Designing a small Solar Power Cost effective Power station designed to run a small domestic refrigeration Freezer at high latitudes is proving to be difficult. Compromises have to be struck due to the main problem of a total lack of sunlight during the winter months and an over abundance of sunshine (by comparison) during the summer months.

The idea was to run a 8 cubic feet Freezer in the garage using a 240 Watt PV array, a MPPT solar regulator and 200 Ahr Battery with a 350 Watt Pure sine wave inverter without getting into some seriously ridiculous expenditure.

The Freezer is going to be a Vestfrost SE255 A++ 9 ft³ Chest Freezer.

http://www.alexanders-direct.co.uk/acatalog/Elcold_Glass_Lid_Freezers.html

I have decided against DC Refrigeration operation as AC would be more flexible (Grid power will still be needed during the winter months and it also reduces DC cabling costs i.e. more flexibility over where the PV station and the Freezer are to be sited and the additional summer PV generation means I can also run other devices such as a large panel LCD TV, lighting or a computer etc during the summer months due to the solar energy excess)

Solar inputs/power availability can be calculated over the year from this helpful tool;

http://re.jrc.ec.europa.eu/pvgis/apps/pvest.php?lang=en&map=europe&app=gridconnected

and I put the data generated into a spreadsheet. The areas in Red background show the deficit between the load and the supplied energy available.



The conclusion is that the Freezer can only be run for 8 months of year off grid. Is a partial off grid solution just to much of a compromise?

So it seems you should run the fridge off solar when you can and in the summer months use the solar to run your TV or other lower power demand stuff. Whatever electricity you make and use is electricity you don't have to pay for.

One other thing, can you make changes to the fridge? Maybe wrap it in more insulation and add a small fan blowing across the evaporation coils to make the fridge more efficient?

-Blast

You can add insulation to help with efficiency, but make sure you don't cover the condenser coils or cover the area of a skin condenser if the coils aren't readily visible. Find out where your refrigerator or freezer dissipates heat before you add extra insulation or you may reduce its efficiency.

Another way to improve the efficiency of chest freezers that many people are reporting success with is to stack foods within as close as possible and fill empty space with jugs of frozen water.

Questions:

In winter, is the ambient temperature low enough in shade to allow frozen stuff to remain that way outside or in an insulated space [is a freezer needed in winter]?

Will the place be continuously occupied in winter [is there a need for continuous freezer storage throughout winter]?

Can the occupant(s) do without frozen food during winter [can a shift in diet habits substitute for frozen foods during winter]?

Does the cost of grid power versus adding more solar breakeven over any reasonable time [is it practical to increase the solar to be viable in winter]?

Oh yeah, I meant condenser coils not evaporitive coils. Would a fan blowing across these coils help remove the heat and so reduce the overall power equation of the system? Maybe coulped with some cooling fins made of old aluminum scraps. Man, now I wish I had one of the kill-o-watt thingies and a fridge on which to experiment.

-Blast

I used one of those kill-o-watt thingies the other day and saved some about 140 KWhr per year (probably works out to about $35 saving in electricity costs per year) simply by turning down the back light on a 40 inch Sony HDTV. The TV was running at 165W and I was able to get it down to around 95W by adjusting the display settings. No one else even seemed to notice the change even though the TV screen was running just slightly dimmer.

I can also run a WD Media player in 1080 HD with a WD My passport external hard drive using only around 10W (very efficient for a 1080 HD video source)

Just to get some perspective the daily PV surplus in the 4 months during the summer works out around 350-400 Whr in addition to running the Freezer or enough to run the 40 inch Sony HDTV and WD media player for over 3 hours each day.

The Vestfrost SE255 Chest Freezer looks to be already remarkably efficient and is easily run during the sunny summer months using the 240Wpk PV and 200Ahr battery setup. If the freezer which normally has to maintain -12 to -18C (** or *** rating) was operated as a normal refrigerator i.e between 2 and 6C it would be possible to run under these conditions off grid entirely although it might be advisable to increase the battery capacity to cover for the long overcast periods during the certain winter weeks.

Even if the freezer was operating during the winter months on grid and the grid supply failed then it would be possible to keep the freezer operational at -5C (* rating) for at least 7-10 days.

Another interesting article I have come across recently is the Solar Powered PC on Toms Hardware.

Yes, good point! A fan would help. There are a couple of good articles online about using computer fans to blow air over condenser coils like the fan on a car's radiator.

Another way to help in regards to airflow would be to make sure there's good spacing between the condenser coils and the wall or anything else that could trap or hold heat. Some people have moved the condenser coils and compressors away from the actual box so that they could further insulate around the entire refrigerator/freezer

I must admit here that I'm not a refrigeration expert. This information comes from various places on efficiency, off grid living etc.

There are some PCs out now that use <10watts while running.

Unfortunately the monitor will use a lot more!

I just read something very interesting in the Spring 2009 issue of the Permaculture Activist magazine, written by a guy in Australia who uses photo voltics.

The article is titled "A Fridge That Takes Only 0.1 kW a Day".

Fact: chest style freezers contain the cold due to their design. In upright freezers the cold air runs out like water every time the door is opened. So he wondered what would happen if he converted a Vestfrost SE255 chest freezer into a refrigerator.

He bought a $40 battery-powered thermostat equipped with digital temperature display and an internal 5A/240V latching relay. The latching relay consumes battery power only during actual switching so that the thermostat equipped with it is a true micro-power device and its two AAA batteries last for many months.

"Connection is really simple. The thermostat relay cuts the power to the freezer, much like a light switch cuts the power to a lamp. The thermistor (the temperature sensor) is placed inside the freezer at the end of a thin 2-wire flexible cable. I used the freezer drain hole to pass the thermistor cable inside the cooling compartment. An alternative is to insert it from the top via the chest door. If the thermistor is left near the bottom of the chest fridge -- the minimum fridge temperature is controlled by thermostat. If the thermistor is located near the top of the cooling compartment -- the thermostat will control the maximum temperature there. The best position for the thermistor is somewhere in the middle.

"It took me about 30 minutes to make all connections. The most time-consuming part was removing the thermistor from inside the thermostat (I cut it out from the circuit board using wire clippers) and soldering it at the end of a thin two-wire flexible cable. I protected the thermistor from moisture and mechanical damage using shrink-wrap tubing and a tiny bit of silicone.

"The external thermostat can be installed anywhere on the fridge or outside it. I decided to place it on the wall behind the fridge, so that the temperature display is easy to read at eye-level.

"I have also removed the interior light bulb, rated 15 watts, because I avoid using energy-wasting devices as a matter of principle. I will consider installing LED interior illumination if I find a reason for opening my fridge in the dark.

"I set the thermostat to +7ºC (46ºF) and switched on the AC power through an energy measurement gadget called Sparometer. After about two minutes my thermostat displaced +6.5ºC and the power to the freezer was cut off. The temperature continued to drop down to about +4ºC. I thought that there was something wrong with the digital display, because everything happened too quickly. I took another thermometer, and to my surprise, ti confirmed readings of the thermostat.

"... In the first 24 hours my new chest fridge took 103Wh (0.103kWh) of energy. About 30% of this energy was consumed during the initial power up and rearranging of the fridge content... The fridge interior temperature was kept between +4º and +7ºC. The fridge compressor was working only for about 90 seconds per hour. When the thermostat intervened-- the fridge consumed ZERO power. The only active part was a battery powered temperature display.

"Results of my experiment exceeded all my expectations. My chest fridge consumes as much energy in 24 hours as a 100W light bulb does in just an hour... I have never seen a fridge that was SO quiet. It only works 90 seconds or so every hour. At all other times it is perfectly quiet and consumes no power whatsoever."

He uses stacked basket to hold foods, placing the most frequently used foods in the top baskets that slide on the top edges of the fridge walls.

Solar is one of the most difficult areas to get a straight answer on, IMO. People that are very pro-solar tend to be very religious about it. It can work for small scale operations, if you are willing to compromise. But it does not scale well.

You will have to decide if the trade-off is worth it.