South east facing is likely to do a lot worse than south facing in the middle of the winter, I think; at 56°, or so, from the equator the sun is not up for long and when it is it's pretty much south when it'll be at a bit of an oblique angle whatever time of day. On days when the hour's sunshine happens to be a bit after solar noon it'll be at an even steeper angle.

My intuition, therefore, would be that this will make a good contribution to your year-round DHW but not much to the winter UFH.

On the solar warm air collector I built to be (regrettably) east facing at a slightly more northern latitude I chose to use corrugated PVC for the front of the collector with the idea that light at an oblique angle would have a better chance of hitting a surface at a steep angle and therefore be less lightly to be reflected. Still, it gave no appreciable warming after October, even on bright days.

http://edavies.me.uk/2011/12/solar-thermal-end-of-term/

Doing that panel again I'd have made it vertical, twice as wide, and facing more south even at the cost of sticking out from the building a bit.

Posted By: qeiplMaybe a calculation of the volume of air passing through the panel every second and the energy required to heat that volume from 10C to 20C would give you a feel for the plausibility of the concept.

Heating 450 m³/h of air (volumetric heat capacity ~= 1.3 kJ/(m³·K)) through 10 °C would require a power input of 450 * 1300 * 10 / 3600 = 1625 W. Spread over a 4.5 m² panel that'd be 361 W/m². A tad optimistic for relatively high-latitude winter sunshine, particularly at an oblique angle, but not completely out of the ball park. Running the airflow quite a bit slower or doubling the collector size might work.

Posted By: Chris P BaconSolarVenti say that a 3m² panel raises the incoming air temp. of 150m³/h by between 20C to 40C.

Similarly, assuming 30 °C is between 20 and 40: 150 * 1300 * 30 / 3600 / 3 = 541 W/m². Quite reasonable for summer sun seems a bit much to me with the sun only 11° above the horizon.

Ed thanks for those calculations.

Posted By: Chris P Bacon
qeipl, the ufh will be the sole method of heating the house, and the only heat source will be a heat pump of some description.

The Ecocent will struggle to do much UFH in mid winter, regardless of how much sun shines on your air warming panels.
When the sun doesn't shine it won't manage to keep you warm.

If gas isn't available and you don't want the faff of a solid fuel boiler in a shed then I'd recommend an electric boiler fitted in-line with the UFH circuit. Cheap to install, expensive to run, but if your house is insulated/sealed/MVHR'd to the max then the winter hole shouldn't be too deep a one to fill with expensive electricity. The boiler won't come on very often but when you need it, you'll need it.

I'd forget about the warm air panel and make sure you have enough cash for the PV. It'll generate enough to ofset the electric boiler.

I'm very happy with the Ecocent. It's great for DHW and a modest amount of UFH.
It's cheap to install (mine was £1,600) and I believe the new model has a stainless steel cylinder, so no anode to change. Otherwise there is little or no maintenance.

Even when drawing its air from outside it uses solar energy from a wider range of conditions than is possible with ST but when solar energy is scarce and heat loss from the house is high (mid winter, close to zero air temp) it struggles to process enough air to get enough energy to keep me warm.

I meant that you should go for the Ecocent and the electic UFH boiler. Definitely not all straight electric.

The smallest in-line electric boiler that I could find was 6kw and cost c.£400. Easy to install, takes up almost no space, and can be adjusted to kick in to assist rather than pre-empt the heat pump.
Mine has hardly ever been used because I tend to light the boiler, but it's good to know it's there.

Unless you're building a huge palace your 25kW of PV will go a long way to generating what you use in a year.
I have a wee hydro that produces about half of the electricity that I consume and will install PV to do the other half when the price of panels and the contents of my piggy bank converge.

A heat pump, electric boiler, and grid-tied PV is a good combination if your house is proper low energy.

Posted By: Ed Davies

Posted By: qeiplUnless you're building a huge palace your 25kW of PV...

Crispy said 25 m², so around 4 kW.

Oops. Slip of the units. Thanks for the correction.

Posted By: Chris P Bacon
Is there a good argument for spending the money on PV rather than a heat pump?

The problem with PV and ST is that they operate in a relatively narrow range of conditions - they only capture solar energy when the sun is shining on them.

An ASHP captures solar energy day and night, rain, hail or shine, albeit by much less efficient means.

Posted By: SteamyTea: “I think Ed did some calcs that showed heating water with PV can sometimes be better than with ST. Caused a bit of a controversy at the time but made sense to me.”

'Twas here: http://edavies.me.uk/2012/01/pv-et-flat/

Discussion: http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=8396

More: http://edavies.me.uk/2012/01/solar-per-area/

Still haven't done the PV + ST + HP (i.e., using PV to power a heat pump to boost the output of solar thermal panels) calculations. There are a lot of variables involved but a few simplifying assumptions should make a useful calculator possible. Unfortunately, I don't think a nice neat graph can summarise the results tidily.

I spent a few hours last night assembling figures from the electricity bills for our current house together with the estimates from the PHPP for the new house.

If we are to use the 5kW Ecodan ASHP for space heating and DHW production year round I estimate that our total electricity use including general domestic use & HRV will be between 5,000kWhr and 6,000kWhr.

The feedback from Ed, qeipl and Skyewright has pretty well put me off the notion of using the Ecocent with solar air preheat although I would still like to experiment with a solar air heater in the future.

Looking at the issue of installing PV, the payment system for PV is completely different here in Sweden compared to the UK.

Not sure how the electricity price is broken down in the UK but it might help to explain how we pay here first, here we pay a standing charge for the meter which varies according to the size of the fuse. All houses have a 3 phase supply here and the standing charge for a 20A fuse is approx. £365 a year and a 25A fuse is £475. There is also an account charge of £36 a year.

We then pay an electricity supplier either a floating or a fixed price per kWhr in July the floating price was 2.27pence per unit (the lowest I have ever seen it) and in August it was 2.86p per unit. By comparison in February it was 5.2p a unit.

On top of that there is an energy tax of 2.7p per kWhr.

Then there is a delivery charge of about 1.5p per kWhr.

And 25% VAT on top of all that.

As a micro producer you get paid a fraction below the Nord pool spot price so this July when PV production would be near it's highest point in the year you would only be getting a fraction over 1p per kWhr fed to the grid.

You also get paid a carbon credit of about 2p per kWhr for all production. Obviously the most benefit is displacing electricity you would normally purchase from the grid as you are saving the unit cost, delivery charge, energy tax and VAT on that purchase.

Another killer is that if you produce more electricity than you consume over the entire year you have to pay a standing charge of £175 a year to feed electricity into the grid. This charge is waived for producers who consume more than they produce.

I have estimated that if I consume and produce 5000kWhrs a year I reckon the absolute best case scenario is that I would save about £350 a year so even with a grant available of up to 45% of the installation costs the return on investment is not good and could be completely wiped out by on-going maintenance costs.

I know the above info is not of benefit to anyone but thought some might be interested to see how the situation here in Sweden compares to the UK.

@ST The normal electricity bill is every two months and PV payments are made every 3 months.

The fuse charge is the total for all 3 phases.

I'm not sure what the fixed price is at the moment it varies all the time. You can fix for 1, 2 or 3 years in advance or you can fix just for the Winter and have the floating price during the Summer.

There was no digging required for the breakdown of the bill it is shown as a pie chart on the reverse of the bill together with a bar chart of monthly consumption for the last 12 months.

I'm not sure what the incentives are but there has been a lot of investment in commercial wind here in the last 10 years or so. But as you point out with the huge amount of Hydro in the mix here already there is no need to incentivise domestic scale production to the scale that has happened in Germany and the UK.

I have just come across a Government press release from last week which mentions the introduction of nett charging for micro producers, it doesn't specify over what time period the netting would occur, daily, monthly, quarterly or yearly. If it is any of the longer time periods it will significantly improve the return on investment, I will have to keep my ear to the ground on that one.

I'm only living here a little over 2 years so can't speak with any great authority, but the Swedes are generally very good at having a public debate on these things and reaching a consensus which pretty much everyone will accept.

In 2005 the Government reversed the previous policy (decided in a 1980 referendum) of phasing out Nuclear. The current policy is to stick with nuclear and replace the current plants when required.

There are various biofuel and waste to energy projects, Malmö's food waste goes to biogas production and other waste that can't be recycled is incinerated for electricity production and district heating, all the ash is reused in various products so that none goes to landfill.

There is also a pilot plant just down the road from me producing biogas from seaweed.

But they know that it is a huge ask to replace the huge amount of nuclear here with renewables but are chipping away at it.

The main policy is to reduce consumption, in the current building regs for example a 130m2 house is only allowed to install a maximum of 4.5kW of electrical consumption for all space heating and DHW, if you have a 3kW immersion for DHW it doesn't leave you with much for space heating!

http://www.youtube.com/watch?v=RAaLwSoEMMM

http://translate.google.com/translate?hl=en&tl=en&sl=sv&u=http%3A//www.biogassys.se/