The motel solar power system has now been successfully installed. I’m able to log in to my inverter system (through Enphase Enlighten) and get a near-real-time reading of the energy consumption versus production through the solar panels. This reading quickly threw up an unintended side effect, which is that the motel solar system is producing way more power at present than the original estimate.
While the original forecast of power production (based on setup and regional factors, using NIWA data) was 5.148 kWh per day for the system, the actual production that the system is returning is around 56 kWh per week, or around 8 kWh per day, about 55% more than estimated.
No doubt this is somewhat seasonal, and it’s not the worst problem to be having. But it is slightly annoying, in that each day I’m returning a large amount of energy to the grid that doesn’t offset our household energy use. Because we’re not with a retailer who allows us to sell power back to the grid (doing so would force us to switch to another retailer), all of this surplus power is essentially going to waste. So I came up with a pretty creative way to get more bang for our buck from daytime solar power production.
What’s Cooking
I used to be a huge fan of the slow cooker, back in the days when I was working long hours in a sales job and had very little time left in the evenings to prepare meals. While people from various sectors debate the overall energy efficiency of a slow cooker compared to other cooking means such as an oven or electric element, there’s no doubt in my mind that slow cookers are more time efficient, given that you can spend about five minutes chopping some ingredients, and then just leave them to stew for 10-12 hours until you’re ready to eat. You can then enjoy a glass of wine in the evening and do some reading instead of hustling through a kitchen.
Solar systems are great because they can produce a fairly large amount of practically free energy to cover daytime consumption during sunlight hours. But their limitation is the movements of the sun and the clouds – unless you have a battery to store power (which generally isn’t economical), they only supply power during daylight hours when the sun is up.
The other limitation is that they supply only a constant stream of power – anything in addition to this needs to come off the grid. Because ovens and electric elements generally consume energy in short, sharp bursts, they really can’t be powered by a solar power system – additional amounts of energy will almost always need to be drawn from the grid.
I think that this reading kind of demonstrates the situation. The above chart is based on a reading of my inverters on a day when I had the slow cooker making stock in the morning and then a batch of soup in the afternoon – which the solar power system could easily handle. The two heavy orange bars at around the 5.30pm mark are where I decided to fire up the oven and the element to make some garlic bread. The intense burst from these appliances led to a huge over-consumption of what our panels could produce at that time of day, leading to us draw around 0.8 kWh from the grid in less than 30 minutes. This is an anathema to the solar philosophy – using low and slow amounts of energy over a longer timeframe – and means that the more concentrated energy appliances used for cooking effectively can’t be powered by a solar system.
My general view is that evening cooking probably consumes at least 2.5-3 kWh per household per evening. Not only is this a fairly large amount of consumption during peak peak evening time, which is bad so far as environmental efficiency is concerned, it also occurs at a time of day when solar power production is at its weakest. With a little bit of planning, you can use a slow cooker to take pressure off the grid at this peak time of day.
I won’t go into specifics about the recipes I used – there are plenty of them out there on the internet and in libraries. But the suitability to a solar power system was interesting. Most slow cooker recipes take 6-8 hours on low to cook, or 3-4 hours on high. According to my ammeter, the slow cooker uses 154 watts on a low setting, and 306 watts on high setting. This was perfect for me – on a cloudy day the 1.5 kWh system was bringing in around 150 watts surplus energy per 15 minutes, and during sunny day it was bringing in up 300 watts surplus per 15 minutes, so using a slow cooker manages to eat up around 25-50% of this available usage, and I can easily adjust the settings if I need to. That gave me a nice margin of safety for additional appliances, just in case I was worried that I ran the risk of ever having to actually pay for my electricity use during daytime. Most importantly, the slow cooker uses energy gradually over the span of a day, meaning that virtually all of that energy could be fitted in to our surplus solar power production.
As a result of this 5 minutes of “analysis”, I began migrating all of my daily meals over to the slow cooker. I generally like to eat my food fairly early in the evenings, and if we can get the daily cook out of the way using no net energy, then I’m pretty happy with that.
Below is a contrast of the energy consumption pattern from a solar panel before I started using slow cookers versus after:
Before the Slow Cooker:
After the Slow Cooker :
The two screenshots are taken on different days with different amounts of power generated. Nevertheless, notice the much gentler level of power consumed in the evening time with a slow cooker cooking gently across the day (and powered exclusively by solar). This is because the use of cooking elements and ovens is one of the primary drivers of evening power consumption.
Perhaps the most interesting thing about switching to solar is that it begins to reshape your whole life around energy efficiency, beginning with learning your basic energy consumption patterns, to actually designing power use applications that maximise your energy use efficiency.
Now that I’ve discovered this application, I can’t help but think of additional ways to extend it. Perhaps my next blog will be about a solar powered restaurant or even a food truck powered entirely by solar?
