Schema of the whole idea:
Interseasonal thermal storage
The idea of 'Charging the Earth' is to RECYCLE SUNSHINE! The practical method is in having south facing solar collectors on the wall whose purpose is to pump solar heat deep down into the ground. The building's heat pump gets all of this back immediately or later. Along with the PV roof, the house is Net-Zero carbon emitting for heating. Despite 2012-13, a recent year of rain and overcast conditions, it is nearly Net-Zero to include hot water.

Our aim is to explore four ways in which solar-air collectors can augment a ground source heatpump, thus increasing its coefficient of performance, and reduce its power consumption:-
  • by Realtime heating in Winter (supporting the heat pump while it works, based on the 'delta-T' between pumping circuit and panel), 
  • by thermal charging Diurnally in Equinox times (storing heat on warm days to help the GSHP on cold evenings) 
  • and by thermal charging Interseasonally in Summer (storage of thermal energy helps it through the winter). 
  • The realtime mode also works in all seasons as a form of Restorative action, immediately after the heat pump has performed a heating cycle.
The Sunboxes Mar'10 to July'11:
rebuilt during August 2011 
Our Heatpump is a Swedish IVT Greenline C6, from Ice Energy. The thermal collectors charge from Sunlight, but because they are enclosed in glazed boxes, they can also pick up heat from Warm Air caused by the greenhouse effect. This makes our system into a combined "Solar-Air-Ground hybrid source Heat pump".

The name of the blog is intentionally a double meaning - Charging the Earth implies 'filling the earth with power or heat' (as I use it). It also implies 'making the product very expensive'! Well that is an intentional pun, because that is what Energy will become - in our quest to burn energy fast to maintain our wasteful lifestyle, we are literally using more resources than the planet can provide sustainably.
So can this technology be used to get closer to carbon neutrality? The answer, in the case of this house is Yes! We have done it!

  • Borehole drilled: Nov 2006
  • Heat pump installed and house occupied: March 2007
  • Early 2009: Dissatisfaction with performance of heat pump, compared with expectations.
  • Charging idea, Metering and Blog started: Aug 2009
  • PV installed: Oct 2009
  • First Sunbox system March 2010, with 'parallel' circuit.
  • May 2010, the circuit was modified to 'serial' to flush entire ground loop through solar sunbox.
  • September 2010: Aluminium sheets added above and below as 'mirrors' to boost thermal capture.
  • July-August 2011, the original Sunboxes have been completely rebuilt, with 70ยบ sloping fronts and triple wall polycarbonate walling.
  • Nov 2011-Mar 2012 - Second full winter with Sunbox actively augmenting the Heat Pump.
  • Feb 2012: Decision to instal evacuated Tubes.
  • Mar 2012: Change circuit back to parallel (Trickle-all-the-Time) layout.
  • Mar 2012: Evacuated tubes fitted, but in direct linkage to ground loop they do not work.
  • April 2012: DNC's paper to CIBSE on design and performance of the solar charging system wins audience vote for best paper at 2012 Annual Technical Symposium
  • April 2012: Major leak in Sunbox circuit, repaired with new expansion tank.
  • May 2012: Heat exchanger fitted to Evac tubes circuit, now working well.
  • July 2012: Thermal model developed: establishes curve form of borehole energy level.
  • August-November 2012: Construction of House extension.
  • October 2012: The south facing parts of the polycarbonate panels have been replaced with ETFE panel fronts, donated by Holscot. The mirrors have been removed.
  • December 2012: Additional Sunbox placed on the roof of the house extension using 2 sqm of metal radiators, designed to test the idea of unitised Sunbox construction and small bore pipes.
  • April 2013: DNC's paper to CIBSE on thermal modelling of the solar charging system wins audience vote for best paper at 2013 Annual Technical Symposium
  • May 2013: Scaffolding up, to replace tee-piece between panels - to solve leak.
  • July 2013: Leaking hosing repaired, without needing scaffolding. 
Our two storage boreholes go 48 metres below the house, reaching directly to about 6,800 tons (3600 cu.m) of mixed clay and rock, with an infinite mass beyond that. Theoretically that means we could need to get more than 60 watts/metre when the GSHP is working, and as clay is expected to yield 40-50 watts/metre, we could expect a progressive chilling, unless we put solar heat down.

With successive years, the soil temperature does
not fully recover in summer, until a new but lower
equilibrium is achieved.
• How much of the heat put down will disperse into the mass of dense soil surrounding the boreholes, and how much will we get back (assuming that a surplus of summer heat leaks away)? (So far the finding seems to be that All of it comes back, because the rate of losing heat is so slow that by the time it is about to get totally lost, it is October and the heat pump is sucking it back again)
• How much electricity will it save annually? (We save electricity by having PV, and in addition, the heat pump augmentation reduces our former annual consumption from an annual average of 8,500 to an average of 5,000 kWh)
• Will the heat pump's COP (coefficient of performance) be improved? We are still finding out. (It's looking good so far! As the effect of these accumulates, the figures show that the house is carbon zero for heating and for hot water. A former GSHP consumption of 5,200 kWh is reduced to 3,000 kWh.)
• Will this work just by heating the soil and doing a direct exchange to get the heat back, to save the cost of a heat pump? (You need a heat pump, which moves Energy from one temperature to another. Deep thermal storage is actually quite cold, 8-12degrees, and houses need temperatures of 30 for the underfloor heating and 52 for the hot water. Only a heat pump has the control to do this.)

Heat Pumps also have a SPF (seasonal performance factor) in which the COP has seasonal variations - HPs work more efficiently when the energy source is rich, compared to the demand. Solar earth charging that contributes directly to the borehole and replenishes immediately after each heating cycle improves the SPF. It causes the HP to perform as if it is Equinox during the Winter, and as if it is Summer during the Equinox. During the real Summer, the HP has little to do, but the energy can be stored, stored, stored!

A prime definition of Sustainability is the 'capacity to endure'. In my view, a standard GSHP may be sold to you as 'sustainable' technology, but I don't believe it is if there is progressive permanent chilling of the ground. By maintaining the ground temperature at 'tip-top' condition, we are enabling the heat pump to be more sustainable, run more smoothly with fewer operating hours and less use of 'direct heating'.
     Part of the research in this project has been to avoid using a commercial solar panel, but to evolve a solar collector that is much cheaper and uniquely suitable to this purpose of recharging the earth, by exploiting the 'solarium' effect in a glass box - these ones work on cloudy days and even at night. An industry standard solar panel could have been used, but would need a large water storage tank or heat exchanger, and quite different plumbing. The wall panel system that has evolved with Sunboxes works better in winter and is easier to build and maintain. See the System page on this site for a comparison.

3D schema of the south facing Sunboxes and
the link to the Heat pump on the ground floor
Since March 2010, the Surya Sunbox system has been working, and we are reducing electricity consumption and heat pump workload. Meter readings of everything are taken every 1-7 days, and the results are published the results on the web, including weekly summaries of the key performance indicators. In the first year since installing the PV roof, we reduced annual electrical consumption by 30%. In the following year, 2011 with the Sunboxes operating, we experienced further reductions in energy consumption, recalculated weekly. We have completely rebuilt the Sunboxes to form one large Sunbox and it is about 7.5% more efficient, so far. During 2012, we have added 2 sqm of Kingspan evacuated tubes, and in Dec 2012, we have added 2.0 sqm of roof mounted sunbox with metal radiators panels, each of which are independently controlled and monitored.

How do these things get made? Can they be found in B&Q? No, they have been made by the author. I have a philosophy, which is, that if the thing you need doesn't exist, DESIGN it, MEASURE the site precisely, and then MAKE it! If it is going to be complicated, the DESIGN process subdivides into Sketch it out first, Model it in 2D drawings, Model it in 3D models. Do this before you cut any metal or order materials.

The east roof of the house is now fully Photovoltaic (PV). There is also quite a lot about PV micro-generation on this blog site. PV is also part of the overall Solar House project, and may be of great interest to the blog followers, because the feed in tariffs (since April 2010) make it into a very good investment that helps you have zero energy bills. Home generation also reduces burning coal or oil at centralised power stations, and the consequent transmission losses. It is a further component in reducing our total carbon footprint, and the surplus power is eagerly purchased by Good Energy, our supplier. If the entire electrical consumption of the heating system is less than or equal to the entire annual output of the PV, then the house is Net-Zero.

3D schema of the house related
to the volume of the boreholes
The Concept and the Technology
The Solar Thermal collectors for our Solar earth charging are SolarFocus swimming pool panels positioned vertically on the South Wall. They are enclosed in Polycarbonate sunboxes, to maximise the air temperature. We call them Surya Sunboxes, named after the Hindu Sun-God. As they have evolved, they have increasingly come to resemble Solar Cookers, of which there are millions in rural villages of India and Africa - I like that, and the results show it.
    When the thermostat decides there is enough temperature difference, it diverts part of the liquid in the ground loop up to the solar collectors, and then to the ground. The ground loop is to the north of the house, and the volume of the earth that we are warming is the shape of an overlapping pair of bottles. Normally the loop circulates at 5-6 litres/min, and injects this into the flow, even if the heat pump is asleep.

Are we really going to raise the temperature of the earth significantly? The answer to this is No! - the house pulls about 9,000 kWh/annum out of the ground, and our solar collectors put down 3,000 kWh/annum. What this will do is to reduce chilling of the ground. This difference of approx 3-1 ensures that all the heat we put down will come back up to the house.  
    This makes the Sunboxes very efficient - they manage to capture about 1,800 kilowatt hours in Summer (average 1.1kW) and 1,000 kilowatt hours in Winter. The rest of the heat needed for the house comes from the vastness of the remaining earth around our boreholes, heated by solar warmth landing on the tarmac and fields around.
New sunboxes under construction August 2011
   A recent visitor, since Sept 2011, will notice that the shape of the sun boxes has changed markedly. They have sloping fronts and nearly 3 times the volume inside. This has been my major construction project during August 2011.

The scientific principles behind ground storage are discussed in more rigorous detail under the title Seasonal Thermal Store. 'Solar Earth Charging' as I call it is just a Concept but it is also a Technology arising from the concept - the Materials, Components, Systems and Control mechanisms required for the practical application of this process of Seasonal Thermal Storage on real life buildings.
Note, that we do still have a net import of power from the Grid, because we still need it for lighting, cooking and appliances. But for the building emissions (as opposed to lifestyle emissions), we have achieved a balance of the regulated quantities, as metered daily.
Therefore, this project and this blog is mainly about the evolution of this new Technology - hybrid Solar-Air augmentation of Ground source heat-pumps. In the long term, I hope it can be manufactured and replicated in other buildings. The Blog honestly includes all the mistakes, the diversions, dead ends, joys, sadness, tweaks, helpful ideas, the delays etc that happen inevitably. I try not to go back and alter things that were written. And finally, if we prove the concept, there may be more.

Thermal modelling diagram illustrates energy levels in borehole
based on data recorded from Oct 2009 to Feb 2013.
There is a rapid fall off in winter, with a long slow climb-out in summer.
Without solar charging, the energy level recovers at a lower than at the start.
A small amount of charging maintains a good energy level even in cool years (2010)
and raised the level in a warm year (2011). 2012 was a rainy, cool year, and we enter 2013
with reduced energy level.

Written work: My PhD colleague did a presentation in Shanghai at the global conference of Sustainable Energy Technologies August 2010, exactly a year after starting this research. My head of department presented an updated version to the Istanbul conference in September 2011, with the benefit of a year's worth of results to prove that it worked. I've written about it for a conference in Ningbo, China, and for CIBSE/AHRAE Technical symposium, London in April 2012. My paper for the April symposium won the audience vote for best paper of the event.
   Things are moving along! I added 2 square metres of Kingspan Varisol Evacuated Tubes in April 2012, to test the effect of a high temperature contributor to the charging. We are planning to add 2.7 sqm of PV-Thermal in Autumn 2012.
     If you know of another somewhere on a single house, please write to me as the only other ones I know of are large group projects, headquarters buildings, or have insulated silos to store into. Ice Energy have supplied this project with technical advice, plus essential pieces of kit like thermostats, pumps and flowmeters. Kingspan and MG Renewables are supporting the 2012 part of the project using evacuated tubes.
I did a lecture to CIBSE in 2012 which earned the 'best lecture' award, see the link:

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Blog started 17 August 2009.

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