Heating News Spring 2021



Microinverters have passed an important tipping point and will soon be all the rage, but first, what are they?  Grid tied PV panels usually feed high voltage DC current to a single inverter which converts that power to 240v AC. High voltages present safety issues and shading can reduce efficiency of the whole set, although, as thousands of examples testify, this system works well enough. But there is another way gaining traction – microinverters. These neat little boxes bolt up under each solar panel and make 240v right there, on the spot, with simpler wiring too. At a stroke the shading problem disappears, voltages are reduced and individual panel monitoring is possible. The monitoring is the best bit with the whole array mirrored on your PC screen. Each panel shows how it is performing and all the relevant history is retained for your viewing pleasure. The system is completely expandable and more panels can be clipped on at any time. The only drawback is higher cost with prices around £100 for each microinverter compared to a single inverter like the £1,000 Sunny Boy 5kW, but as you will see below that balance will soon swing the other way.

Panels – More power for same money

The case for going solar gets more compelling by the day. How about an all black JA 370W for just £130! Three of these with micro-inverters would cost £690 plus fitting etc so the ball park is around £1,000 for 1,000W of power (or better) and just over 1,000 kW.hrs a year of production. 1000 for 1000 for 1000!

So how many panels do you want? And what do you get back? Well, that 1kW pack of 3 will make £180 worth of electricity (at 17p/kW.hr) if you consume all they make, but only £58 if you sold the remainder to Octopus for 5.5p. That makes annual paybacks of a rather good 5.5 years or a bad 17 years so there must be a sweet spot in the panel count. Your background domestic consumption with lights computers and fridges will often be around 1kW so the first 3 panels/1kW are definitely worthwhile. However because panels rarely produce their rated output, and never in winter, the first 9 panels/3kW should be deemed good. All the rest will  boil kettles and run appliances from time to time but after around 4kW and 12 panels any extra will be bad ones unless you can increase your self consumption. One great way of doing this is to route any excess production to your immersion heater and a SOLiC 200 for £195 will do that for you. With that fitted your 12 panels will always be enough to spin up a domestic appliance with all the excess being used to heat water and give a 5.5 year pay back. A couple more panels might be justified to give better utility without diluting the payback too much so it looks like 14 panels might be the sweet spot for most households. All this kit is expected to last for 20 years: pretty compelling when electricity prices have been increasing by 8% a year.  If that 8% persists then payback falls under 5 years and you’d recoup the same amount again after just three more years and then 10 times your money over the expected life of the panels. As I say, it’s pretty compelling

 Of course, if you are running a heat pump then more self consumption will justify more panels but If you have town gas you’ll be making hot water much cheaper than with electricity and that will drop your panel count.

And what about car charging you say. Well, yes, that too makes for more self consumption but, just to rain on that parade, Octopus are offering power for car chargers at 5p/kW.hr for 4 hours a night so don’t up your panel count too much and maybe not at all.

Astonishing high power panels – 540W!

High powered panels are here. For example Canadian (it’s a company) are offering a 540W panel for £200. Expensive alright but with micro-inverters it’s a game changer. Take our 3 panel set above for 1,020W and, with 3 micro-inverters, £690. Then compare 2 x 540W Canadian panels for 1,080W and only 2 inverters for a total of £600. Overnight, higher powered panels have made microinverters the best choice. The best you can get is the cheapest option. No doubt that is going to be the way forward from now on and it would make sense if panels started to come with inverters built in too.

C.E. approved ground source pump for £1,600

You might recall my design for a hybrid ground source heat pump that optimally combined air and ground heat sources. Full RHI payments and less digging etc. If you are contemplating this you’ll be interested to know that a 10kW C.E. approved ground source heat pump unit can be found on Ebay for £1,600. That makes a great start when you think that around £20,000 is the usual cost of a regular installation.

Mini-split heat pump – up and running

We had an unheated laundry room and a small Mitsubishi mini-split (an air to air heat pump) has made a perfect addition. It heats the room while blowing warm air over the clothes racks. In summer the cooling setting will make ironing bearable and some cold air will spill out to make a cool refuge in the adjacent room. Brilliant.

The kit was installed in about 4 hours and the total cost, fitted, was under £1,000. As soon as the solar panels are installed it will run for free but when I checked recently it was only drawing about 350W so no stress there. Solar panels output can be excessive in the summer so running the air conditioning will increase self consumption and be guilt free too.