premelec - thanks. I'm ordering the book. www.homepower.com looks useful.
EMC Testing – my experience
- Thread starter ed1066
- Start date
Jeremy Harris
Senior Member
For a new house (like our build) with a new in-roof PV system, quite apart from the no-brainer advantage in terms of panel cost and improved "shoulder" efficiency at water heating (i.e. PV ALWAYS heats the water, even if it's only receiving a few watts of solar irradiation - solar thermal ONLY ever heats water when the panels exceed the the tank temperature), there is the big saving in roof covering cost. Our in-roof PV system is around 44 square metres, and that alone saved us around £1000 in slates, plus the labour cost of fitting them. Even if our 6.25kW system is only producing 100W more than the house consumption at that time, then my power diverter (see here: http://www.picaxeforum.co.uk/showthread.php?24286-Photo-Voltaic-Immersion-heater-power-diverter-SAFETY-WARNING!) will send that excess to the immersion heater, and even if the thermal store is at 60 deg C that 100W will still increase the water temperature a little bit. As our thermal store normally runs at around 70 to 75 deg C (to produce "instant" hot water at around 45 deg C via the in-tank heat exchanger and thermostatic mixer) it makes no sense at all to use solar thermal, as even with evacuated tubes there would be very few days in the year when the solar thermal system would get the system up to temperature.
I should add that our thermal store is pre-heated via a heat pump (to around 35 deg C) and that much of the time this small heat pump is powered by the PV system.
For a solar thermal system to do the same then the panel temperature would need to exceed 60 deg C, which would require far, far more sunlight.
I should add that our thermal store is pre-heated via a heat pump (to around 35 deg C) and that much of the time this small heat pump is powered by the PV system.
For a solar thermal system to do the same then the panel temperature would need to exceed 60 deg C, which would require far, far more sunlight.
That's very interesting Jeremy. Sounds like you have a powerful system.
Can you clear up a few points for this thicko please:
1. How much did all those panels cost (to save £1000 on slates)?
2. Is there a reason why similar heat-pump techniques can't be used with solar-thermal?
(i.e. between panels and hot tank as a cold 'absorber/receiver' is thermodynamically more efficient and the panel temperature can be lots lower).
3. If you get FIT payments who ultimately pays for that massive differential in pence/KWh?
4. Is any power returned to grid metered? If not how is your FIT payment determined?
5. What is your solar-PV degradation?
There have been some worrying reports (I've read a significant number) about power o/p degradation from solar-PV panels.
All obviously degrade but certain ones made by certain companies in a certain country degrade and fail at a worrying rate (statistically) - don't confuse 96 hour PID tests with real-life material degradation.
Can you clear up a few points for this thicko please:
1. How much did all those panels cost (to save £1000 on slates)?
2. Is there a reason why similar heat-pump techniques can't be used with solar-thermal?
(i.e. between panels and hot tank as a cold 'absorber/receiver' is thermodynamically more efficient and the panel temperature can be lots lower).
3. If you get FIT payments who ultimately pays for that massive differential in pence/KWh?
4. Is any power returned to grid metered? If not how is your FIT payment determined?
5. What is your solar-PV degradation?
There have been some worrying reports (I've read a significant number) about power o/p degradation from solar-PV panels.
All obviously degrade but certain ones made by certain companies in a certain country degrade and fail at a worrying rate (statistically) - don't confuse 96 hour PID tests with real-life material degradation.
inglewoodpete
Senior Member
When I read about using excess PV energy for electric heating of water, I thought it would be a much more effective and flixible than mounting heavy thermo-solar panels, piping and tank etc on my roof.
...and I've now discovered that our government has banned the installation of electric heaters whereever reticulated natural gas is available. I wonder if they even imagined solar-electric heating when they made that regulation.
...and I've now discovered that our government has banned the installation of electric heaters whereever reticulated natural gas is available. I wonder if they even imagined solar-electric heating when they made that regulation.
BeanieBots
Moderator
I can answer a few of those questions for you Dippy.
The FIT rates are paid for by an increase in fuel bills that are paid for by everyone. (Thanks!).
Energy put back is NOT metered. So why bother putting any back?
You get paid for generating it irrespective of what you do with it.
Very wrong, very unfair but that's the way it is (in the UK).
I had my system installed just before the drop in FIT.
I get paid 43p per kWhr GENERATED.
It is assumed that I will put 50% back and I also get paid for that (even though I use it all to make hot water)
Solar PV actually gets MORE efficient over the first year and then gradually drops off to about 70% over the next 20 years.
I have not had them long enough to know if this is true for my panels yet.
A recent TV broadcast about pensions stated that you would need to invest £1k for every £/week increase in pension.
My PV cost about £8k and can give me £5/day (plus electric saving plus free hot water) even when partially cloudy. So, a better investment than a pension.
The FIT rates are paid for by an increase in fuel bills that are paid for by everyone. (Thanks!).
Energy put back is NOT metered. So why bother putting any back?
You get paid for generating it irrespective of what you do with it.
Very wrong, very unfair but that's the way it is (in the UK).
I had my system installed just before the drop in FIT.
I get paid 43p per kWhr GENERATED.
It is assumed that I will put 50% back and I also get paid for that (even though I use it all to make hot water)
Solar PV actually gets MORE efficient over the first year and then gradually drops off to about 70% over the next 20 years.
I have not had them long enough to know if this is true for my panels yet.
A recent TV broadcast about pensions stated that you would need to invest £1k for every £/week increase in pension.
My PV cost about £8k and can give me £5/day (plus electric saving plus free hot water) even when partially cloudy. So, a better investment than a pension.
Jeremy Harris
Senior Member
The total cost of the 6.25kWp system, in-roof, was around £8k fitted. The cost of covering that area with slates would have been around £2k (inc labour). The system is too big for domestic FIT, so is rated as a commercial installation, so a much lower FIT rate and we needed approval from the DNO to export more than 16A into a single phase (we will be running under a G59 approval, rather than the G83/1 small scale exemption that most domestic PV installations run under).
FIT isn't really a consideration for us, as the income from it is small. The main reason for fitting a big array was that it was the cheapest way to both heat our hot water and provide more energy (over the course of a year) than the house ever consumes. In effect we will be "borrowing" power from the grid in winter (and paying for it) but exporting power during the summer (and being paid for it). We will have an export meter as part of this install, as it's a commercially rated system (even though it's on a small 2 bedroom house).
There is no "masssive" FIT rate for us, as it's a commercially rated system and exported power is metered, unlike a domestic small scale system running under the G83/1 exemption.
The solar panels have a 25 year life and there is a lot of evidence to show that output degradation over that lifespan is modest (of the order of 10 to 20% or so, maybe 30% in extreme locations). The panels themselves are cheap, so replacing them wouldn't cost anywhere near the cost of installing them.
You can indeed use staged heat pumps to increase the sensible heat output from a solar thermal system. AFAIK there aren't any readily available systems like this, but it would be relatively easy to use a small water source heat pump and feed it from a buffer tank fed by a solar thermal system. This would then boost the sensible heat output temperature up to thermal store temperatures and allow sensible heat to be extracted even when the temperature of the solar thermal system output was well below that of the store.
FIT isn't really a consideration for us, as the income from it is small. The main reason for fitting a big array was that it was the cheapest way to both heat our hot water and provide more energy (over the course of a year) than the house ever consumes. In effect we will be "borrowing" power from the grid in winter (and paying for it) but exporting power during the summer (and being paid for it). We will have an export meter as part of this install, as it's a commercially rated system (even though it's on a small 2 bedroom house).
There is no "masssive" FIT rate for us, as it's a commercially rated system and exported power is metered, unlike a domestic small scale system running under the G83/1 exemption.
The solar panels have a 25 year life and there is a lot of evidence to show that output degradation over that lifespan is modest (of the order of 10 to 20% or so, maybe 30% in extreme locations). The panels themselves are cheap, so replacing them wouldn't cost anywhere near the cost of installing them.
You can indeed use staged heat pumps to increase the sensible heat output from a solar thermal system. AFAIK there aren't any readily available systems like this, but it would be relatively easy to use a small water source heat pump and feed it from a buffer tank fed by a solar thermal system. This would then boost the sensible heat output temperature up to thermal store temperatures and allow sensible heat to be extracted even when the temperature of the solar thermal system output was well below that of the store.
Last edited: