Solar PV v thermal

Superdaddy

Trying to decide on PV or solar thermal. I am leaning towards PV, I want it to heat water in the summer. I am putting in a heat pump. I know I can send the PV power to an immersion to heat water, but would it be more efficient to send it to the heat pump to heat? And can it be done?
Given that the feed in tariff is gone, is PV still the best option for solar energy?
I have heard that a 1kw PV system will satisfy part L, but is it too small to heat enough water for two adults and two kids?

quentingargan

I think PV has crossed the line on price. A 2kw system will produce over 1800kwHrs of electricity. This is about the same amount of energy as you would get from a 4 sq m solar thermal panel or equivalent tubes. Some of this electricity will save you the 18c retail price of electricity, and the balance will save you about 9c in heating from oil, gas or off-peak electricity. Your heat pump may be slightly cheaper.

The hardwre for a PV system like this will be about €2500 plus the gizmo to do the immersion switching - about €500. The advantage of this over solar thermal is that there is no need to change glycol every three years, no moving parts or pumps to break down, no expansion vessels to fail and the system is basically "fit and forget".

The device that does this switches your immersion like a dimmer switch, monitoring your incoming grid and cranking the immersion up and down to prevent free exports. But a good unit to do this is not cheap - an export meter would be cheaper if utilities would buy back your power, so you might spend €500 on one of these gizmos and then find that your provider is willing to buy your electricity again. Environmentally it would be better to export your electricity to the grid and buy it back at night off-peak to heat your water.

If you could run your heat pump at variable speed, that would be an interesting option. We have done this for variable speed water pumping using solar and wind power, but have not been able to find a heat pump manufacturer who will allow us to interfere with their motor drives. It should be possible to vary the pump speed to keep exports at zero, within certain limits. Anyone out there with a tame heat pump manufacturer willing to allow us to play with that? This would preserve some of the COP of the heat pump and preserve the high primary energy conversion factor of electricity.

By the way, 2kw solar would need planning - you can get to about 1.78kw on the 12sq m planning exemption. But that would be enough for most hot water use.

Superdaddy

Thanks Quentin, this is a new build, with planning for solar. I'd put 6kw up if I thought I'd get paid for it. Any sign of a new scheme? I have to install something to meet building regs part L.
I see what you mean re dimmer switch, if I understand you correctly I can set it just to use solar power?
Bit of a loose question but will a 2kw setup heat enough water on an average summer day for 4 people in an 2500sqft A2 rated house? In other words does it work for people out there?
If it does that's great as it will allow me to add further panels if I wish when it can be sold back to the grid (bring back the Green Party:)). And as you say it is hassle free.

freddyuk

The Immersion diverter "only" uses solar power as it is wired into the PV circuit to measure what is spare free solar power. A switch will just switch on the immersion and drag 3kw from the supply be it solar or grid or both. A diverter measures the free spare power after the house loads are satisfied and balance is sent to the immersion. More PV means more is going to be diverted.

Superdaddy

Thanks Freddy. I want cheap hot water and to get the most from my investment. Trying to get my head around it all. Would it be better to heat water at night rate with the heat pump and top it up with the surplus electricity from a small PV system?

freddyuk

The PV is supplying power all day to some degree to your home not just the hot water so that includes the heat pump. You need to design the PV around your usage and budget. If you have 2kw of PV then this will be contributing to the whole house electric bill and with a diverter only free surplus power goes into the cylinder.
If you use the night rate (which is more expensive) there is no point in filling your cylinder at night and paying for it if the next day is sunny and the PV has nowhere to dump the free energy so manage the hot water according to your habits. You only need enough for the morning peak usage. When you have PV you have power all day but need to use everything you can or it will be sent back to the grid for free. Once you know your base load and average daily usage you can get an idea of how much power you need and when, then design system around that. You can always add more PV.
If it is a dark day you know you need to override the heap pump for a top up or even watch the forecast and if clearly it is bad then use the night rate for a full cylinder. An immersion heater can always be used for rapid hot water if required urgently but how often is that?
My wife now watches the weather and if it is clearly sunny for a few hours the washing machine or oven goes on. If the sun disappears it has still saved energy but it is not a 100% free wash. If you want to save energy it takes a bit of effort. Designing from scratch is more difficult but your lifestyle is starting point and how keen you are to adjust so when free power is available you react and use it (or lose it).

quentingargan

Superdaddy wrote: »

Thanks Quentin, this is a new build, with planning for solar. I'd put 6kw up if I thought I'd get paid for it. Any sign of a new scheme? I have to install something to meet building regs part L.
I see what you mean re dimmer switch, if I understand you correctly I can set it just to use solar power?
Bit of a loose question but will a 2kw setup heat enough water on an average summer day for 4 people in an 2500sqft A2 rated house? In other words does it work for people out there?
If it does that's great as it will allow me to add further panels if I wish when it can be sold back to the grid (bring back the Green Party:)). And as you say it is hassle free.

Just to mention that to my mind, the diversion device needs to be installed after you have done your BER assessment. Otherwise, you lose the primary energy conversion factor in DEAP. There are a few devices - the cheap ones use a triac and zero-crossing. These put quite a spike on the sine wave on the grid throughout the house (and usually next door as well...) The dearer ones use PWM and leave the sine wave as clean as a whistle.

If you have 2kw PV and your heat pump it 3kw, then using your heat pump will result in you importing 1kw or more, depending on the level of light at the time. That may end up costing you more to heat your water... 3kw of PV gives you a bit more wriggle room in terms of running 2kw devices like washing machines etc. But it may be outside your budget, and generally the larger a PV system is, without a feed in tariff, the longer your ROI is as you will not use all the power from it.

air

I'd recommend going with PV unless you use a lot of hot water for some reason or another.
Put in whatever you can afford now but install enough roof hooks to max out your roof space.
This means it will be easy to come back later and add more rails and panels when the time comes.

BarneyMc

Not sure if this is a valid question but if going down the route of using PV to power a heat pump & UFH then does it lean towards a thick sand/cement floor or thin screed?

air

BarneyMc wrote: »

Not sure if this is a valid question but if going down the route of using PV to power a heat pump & UFH then does it lean towards a thick sand/cement floor or thin screed?

I'd lean towards a thicker screed to allow you store up some heat energy on sunny days to keep you going through subsequent cloudier ones.
Bear in mind though that the PV will only make a direct appreciable contribution to the heat pump's consumption on rare sunny days in spring and autumn.
You presumably won't use the heat pump in summer and the PV won't produce any significant energy during the winter months when demand on the heat pump will be greatest.
In truth the PV / Heat pump combination relies on a feed in tarriff to make economic sense.

BarneyMc

air wrote: »

I'd lean towards a thicker screed to allow you store up some heat energy on sunny days to keep you going through subsequent cloudier ones.
Bear in mind though that the PV will only make a direct appreciable contribution to the heat pump's consumption on rare sunny days in spring and autumn.
You presumably won't use the heat pump in summer and the PV won't produce any significant energy during the winter months when demand on the heat pump will be greatest.
In truth the PV / Heat pump combination relies on a feed in tarriff to make economic sense.

I'm leaning towards a 3 inch sand/cement floor so I'm probably on the right tracks.

Superdaddy

quentingargan wrote: »

Just to mention that to my mind, the diversion device needs to be installed after you have done your BER assessment. Otherwise, you lose the primary energy conversion factor in DEAP. There are a few devices - the cheap ones use a triac and zero-crossing. These put quite a spike on the sine wave on the grid throughout the house (and usually next door as well...) The dearer ones use PWM and leave the sine wave as clean as a whistle.

If you have 2kw PV and your heat pump it 3kw, then using your heat pump will result in you importing 1kw or more, depending on the level of light at the time. That may end up costing you more to heat your water... 3kw of PV gives you a bit more wriggle room in terms of running 2kw devices like washing machines etc. But it may be outside your budget, and generally the larger a PV system is, without a feed in tariff, the longer your ROI is as you will not use all the power from it.

I see what you mean with deap. You've lost me with the sine waves, I feel a steep learning curve coming:). So be sure to get a PWM one?

BarneyMc wrote: »

Not sure if this is a valid question but if going down the route of using PV to power a heat pump & UFH then does it lean towards a thick sand/cement floor or thin screed?

I presume you are thinking of thermal mass for slow release of the heat. I think it would very much depend on how much insulation you put under it for starters. I have gone for 300mm of insulation (passive slab) and 100mm slab.

PWM


Triac

BarneyMc

Superdaddy wrote: »

I presume you are thinking of thermal mass for slow release of the heat. I think it would very much depend on how much insulation you put under it for starters. I have gone for 300mm of insulation (passive slab) and 100mm slab.

Yes, I guess so. I'll be placing 150mm PIR under the 3 inch slab (or that's the plan anyway). I suppose I'm looking for the ideal slab to be used for slow release but also allow for some control. I don't want to veer too much off topic here so I'll quit!

quentingargan

Sir Liamalot has shown the difference between PWM and TRIAC switching. The resulting sine wave shown at our neighbours house when using a TRIAC on a 2kw load was as per the picture here..

What value are the scope divisions Q? Could you not filter it with a beefy choke?
Just curious, I'd go PWM anyways it'll react much faster too.

Edit: ~15V drop next door?
Did their appliances notice?

quentingargan

Sir Liamalot wrote: »

What value are the scope divisions Q? Could you not filter it with a beefy choke?
Just curious, I'd go PWM anyways it'll react much faster too.

Edit: ~15V drop next door?
Did their appliances notice?

That was 50V divisions. Appliances don't seem to notice, but my wind inverter gets noisier with the grid spikes. My solar inverters don't seem to notice.

PWM is better of course, but devices on the market are more than double the price for PWM. about €220 for Triac and €480 for PWM. The PWM converts AC to DC and switches DC using mosfets or IGBTs so you can see where the cost comes from.

Hard to justify 'cause if Electric Ireland starts buying power again, it will make more sense to export your electricity during the day and use cheap off-peak to heat your water. And that option is also more ecologically sound.

Oh right yeah that's only ¾ of the wave shown, of course, 25V drop then.
That'd be out of spec of a lot appliances but just milliseconds. Does that affect the RMS voltage much in the offending dwelling?
If the device was reacting fast enough it shouldn't be visible because it's on the PV end of things.

I thought your windy was a battery job.

Superdaddy

BarneyMc wrote: »

Yes, I guess so. I'll be placing 150mm PIR under the 3 inch slab (or that's the plan anyway). I suppose I'm looking for the ideal slab to be used for slow release but also allow for some control. I don't want to veer too much off topic here so I'll quit!

Eliminating any cold bridging is very important, if I was using PIR I'd go for 200mm to improve the u value. Thermal mass is great but a disaster if not done right, you have got to retain the heat.

Sir Liamalot wrote: »

Oh right yeah that's only ¾ of the wave shown, of course, 25V drop then.
That'd be out of spec of a lot appliances but just milliseconds. Does that affect the RMS voltage much in the offending dwelling?
If the device was reacting fast enough and it shouldn't be visable because it's on the PV end of things.

I thought your windy was a battery job.

Ah lads, ye have totally lost me now. 20 years since I left school, knew feck all about sine waves then too.

nice_guy80

air wrote: »

I'd lean towards a thicker screed to allow you store up some heat energy on sunny days to keep you going through subsequent cloudier ones.
Bear in mind though that the PV will only make a direct appreciable contribution to the heat pump's consumption on rare sunny days in spring and autumn.
You presumably won't use the heat pump in summer and the PV won't produce any significant energy during the winter months when demand on the heat pump will be greatest.
In truth the PV / Heat pump combination relies on a feed in tarriff to make economic sense.

I'm interested in teasing out this statement

Surely most houses are empty during the day as people are off at work/school and so the PV would generate energy that could be used by the heat pump, washing machine, dish washer or whatever meaning those devices would run free off the PV? Even during the darker winter months?

The whole area of using PV panels to run a heat pump system is very interesting, and would make a lot of sense

BryanF

nice_guy80 wrote: »

I'm interested in teasing out this statement

Surely most houses are empty during the day as people are off at work/school and so the PV would generate energy that could be used by the heat pump, washing machine, dish washer or whatever meaning those devices would run free off the PV? Even during the darker winter months?

The whole area of using PV panels to run a heat pump system is very interesting, and would make a lot of sense

And how are you storing the energy, to run these devices? The feedin tariff ?

freddyuk

You need a device that can switch on AC appliances only using spare solar power. The hot water diverters can only switch resistive loads not normal appliances with motors connected to sockets so this restricts it to heaters basically. Furthermore you only want appliances (washers/dishwashers) to come on when there is sufficient solar to complete the cycle which is nigh on impossible. So the best you can do is measure the solar and program the system to maybe leave it 30 minutes so if there is uninterrupted sun for 30 minutes then start switching on loads without exceeding the solar available. As for heat pumps if they have the variable speed option then the system needs to be programmed to give this priority and get heat into the house and any spare can be dumped into DHW cylinder. If it is a really good day other appliances can be started but in reality you may lose the "free" solar if the appliance completes the cycle and the sun has gone but you have still saved energy by using that free power when it was there.I think most washers need high power early on to heat water and then the rest of the time is cool rinsing. If you do it when you get home it may be 100% paid for as too late for solar.
What we need is a sophisticated monitoring and control system to achieve this complicated scenario. Or hope there is a new government scheme to pay for excess exported solar which maybe will happen but as every other country is reeling back in the solar payments I feel it is unlikely the payments will be significant especially based on the existing exempted planning limit of sub 2kw of solar input.
Maybe Wednesday will bring some news of the renewables direction we are going in......

quentingargan

nice_guy80 wrote: »

The whole area of using PV panels to run a heat pump system is very interesting, and would make a lot of sense

Running other appliances when there is available power makes sense, but getting heat from solar, whether via a heat pump or not, seldom makes sense.

If you have a house unoccupied during the day, even running an odd washing machine or dishwasher isn't going to use all your solar output (and you don't run the washing machine every day anyhow).

I'm afraid our hopes are pinned on the utility companies being obliged to buy back surplus power at an acceptable price. It is ecologically more sound to run discretionary loads such as washing machines, car charging etc., at night using off-peak electricity, and export your solar power to the grid so it can be used by industry and hopefully curtail more carbon emitting turf plants that don't run at night.

air

nice_guy80 wrote: »

The whole area of using PV panels to run a heat pump system is very interesting, and would make a lot of sense

In the current environment it makes no sense as has been explained.
The output of PV panels in the winter months (when you would want to run your heat pump) is negligible.
You would be far better off spending your money on additional insulation or air tightness. It will last forever effectively with no maintenance and nothing to go wrong.

nice_guy80

Ok

I'm planning on very good levels of insulation, timber frame.

I was talking recently to a Solar PV company based in NI and they claimed they could run house appliances (in their own homes) such as washing machines, tumble driers for free off the power generated through the solar panels.
I'm eager to see what systems are out there.

Is a battery storage system a solution for the excess power generated? as well as using it to heat a water tank.
I've watched those programs of people going off grid in alaska and canada and they all seem to be at it.

quentingargan

nice_guy80 wrote: »

Ok
I was talking recently to a Solar PV company based in NI and they claimed they could run house appliances (in their own homes) such as washing machines, tumble driers for free off the power generated through the solar panels.
I'm eager to see what systems are out there.

Is a battery storage system a solution for the excess power generated? as well as using it to heat a water tank.
I've watched those programs of people going off grid in alaska and canada and they all seem to be at it.

You can only run a 2kw washing machine for free if you happen to be producing over 2kw of energy at that moment in time. This is the sort of BS you get from sales people. Even if you have a 2kw system, it will only occasionally produce 2kw. You can see a graphs of my system with 1.8kw panels and 1.5kw inverter HERE. It only occasionally got over 1kw today, and this was a good day.

You would need a clever management system to anticipate whether it will be sunny for long enough to run the washing machine. The point is, that if you were getting, say, 12c for exporting your surplus to the grid, it would be cheaper to run your washing machine off-peak at night for the 8c rate.

Batteries are an interesting proposition, but it still costs about 11c per KwHr to cycle batteries. Again, exporting to the grid would be a better way to do this.

nice_guy80

quentingargan wrote: »

You can only run a 2kw washing machine for free if you happen to be producing over 2kw of energy at that moment in time. This is the sort of BS you get from sales people. Even if you have a 2kw system, it will only occasionally produce 2kw. You can see a graphs of my system with 1.8kw panels and 1.5kw inverter HERE. It only occasionally got over 1kw today, and this was a good day.

You would need a clever management system to anticipate whether it will be sunny for long enough to run the washing machine. The point is, that if you were getting, say, 12c for exporting your surplus to the grid, it would be cheaper to run your washing machine off-peak at night for the 8c rate.

Batteries are an interesting proposition, but it still costs about 11c per KwHr to cycle batteries. Again, exporting to the grid would be a better way to do this.

but I cannot export
so that isn't an option at the moment

quentingargan

nice_guy80 wrote: »

but I cannot export
so that isn't an option at the moment

Which is why we're all waiting for this. It would be absurd for Ireland not to offer some fig-leaf to microgenerators

nice_guy80

white papers are pie in the sky thinking

it takes a full government term for things like that to come through the system

I hope to build next year.

murphaph

quentingargan wrote: »

Running other appliances when there is available power makes sense, but getting heat from solar, whether via a heat pump or not, seldom makes sense

This is a hotly contested point of view on the German photo voltaic forum I read. I'd say it's about a 50;50 split between those that think it makes sense and those that don't. The assumption however is that a heat pump is used to multiply the effective energy-using resistive loads to do so is always the last resort.

We're looking at installing just shy of 10kWp (the rules here mean you should stay below this or risk being seen as a business with the goal of making a profit and then different rules apply) on a SSW facing 45° pitched roof (so fairly steep roof angle which optimises for winter when the sun is lower in the sky, consequently we'll produce less power in the summer than the guy next door with a 30° roof pitch....but we'll have an 11kW heat pump to run in the heating season (and in summer too for a little bit of hot water and possibly for cooling on very hot weekend days (during the week we can put the shutters down to prevent the sun over heating the building-not so practical on the weekend)

Our installation is perhaps much larger than the average Irish one and can realistically provide energy for the heat pump in November and January...though December is probably out. We'll run the heat pump during the afternoon and release the energy from the underfloor thermal mass in the evenings when we need it (and from the storage tank for hot water).

nice_guy80

murphaph wrote: »

This is a hotly contested point of view on the German photo voltaic forum I read. I'd say it's about a 50;50 split between those that think it makes sense and those that don't. The assumption however is that a heat pump is used to multiply the effective energy-using resistive loads to do so is always the last resort.

We're looking at installing just shy of 10kWp (the rules here mean you should stay below this or risk being seen as a business with the goal of making a profit and then different rules apply) on a SSW facing 45° pitched roof (so fairly steep roof angle which optimises for winter when the sun is lower in the sky, consequently we'll produce less power in the summer than the guy next door with a 30° roof pitch....but we'll have an 11kW heat pump to run in the heating season (and in summer too for a little bit of hot water and possibly for cooling on very hot weekend days (during the week we can put the shutters down to prevent the sun over heating the building-not so practical on the weekend)

Our installation is perhaps much larger than the average Irish one and can realistically provide energy for the heat pump in November and January...though December is probably out. We'll run the heat pump during the afternoon and release the energy from the underfloor thermal mass in the evenings when we need it (and from the storage tank for hot water).

explain that for me please?

you will use the hot water in the storage tank for underfloor heating?
and the hot water in the tank is heated using the solar PV system?

quentingargan

murphaph wrote: »

This is a hotly contested point of view on the German photo voltaic forum I read. I'd say it's about a 50;50 split between those that think it makes sense and those that don't. The assumption however is that a heat pump is used to multiply the effective energy-using resistive loads to do so is always the last resort.

We're looking at installing just shy of 10kWp (the rules here mean you should stay below this or risk being seen as a business with the goal of making a profit and then different rules apply) on a SSW facing 45° pitched roof (so fairly steep roof angle which optimises for winter when the sun is lower in the sky, consequently we'll produce less power in the summer than the guy next door with a 30° roof pitch....but we'll have an 11kW heat pump to run in the heating season (and in summer too for a little bit of hot water and possibly for cooling on very hot weekend days (during the week we can put the shutters down to prevent the sun over heating the building-not so practical on the weekend)

Our installation is perhaps much larger than the average Irish one and can realistically provide energy for the heat pump in November and January...though December is probably out. We'll run the heat pump during the afternoon and release the energy from the underfloor thermal mass in the evenings when we need it (and from the storage tank for hot water).

I think mainland Europe, or parts of it at least, get more cold bright days than we do in Ireland. I must run a comparative simulation.

In Ireland of course, you would be prohibited from putting more than 6kw on a domestic single phase house, or 11kw on a three phase site, unless you want to pay a small fortune for witness testing of secondary injection tests and additional equipment.

I have worked on devices that can detect rate of export, and so far everyone uses these to control a resistive load. But heat pumps have a variable speed motor and the inverter controlling that speed could be controlled by the amount of excess power being exported. That would be nice...

But I still argue that in Ireland, where we have such dirty electricity in the day, and so much wind at night, it would be economically and ecologically more sound to export surplus power, get paid for that, and then run your heat pump on off-peak electricity at night.

murphaph

nice_guy80 wrote: »

explain that for me please?

you will use the hot water in the storage tank for underfloor heating?
and the hot water in the tank is heated using the solar PV system?

Storage tank just for DHW. The floor screed itself stores the energy harvested at noon until needed on the evening. Our house though should be pretty energy efficient to begin with. Our projection says we'll have a heating demand of 6124W. DHW requires about another 800W for our 4 person household. House is 212m².

nice_guy80

http://www.met.ie/climate-ireland/sunshine.asp
Sunshine hours there

Wind power, oh great.
So basically, I've to wait until the 16th

murphaph

quentingargan wrote: »

I think mainland Europe, or parts of it at least, get more cold bright days than we do in Ireland. I must run a comparative simulation.

In Ireland of course, you would be prohibited from putting more than 6kw on a domestic single phase house, or 11kw on a three phase site, unless you want to pay a small fortune for witness testing of secondary injection tests and additional equipment.

I have worked on devices that can detect rate of export, and so far everyone uses these to control a resistive load. But heat pumps have a variable speed motor and the inverter controlling that speed could be controlled by the amount of excess power being exported. That would be nice...

But I still argue that in Ireland, where we have such dirty electricity in the day, and so much wind at night, it would be economically and ecologically more sound to export surplus power, get paid for that, and then run your heat pump on off-peak electricity at night.

I think we probably have a greyer, more overcast winter period here than in Ireland, but the relative size of our array probably accounts for us still being able to produce usable energy in the darker months and the pre-condition here is a well insulated, air tight house, otherise the PV has no chance of providing more than a tiny fraction of the energy the HP needs.

Of course, you need to be able to send the surplus created by this over sized array somewhere in summer, so the FIT provides that "dump valve"...though feeding in is last resort for anything installed today as the FIT is so low compared to the cost of power from the grid.

In summer, we'll make our hot water at noon too and we'll buy all new appliances with timer functions and if possible that can be remotely controlled and integrated (later) with a house management system. The way I look at the heat pump though is a bit different...you can maybe delay washing the clothes for a day or two until bright sunshine is forecast, but you have to run the heat pump more or less every day and just use the averaging out effect that says on some days you'll need grid energy and on others you'll get it from the PV or (more usually) a mix of both. You don't want to be cycling the HP according to sunshine anyway IMO...that's the sure way to shorten its life.

The single phase distribution system I'm afraid certainly doesn't help matters but 6kWp is still a good number, especially if no HP is in play. Here in Germany we are limited to an even lower 4.6kW on a single phase but our local network operator allows up to 30kW with no extra checks if balanced across all three phases and 3 phase supply is the norm to domestic properties. 10kWp suits me based on the (somewhat silly) rules here that mean going over 10kWp results in you being considered a generator like e.on (normally you are considered a "small business" generator even below the 10kWp) and then you have to charge yourself a tax something like VAT (but more punitive) on your self consumed energy and send it to the tax man. It's a bureaucratic nightmare even before this 10kWp level is reached, I don't want to even think about going over it!

For the small scale (<10kWp) generators here, we are treated like a small business with VAT turnover. The benefit of this means you can claim the VAT back on your initial PV investment, which is a lot of money. The "penalty" you pay for this is that you then get paid for your fed in electricity by the network operator with VAT included. This VAT must be deducted and sent to the tax man. This has to be done monthly.

To your last point well I couldn't agree more. Ireland is the perfect candidate for running heat pumps off wind power at night. It's a disgrace that this isn't higher up the agenda for a country importing so much energy in the form of fossil fuels and with much more reliable wind than around here. The cost has to be right though...here PV owners are removing their heat pump meters and just connecting them to the normal household meter and taking as much PV energy as they can for the HP. You can't feed in via the HP meter, so it's one or the other here (except in a handful of cases where it's allowed to install a switch to run the HP from household + PV OR HP only supply). The reason is the price difference between household electricity and heat pump electricity is just too small now.

quentingargan

I ran a simulation on PVSyst with 12 X 260W panels at 60 degree pitch in Tuam and Stuttgart. The results are in the picture. Left side is Ireland, right is Stuttart. The total production in Germany was 10% up on the same system in Ireland, but the seasonal variation is worse in Ireland than in Germany.

I had expected more of a difference, so the point is proven - the difference in winter isn't as significant as I had expected. And yes - if you put in a big enough system, you will get enough to run your heat pump in winter, but of course it depends on getting paid for your surplus energy in the summer.

10-10-20

quentingargan wrote: »

Running other appliances when there is available power makes sense, but getting heat from solar, whether via a heat pump or not, seldom makes sense.

If you have a house unoccupied during the day, even running an odd washing machine or dishwasher isn't going to use all your solar output (and you don't run the washing machine every day anyhow).

Sorry to digress slightly from the later momentum of this thread, but I was thinking about this element a little.

There is a way to obtain a reasonable gain from solar when using washing-machines even when the sun isn't shining and part of it relies on building design to effect the gain. Dishwashers are less-easy as the heat capacity of the crockery is high, so you need to heat the whole enclosure and crockery with very little water, and this doesn't suit the method below.

Most washing machines have separate hot water supply inlets so you can pipe your solar heated water into the device directly. Easily done, but there is a caveat - if your supply-line is excessively long and the device is miserly with it's water consumption - as are most devices these days - you won't ever draw any hot water and you'll then have to electrically heat the cold water which you drew from the piping and inversely loose the heat from the replacement water.
Ideally, if the run from the machine is short, or uses narrow-bore piping the effect is enhanced as there is less cold water to subsequently heat.

So that's where the element of building design comes in: keep your energy consumers as close to the source of the hot water as you can and you eliminate the in-pipe losses and all you have to "pay" for is the spinning motor and some top-up electricity, and you have a partial-assist from solar.

Small, but a point worth mentioning.

cerastes

quentingargan wrote: »

I think PV has crossed the line on price. A 2kw system will produce over 1800kwHrs of electricity. This is about the same amount of energy as you would get from a 4 sq m solar thermal panel or equivalent tubes. Some of this electricity will save you the 18c retail price of electricity, and the balance will save you about 9c in heating from oil, gas or off-peak electricity. Your heat pump may be slightly cheaper.

The hardwre for a PV system like this will be about €2500 plus the gizmo to do the immersion switching - about €500. The advantage of this over solar thermal is that there is no need to change glycol every three years, no moving parts or pumps to break down, no expansion vessels to fail and the system is basically "fit and forget".

The device that does this switches your immersion like a dimmer switch, monitoring your incoming grid and cranking the immersion up and down to prevent free exports. But a good unit to do this is not cheap - an export meter would be cheaper if utilities would buy back your power, so you might spend €500 on one of these gizmos and then find that your provider is willing to buy your electricity again. Environmentally it would be better to export your electricity to the grid and buy it back at night off-peak to heat your water.

If you could run your heat pump at variable speed, that would be an interesting option. We have done this for variable speed water pumping using solar and wind power, but have not been able to find a heat pump manufacturer who will allow us to interfere with their motor drives. It should be possible to vary the pump speed to keep exports at zero, within certain limits. Anyone out there with a tame heat pump manufacturer willing to allow us to play with that? This would preserve some of the COP of the heat pump and preserve the high primary energy conversion factor of electricity.

By the way, 2kw solar would need planning - you can get to about 1.78kw on the 12sq m planning exemption. But that would be enough for most hot water use.

What is this device? any examples of what it is and how it does this?

Why is it not possible to alter the motor drives without input from the manufacturer? other than the warranty may be invalidated? how much are these pumps? is there some technical limitation? the advantage? you say to preserve the COP, is this for when there is less opportunity to extract heat energy? or possibly when it's colder or both?

I dont understand fully how these devices work myself although Ive a technical background but looking to better understand, no significant training in electronics or thermodynamics.

quentingargan

cerastes wrote: »

What is this device? any examples of what it is and how it does this?

Why is it not possible to alter the motor drives without input from the manufacturer? other than the warranty may be invalidated? how much are these pumps? is there some technical limitation? the advantage? you say to preserve the COP, is this for when there is less opportunity to extract heat energy? or possibly when it's colder or both?

I dont understand fully how these devices work myself although Ive a technical background but looking to better understand, no significant training in electronics or thermodynamics.

The units on the market come in two types. Ones like this use high frequency switching to work in a similar way to a dimmer switch. There is a clamp meter on your line out to the grid measuring current exported. As you start to export power, the high frequency switching on your immersion circuit gradually increases its pulse width to send more and more power to the immersion.

Cheaper units use a simple triac, switching the immersion on and off 100 times per second in line with the AC phase. These can cause distortion of the grid because of the pulsed switching

quentingargan

On a lighter note, there are other reasons not to opt for PV in todays Irish Times. :rolleyes:

hexosan

quentingargan wrote: »

On a lighter note, there are other reasons not to opt for PV in todays Irish Times. :rolleyes:

Good god

murphaph

quentingargan wrote: »

I ran a simulation on PVSyst with 12 X 260W panels at 60 degree pitch in Tuam and Stuttgart. The results are in the picture. Left side is Ireland, right is Stuttart. The total production in Germany was 10% up on the same system in Ireland, but the seasonal variation is worse in Ireland than in Germany.

I had expected more of a difference, so the point is proven - the difference in winter isn't as significant as I had expected. And yes - if you put in a big enough system, you will get enough to run your heat pump in winter, but of course it depends on getting paid for your surplus energy in the summer.

I am pretty sure they get more sunlight in Stuttgart than here in Berlin. Maybe you could try again with Berlin? I'd be interested in seeing that if you have the inclination :-)

quentingargan

murphaph wrote: »

I am pretty sure they get more sunlight in Stuttgart than here in Berlin. Maybe you could try again with Berlin? I'd be interested in seeing that if you have the inclination :-)

You're pretty spot on. Funnily enough, PvSyst didn't give Berlin, so I used Potsdam to save the hassle of looking up long and lat etc. Very like Ireland. Can send you full simulation if you want it.


So putting in 6kw and at a steeper angle would probably do the same here, provided you could get paid for your surplus exports in the summer.

Oops - put in the simulation as an attachment and the picture didn't appear, but you get the idea...

murphaph

Thanks for running again. We're actually building just north of Potsdam as it goes lol. I like seeing the "fairly good" performance in February and March. That's still winter here. and the heating will definitely be on to at least mid march...though maybe not in the new house if we let the sunlight warm it up during the day.

@10-10-20: Actually I think your washing machine point is really well made and I hadn't considered the problem of low consumption leading to the water having to be heated by the WM itself anyway and then the added problem of heating the water again only for it to go cold in the line. I had planned to use HP generate hot water for the WM and our WM is planned to go 3 metres away from the DHW cylinder in the utility room. I think this will be ok, but I'll insulate the run and keep the bore as narrow as possible to minimise the losses. If I could go back I'd probably put the WM right beside the tank, but that's not an option now as the pedestal for the WM is built (we'll have it raised up on a concrete plinth to both enable easier loading and also because it's in the cellar and I want the WM to be able to discharge the grey water to the sewer using it's own pump. If it was on the floor it would have to discharge via the lifting system, which I really only want to be used by the guest shower room or it'll cost a bloody fortune to run). We need a lifting system as the flood level is around 1.45m above cellar floor level.

cerastes

quentingargan wrote: »

The units on the market come in two types. Ones like this use high frequency switching to work in a similar way to a dimmer switch. There is a clamp meter on your line out to the grid measuring current exported. As you start to export power, the high frequency switching on your immersion circuit gradually increases its pulse width to send more and more power to the immersion.

Cheaper units use a simple triac, switching the immersion on and off 100 times per second in line with the AC phase. These can cause distortion of the grid because of the pulsed switching

So the gizmo itself is a switching device that directs and converts DC to AC?
Is it a combination of devices? Does an an IGBT do this or is this in conjunction with other devices?
I dont really fully understand the pulse width modulation, how does this cause an increasing pulse width at the immersion? and other than directing power in particular direction, is increasing the pulse width not a bad thing?, does that not itself cause a distortion of a waveform?

quentingargan

10-10-20 wrote: »

Most washing machines have separate hot water supply inlets so you can pipe your solar heated water into the device directly. Easily done, but there is a caveat - if your supply-line is excessively long and the device is miserly with it's water consumption - as are most devices these days - you won't ever draw any hot water and you'll then have to electrically heat the cold water which you drew from the piping and inversely loose the heat from the replacement water.

I bought a hot and cold feed machine, and found that on a 40degree wash, it ONLY uses the cold feed. On a 60 degree wash, it uses both feeds. So that is less than useless. I bored a hole in the top of the machine above the detergent tray, and I simply switch it on, pause it when it starts to fill with water, fill it from the hot tap, and then let it run.

quentingargan

cerastes wrote: »

So the gizmo itself is a switching device that directs and converts DC to AC?
Is it a combination of devices? Does an an IGBT do this or is this in conjunction with other devices?
I dont really fully understand the pulse width modulation, how does this cause an increasing pulse width at the immersion? and other than directing power in particular direction, is increasing the pulse width not a bad thing?, does that not itself cause a distortion of a waveform?

It doesn't convert DC to AC. Well... actually, I haven't stripped it down, but I think the better version of the two takes the AC, separates it into two DC channels, PWMs them using mosfets or IGBTs and then merges the result back to AC

The cheaper versions just use a triac and switch on at various points in the waveform and switch off again at the zero crossing point.

But effectively both of them switch the immersion on and off fast for a shorter or longer percentage of the time, so each pulse has a different width depending on how much power you want to send to the immersion. The better one does that a lot faster.

cerastes

quentingargan wrote: »

It doesn't convert DC to AC. Well... actually, I haven't stripped it down, but I think the better version of the two takes the AC, separates it into two DC channels, PWMs them using mosfets or IGBTs and then merges the result back to AC

The cheaper versions just use a triac and switch on at various points in the waveform and switch off again at the zero crossing point.

But effectively both of them switch the immersion on and off fast for a shorter or longer percentage of the time, so each pulse has a different width depending on how much power you want to send to the immersion. The better one does that a lot faster.

This may become tiresome for you but,
PV outputs DC, are you saying that this is converted to AC first? using an inverter or feeding a battery which is then inverted to AC?
and then -->
"takes the that same AC, separates it into two DC channels, PWMs them using mosfets or IGBTs and then merges the result back to AC"

(seems convoluted?) is it not possible to take two DC channels before inverting it? with some kind of smoothing of that waveform to limit dips or spikes? and PWM that?

Why two channels of DC? whats the benefit? is it for some reason to create the output AC completely +-? (simulated waveform?)

Excuse my ignorance, I'm just trying to get my head around the steps involved.

quentingargan

cerastes wrote: »

This may become tiresome for you but,
PV outputs DC, are you saying that this is converted to AC first? using an inverter or feeding a battery which is then inverted to AC?
and then -->
"takes the that same AC, separates it into two DC channels, PWMs them using mosfets or IGBTs and then merges the result back to AC"

(seems convoluted?) is it not possible to take two DC channels before inverting it? with some kind of smoothing of that waveform to limit dips or spikes? and PWM that?

Why two channels of DC? whats the benefit? is it for some reason to create the output AC completely +-? (simulated waveform?)

Excuse my ignorance, I'm just trying to get my head around the steps involved.

The output of a solar panel is optimised using MPPT tracking on a grid tie inverter, so you need an inverter anyhow, not just for this, but also so that the electricity can be used for other household loads.

Also, the immersion is designed to run on 230V AC. The voltage from the panels can be anything from 60V to 600V depending on the number you have in series.

These devices only take your surplus power from the grid. So if you switch on a kettle for example, the diversion to the immersion knocks off instantly. It is easier to manage all that on the same grid.

BTW, I am not certain of how the more expensive devices work - I am only surmising because I don't know any other way of high frequency switching an AC supply. I do understand how the cheaper ones work with a triac. That's fairly simple, and you can find DIY kits to make them. See here for example.

cerastes

I thought resistive loads worked happily on AC or the equivalent (not equal) DC voltage