Just realised!! The boilers are thermecon bfo190 and bfo80/95 verses two mega flow one 300 litre and I guess the other slightly smaller. My maths wasn't partically good at school

air source heat pump is cheaper and greener than oil or electric.

Edit: if you already have oil installed, its cheaper and greener than electric.

Posted By: dilangarJust realised!! The boilers are thermecon bfo190 and bfo80/95 verses two mega flow one 300 litre

If your choice is between an existing thermecon Oil boiler and an existing megaflo with electric immersion coil then the oil boiler should be a lot cheaper to use. Possible exception would be if the electric is on E7 or some other discount tariff. Even then need to do the sums.

http://www.nottenergy.com/energy_cost_comparison/

E7 may cost more by the kWh, but has less seasonal price fluctuation, takes up little space on site and can be used for 'other things'. You may or may not have noticed that when we have a price increase in gas and electricity that th erise in electricity is generally less than gas, this is because gas prices are currently linked to oil prices (though they have not come down in the last few weeks but probably will). Long term (over 20 years), the price of electricity will probably be linked to the price of nuclear and wind, with only a small part based on gas and oil prices, unless we sort out CCS on coal fired, then about 30% more than today's coal generation prices.

May be worth looking at the installation costs of an E7 system versus and ASHP versus an Oil Burner.

Your water type may effect the maintenance, I am in a soft water are and my E7 system is now about 26 years old, but when I lived in a very hard water area it lasted less than 10 years.

Also think about how much water you use, halve that and you almost halve the running costs.

Yes, why usage patterns are important. Last year my mean price all in was 10p/kWh, which is cheaper than standard electricity at 12p.

Posted By: woodgnomeunless you use most of the water in mornings.

E7 is fine for using water any time of day because you know that there is a consistent supply of energy every night.
Solar is the issue here as if your store is already at maximum temperature when the sun comes up, you are not going to be able to pump any more energy into it. So no point in having the ST system unless you are going to discharge the hot water at dawn (as long as Dawn don't mind).
One way around it is to pre heat the header/feed tank with solar and then let the E7 top up if needed. More plumbing and tanks though.

Starts to get complicated now, and complication is just another work for cash.

Not as complicated as an oil burner though.

Yes, or the temperature is higher.
Pretty easy to work the amount and temperature needed for a typical day, not so easy to work out the amount of solar on a typical day.
Not that I am saying that it is not a valid way to heat water (solar that is), just that it is not the most reliable for the money.