Solar PV – Frequently Asked Questions and Answers

zeupater

jimmyboy420 wrote: »

What's wrong with running 240 volt LEDs?

Hi

... absolutely nothing, but what John's trying to describe is a way of using stored energy from your own generation at night. Sizing storage which would be capable of running some 12V lighting on a dedicated circuit would be quite cheap (certainly well under £200) ... it would also be relatively cheap to store enough energy to run your house 'off grid' during the night as long as all you want to do is run 240V LED lights, but as soon as you start factoring in the storage requirement to supply standard appliances such as a fridge, freezer and TV the cost rises substantially beyond what would be considered as being either economical or sensible - add in the ability to cope with a toaster (or microwave/cooker/iron/hairdryer/electric shower etc) and you would certainly be considered by anyone here to have far more money than brains ....

HTH
Z

jimmyboy420

Robwiz wrote: »

From daily meter readings with the heating off, my typical gas usage was 44 kWh per day for hot water and towels. The cost of gas is £1.54 (daligas 3.5p/kWh) plus 60W x 24 hours for the electricity powering my boiler and controller on (1.5 kWh of electricity at 11p/kWH, say 16p) which takes my daily cost to £1.70. I have ignored the cost of running the circulating pump.

I have a 1kW element in my immersion heater. It is timed to be on for 3 hours before we get up in the morning and 3 hours at lunch time

You use 44kWh of gas, but only 6kWh of electricity to do the same job? You could really do with lagging your hot water pipes if that's where you think the loss is coming from!

Or you think that in around 44kWh/28kW = 1.57 hours your towel radiators are using 38kWh of hot water? They're some beasty towl rads. I'd be stunned, as I heat my whole 3 bed semi-detached house *and* hot water for around 38kWh of gas per day. (I actually calculated and it turns out to be the same figure of 38kWh!)

John_Pierpoint

zeupater wrote: »

Hi

... absolutely nothing, but what John's trying to describe is a way of using stored energy from your own generation at night. Sizing storage which would be capable of running some 12V lighting on a dedicated circuit would be quite cheap (certainly well under £200) ... it would also be relatively cheap to store enough energy to run your house 'off grid' during the night as long as all you want to do is run 240V LED lights, but as soon as you start factoring in the storage requirement to supply standard appliances such as a fridge, freezer and TV the cost rises substantially beyond what would be considered as being either economical or sensible - add in the ability to cope with a toaster (or microwave/cooker/iron/hairdryer/electric shower etc) and you would certainly be considered by anyone here to have far more money than brains ....

HTH
Z

I think I am suggesting something a bit more radical.
LEDs don't like heat and don't like variations in voltage and current surges.
[I am cursed with being the last house on the circuit and get a voltage varying from a mean of 250V - my LEDs can drop to half output in a disconcerting way]

Big thick chunks of twin & earth and the same chunky switching is not needed for an all LED lighting circuit.

Here I might be right off my trolley, but why not run the lighting circuit directly off a 12v battery system (say) kept topped up by the PV panels on the roof plus the occasional charge from the mains over night?.

No need for the current regulations about electrical safety and very much simpler to instal.

At the moment we have LEDs balanced on top of "a transformer" plus ugly aluminum fins attempting to dump the excess heat.

http://en.wikipedia.org/wiki/Light-emitting_diode

zeupater

Robwiz wrote: »

The difference between using solar PV and a gas boiler is not as simple as comparing the rates per kWh between the two fuels.

I have a non-condensing boiler rated at 28 kW. It takes around 30 minutes for the circulating water in the pipes to come up to temperature and to heat 162 litres of water in the cylinder, I need to run the gas CH for one hour in the morning and another hour in the evening. If the flow temperature is set on its lowest, the boiler uses 14 kWh per hour but the flow temperature is not sufficient to raise the DHW to 60º. If I set the flow temperature on maximum, the boiler uses 32 kWh per hour until the DHW thermostat temperature is reached.

Obviously the pipe run between the boiler and the cylinder coil in the airing cupboard is losing heat - which in our case is wasted as the pipes run through the loft. Furthermore, we have two bathrooms with towel rails that are plumbed in before the three way valve and are alway heated when the boiler is running. I can't close them off as they were a design requirement to protect the boiler from overheating/short cycling.

From daily meter readings with the heating off, my typical gas usage was 44 kWh per day for hot water and towels. The cost of gas is £1.54 (daligas 3.5p/kWh) plus 60W x 24 hours for the electricity powering my boiler and controller on (1.5 kWh of electricity at 11p/kWH, say 16p) which takes my daily cost to £1.70. I have ignored the cost of running the circulating pump.

I have a 1kW element in my immersion heater. It is timed to be on for 3 hours before we get up in the morning and 3 hours at lunch time (when our panels should be producing at least 1kW surplus between March and October). The gas boiler is switched off. Therefore, my hot water costs me a maximum of 33p per day in summer – a saving of £1.37/day and at worst 66p/day in winter on days when the panels don't generate 1kW at midday. It could be that in mid-summer our panels will generate 1 kW at 7 am – I don't know yet.

The conclusion I draw from my monitoring is that generalisations like 'it's cheaper to heat water with gas than electricity' may not always be true – so much depends on the boiler efficiency, the design of the house and how your central heating has been installed. I suggest people experiment with their own system to find out how it performs and then look at your own cost comparisons.

Hi

Is that serious ? ....

From the electricity usage you can deduce that the DHW requirement is 6kWh.t/day (1kWx3Hrsx2periods). Independent of what the efficiency of the boiler or system losses were, the DHW was heated by a 28kW boiler for 30minutes to achieve temperature, so assuming that you would need to do this twice in a day the maximum usage would be 28kWh (28kWx0.5Hrsx2Periods). If the boiler had a massive pilot light to cope with windy conditions you could possibly add another 5kWh to that, but that only gives 33kWh/day (which would be similar to the "boiler uses 32 kWh per hour until the DHW thermostat temperature is reached" ...

Regarding the towel rails ... our old boiler was a sturdy piece of iron-age engineering and looked like it too, therefore when it was replaced we needed a bypass circuit to be installed to allow the new boiler to overrun when required. This was done with a bypass valve before the 2-way valves (S-Plan) in case both were closed, but I was under the impression that an overrun bypass circuit wouldn't be necessary in a Y-Plan circuit because a 3-way valve could be set to default to either DHW or heating when 'off', so it would be normal for the default to be water. If there's a known problem with heat-loss in the main pipe-run, especially in the loft, then there's a case for some lagging ...

So what do we have ? ... a 6kWh.t DHW demand which was satisfied by a measured 44kWh of gas usage ... that's 38kWh wasted. Now a couple of average towel rails should be rated at 200W each, so even running them 24x7 at deltaT50 would only deliver (/waste) 9.6kWh, say the main circuit pipework wasn't insulated and lost another 14kWh/day at deltaT50(60W/m*24Hrs*10(?)m), which would then suggest an average boiler efficiency somewhere around the 70% mark when pipe cooling is considered (average deltaT30 ?) ....

Are you sure that you're not comparing two 3Hr heating periods/day with electric to leaving the GCH for DHW on constant ? ... which would be supported by the statement that the pump & controls were consuming 1.5kWh of electricity/day, which would normally be pretty hard for a (say) 120W pump .. that suggests that, allowing for cycling, the pump is pumping for >10Hrs/day - so somewhere around 50% of the time heating, 50% cooling ....

I really am struggling to see how the figures can be from the result of a direct comparison as even with a similar DHW usage requirement and a long pipe-run we were using below 20kWh/day with a chunky old floor mounted boiler with a massive pilot-light.

HTH
Z

zeupater

John_Pierpoint wrote: »

I think I am suggesting something a bit more radical.
LEDs don't like heat and don't like variations in voltage and current surges.
[I am cursed with being the last house on the circuit and get a voltage varying from a mean of 250V - my LEDs can drop to half output in a disconcerting way]

Big thick chunks of twin & earth and the same chunky switching is not needed for an all LED lighting circuit.

Here I might be right off my trolley, but why not run the lighting circuit directly off a 12v battery system (say) kept topped up by the PV panels on the roof plus the occasional charge from the mains over night?.

No need for the current regulations about electrical safety and very much simpler to instal.

At the moment we have LEDs balanced on top of "a transformer" plus ugly aluminum fins attempting to dump the excess heat.

http://en.wikipedia.org/wiki/Light-emitting_diode

Hi

12V LEDs is what I thought you meant. I've had a small 12V set-up for years which is in the garage at the moment. It used to run some 12V lighting and a radio on a shed which I demolished (planned-honest ... ) when cutting down some trees a few years back and is planned to be reinstalled on a new garden room or gazebo when I get around to building it ....

Whether a new standalone on a shed or connected to the main pv with the charging controlled by a wattson (or similar), the LED lights, wiring and battery requirements would be the same, so it's only really the cost of a wattson (or similar) against the cost of a small pv panel .. and they should be pretty similar, so either solution should be well under £200.

HTH
Z

John_Pierpoint

I think I am suggesting something a bit more radical.
LEDs don't like heat and don't like variations in voltage and current surges.
[I am cursed with being the last house on the circuit and get a voltage varying from a mean of 250V - my LEDs can drop to half output in a disconcerting way]

Big thick chunks of twin & earth and the same chunky switching is not needed for an all LED lighting circuit.

Here I might be right off my trolley, but why not run the lighting circuit directly off a 12v battery system (say) kept topped up by the PV panels on the roof plus the occasional charge from the mains over night?.

No need for the current regulations about electrical safety and very much simpler to instal.

At the moment we have LEDs balanced on top of "a transformer" plus ugly aluminum fins attempting to dump the excess heat.

http://en.wikipedia.org/wiki/Light-emitting_diode

zeupater wrote: »

Hi

12V LEDs is what I thought you meant. I've had a small 12V set-up for years which is in the garage at the moment. It used to run some 12V lighting and a radio on a shed which I demolished (planned-honest ... ) when cutting down some trees a few years back and is planned to be reinstalled on a new garden room or gazebo when I get around to building it ....

Whether a new standalone on a shed or connected to the main pv with the charging controlled by a wattson (or similar), the LED lights, wiring and battery requirements would be the same, so it's only really the cost of a wattson (or similar) against the cost of a small pv panel .. and they should be pretty similar, so either solution should be well under £200.

HTH
Z

Perhaps the time is rapidly approaching, code for sustainable homes/passive-haus etc, when these temporary storage ideas for PV power, ideas should be mandatory?

As we head for a big fine for not achieving air quality standards in London the present government, seems hell bent in rolling back environmental standards, not just things like insulating homes, as the pressure is on to get re-elected, come what may in the long term.

Here in S.Essex there is a local authority who has had its new community local plan rejected at only 9,000 new dwelling had been identified. It has responded with OK let it rip and say yes to all the planning applications rejected on Green Belt grounds in the last 50 years. Voila 7,000 more dwellings by 2031.

Something very "radical" needs to be done, if those extra 16,000 dwellings are going to produce less CO2, when added to the existing 70,000 odd households, especially as they are likely to be low density and so forced to be car owners..

Judge a government by what it does, not what it says to get re-elected.

theboylard

Just a quickie, as my eyes/head hurt after reading lots of stuff on here - thanks to all who contribute, especially the green man for his funny bits!

Martyn - fantastic faq, noticed a slight problem last night and just confirmed it this morning: the forum links in Index PTII, post #37, points 6. and 8 don't resolve? The link itself is missing data.
The forum comes up with a Whoops not found message.

Martyn1981

theboylard wrote: »

Just a quickie, as my eyes/head hurt after reading lots of stuff on here - thanks to all who contribute, especially the green man for his funny bits!

Martyn - fantastic faq, noticed a slight problem last night and just confirmed it this morning: the forum links in Index PTII, post #37, points 6. and 8 don't resolve? The link itself is missing data.
The forum comes up with a Whoops not found message.

Many thanks TBL, quick check and you're right, but the other thread links work, very strange. Will try to track them down and replace. Probably a good idea if I use thread titles with hyperlinks for the future, and will try to replace old links with such too.

Off the top of my head, I'm wondering if the 'circuits' thread links could be due to MSE policing as previously there was an enormous amount of deleting of Dave Fowler's posts when he tried to give free advice. Despite him being a great guy who was genuinely trying to help. Could just be a co-incidence.

Anyway, thanks again and I'll attempt some tidying up.

[Edit: Hopefully working well/better now. Just a co-incidence I think with Dave Fowler's posts. Thanks jimmyboy I'll be more careful. Probably should go through and give proper titles to all the non MSE links too now ...... strewth! M.]

Mart.

jimmyboy420

Yes, looks like the link was shortened for presentation/display purposes automatically by the forum, and then the shortened text was copied.

e.g. LONG_PIECE_OF_TEXT_URL became LONG_P...T_URL, but you then need to be careful not to copy and paste the shortened text or you will get corrupt links.

jimmyboy420

For example, the link to this page is

http//forums.moneysavingexpert.com/showthread.php?t=3872445&page=3

(with an extra colon in there) but the forum displays it as

https://forums.moneysavingexpert.com/discussion/3872445

(eg, shortened so it doesn't take too much space, but the hyperlink still works). Copying the shortened text leads to problems.