Use PV electricity for appliances, then use spare to heat water store, then export surplus to grid ?

I am assuming that there is no great cost to getting gas connected.

I would drop the solar thermal panels; the PV will give enough output to heat water for a lot of the year.

Given you have mains gas, I would use it! So have a DHW tank that is heated by a gas boiler and an Immersion heater connected to an immersun.

Or a thermal store heated by an Immersion heater connected to an immersun, with the output going into a combi boiler that is design to take preheated water. This setup has less thermal loses, as you are not using gas to heat a tank of water you may not then use. But it may not run two showers well.

Put 1 or 2 radiators on the boiler, as you may need heating at times, adding them has little cost.

Then spend the saved money on all the cost overruns..... Or better air-tightness, or passive house inspections.

If you go the PV and immersion route, make sure to get two coils - one at the top which is heated first and provides enough for a couple of showers and one at the bottom to heat the rest of the tank.

Probably best to go for on demand DHW if possible though.

About the space heating, sounds ideal for A2A HP if demand is so low? In such a case you probably don't need anything powerful so makes sense to split DHW from space heating (?).

Welcome

Have a look around Ed's site:
http://www.edavies.me.uk/2012/01/pv-et-flat/
He has done a fair bit of work on calculation performance and costs.

It is difficult to compare ST and PV as they don't work in the same way, it is not down to just the efficiencies. With ST you always need the collector to be at a higher temperature than the store. With PV it just needs to be producing power at the inverter to do something, even if that is just exporting to the grid.

The other reason that PV tends to win out is that it is simpler to install and maintain. Routing 4mm wires is easier than water pipes.

Hi lesp, I'm a newbie too.
Re the merits of solar pv with immersion-

A snapshot of our experience with a 3.25kw pv array, linked via an Immersun to one immersion coil in a 210l tank from mid May to mid August 2014:

South facing, Scottish Borders sun, we had four instances in four months where the gas boiler was needed to supplement the immersion. There are many other factors ie: I have a somewhat excessively lagged tank, we are a family of five but it is only the adults that daily use showers, baths were rare and weather loaded, the array is ideally orientated and unshaded, we run a dishwasher, hot-pipe runs to kitchen sink have been shortened, etc.

It becomes a bit of a game, adjusting patterns to suit the weather, although either side of these optimal months it was a game that the wife was less prepared to play... This is perhaps the crux of the matter, how much do you wish to respond to the elements? You have grid connection and mains gas, so unlike off-gridders, your system design isn't crucial. Ringi speaks da truth! Can you expand on saying that you don't need space-heating?

Mains gas is generally considered the best option if available i think.

I have a hot water cylinder in my airing cupboard with an immersion in it fior emergencies, this if fed by a second cylinder in my loft with pre warmed or even hot water made with surplus solar from previous dayd, in summer it gets too hot so I dump excess heat under my houdse for use next winter.

Then solar pv, no point in exporting if you can use it so get a piece of equipment to divert excess generation into your hor water, top first then bottom, when heated tell it to heat the second cylinder, when all three done direct to fan heater.

One control box wit three subsiduary relays to move the excess.

Posted By: lesp• Ideal size for DHW tank?
• Size of the thermal panels - more than 4.6m2?

i have 80 tubes say 8m2 connected to a 220l tank, recharge is super fast in most condition but i do need to duct heat away in high summer into AGS/solar dump under house also powers a couple of towel rails in bathrooms, but need a heat source for cloudy winter days (even with 80 tubes) i chose a wood burning oven stove (pertinger oven)

My 2 cents.

I would suggest that you should first quantify what your expected demands for space heating and DHW will be.

You haven't mentioned what size the house will be but I will pluck a figure of 150m² out of thin air.

So if you get to certified passive house levels your heat demand will be something under 15kWhr/m²/a so roughly 2,250kWhr/a and I would think that your DHW demand for a predominantly 2 person household would be around the same level.

So about 4,500kWhr per year in total. Assuming a current electricity price of 16p a unit that would be £720 a year at full rate electricity or probably less than £500 a year on E7.

So it is good to bear in mind that that is the maximum saving you can make against a simple hot water tank and either electric underfloor heating in the slab on E7 or a water borne duct heater in the ventilation system drawing off the hot water tank.

Of course RHI payments for some technologies distort that, so also have to be factored in.

I would suggest that you look at the new Panasonic Aquarius 3.2kw split air to water heat pumps which are specifically designed for low energy houses. If you get to Certified Passive House levels of heat demand then you will by definition be able to satisfy your heat demand via a duct heater in the ventilation system so I would go that route.

You should get RHI payments on the heat pump and use it for DHW for the winter and shoulder months and you should also go with the maximum permitted amount of PV and get payments for it also, your PV can be set up to power the heat pump in the summer months.

[edit] Just realised that you probably can't get RHI payments on the heat pump as you are on the gas grid but I'm not fully conversant with the rules as I am in Sweden.

Where to buy Panasonic a to w?