Your doubts are well founded ratman. Your people are asking too much. Heat pumps need far more electricity than any sensibly sized solar pv system can produce in the UK. I am totally off-grid using pv, wind and small hydro and I can only 'dream' of ever running a heat-pump.

<blockquote><cite>Posted By: ratmin</cite> Any comments, ideas or links please?</blockquote>

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=4174&page=1#Item_5

Posted By: CWattersFor example in the summer sell excess electricity to the grid and buy it back in winter?

That'll work well but it doesn't solve the planet's problem of reducing peak demand!

And it may not work so well if demand pricing becomes widespread! Sell it cheap in summer and buy it dear in winter. There's an interesting consultation at http://www.nationalgrid.com/uk/Electricity/Operating+in+2020 that talks about pricing among other things.

PS Welcome back "Keith"

If this is for a UK installation have they thought about using the electricity from the PV to directly heat storage heaters. Remember it is the control of the heaters that lets them down not the fundamentals of heat storage.
Reason I ask if it is a UK installation is that when it is cloudy here it tends to be warmer (in winter) than when it is clear so the usable power from PV can be better used.

I know that people hate storage heaters but if someone is going to spend thousands on PV then they can easily modify a standard storage heater to respond better to temperature differences.

Ratman

Have been pondering your original question and though I have no evidence, and now that the university is almost totally empty I cant ask anyone there either, I have thought up an idea. Hear me out and then lets rip it to shreds in the best academic fashion, then we can put numbers to it.

Option 1: PV charges batteries-->batteries run inverter-->inverter runs heat pump

Now we know that charging batteries is pretty inefficient (0.5) and ASHP have a COP of about 2 (open to debate I know), so no net gain there then.

Option 2: PV runs Storage Heater (can get elements made to run at low voltage)-->Storage Heaters heat house

Trouble with storage heaters is they are uncontrollable on a short time scale (I know as I live with them) but they do convert near enough all the electrical power to heat so efficiency pretty high (maybe 90%) and a cheap installation.

Option3: PV charges batteries-->Inverter (or re-wound heaters)--> Fan Heaters (or convection) when needed

Reasonably cheap option and controllable with switches, sensors and timers.

Could do a combination of Option 2 and 3, some storage heating, some 240V AC heating and some battery storage.

Comments anyone?

CWatters

I tend to agree with you there, there are some losses in the cabling but they are not worth bothering with.
There are entropy losses, but again still very low in converting electricity to heat. I just picked 90% as a figure, no real basis for it other than it was not 100%.
More interested in the concept of turning PV electrical power to heat, either via a heat pump or through direct heating.

PMCC

I think your right if you have the room to store the energy as hot water. What is really needed is better storage rather than better collection. Solar thermal collection has probably gone as far as is practical (except for micro concentrated) and PV does have a fundamental quantum limit of just over 30%. Water Source Heat Pumps are a very underused technology, every time I look into Penzance Harbour when the tide is in, I wonder why the town is not heated by it.
Greening up the grid does seem to be the way we are heading slowly along with reduced consumption through better insulation on dwellings.

The point I was making I suppose was that coupling ASHP with PV is am expensive option and there are alternatives.

How about an oversized solar thermal system, sized to support most of the winter heat, then...

A low pressure steam turbine or sterling engine to make the "waste" heat in summer into electricity and sell electric back to the grid or use it on site.

Given solar thermal is 5 times more effective at colleting suns energy(figure above not verified), and it's heating you actually want then the money may be better spent on lots of solar thermal which is also much cheaper per KW to buy. Rough guess less than £1000 /kw for tubes VS more than £3-4,000 per kW for PV.

I had a look a while ago and unformatuntely this kind of thing isn't available "off the shelf" yet, but a few people have been having a go. A really promising set up is from these guys... http://matteranenergy.com/

A set of clever plumbing stuff near to the themal collectors, and a new kind of valve which removes the losses of the feed pump of in a the condensor of a normal turbine. Also can produce cooling - ideal if you have a comms room that needs cooling too!

Alternatively ....

Even if you can't get electric generation yet, you could bury pipes in the ground, and store heat in the soil for the winter. Like this... http://www.icax.co.uk/. UK Based = UK jobs etc ;-) the advantage of this one is they have a working system. Soil is free, plumbing won't cost loads (compared to fossil fuel running costs) - it's the design and knowledge you'll probably pay a lot for!

You might then want space for a heat pump as heating of last resort, if the building design fails to live up to expectation.

I'm currently in a 1960's building with no insualtion, and poor quality secondary glazing. With 50 pc's monitors, lights and people, it overheats in february so we have the windows open as there's no air con :-(

Does anyone have any data logged from an ASHP that has been running for a few years. Would need more than just the kWh consumed and the COP. That is the best way to determine the workability of a system. It does seem that there is the risk of heading down "the road to hell is paved with good intentions" all for the sake of decent data analysis. Sometimes people put up charts of their turbine/PV output but what is really needed is the raw data so that standardised techniques can be applied.

The debate is heading in the right direction though.

Interesting question, will know more when then RHI kicks in, but will work best in an old house with less insulation if the stories that the RHI is based on the SAP rating of a house are true.

PV for heating ... we had PV panels commissioned early June. By lucky chance an innovative heating engineer had installed a DPS thermal store a couple of years ago for gas central and water heating. It's got an immersion heater so I switched off the gas water heating (night and morning) and switched on the immersion heater midday. Turns out running the immersion heater for 2 hours 13.00 - 15.30 provides hot water right through the 22 hours to next boost. I'm going to try less time still. This sunny weather we use practically no electricity for water heating alone.

Now in winter when we run the central heating radiators I plan to continue this. At least we should get some free electric heat. Radiators seem a much better bet than storage heaters, at least if there's an existing system. We'll see!

Damon
Do you mean let someone else heat their water with it after transmission losses.

Suz
You don't say what size system you have installed and what your water usage is, but personally I think you are doing the right thing. Assuming your cylinder is well insulated. Use as much of your own as you can is the way to go. Have you thought of putting your fridge/freeze on a timer. If that can store enough 'coolth' during the night then you can recharge it during the morning after the early flurry of use. Think I may try turning mine off tonight and logging the temperature rise.

Posted By: SuzPV for heating ... we had PV panels commissioned early June. By lucky chance an innovative heating engineer had installed a DPS thermal store a couple of years ago for gas central and water heating. It's got an immersion heater so I switched off the gas water heating (night and morning) and switched on the immersion heater midday. Turns out running the immersion heater for 2 hours 13.00 - 15.30 provides hot water right through the 22 hours to next boost. I'm going to try less time still. This sunny weather we use practically no electricity for water heating alone.

Now in winter when we run the central heating radiators I plan to continue this. At least we should get some free electric heat. Radiators seem a much better bet than storage heaters, at least if there's an existing system. We'll see!

presuming you've got a bog standard 3kW (or probably 2* 3kW in a DPS thermal store set up) immersion heater, even if you've got the biggest standard domestic pv set up (4kWp) there are going to be very few days even in summer when the PV will be generating all the electricity needed to run both the immersion heater and the rest of the houses base load.

Heating water by imported electricity will cost you in the region of 3.5-4 times the cost of heating water via a high efficiency condensing gas boiler, so you'd need to be averaging at least 75-80% of the electricity used being generated by the solar PV simply to break even on cost terms. In environmental terms, the carbon impact isn't much different either in that gas used in condensing boilers is around 1/3 the carbon impact of the average grid electricity per kWh.

On environmental terms, ok there could be nominal carbon savings within your household, but given that the PV generated electricity would have been used by your neighbours to offset high carbon grid electricity, while you used gas to heat the water, the overall impact would be negative. Then there'd be the impact on increased grid demand if lots of people started doing this, which could result in extra fossil fuel generators needing to be used.

Even thinking about running your space heating from immersion heaters is simply going to mean you're costing yourself a fortune in imported electricity when you've got a a much cheaper and more efficient option available to you in the form of a (presumably) condensing gas boiler.

Switching the use of non-time critical demand such as washing machines and dishwashers to daytime to make use of pv generated electricity is one thing, switching from a condensing gas boiler to immersion heater for your hot water though is IMO not likely to be a sensible idea on either financial or environmental grounds.

solar water heating backed up by a secondary source that'd usually be the same as the heating source unless in a genuinely passive house, or could be a biomass boiler in addition to any existing oil boiler / heat pump.

if the second source were ASHP / GSHP then an immersion heater on a timer once a week to boost the gshp/ashp/solar upto 65 degrees to reduce legionella risk / comply with regs would be sensible.

if it were a genuinely passive house with no heating source at all, then there could be an argument to be made for oversizing the solar, and putting it on a steeper angle for peak winter impact, then using an immersion heater for backup water heating, as the cost / benefit of using ashp when at it's lowest efficiency in winter would be negligable, and GSHP would be overkill for such a relatively small annual energy use.

I'm looking to replace our old oil heating system this spring. Currently looking at a wood burner with a wetback and a thermal store as the primary source of heating and hot water in the winter.

The question is what to do in summer to produce HW?

Solar thermal is an option.

We have 6 kWp PV on site already, so could put peak generation of PV into thermal store by way of an immersion element on a timer.

The other option that I've been told about is locating the intake of a ASHP behind the PV panels to remove the warm air from behind the panels (I've got some data loggers installed to monitor this over the winter) and use it in the ASHP which should help COP and in theory if air removed is of higher temp than ambient then help reduce inefficiencies PV panels experience when they get too hot.

Anyone have any experience of this relationship working in practice?