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solar pv to storage heater
Id like to find out if its possible to buy a few solar pv panels, and take the feed
from that direct to a storage heater or underfloor heating pad. Not plug into the grid, or even the house electrical circuit. And not have the heater or heating coil attached to the mains either to avoid any shocks etc. Straight from pv to dedicated electric heater. It doesnt matter if the heat only comes in the day. Thats when I need the heat anyways. Ive seen underfloor heating kits. And seperate pv solar panels. Can the pv panel plug straight into the coil of the kit? One reason I ask is that a few months ago I had seen a solar powered pv panel to underfloor heating kit for a few hundred pounds online. Ive lost the link, but I know its possible. What Id like to do Is buy something like that, wrap the coil in bricks and some sort of cover and get cheap heat. Any thoughts advice etc? For instance can the electric output from a pv panel go straight to the heating coil and trickle feed it. and slowly heat the coil Or does it need an intermediate pulse convertor? |
solar pv to storage heater
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solar pv to storage heater
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solar pv to storage heater
On Mon, 15 Dec 2014 14:10:04 +0000, Andy Burns wrote:
Id like to find out if its possible to buy a few solar pv panels, and take the feed from that direct to a storage heater What time of year do you want the heating? What time of year do solar panels give their lowest output for the shortest time? And this is Solar PV at about 30% effciency not Solar Thermal which will be more than double that. Even in mid summer with bright sunshine all day you aren't going to get a great many kWHrs, it's not worth the effort with Solar PV. Solar thermal would be a better bet and dump the heat into a smallish thermal store and circulate that for heating but you still aren't going to get a great deal of heat and in winter more or less forget it. -- Cheers Dave. |
solar pv to storage heater
On Monday, December 15, 2014 2:05:39 PM UTC, wrote:
Id like to find out if its possible to buy a few solar pv panels, and take the feed from that direct to a storage heater or underfloor heating pad. Not plug into the grid, or even the house electrical circuit. And not have the heater or heating coil attached to the mains either to avoid any shocks etc. Straight from pv to dedicated electric heater. It doesnt matter if the heat only comes in the day. Thats when I need the heat anyways. Ive seen underfloor heating kits. And seperate pv solar panels. Can the pv panel plug straight into the coil of the kit? One reason I ask is that a few months ago I had seen a solar powered pv panel to underfloor heating kit for a few hundred pounds online. Ive lost the link, but I know its possible. What Id like to do Is buy something like that, wrap the coil in bricks and some sort of cover and get cheap heat. Any thoughts advice etc? For instance can the electric output from a pv panel go straight to the heating coil and trickle feed it. and slowly heat the coil Or does it need an intermediate pulse convertor? Possible yes, but it doesn't make sense to do things that way. Solar thermal harvests more power for much less cost. NT |
solar pv to storage heater
wrote
Id like to find out if its possible to buy a few solar pv panels, and take the feed from that direct to a storage heater or underfloor heating pad. Not plug into the grid, or even the house electrical circuit. And not have the heater or heating coil attached to the mains either to avoid any shocks etc. Straight from pv to dedicated electric heater. Corse it is. But a solar air heater works rather better and you get a lot more heat out of that and is a hell of a lot cheaper too. It doesnt matter if the heat only comes in the day. Thats when I need the heat anyways. Ive seen underfloor heating kits. And seperate pv solar panels. Can the pv panel plug straight into the coil of the kit? No, because the underfloor heating kits are normally designed for 240V and you only get 240 from the panels with an inverter. One reason I ask is that a few months ago I had seen a solar powered pv panel to underfloor heating kit for a few hundred pounds online. Ive lost the link, but I know its possible. That would have had an inverter as well as the solar panels. What Id like to do Is buy something like that, wrap the coil in bricks and some sort of cover and get cheap heat. Any thoughts advice etc? A solar air heater is a lot cheaper to do, but not as easy to buy already done. For instance can the electric output from a pv panel go straight to the heating coil and trickle feed it. and slowly heat the coil Electrically, yes, but the heating coil would normally be 240V and the panels don't produce that without an inverter. Or does it need an intermediate pulse convertor? An inverter actually. They are readily available for solar panels tho. |
solar pv to storage heater
On Monday, December 15, 2014 7:55:31 PM UTC, Rod Speed wrote:
wrote Id like to find out if its possible to buy a few solar pv panels, and take the feed from that direct to a storage heater or underfloor heating pad. Not plug into the grid, or even the house electrical circuit. And not have the heater or heating coil attached to the mains either to avoid any shocks etc. Straight from pv to dedicated electric heater. Corse it is. But a solar air heater works rather better and you get a lot more heat out of that and is a hell of a lot cheaper too. It doesnt matter if the heat only comes in the day. Thats when I need the heat anyways. Ive seen underfloor heating kits. And seperate pv solar panels. Can the pv panel plug straight into the coil of the kit? No, because the underfloor heating kits are normally designed for 240V and you only get 240 from the panels with an inverter. One reason I ask is that a few months ago I had seen a solar powered pv panel to underfloor heating kit for a few hundred pounds online. Ive lost the link, but I know its possible. That would have had an inverter as well as the solar panels. What Id like to do Is buy something like that, wrap the coil in bricks and some sort of cover and get cheap heat. Any thoughts advice etc? A solar air heater is a lot cheaper to do, but not as easy to buy already done. For instance can the electric output from a pv panel go straight to the heating coil and trickle feed it. and slowly heat the coil Electrically, yes, but the heating coil would normally be 240V and the panels don't produce that without an inverter. Or does it need an intermediate pulse convertor? An inverter actually. They are readily available for solar panels tho. Another option to an invertor is to run the panels in series, producing eg 120v etc. If you had enough panels to do this there would be no point using an invertor. NT |
solar pv to storage heater
wrote in message ... On Monday, December 15, 2014 7:55:31 PM UTC, Rod Speed wrote: wrote Id like to find out if its possible to buy a few solar pv panels, and take the feed from that direct to a storage heater or underfloor heating pad. Not plug into the grid, or even the house electrical circuit. And not have the heater or heating coil attached to the mains either to avoid any shocks etc. Straight from pv to dedicated electric heater. Corse it is. But a solar air heater works rather better and you get a lot more heat out of that and is a hell of a lot cheaper too. It doesnt matter if the heat only comes in the day. Thats when I need the heat anyways. Ive seen underfloor heating kits. And seperate pv solar panels. Can the pv panel plug straight into the coil of the kit? No, because the underfloor heating kits are normally designed for 240V and you only get 240 from the panels with an inverter. One reason I ask is that a few months ago I had seen a solar powered pv panel to underfloor heating kit for a few hundred pounds online. Ive lost the link, but I know its possible. That would have had an inverter as well as the solar panels. What Id like to do Is buy something like that, wrap the coil in bricks and some sort of cover and get cheap heat. Any thoughts advice etc? A solar air heater is a lot cheaper to do, but not as easy to buy already done. For instance can the electric output from a pv panel go straight to the heating coil and trickle feed it. and slowly heat the coil Electrically, yes, but the heating coil would normally be 240V and the panels don't produce that without an inverter. Or does it need an intermediate pulse convertor? An inverter actually. They are readily available for solar panels tho. Another option to an invertor is to run the panels in series, producing eg 120v etc. If you had enough panels to do this there would be no point using an invertor. Sure, but when the whole scheme makes no sense at all in the first place, it makes no sense to have that many panels. And a solar air heater makes a lot more sense that PVs too. Much better than a solar water heater too, no problem with a solar air heater freezing up overnight. |
solar pv to storage heater
This sounds very inefficient if it would work at all.
Brian -- From the Sofa of Brian Gaff Reply address is active wrote in message ... Id like to find out if its possible to buy a few solar pv panels, and take the feed from that direct to a storage heater or underfloor heating pad. Not plug into the grid, or even the house electrical circuit. And not have the heater or heating coil attached to the mains either to avoid any shocks etc. Straight from pv to dedicated electric heater. It doesnt matter if the heat only comes in the day. Thats when I need the heat anyways. Ive seen underfloor heating kits. And seperate pv solar panels. Can the pv panel plug straight into the coil of the kit? One reason I ask is that a few months ago I had seen a solar powered pv panel to underfloor heating kit for a few hundred pounds online. Ive lost the link, but I know its possible. What Id like to do Is buy something like that, wrap the coil in bricks and some sort of cover and get cheap heat. Any thoughts advice etc? For instance can the electric output from a pv panel go straight to the heating coil and trickle feed it. and slowly heat the coil Or does it need an intermediate pulse convertor? |
solar pv to storage heater
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solar pv to storage heater
On 16/12/2014 11:35, Andrew Gabriel wrote:
In article , writes: Another option to an invertor is to run the panels in series, producing eg 120v etc. If you had enough panels to do this there would be no point using an invertor. Grid tie inverters run the panels in series anyway - the inverters normally take 600VDC input, depending how many panels you have. (That's why fire brigades won't enter houses with solar panels to put fires out.) Pretty stupid really. A 240V AC supply can have about 350V peak on it which is only a bit less than 10 solar panels in series would be operating at. Any more than 10 panels would probably be two strings and be less than that. |
solar pv to storage heater
On Tue, 16 Dec 2014 15:08:36 +0000, Dennis@home wrote:
Grid tie inverters run the panels in series anyway - the inverters normally take 600VDC input, depending how many panels you have. (That's why fire brigades won't enter houses with solar panels to put fires out.) Pretty stupid really. A 240V AC supply can have about 350V peak on it which is only a bit less than 10 solar panels in series would be operating at. Yeah but the 240 mains supply has a big switch that can isolate the house wiring. With Solar PV and those volts and appreciable current are "just there". The grid tie invertor should shut down when it loses the grid but that DC is still present in wiring which is located where? At least CU's or cutouts are normally in fairly common places and within feet of where the mains enters the property. -- Cheers Dave. |
solar pv to storage heater
Andrew Gabriel wrote:
(That's why fire brigades won't enter houses with solar panels to put fires out.) Isn't this an urban myth? |
solar pv to storage heater
In message , Capitol
writes Andrew Gabriel wrote: (That's why fire brigades won't enter houses with solar panels to put fires out.) Isn't this an urban myth? Set fire to Harry's house and find out? -- Tim Lamb |
solar pv to storage heater
On 16/12/2014 16:25, Capitol wrote:
Andrew Gabriel wrote: (That's why fire brigades won't enter houses with solar panels to put fires out.) Isn't this an urban myth? "wont enter" might be an urban myth, but "are urged to be cautious" looks more reasonable http://www.bbc.co.uk/news/uk-england-22462664 |
solar pv to storage heater
Interesting feedback thanks. Obviously not a good idea is the general consensus.
Just as a matter if interest I thought Id run these figures by and see if I can get a clearer picture... My electric storage heater uses 12kwh a night on cheap rate night tariff. (Thats 85 p/night) That gets it nice and hot. Im trying to calculate how many panels would give me the equivelent of 12kwh mains a day...so... How does one calculate average annual UK output for each 100W panel? Assuming more in summer less in winter etc. And how can that be converted into 12kwh/day? In other words in the UK, if one wanted 12kwh for *general use heating* during the day, how many 100w panels, on average, would be needed to get the the equivelent of a mains 12kwh/day input? Thanks ahead. |
solar pv to storage heater
Dave Liquorice wrote
Dennis@home wrote Grid tie inverters run the panels in series anyway - the inverters normally take 600VDC input, depending how many panels you have. (That's why fire brigades won't enter houses with solar panels to put fires out.) They aint that stupid here. Pretty stupid really. A 240V AC supply can have about 350V peak on it which is only a bit less than 10 solar panels in series would be operating at. Yeah but the 240 mains supply has a big switch that can isolate the house wiring. So does solar. In fact it's the same switch. With Solar PV and those volts and appreciable current are "just there". Nope, they have to have the same system. The grid tie invertor should shut down when it loses the grid And that is a legal requirement, because otherwise you can electrocute someone trying to fix a grid fault. but that DC is still present in wiring No it is not. which is located where? At least CU's or cutouts are normally in fairly common places and within feet of where the mains enters the property. And using those sees the solar system disabled too. |
solar pv to storage heater
wrote
Interesting feedback thanks. Obviously not a good idea is the general consensus. Just as a matter if interest I thought Id run these figures by and see if I can get a clearer picture... My electric storage heater uses 12kwh a night on cheap rate night tariff. (Thats 85 p/night) That gets it nice and hot. Im trying to calculate how many panels would give me the equivelent of 12kwh mains a day...so... A hell of a lot in winter at that latitude. How does one calculate average annual UK output for each 100W panel? There are calculators that do that. Assuming more in summer less in winter etc. And how can that be converted into 12kwh/day? You need to know the instantaneous W as it varys during the day and get the area under the curve to get the KWh. In other words in the UK, if one wanted 12kwh for *general use heating* during the day, how many 100w panels, on average, would be needed to get the the equivelent of a mains 12kwh/day input? The short story is too many to make any sense. |
solar pv to storage heater
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solar pv to storage heater
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solar pv to storage heater
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solar pv to storage heater
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solar pv to storage heater
On Tuesday, December 16, 2014 10:26:03 PM UTC, Dennis@home wrote:
On 16/12/2014 18:48, wrote: Interesting feedback thanks. Obviously not a good idea is the general consensus. Just as a matter if interest I thought Id run these figures by and see if I can get a clearer picture... My electric storage heater uses 12kwh a night on cheap rate night tariff. (Thats 85 p/night) That gets it nice and hot. Im trying to calculate how many panels would give me the equivelent of 12kwh mains a day...so... In winter a 2kW array will give you less than 1 kWhr if its cloudy and about 1.5 kWhr if its sunny. In summer its about 2kWhr and 10kWhr for the same array. The same area of thermal panels will give you about four/five times as much. With solar thermal you get a lower grade heat from flat panels than from evacuated tubes. The same amount of energy if the store is cold enough to make use of the lower grade. From a cot point of view you should have solar PV fitted as the fits will pay fo it and return a profit. Then fit an immersun or similar to heat during the day when power is available. Flat panel solarthermal yield much more than tubes per area and per pound when heating cold water (and only when heating cold water). NT |
solar pv to storage heater
wrote
Dennis@home wrote wrote Interesting feedback thanks. Obviously not a good idea is the general consensus. Just as a matter if interest I thought Id run these figures by and see if I can get a clearer picture... My electric storage heater uses 12kwh a night on cheap rate night tariff. (Thats 85 p/night) That gets it nice and hot. Im trying to calculate how many panels would give me the equivelent of 12kwh mains a day...so... In winter a 2kW array will give you less than 1 kWhr if its cloudy and about 1.5 kWhr if its sunny. In summer its about 2kWhr and 10kWhr for the same array. The same area of thermal panels will give you about four/five times as much. With solar thermal you get a lower grade heat from flat panels than from evacuated tubes. The same amount of energy if the store is cold enough to make use of the lower grade. From a cot point of view you should have solar PV fitted as the fits will pay fo it and return a profit. Then fit an immersun or similar to heat during the day when power is available. Flat panel solarthermal yield much more than tubes per area and per pound when heating cold water (and only when heating cold water). Not sure that last bit in brackets is true. Why isnt it just as true with a solar air heater ? |
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solar pv to storage heater
On Wednesday, December 17, 2014 4:41:30 AM UTC, Rod Speed wrote:
wrote Dennis@home wrote wrote Interesting feedback thanks. Obviously not a good idea is the general consensus. Just as a matter if interest I thought Id run these figures by and see if I can get a clearer picture... My electric storage heater uses 12kwh a night on cheap rate night tariff. (Thats 85 p/night) That gets it nice and hot. Im trying to calculate how many panels would give me the equivelent of 12kwh mains a day...so... In winter a 2kW array will give you less than 1 kWhr if its cloudy and about 1.5 kWhr if its sunny. In summer its about 2kWhr and 10kWhr for the same array. The same area of thermal panels will give you about four/five times as much. With solar thermal you get a lower grade heat from flat panels than from evacuated tubes. The same amount of energy if the store is cold enough to make use of the lower grade. From a cot point of view you should have solar PV fitted as the fits will pay fo it and return a profit. Then fit an immersun or similar to heat during the day when power is available. Flat panel solarthermal yield much more than tubes per area and per pound when heating cold water (and only when heating cold water). Not sure that last bit in brackets is true. I guess I should be more precise and say below the temp where the yield of both technologies become equal, which is between cold & the wanted hot water temp. Why isnt it just as true with a solar air heater ? they dont heat hot air, plus they generally use dfferent designs. NT |
solar pv to storage heater
On Wednesday, December 17, 2014 8:43:06 AM UTC, Dave Liquorice wrote:
On Tue, 16 Dec 2014 19:41:05 -0800 (PST), wrote: With solar thermal you get a lower grade heat from flat panels than from evacuated tubes. The same amount of energy if the store is cold enough to make use of the lower grade. Flat panel solarthermal yield much more than tubes per area and per pound when heating cold water (and only when heating cold water). Isn't the whole idea that the water doesn't stay cold? I believe so :) The bottom of a thermal store ought to be at 40 to 50 C, coolest. Once the solar has been running for a while it'll be pushing 60 C or more. This'll be the minimum temperature of the circulating water, it needs to be highre to actually transfer any heat... Ours (tubes) circulates at about 80 C. Min temp a panel heats is mains cold water temp, maybe 5C in winter. In an ideal world one would optimise a system by using flat panel to raise cool water temp, then vac tubes to get it hot. In a large system this maximises return. In a small system the cost of a 2nd pump, piping, control etc isnt necessarily justified. NT |
solar pv to storage heater
wrote
Rod Speed wrote wrote Dennis@home wrote wrote Interesting feedback thanks. Obviously not a good idea is the general consensus. Just as a matter if interest I thought Id run these figures by and see if I can get a clearer picture... My electric storage heater uses 12kwh a night on cheap rate night tariff. (Thats 85 p/night) That gets it nice and hot. Im trying to calculate how many panels would give me the equivelent of 12kwh mains a day...so... In winter a 2kW array will give you less than 1 kWhr if its cloudy and about 1.5 kWhr if its sunny. In summer its about 2kWhr and 10kWhr for the same array. The same area of thermal panels will give you about four/five times as much. With solar thermal you get a lower grade heat from flat panels than from evacuated tubes. The same amount of energy if the store is cold enough to make use of the lower grade. From a cot point of view you should have solar PV fitted as the fits will pay fo it and return a profit. Then fit an immersun or similar to heat during the day when power is available. Flat panel solarthermal yield much more than tubes per area and per pound when heating cold water (and only when heating cold water). Not sure that last bit in brackets is true. I guess I should be more precise and say below the temp where the yield of both technologies become equal, which is between cold & the wanted hot water temp. Why isnt it just as true with a solar air heater ? they dont heat hot air, plus they generally use dfferent designs. Regardless of that, tubes just don't work as well with solar air heaters. |
solar pv to storage heater
On Tuesday, December 16, 2014 7:55:12 PM UTC, Rod Speed wrote:
Dave Liquorice wrote Dennis@home wrote Grid tie inverters run the panels in series anyway - the inverters normally take 600VDC input, depending how many panels you have. (That's why fire brigades won't enter houses with solar panels to put fires out.) They aint that stupid here. Pretty stupid really. A 240V AC supply can have about 350V peak on it which is only a bit less than 10 solar panels in series would be operating at. Yeah but the 240 mains supply has a big switch that can isolate the house wiring. So does solar. In fact it's the same switch. With Solar PV and those volts and appreciable current are "just there". Nope, they have to have the same system. The grid tie invertor should shut down when it loses the grid And that is a legal requirement, because otherwise you can electrocute someone trying to fix a grid fault. but that DC is still present in wiring No it is not. Are you asserting that the grid isolator is also required to disconnect all the series wiring between the individual panels? Maybe the fire brigade only tackle such fires at night. Robert |
solar pv to storage heater
Thats answered my questions, Thanks to all, for the
info and calculations |
solar pv to storage heater
In article ,
RobertL writes: Maybe the fire brigade only tackle such fires at night. Moonlight will generate almost the full voltage, although limited to just enough current to electrocute someone. -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
solar pv to storage heater
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solar pv to storage heater
On 17/12/2014 11:29, RobertL wrote:
Are you asserting that the grid isolator is also required to disconnect all the series wiring between the individual panels? Maybe the fire brigade only tackle such fires at night. Nearly all the dc wires are external, under the panels and it is all much better insulated than the mains. Its waterproof and if the roof is disrupted then its easy enough to rip the wires apart with one of their long poles leaving 40V dc if the panel is working. |
solar pv to storage heater
RobertL wrote
Rod Speed wrote Dave Liquorice wrote Dennis@home wrote Grid tie inverters run the panels in series anyway - the inverters normally take 600VDC input, depending how many panels you have. (That's why fire brigades won't enter houses with solar panels to put fires out.) They aint that stupid here. Pretty stupid really. A 240V AC supply can have about 350V peak on it which is only a bit less than 10 solar panels in series would be operating at. Yeah but the 240 mains supply has a big switch that can isolate the house wiring. So does solar. In fact it's the same switch. With Solar PV and those volts and appreciable current are "just there". Nope, they have to have the same system. The grid tie invertor should shut down when it loses the grid And that is a legal requirement, because otherwise you can electrocute someone trying to fix a grid fault. but that DC is still present in wiring No it is not. Are you asserting that the grid isolator is also required to disconnect all the series wiring between the individual panels? Nope. Maybe the fire brigade only tackle such fires at night. Nope. |
solar pv to storage heater
On Wednesday, December 17, 2014 3:55:56 PM UTC, Dennis@home wrote:
On 17/12/2014 09:11, wrote: Min temp a panel heats is mains cold water temp, maybe 5C in winter. In an ideal world one would optimise a system by using flat panel to raise cool water temp, then vac tubes to get it hot. In a large system this maximises return. In a small system the cost of a 2nd pump, piping, control etc isnt necessarily justified. Tubed panels aren't any worse than flat panels once you have a reflector behind the tubes. In the winter you really need tubed panels to get much heat. http://wiki.diyfaq.org.uk/index.php?...nd_Vacuum_Tube NT |
solar pv to storage heater
On 17/12/2014 23:32, wrote:
On Wednesday, December 17, 2014 3:55:56 PM UTC, Dennis@home wrote: On 17/12/2014 09:11, wrote: Min temp a panel heats is mains cold water temp, maybe 5C in winter. In an ideal world one would optimise a system by using flat panel to raise cool water temp, then vac tubes to get it hot. In a large system this maximises return. In a small system the cost of a 2nd pump, piping, control etc isnt necessarily justified. Tubed panels aren't any worse than flat panels once you have a reflector behind the tubes. In the winter you really need tubed panels to get much heat. http://wiki.diyfaq.org.uk/index.php?...nd_Vacuum_Tube The main thing that flat plate excels at is a small temperature rise which is damn all use for hot water or heating bulk space unless you have designed in huge low temperature difference fan assisted radiators. Vacuum tube designs have the merit of producing water that is usefully hot when the sun is actually shining even in winter. Since you are generally dealing with weak or diffuse sunlight in winter and not very much of it you ideally want non focusing flux concentrator designs rather than simple half cylinder mirrors. The simplest of these is a part parabola with the focus of one side at the base of the other. Every ray entering the aperture will hit the back plate collector in finite time. Real ones can be optimised a bit more to take account of the shape of the pipe. Another is a sort of spiral these designs have never really caught on. You can double the output of a PV array by surrounding it with mirrors as a crude variant of this game (though the plastic bits may cook). sun |||||| \||||/ \__/ 60 All lengths the same. Mirrors are cheap PV cells are not. Light incident on the mirrors hits the PV array after reflection. Mainly of interest for portable solar chargers. -- Regards, Martin Brown |
solar pv to storage heater
On Thursday, December 18, 2014 11:07:44 AM UTC, Martin Brown wrote:
On 17/12/2014 23:32, wrote: On Wednesday, December 17, 2014 3:55:56 PM UTC, Dennis@home wrote: On 17/12/2014 09:11, wrote: Min temp a panel heats is mains cold water temp, maybe 5C in winter. In an ideal world one would optimise a system by using flat panel to raise cool water temp, then vac tubes to get it hot. In a large system this maximises return. In a small system the cost of a 2nd pump, piping, control etc isnt necessarily justified. Tubed panels aren't any worse than flat panels once you have a reflector behind the tubes. In the winter you really need tubed panels to get much heat. http://wiki.diyfaq.org.uk/index.php?...nd_Vacuum_Tube The main thing that flat plate excels at is a small temperature rise which is damn all use for hot water or heating bulk space unless you have designed in huge low temperature difference fan assisted radiators. When hot water is heated, it starts stone cold, and progresses up to piping hot. Flat plate work better at the cold to warm region, tubes work better in the warm to hot region. Hence the upside of using both together with 2 water zones, one hot one warm. Vacuum tube designs have the merit of producing water that is usefully hot when the sun is actually shining even in winter. Since you are generally dealing with weak or diffuse sunlight in winter and not very much of it you ideally want non focusing flux concentrator designs rather than simple half cylinder mirrors. Yes, the same trick can be done with flat plate too, if not quite so easily. The simplest of these is a part parabola with the focus of one side at the base of the other. Every ray entering the aperture will hit the back plate collector in finite time. Real ones can be optimised a bit more to take account of the shape of the pipe. Another is a sort of spiral these designs have never really caught on. You can double the output of a PV array by surrounding it with mirrors as a crude variant of this game (though the plastic bits may cook). sun |||||| \||||/ \__/ 60 All lengths the same. Mirrors are cheap PV cells are not. Light incident on the mirrors hits the PV array after reflection. Mainly of interest for portable solar chargers. Yes, so long as you get even lighting on the PV. What the higher temp does to panel life I don't know. NT |
solar pv to storage heater
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solar pv to storage heater
On 18/12/2014 20:05, Dennis@home wrote:
On 18/12/2014 13:52, wrote: When hot water is heated, it starts stone cold, and progresses up to piping hot. Flat plate work better at the cold to warm region, tubes work better in the warm to hot region. Hence the upside of using both together with 2 water zones, one hot one warm. I have tubes, with a compound reflector behind them, I can see no reason why a flat plate of the same area would work any better. I can see several reasons why flat panels wouldn't work as well. But then you always were rather dense. Assuming the same grade of absorber with efficiency 1-a (a 1 probably around 0.04 in a typical matt black finish) eg http://www.aviantechnologies.com/pro...fuse_black.php And a typical aluminised mirror with an efficiency 1-b (b 1 but probably around 0.08 or worse) eg http://en.wikipedia.org/wiki/Reflect...eflectance.png Flat plate efficiency = 1-a ~ 96% Mirror tube efficiency = (1-a)(1-b) ~ 88% Acting against that is that with evacuated tubes there is no convection robbing heat off the tube based designs so long as their vacuum holds. At higher temperatures the tubes win out with lower convection losses. t makes me wonder what panels were being compared and what assumptions were made. That the mirrors are not perfect ones - which is *very* true. A typical production mirror scatters or absorbs about 8% of the incident light where as a decent matt black paint scatters less the 4%. The concentrators allow you to trade some minor loss of efficiency for a much higher output temperature which is usually worth it. There are additional losses off the air-glass surfaces of the front cover plate as well but they are common to both designs. -- Regards, Martin Brown |
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