Small / simple solar panels?

[JP_]

I used to get loads of calls about solar panels and government grants etc. etc. and always ignored them. But, I have always thought about solar panels.

A friend has them and said that they advise against feeding them into the grid, because if there is a powercut you have to turn yours off - better to have batteries.

That go me thinking ...

Well, one reason I have done nothing is because we are thinking of a loft conversion so do not want to cover the roof in panels. But I have a pitched, south facing garage roof and also a flat roof (vaulted with central flat part) above my living room, that will also get south + west light.

I have searched online but found nothing .... but what I was thinking, is there a solution to set up solar panels on their own circuit, with batteries I guess, so that you use it when powered up and switch to the grid when / if you run out?

For example, I have a fair amount home cinema stuff in my living room and it is left on standby most of the time. I did some testing with the BG live electric meter thing and they really do use a fair bit of juice.

I was thinking, if I had my own panels on the living room roof that feed a couple of sockets, I could maybe use solar for all the home cinema stuff, but easily unplug it and use the mains when the sun goes down.

Is this feasible? Or is it going to be a total waste of my money and time?

 

[bernardgreen]

Converting the electrical energy into heat in storage radiators and / or hot water could be the most cost efficient means of utilising the output from solar panels. No need for invertors, just a bit of switching to match the variable DC voltage from the panels to the heating elements. Bright sun, panels producing 500 volts so connect two matching 240 volt elements in series, or in low sunlight, panel producing 120 volts, connect one element. It will only provide 1/4 of its rated power ( at 240 volts ) but it is still useful heat if it is stored in something.

 

[winston1]

Much easier to unplug your home cinema stuff when not in use.

 

[winston1]

Converting the electrical energy into heat in storage radiators and / or hot water could be the most cost efficient means of utilising the output from solar panels. No need for invertors, just a bit of switching to match the variable DC voltage from the panels to the heating elements. Bright sun, panels producing 500 volts so connect two matching 240 volt elements in series, or in low sunlight, panel producing 120 volts, connect one element. It will only provide 1/4 of its rated power ( at 240 volts ) but it is still useful heat if it is stored in something.

Solar voltaic panels are very inefficient. If you want heat much better to use solar thermal panels that heat water directly.

 

[bernardgreen]

Solar voltaic panels are very inefficient.

I agree with that.

If you want heat much better to use solar thermal panels that heat water directly.

To an extent I agree with that but when you take into account the need to circulate the collecting fluid and protect against freezing and boiling the simplicity of photo-voltaic panels supplying resistive heating elements more than compensates for the in-efficiency..

 

[JP_]

Still not sure what most electric is actually used on. I guess washing machine, dishwasher and fridge are probably the main culprits. Maybe solar-circuit could power these? Well, not fridge...

 

[Grenage]

I would have thought it would have been far easier to feed back into the grid, then use the money earned to offset your bills.

Sure beats the film you're watching turning off, every time a cloud passes across the sun.

 

[winston1]

Still not sure what most electric is actually used on. I guess washing machine, dishwasher and fridge are probably the main culprits. Maybe solar-circuit could power these? Well, not fridge...

One solar panel produces max 250 watts, bright sun mid summer etc. A washing machine or dishwasher up to 3000 watts. Do the sums.

 

[westie101]

A friend has them and said that they advise against feeding them into the grid, because if there is a powercut you have to turn yours off - better to have batteries.

Mythbusters #100 totally, totally untrue! The electronics in the inverter do this without any intervention.

Best get a friend who knows what he is talking about!

 

[JohnW2]

A friend has them and said that they advise against feeding them into the grid, because if there is a powercut you have to turn yours off - better to have batteries.

Mythbusters #100 totally, totally untrue! The electronics in the inverter do this without any intervention. ... Best get a friend who knows what he is talking about!

I think you're possibly being a little harsh - the friend may well have said (or, at least meant) that the inverter has to be turned off (as you say, automatically, not manually) in the case of loss of the grid supply.

Kind Regards, John

 

[JP_]

Yeah, I do not know the details of how they had to turn their electric off, only that they live in a rural area where powercuts are still common during bad weather and they were a bit annoyed that they had to turn off theirs so the electric repair people could get to work on the line. It happens, don't ask me for the technical details!

Sounds like solar is not up to much then? Just heating water? I was hoping to have a stack of batteries storing enough juice to get me through the night.

Looks like we might be doing that loft conversion first anyway, so the carbon footprint will have to just stay as it is.

 

[ScottishGasMan]

To get useful sizes of batterys, which have a decent enough quality to be charged/discharged every day, sometimes from half charge sometimes from empty would cost an absolout fortune, and probably use up a hell of a lot of space.

Thats where the cost in electric cars comes in, apart fro R+D/Design, the big outlay is in the batterys, and they certainly dont last forever.


Out of curiosity, as I always wandered about that, hight of summer, 4kw solar pannels producing full power during the day, if for some reason you had a power cut from the mains, the inverter would turn itsself off/stop feeding your house with the panels then?

 

[JohnD]

if for some reason you had a power cut from the mains, the inverter would turn itsself off/stop feeding your house with the panels then?

Yes.

 

[bernardgreen]

if for some reason you had a power cut from the mains, the inverter would turn itsself off/stop feeding your house with the panels then?

Yes.

Only if your invertor is tied into the grid. If you are not tied in and it is impossible for the invertor to feed into the supply cable then your solar panel(s) can be used to power ( some of ) your house during a sunny power cut.

 

[ericmark]

Forget direct water heating my father-in-law was conned into fitting this it looked good an he thought he was getting the water heated by solar however when he turned the gas off to fit a new cooker he found he has no heat in his water not even the chill was taken off. When fitted they disconnected the immersion heater and connected to central heating instead so his electric bill dropped but only because heated with gas not electric the panels did not even remove the chill.

So from his experience yes using electric panels to heat water is likely better as the electric panels work on light not direct sun light so any clouds the direct water panel does noting but the electric one still works.

The technology in the inverter changes the voltage of the panel to get the maximum output so be it charge a battery or put power into the mains with a grid tie inverter it needs an inverter to be able to alter the voltage to get as much power as possible.

People on narrow boats often have some solar panels to top-up their batteries there is a big debate 12 or 24 volt as the higher voltage means less current and inverters work better but their are cheap things for 12 volt designed for car and caravan.

Using an inverter from the battery does mean power 24/7 but inverters use some power to works as well as power to convert and you need one panel just to work inverter and the rest give useful output. Plus cost of batteries. In theroy batteries should last 7 years in practice because the sun does not come out enough every day and batteries are deep cycled about 2 years maximum is what most boat owners find.

Clearly the boat owner has no option can't grid-tie but for home owner not to get the government money would be silly. So really no option but grid-tie.

Because the role out of smart meters has been slow while waiting for them you get paid what the estimate you would pump into grid not what is actually pumped in and until the smart meters are fitted having a device which puts excess power into the water pays for its self. However once the smart meter is fitted likely these devices will not pay for themselves they will save some money if already fitted but not enough money to pay the interest on the money borrowed to fit them.

There is also much debate East - West roof or South roof. The sales men who have called seem to tell different stories on if the tariff changes due to maximum output on the roof fitted or maximum output if used in ideal conditions. If the former is true then you can have more panels facing East - West and they will produce for a longer time each day but with latter the limit to number of units before it hits lower tariff would mean the fitting cost would take too long to recoup so East - West not worth doing.

So much of the fitting of solar panels is dependent on the government payments it means DIY is clearly out as installer has to be registered to get the feed in payments. And also the quality also varies and quality varies the point when it starts and finishes rather than maximum output.

From the information I can find out it would seem a high quality East - West system can give between an hour to three hours extra charge per day depending on angle of roof and time of year but non of the companies will stick their neck out and say how much extra power one gets so you pay your money and take a chance.

From memory 7kW is the point where tariff changes so most fit 7kW but it's the kWh per day which varies between good quality and poor quality and East - West and South facing and non of the figures given by the different firms seem to match so it would seem impossible to work out.