still not within my grasp.
There are a lot of pitfalls out there for the DIYer and not much solid advice. If I get time I may try and include a list of good articles - If I can find them again - to explain the DIY principles for on-grid solar generation for the home.