We quite often get asked by prospective customers "I want a solar p.v. system so I can use it to power my heat pump" because, hey the Sun is free, right?  And therefore the electricity generated by the Sun is free as well?  Right?

....So If we use the free electricity to run the heat pump we'll get free heating & hot water!  Here's where you need to hit the "Pause" button, rewind a little and think about heat and when you need it, compared to sunshine and when you get it.  Ready?  Press "Play"

A typical solar p.v. installation of 4 kW (could be larger but lets not confuse the issue just yet) in our Latitude will generate around 3,500 kWh of electricity per year.  At current prices from Octopus, you'd be saving the equivalent of 15p for every unit you can use - that could be equal to around £525 a year.  All well and good (lets ignore the Net Present Value calculations of the £4-5,000 you've invested in the solar system for the moment).

Problem No. 1 - See graph!  When you most need heat is when the p.v. system is at its most inefficient - cloud cover, shorter daylight hours, Sun low on the horizon....

Problem No. 2 - What are you consuming at 0500 in the middle of Summer to make the most of the p.v. system output?  The heat pump is mostly producing hot water for you - no need for space heating...

Solution No. 1 - store the surplus electricity in a battery!

Lets do the Maths - assume you can use 40% of the electricity generated in real-time, that leaves around 2,100 kWh to be stored and used later.  That 2,100 kWh is worth around £315.  How much did you pay for your Tesla Powerwall?  £8,000+ you say? So, that's a (£8,000/£315) 25 year payback - and we haven't even considered the reduction in storage capacity due to repeated cycling (main problem with current battery technology), child labour involved in mining Lithium in the Congo and let's not forget that £8,000 invested now is worth a lot less in the future....

You trust them Right?  Manufacturers?  Well, they spend lots of money advertising and researching and manufacturing so that you get exactly what you want - Right?
Except, what you thought you wanted, is actually not quite what you needed.....

Let's take POWER! (as Jeremy Clarkson might say) - we do all the hard work, assessing your property, checking the levels of heat you need, the amounts of hot water, how draughty it is etc. etc. and then we go off and configure a system for you that's just right - I call it the "Goldilocks" solution.  Anyway, there you are, reading our erudite proposal that says you need a 16kW heat pump for your Bijou residence to make it always warm and cosy.  Hold on!  Your mate down the pub says he got one off of eBay for a song and it was 11kW and his house is the same as yours, so why are you paying extra for all that gear?

That's where you start to suspect the manufacturer didn't quite tell you everything you needed..."yes", they admit, "our heatpumps do generate 16kW of heat.......but only at 25°C outside air temperature..."  "Sorry?!" you say "at 25°C?!  Why, I actually don't need any heat when its that hot outside!?"  "What about when its actually cold - say -7°C?"   .....and that's when they say "...errr, well,...actually...err, it only delivers -cough - mumble -###kW - cough" - "Sorry?" you say "Exactly how much?" - " mumble - inaudible...11kW....".

So there you have it - much like the 98mpg claims (but only in Death Valley with tyres at 60psi, all seams taped over and driven by a butterfly) - "yes, under certain circumstances (please read the detailed specifications whilst taking a Master's Degree in Thermodynamics) our heat pumps do output 16kW - just make sure you speak to an expert before you go and buy one - you may come up short."

Ironic isn't it?  Here we are, working hard to minimise CO2 production to save the environment - and would you believe it?  The most efficient form of heat pump technology today, and something that, if properly implemented, could blow away expensive, messy ground source systems is - wait for it...based on CO2!

The Q-Ton CO2 air source heat pumps from Mitsubishi are exceptionally efficient and, coupled with a class leading HIU (that's a Hydraulic Interface Unit - clever valves and software), can give SCoPs of 6+  At the moment they are only 3-phase and 30kW in size, but once they are scaled down for domestic use, expect a large shift in uptake.  If you (or your friends & neighbours) need 17,000l of 60°C hot water a day, you know what to buy!

Heat losses are a little bit of a "Black Art" in that, academically speaking, where all the values are known, they can be calculated quite accurately.  However, layer onto that the fact that the ų-values of walls built many years ago are at best, a guess, as well as the fact that people's lifestyles vary in terms of what levels of heat they find acceptable and that even manufacturer's output figures are dependent on other variables means that we can only offer a guide within the confines of the regulations.
It may well be that a 14kW ASHP would be perfectly adequate for all your needs, but we don't know until we install it - and even then, it needs to conform to the "academic" regulations in order to qualify for the payments.