In early October 2015, I installed a photo voltaic system for my off grid home (Solar Power System Design Part III), and the plan was to design it in such a way that I can power a chest freezer all year round without a worry. After reviewing different manufacturers and respective freezer models, I concluded that my number one priority would be low power requirements.
As mentioned earlier, grid tied electricity seems to be so cheap that for the vast majority of consumers power consumption is not even of secondary priority. This claim is manifested by the difficulty to find manuals and online specifications that clearly specify average and peak power consumption. Another thing that I cannot grasp is why energy consumption is expressed by a weird and relative Star Rating.
It’s a bit like driving your new car and the speedometer does not specify your speed in km/h but according to a Star rating of 1 to 10…
Anyway, the Danish made Elcold Xtreme Low (XLE) Energy Chest Freezers are not as cheap as other, more popular brands but are unbeaten in terms of power consumption. I purchased the XLE 130 L, in the following product specifications as published by the manufacturer.
Elcold XLE 130 L Manufacturer’s Specifications
- Net Volume = 130 L
- Dimensions (ext.) = 860 H / 720 W / 730 D mm
- Dimensions (internal) = 650 x 450 x 850/650 mm
- Voltage = 220-240 Vac ; Operating Power Consumption = 90 W
- Energy consumption (kWh/24hr at 32 degrees Celsius) = 0.48
- Annual energy consumption (at 32 degrees Celsius) = 177 kWh
- Annual energy consumption (at 25 degrees Celsius) = 157 kWh
- Peak power consumption = not stated!
- Unit must be powered by mains power or pure sine power inverter!
Haier, a popular brand, has two similar products, one with a net content of 105 L and one with 148 L, respectively. According to Energywise, these units have an energy consumption (kWh per year) of 225 and 190, respectively. However, neither Energywise, nor Haier state for what external temperature these values were determined.
The Haier 148 L unit (HCF148WH-2) costs roughly 600 NZD and the Elcold XLE 130 L roughly 1250 NZD.
Factor In Losses Attributed To Inverting and Charging
The losses that occur when inverting DC power to AC power and those attributed to charging AGM batteries are in my case roughly between 30-40 per cent. Another important thing to factor in when relying entirely on solar power are those dark, cloudy and rainy weeks in the winter here on the Barrier.
Battery Bank vs. Operation Time
My 24 V AGM battery bank has a capacity of 390 Ah, and to make them last, I should only use about 20% of the maximum capacity. That means that I only have about 80 Ah at disposal when the batteries are fully charged. 80 Ah at 24 V is about 2 kWh.
At 25 degrees Celsius (nice and cosy inside) the Elcold should require daily about 0.43 kWh. Adding the 40% of losses, I arrive at 0.6 kWh. This means that I can theoretically operate my chest freezer for 3.3 days without recharging the batteries.
My solar panel array consists of four 295 W units, which means that I should be able to operate the freezer even during rainy days via the panels alone. I’ve experienced some dark days when the charge controller states 0.1 A incoming, but on the average rainy day, I receive about 10 % to 20 % of the total theoretical power of the PV array.
In other words, I can operate the chest freezer for 5 to 6 days in the rainy season without draining the capacity of the battery bank below 80 %. AGM batteries can be charged using higher currents than traditional flooded batteries. Thus, in my case, one sunny day in the wintertime should suffice to charge the battery bank completely.
Based on these simple calculations and the fact that I was not able to find reliable power consumption specifications for the Haier products, the decision was clear cut. Pay about twice as much for the freezer but reap the benefits of significantly lower power consumption, and have the ease of mind that I can operate the freezer on PV electricity all year round without discharging my battery bank heavily and/or having to turn the unit off.
Theoretical vs. Real-Life Power Consumption
I am very glad that the Elcold unit uses indeed only 90 W during operation. The operational noise is extremely quiet as well. According to my battery monitor the freezer consumes about 3.8 A at float voltage (27.4 V), which equates to 105 W. It uses about 4 A at night when the battery voltage drops to about 26 V. That is well below 30% loss.
The Big Downside
Unfortunately, oh so unfortunately, Elcold does not specify the peak operational power consumption of its models and of course no one on the Island was able to give me an indication. For stupid reasons and also lack of choice, I assumed that it will just use about 90 W plus the losses inherent to the inverter.
Well, don’t assume, it just makes an “ass” out of “u” and “me”, if you know what I mean.
When the compressor of the Elcold XLE 130 L starts, this unit draws up to 25 A at 26 V, which equates to 650 W. This is a rather big dis-advantage or downside of this unit, even if this high current draw occurs for only 2 seconds (after 2 seconds the amperage drops to the afore-mentioned).
- There is no way that you can know that you require a significantly higher rated inverter than what the manufacturer specifies in terms of operational power consumption. Even a 600 W inverter will not cut it!
- Every time the compressor starts, the inverter has to provide suddenly a lot of power and therefore its cooling fan kicks in.
- Sometimes the fan of the charge controller starts as well.
- The result of this is that there is quite a bit of audible noise. The compressor, the inverter’s and charge controller’s operating fan.
This downside is frankly frustrating. My inverter costs more than 1000 NZD, the charge controller’s cost is similar, and if it weren’t for the peak power surge consumption of the Elcold freezer, their respective fans would never operate. Now, they operate 10 to 20 times a day and that adds up during a year. So yeah, in terms of wear and tear this is a big downside to me.
I mentioned the attributed losses inherent to inverting direct current (DC) to alternate current (AC). It this context, it is important to know that the efficiency of inverters is dependent on performance. A 1200 W inverter is much more efficient when operating at 1100 W than at 100 W.
The big question that I have is: “Why does Elcold not produce freezers that can operate using DC electricity?”
I don’t know for sure, but I would bet that all of these freezers use mains power (AC) and have a rectifier built inside that turns AC back into DC. So yeah, for everyday usage and especially for Off Grid use, these chest freezers could be significantly more efficient if they were also designed to operate using DC only.
I better go and have an ice cream now, you know to cool things down, it is frustrating, we have all the technology for off grid power and the things I am writing here are well known for many decades, yet off grid living remains a challenging compromise. It shouldn’t be!
Last But Not Least
RTFM (Read The F* Manual). I know it is just a chest freezer, but you can damage the unit on day one by plugging it in without thinking! and/or reading the manual.