My Plan to Achieve Energy Freedom - The Road to Zero Energy Bills

(I had to split this post into several posts as I was having trouble linking from external images, and had to use attachments which have a limit of 5)

I started this project five years ago with a simple question: how can I provide for my children's future, whilst ensuring they have a future? That means finding a solution for life that's reconciled with climate change, but in a way that creates wealth and positive returns. Technologies have done us all favors in this regard and I found myself investing in a few simple measures early on that allowed us to save for bigger changes, which saved more money. We saved as much of those savings each month as we could so we had a pot of money that was growing increasingly quickly with money we otherwise would have just spend on light, heat and transport. They were things like replacing our petrol car with a second hand electric car, cycling rather than owning a second car, installing double/triple glazed windows, installing LEDs throughout the house, and adding attic insulation.

Six months ago, we took these accumulated energy savings and invested in achieving a low energy cost household. We wrapped the house in insulation, we switched the heating from gas heating to an electric heat pump, and we installed a 5.8 kW Solar PV array. Additionally, we replaced the gas cooker hobs with electric induction hobs (Ikea sell them starting at €39) to fully remove gas bills from our house forever. We had already switched to an electric car from our old petrol car. Our house now requires a lot less heat, that heat comes from an electric heat pump, and for a lot of the year, that electricity comes from Solar panels on the roof.

All of this is in a bog-standard 1980s three bed semi-d originally built with minimal thought to running costs. If we can do it, anyone can. Five years ago, our energy costs across our car, heating, hot water and electricity totaled €4,703.56 per year. Now they total €778.13 a year.

Had we changed nothing and continued with our 2015 baseline, over the next 10 years we would have spent €47,035 on the energy required for our lives. Instead, with the changes we've made, we'll spend €7,781, freeing up €39,254 and giving us a lot more financial stability. One of the key lessons we've taken from the unpredictable nature of the last two years is that finding ways to earn more money is really hard, and when you do, you pay a lot of those increased earnings in tax. We've realized it's a hell of a lot easier to spend less money that it is to earn more, and the net effect on our cashflow is the same.

SolarPV
We had already installed a 2.5kW SolarPV system on the front of our house three years ago, but as we now are heating our house with electricity, and powering our car with electricity, I saw it as a financially positive investment to increase the size of our SolarPV system to 5.9kW by adding extra panels on our flat back roof.


Our day rate is €0.1874 and our night rate is €0.927. Our SolarPV system generated 1850kWh of electricity in the first 4 months of operation, but this was spring and early summer. Based on previous data from the smaller SolarPV system we had, year round, it will generate 4,260 kWh per year. The battery soaks up almost all export, but I think we'll export about 250 kWh per year, mostly during stretches of long blue-sky days in May/June. That leaves 4,260-250 = 4,010 kWh per year that we'll consume, offsetting the need to pay for it. Taking a simple day rate calculation for the value of this electricity is €0.1874 * 4010 = €751.474 per year. The figure is more complicated for two main reasons:
(1) Detracting from this net impact cost, some of the electricity consumption the SolarPV offsets, we would otherwise have consumed at night rate (€0.927). I estimate this to be about 50%. So (4010 * .5 * €0.1874) + (4010 * .5 * €0.0927) = €561.60. The SolarPV system cost €5,198 after the €1,950 grant so the yearly ROI is €561.60 / €5,198 = 10.8% . It's warrantied for 20 years, so the full payback of investing in solar will be in the region of 561.60 * 20 = €11,232. Higher if energy prices go up, which they are very likely to do.

(2) If your original baseline is a petrol or diesel car, and you switch to solar, putting the solar generated electricity into an electric car would save more as it is saving money you otherwise would have been spending on petrol. A litre of Petrol contains 12.8889 kWh, burned in an internal combustion engine with a max. efficiency 38%, so your €1.26 litre of petrol gets you about 4.8kWh, or €0.2625 / kWh. So if you're doing calculations on making a big switch to cut costs in your life by switching to SolarPV + an Electric Car, and you put 2,000kWh of solar into your car, that will give you an extra bonus saving of 2,000 * €0.2625 = €525.00 ( 2,000 * €0.1874 = €525- €374.8 = €150.2

Here's a day in May - solar generated 23.7kWh of electricity. We consumed 21.9kWh of that between powering the house, heating water in the hot water tank via the Heat Pump, and the excess went into the battery. The electricity stored in the battery continued to power energy consumption of the house after the sun went down. So of the total of 21.9kWh we used that day, we imported only 2.7kWh from the grid. Our electricity bill in May was €15.18 - it's quite remarkable to me that on sunnier months like this, we can power our house, transport and heat almost entirely from solar.


If you're working out a solar installation for your house, the SEAI grant will pay you €3,000 for a 4kWp system with a battery, €2,400 for a 4kWp system with no battery, and €1,800 for 2kWp system of about 8 panels. This would fit within the 12m^2 size which requires no planning permission even if it's on the front of your house. Also, the Irish government are mandated by the EU to introduce a feed in tariff scheme by the June 2021, so people with SolarPV installations will be paid for excess electricity back to the grid.


Battery
The battery saves money in two ways: in summer, it stores excess solar which would otherwise have been exported. Looking through the summer figures, the resultant stored solar we used about two third of the time during the day rate (€0.18 kWh) and about a third during the nighttime (€0.09 / kWh). We stored an average of about 5 kWh per day over those 6 months - maxing out the 8.2kWh of storage almost every day during May, June and July, and averaging about 3kWh a day in April, August and September. That translated to a saving of 6 * 30 * .66 * 5 * €0.18 = €106.92 +
6 * 30 * .33 * 5 * €0.09 = €26.73 . So €106.92 + €26.73 = €133.65 per year in the summer months for the battery.

Secondly, in winter, we can charge it at the night rate (€0.09) and use it to power the house to avoid the day rate (€0.18), saving €0.09 per kWh. We do this for the 6 less sunny months of the year, offsetting 8.2kWh of daytime consumption every day, so saving 6 winter months * 30 days per month * 8.2kWh * €0.09 / kWh saving = €132.84 per year.


The battery thus saves €133.65 + €132.84 = €266.49 per year. The battery's net cost was €1900 which gives a 1900 / 266.49 = 7.1297 year payback of the battery, or a 14% yearly return (266.49 / 1900) if the full cost of the battery is written off at the end of the 7 years.

So, right now the battery is not a positive investment. It may be in the future when homes are rewarded for providing flexibility to the grid. It does also provide one other thing however - continued power in the event of a grid blackout. The SolarPV and battery inverter system comes with a power back-up connection which provides a power outlet which will continue to work if the grid goes down. The SolarPV system continues to work with the battery, but not the rest of the house or the grid which is a legal requirement. This means that if the grid goes down, we can continue to power key appliances and the car indefinitely with solar in the event of a prolonged grid blackout. 



Insulation
Insulation is not the most exciting of things to do but it is by far the most important of anything listed here. Before installing SolarPV or a Heat Pump, your house should be really well insulated. A few years ago, we replaced all of our windows with double glazed windows, installed a new airtight front door to stop drafts and insulated the attic. This time we finished the job. We wrapped (e.g. installed external insulation) on the side and back of the house, and installed internal insulation on the rooms at the front of the house (as modifying the front of the house would have required planning permission). The insulation cost €9,300 with the €4,500 SEAI grant, but it has utterly transformed the house from a drafty cowboy build three bed semi into a warm and cozy house that stays at a constant temperature which will require drastically less energy to heat it for the next 50-60 years of its lifespan. It used to be like a leaky bucket into which we had to constantly pump heat (e.g. money) into to keep heated. Now it's cozy and warm through winter without requiring much heat input to keep it that way.

Heat Pump
A heat pump is quite a miraculous machine. Other heating systems, such as gas boilers, wood stoves and oil fired boilers are 50-80% efficient. That is to say 50-80% of the energy you put into them in the form of fuel comes out as useful heat. Heat Pumps can be 200-400% efficient by virtue of that fact that they are not creating heat, they are simply pumping it in from the outside. For every one watt of electricity you power the Heat Pump with, it delivers 2-4 watts of heat into your house. The result is a heating system which is incredibly energy efficient. Couple it with a SolarPV system on your roof and when the sun is shining, you have ultra-efficient, completely free heating and hot water.

Heat Pumps work the same way that a fridge does, but in reverse. A fridge has a loop of piping that runs inside and outside of the fridge. It uses a valve to compress a fluid inside the pipe inside your fridge. As the liquid becomes more dense, it sucks in heat from the air cooling down the air in the fridge. A pump keeps the fluid moving around the loop. Another valve outside the fridge expands the liquid, and as it expands, it can hold less heat, so it dumps the heat it absorbed inside the fridge outside the back. This keeps the fridge cool inside. A heat pump heating system is exactly the same but in reverse. It uses two valves and an electric pump to pump a liquid around in a loop.

The Heat Pump we installed is a Hitachi R32 Yutaki-SCombi 2 5HP 200L. The Coefficient of Performance (unit of heat energy out / unit of electrical energy to power it) varies with a few factors, such as the outside temperature and the temperature you are heating water to. For 35C water, the CoP varies from 2.7 (outside temp of -7C) to 8.35 (outside temperature of 12C). For 55C water, it goes from 1.85 (-7C outside temperature) to 6.35 (outside temp of 12C). It's listed with an all up CoP of 4.4 here. This is the full CoP table and other specs of the system:


So that means for every 1 watt of electricity our heat pump consumes, it's pumping 4.4 watts of hot water into the hot water tank, or out into the radiators.

[Continued in next post]