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 Solar Voltaic Panels & Air Heat Pump Combination

 

Page Update (2018) with 5-Year Data Set 2013-17

 

This page describes personal experience of installing solar panels on our roof together with a small air-to-air source heat pump. It gives summary data over the first 5 years 2013 - 2017 inclusive, and a link to an article that has extensive technical and financial endnotes.

Our 4 kW 16 panel solar voltaic system on our 35 degrees south facing roof. Every house in our street could benefit, saving money and carbon, but only two do. This is the air-source heat pump outdoors unit, a Worcester-Bosch Greensource. It draws 500 - 1200 W of power running normally.
My amateur enthusiasm for renewables began in Papua New Guinea in 1979 when I got set loose on completing this village hydro electricity system. Story here. The warm air from the heat pump blows through the house from this unit above the door. Gives around 4 units of heat for every 1 put in.

At the start of 2013 we installed 4 kW capacity of solar panels on our roof in Glasgow. The deal with feed-in tariff is that it is assumed that you will use half the power you generate and that the other half will be sold back to your electricity provider. In practice, most homes that try to live a green lifestyle will consume nothing like half of what they generate. Yes, if you put the kettle and the toaster on when the sun comes out, but for the mostpart, you will be drawing a baseload of a few hundred watts and giving away the rest unless (like somebody I met) you're heating the swimming pool.

When we installed our panels and I saw how well they were working, my thoughts turned to how we could use a greater share of of our power. I researched the options, and we ended up installing a small heat pump that takes heat out of the outdoors air, even when the temperature is below freezing, and pumps it indoors at an enormous gain to the energy put in. If that sounds contrary to Newton's laws, then realise that what you're doing is using energy not to produce heat, but to move it, like when you pump a bicycle and the end of the pump gets hot because you've compressed the heat that was in the air of the full pump length into a smaller space.

I published the story of what we did in a little journal with which I have a long involvement, and here you can download the Reforesting Scotland article: Wood, Wind and Sunny Govan (5 MB). On this page, you will also find pictures of our system, and a table with summary statistical information for the past 4 complete calendar years. I doubt that I will update this further, because I have produced this data on a constantly shifting backdrop of changing energy prices, modes of use of our house where we work from home, and increasing wall insulation. What I've tried to do for these years is produce a reasonably standardised view and to draw averages based on prices, tariffs and carbon intensity standardised to what they were in 2013. You'll see all those assumptions at the foot of the table. The bottom lines are:

  • Our domestic carbon footprint has fallen from 5.4 tons of carbon dioxide per annum, to just under 2.0 tons, a reduction of 64%.

  • We previously spent 1,405 per annum on gas and electricity. Now it costs us an incredibly low average of just over 100 per annum, calculated at 2013 prices for standardisation and inclusive of the feed-in tariff payments.

  • The complete system - panels and heat pump - have, as of spring 2018 which is just under five and a half years, paid back their costs. Note, however, that our roof is ideal for solar, and the design of our house is such that the warm air from the unit above the door blows it along the corridor and up the stairs to our offices, exactly as we need it. Note also that we have a wood-burning stove in the living room that burns offcuts, and such wood is counted as carbon neutral. Without that, our gas/electric consumption both before fitting renewable energy systems and after, would have been higher.

  • Over this five year period we have been heating far more of the house than previously as our work needs have expanded. We have also benefited from the air filtering and ionising by the heat pump and the asthma that I had been developing - we live downwind from the M8 - went away after a few months. Verene, my French wife, is particularly happy. As I was posting this she reminded me how she used to burn herself on hot water bottles that she'd be carrying around in winter. I've stopped getting complaints about "your cold and rainy country" ;)

  • I will not be producing further analysis in this form because too many parameters have changed. Energy prices have shifted, the carbon intensity of Scottish electricity has dropped, and during 2016 we added insulation to our house. The basis for comparison has therefore been a shifting one, but nevertheless, the underlying pattern of radical gains from these technologies is clear.

  • It is tragic that the UK government has cut its support for domestic energy production and conservation. It can be argued that money is better spent on big projects, but that ignores the empowerment and awareness of helping people to take their own responsibility.

   

 Download the Reforesting Scotland article: Wood, Wind and Sunny Govan (5 MB)

 

 

Alastair McIntosh

(Author of Hell and High Water:

Climate Change, Hope and the Human Condition

Last updated: 10 July 2018

 

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