There’s lots of discussion right now about ‘Net Zero Energy’ homes – homes that over the period of a full calendar year produce as much energy as they consume from the grid. Energy ‘produced’ typically comes from solar panels of which there are two types, solar thermal (producing hot water) and solar ‘PV’ (producing electricity).
At the end of the year, a ‘Net Zero Energy’ home should be able to demonstrate that the total amount of energy taken off (purchased from) the grid equals (or is less than) the total amount of energy produced from the sun (or from wind in the case of wind turbines). They both cancel each other out, leaving you with ‘Net’ Zero.
The problem here is with the slippery concept of ‘Net’ in ‘Net Zero’. In a climate with short daylight hours and low temperatures in the winter you don’t have to be a genius to figure out that production of energy from the sun will be significantly lower than it would be in the summer.
So, there’s the catch. In the winter we typically use a lot more electricity for lighting, cooking hot comforting meals and heating. Our energy consumption peaks in the winter, just when production from solar (or wind) sources is lowest.
See the problem now with this co-called ‘Net Zero’ home?
In my own (certified Passive House) home between 28th December 2014 and 4th January 2015 (7 days) we consumed a whopping 289 kWh of electricity from the grid, or an average of 41 kWh per day (everything in our home is electricity based, including heating – no gas or oil). That’s a lot, but we had a number of ‘invasions’ over those days including two family feasts catering for 19 persons on both occasions. Plus kids watching endless re-runs of Harry Potter. Plus charging multiple Apple products. Plus, Plus, Plus. Normal Christmas stuff.
Checking my solar PV panels over the same period, the total electricity produced was, wait for it, 5 (yes, five!) measly kWh of electricity, just less than an average of 1 kWh per day.
To recap, we consumed 41 kWh per day and produced approximately 1 kWh, leaving a ‘gap’ of 40 kWh per day. Our not-so-smug-anymore PV panels produced just 2% of what we consumed. Not very impressive and definitely not what you might call ‘living off the grid’.
This ‘gap’ will lessen as the days lengthen and the external temperatures rise. And I fully expect that in the height of the summer, there will be a ‘gap’ of a different kind where we will (hopefully) produce more than we consume. Not that excess production is anything to shout about at least in Ireland, because the utility companies don’t give you a red-cent for any unused energy you ‘donate’ to the public grid. That’s not very incentivising, right?
Don’t get me wrong. I’m a firm believer in using technology on my roof that generates energy from the sun. But we first of all have to figure out a way to reduce our electricity needs very significantly (including building to the Passive House standard). Santa Claus is great, but he doesn’t include electrons in his wish list - every kWh of electricity we consume has to be paid for and this power generates a lot of pollution in its production.
Next year, I’m bringing my clan to someone else’s house for Christmas to reduce my 2015 winter gap ;-)
Happy New Year!