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What size House Battery

So I need an idea of the size of House Battery to get.  To Store the excess solar energy from our solar panels.


Well the CUMonitor plus the tel-tec web calculator lets you model the problem so you can try out different house battery capacities at the different times of the year. see example logging data here.

If you are interested in joining the CUMonitor user group fill out the form here. Note you will have to purchase a CUMonitor box to log your house it you want to take part as a member

The Battery size is entered at the top of the page and the first (light green) bar chart is of the Power remaining in the Battery and the second is the Power from the solar panels. The Assumption is made that the 24 hr period starts with the Battery full.

Some CU Meters have an LED that illuminates when the Meter is exporting the to Grid CUMonitor can optionally monitor this or use an internally calculated flow,

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Actions to take before getting an EPC

Before getting an EPC there are a number of measures we can take to improve the outcome of the EPC

  • Fit energy saving lighting
    • We already have energy efficient lighting
  • Double glaze all windows
    • We already have double glazed windows
  • Improve loft insulation
    • We currently have 10cm of loft insulation this should be increased to 27cm
  • Cavity Wall insulation
    • We have cavity wall insulation. But this was done to the property before we bought it and we have lived here for nearly than years. I will see if we have any documentation for this.
  • Upgrade to an efficient boiler
    • Our gas central heating boiler is a condensing boiler and less than 10 years old. Nominally considered efficient so our energy rating from this should be OK

The main deficiency our house has is the loft insulation. So we will increase this to 27cm.

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To apply to join the RHI you must have a current (within two years) energy performance certificate EPC. The EPC needs to be generated by an accredited energy assessor. Which essentially means you have to pay someone to assess your home. The sort of questions you have to answer are:

  • When was the property built? When were any extensions and conversions made?
  • If you converted the loft into a room, when was the work carried out?
  • Has the property been inspected for, or does it have any cavity wall insulation?
  • Have you very recently added any double glazed windows or doors?
  • Does the property have any under-floor insulation? Can this be seen, or do you have the receipts for this work?
  • Are you on a single or double electricity meter?
  • Have you installed any heat recovery technology

The rating of your home will depend on many factors. But typical recommendations are :

  • Insulation for your floor, roof, loft or walls. Better insulation reduces the need for heating, thereby lowering your energy bill.
  • Double glazing: windows keep in significantly more heat when they’re double-glazed, again reducing the need for heating. Solar panels: these produce cheaper, greener energy.
  •  Low-energy lighting: a smaller change that involves no structural alteration, using low-energy light bulbs is a cheap, easy way to lower energy bills.

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The most cost effective way forward appears to be applying for the RHI (Renewable Heating Incentive): The Domestic RHI is A government scheme to pay incentives for using renewable heat.

Options include:

  • biomass boilers (Our house is old enough to have chimneys but is in a smokeless area)
  • solar water heating (Our house has solar panels fitted on the south facing roofs)
  • certain heat pumps (The plot our house is on has space for either a air based heat pump or a ground based heat pump)

We will consider each in turn.

Biomass boilers:

  • Burn wood or pellets which require storage :
    • We have room to store fuel for a biomass boiler.
    • Fuel will need to be bought in.
  • Require manual feeding (CON)
  • Can function on demand(PRO)
  • Require tending ash disposal and cleaning (CON)

Solar water heating : Our southern facing Roofs are in use so this option is not suitable. We have out buildings that may be used but the piping and insulating of water to these locations make this problematic.

Heat Pumps :

  • Air source heat pump
    • Electrical power required to run pump.
    • Requires suitable space away from property boundaries
    • Lower Operating temperature requires resizing of radiators (CON)
    • Potential for icing in cold weather (CON)
  • Ground source heat pump
    • Electrical power required to run pump
    • Requires more space close to the house (CON)
    • Lower Operating temperature requires resizing of radiators (CON)
  • Heat pumps have a COP (Coefficient of performance) a good COP is anything over 3 with 4.5 being the max possible. The heating for our house for the last year required 26834.5 KWH. Assuming a COP of 3 we would need 8945 KWh of electricity to do this. About 50KWH per day in winter.

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The scale of the heating problem

Trying to quantify the heating requirements for the house: Using the last year as a benchmark, we consumed 1669 m3 of gas – found by subtracting last August’s gas meter reading from this years. This equates to 53669 KWH purely from the calorific value of the gas. The last year was unusual due to the pandemic (more time was spent at home) and the heating was set to run from the thermostat for about 50% of the year. Our bedrooms are heated to 20 Celsius with the rest of the house running colder but acceptably so. So if we use this as a benchmark we would be in the right range. Assuming the boiler is 50% efficient at turning power into heat, the power required to heat the house for the last year was 26834.5 KWH. This ignores the gas used to cook food as this can be assumed to also heat the house.

Starting point

We will aim to keep the same level of heating with a new green heating solution and re-use as much of the plumbing and infrastructure as possible to minimise the cost of the upgrade.

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Understanding the problem

Before you can find a solution you need to know what the problem is. We have solar panels. How much power do we generate? How much of that do we use locally? How much goes back into the Grid?

There is a need to quantify these figures (so being an engineer) I have created the CU monitor to measure these electrical data. Any heating solution is likely to need electrical power and knowing what we can source from the solar panels is a factor we need to quantify.

Currently our heating is performed by a our gas boiler. We may use the fuel burnt by this to approximate our future needs, or at least how much energy it took for a year. How much gas did we use in heating the house and cooking our food in a year?

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How to step forward into future energy

The Government is trying to find ways to make fossil fuel heating in homes a thing of the past. But the way forward is proving unpopular With the Government’s commitment to renewables it’s only a matter of time until it becomes punitive to do nothing So I am taking some positive action. My mission is to find a cost effective way forward.

The current energy state of our house:

  • 10 years ago I joined the minority of UK householders who paid to have solar panels fitted. These have generated power steadily and reliably for all that time. The FIT (Feed In Tariff) paid for the installation in about 6 years. The FIT payments are due to continue for another 10 years.
  • We have gas fired central heating.
  • Our house has cavity wall insulation and 10cm of loft insulation.

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Goals aims and reasons

I am an Engineer educated in Chemical Engineering, Electronic Engineering and Software Engineering. I can see solutions to problems that no one  is solving. This website  it my attempt to take my solutions an share them with the world perhaps this is pretentious and no one will want my solutions and I’m OK with people who think that. Perhaps my solutions will genuinely help people (which is my hope) and if I can make a little money from the venture that works for me.

Solutions and their  focus:

  • Renewable energy : I think everyone needs to make this a priority and I have electronic solutions for people with legacy solar systems to try to optimise energy generation and usage.
  • Electronic and or software projects: These are solutions I am developing to problems I see. Mainly IOT and Domestic LAN in scope.
  • Gaming: There are solutions to Fantasy Role Playing games like D&D or Online Gaming that I have solutions to.

I will document the problems and my solutions to them is this Blog.