Solar Power Calculations

Yes, our current solar system is dying...yesterday was a mostly cloudy day, and when I tried to charge the cell phone in the late afternoon, the batteries were drained almost immediately and the inverter screamed at us.

So, we did the calculations to find out how much power we need per day (in watt hours). For example, the cell phone is .2A which means it draws (at 110V alternating current) 22 watts. It takes about half and hour to charge so that means we need 11 watts for that. The Apple laptop needs 1.5 Amps, again at 110 for 165 watts. It takes longer to charge, but it doesn't need to be charged every day so I allowed 82.5 watts per day for that. Our total daily watt hours turned out to be 245 Watt hours.

Step 2 is to figure out how big a PV system we need to produce this amount of power. For this we take the 245 watt-hours and divide by (3.9 peak sunlight hours *.77) equals 79.28 watts array size needed. The .77 factors in an 85% battery efficiency and a 90% charge regulator efficiency. The Kyocera 135 (our candidate new panel) gives us about double that!

Finally, we need to see how much battery capacity we need. Ideally, we would like enough power stored to last through three days with no charging possible. The number of ampere-hours is (245 * 3)/(12V * .42) or 146 amp hours. The Surettte S460 has 460 amp-hours - so we are way ahead of the game there, too.

We did all the calculations with a book published by Natural Resources Canada in 2002: Photovoltaic Systems, A Buyer's Guide. It was oddly satisfying to get through all this and to actually better understand the system.

It will be great to be able to read comfortably and even sew in the evenings!

The solar4power website has more information about PV systems.

Solar Photovoltaic Systems

For years Before Jan (BJ) Alan came to the cabin for most of the month of August. In those days, no cellphone or laptop was needed (he was only away for a month after all), in August it is light more or less until 8 p.m., and since after dark he would sit in the screened porch drinking beer with friends, lack of electric power was never an issue. Okay maybe he would light a couple of kerosene lamps. In fact, my first year here, I didn't know how to blow out a lamp and burnt my fingers trying to lift the glass chimney. Lesson learned. Anyway, once we retired and started spending several months a year here, I decided I needed a few more creature comforts. The first major new comfort was a propane (only) fridge. The next thing was a way to produce a little light for the evenings -- especially in September when it starts getting dark earlier, the company falls off and I would like to do a little reading or sewing in the evenings.

Our first PV system is a 30W, 2amp panel, as pictured, which goes to a controller (in case of overcharging) then to our two RV 12Volt batteries, and then to a little inverter which changes the Direct Current DC to Alternating Current at about 110 Volts. Total cost of system to us was about $400. This was six years ago and we were thrilled to be able to run a couple of lights (15 watt flourescent) and to charge up the cell phone.

Now the RV batteries are not holding a charge and our power needs have grown -- we would like to be able to charge laptops, cordless drills, camera batteries and so on. We have been working through our needs and have discovered that we need a system that can deliver 146 Amp hours per day. We are considering the Kyocera 135W - just one panel.

First Agricultural Success

The garden has sprouted: first radish, carrot, and lettuce leaves have appeared. I bought some tomato and basil transplants while we were away on our little road trip and planted those yesterday. It was windy with gusts up to an incredible 80K/hr so needless to say the bugs were not a problem.

The fence that Alan put up for me is one width of chicken wire stapled or hooked onto wooden laths. To plant the tomato (and basil), I just unhooked the wire and peeled it back. Works like a charm! So far the varying hares are foiled.

-- Jan

Suffering for the Organic Garden

This is the earliest we have ever made it to the cabin. I love it here this time of year. Right now there is a sea of flowering bunchberry (cornus canadensis) in front of the cabin and I am putting in my first "serious" garden in years. The thing is, you can have cold, windy weather or black flies. This get-up actually didn't even save me. I forgot to tuck in my shirt and they climbed up and removed several juicy bites from my belly (not enough to qualify for liposuction).

This next picture shows me preparing the raised bed by the cabin for the "square foot" gardening technique. It's a windy day so I am not wearing the bug hat. The idea of the raised bed is that it warms up faster and one stuffs lots of organic material into the soil so that it can support more intensive growth. Then you divide the plot up into sections and plant a small number of seeds (or transplants) into each section. We'll see. Whatever happens we will have to build some kind of barricade against the varying hares. Last year they ate everything I planted! I hope to get the rest of the garden planted this weekend and will post a picture as soon as we get the fence up.

---- Jan