My colleague said the other day, as I recounted my recent problems with my alternative energy system, “Sometimes I can’t tell whether you’re High Tech or Third World”. At which point I realized that sometimes it takes just a few minutes to go from one to the other.
I’ve learned some important lessons recently about solar power. When we moved into our new cottage I wanted to keep it off-grid. Knowing that getting power delivered to our home by Nova Scotia Power would cost between ten and twenty thousand dollars, I felt that we could do a lot with that money. We began by having a 24V DC well pump installed with a 100W photovoltaic panel and 400 amp-hours of battery backup. The cook stove, water heater and fridge all run on propane and our heat is provided by an oil stove. Since we had 24V available, I ran it into the household wiring (not yet needed for AC) and hooked up lighting using dual 12V fixtures. This worked well for a while.
The trouble began when my brother-in-law – possessed of a million pieces of exotic electronica, most of which he will never get around to using – offered me a free, large capacity, UPS that he thought I could use as an AC inverter.
Lesson #1: look gift horses in the mouth – especially if you don’t understand how they work.
When I tried to test it out, without any AC load, my wife suddenly started yelling something about a fire: It turns out (I’m told) that a UPS scavenges power – when input voltage gets too low, it starts to draw higher and higher current. This is exactly the wrong thing to do with a solar power system. When voltage drops too far you need to disconnect load to save your batteries.
The US National Electrical Code requires manual disconnects and fuses for DC power systems – including solar systems. I don’t know what the Canadian code requires because you can find the US NEC online, but in Canada you have to pay money for a large (and largely unreadable) book to get this sort of important safety information.
Lesson #2: Whether it’s required or not, you need manual disconnects.
Disconnecting an arcing battery cable, while using the fire extinguisher with your left hand, is almost certain to leave you with burns. Fortunately, mine were inconsequential.
Once I got the fire out, I learned:
Lesson #3: always have a spare charge controller.
Buying a new one on a Sunday will cost you $200+ – and it will still be Wednesday before you get it. Waiting until you can find what you need on eBay, you can get it for about $50. In fact, I got a much better one for $75 with shipping. eBay is a wonderful place to shop for solar power products. I recently got two 175W panels for US$1500 (with shipping) which is significantly less than the California renewable power rebate of $4.50/watt (I had thought that the cost of PV panels would never be any lower than the available rebates).
At this stage, we had arrived in the third world, with no water and no lights. I plugged the well pump directly into the solar panel and that gave us intermittent water. When the new charge controller arrived we started recharging the batteries but they had discharged below the “load disconnect” point, so they still couldn’t be used to run the pump or lights at night. It took two days with a backup generator to get them up to full charge.
Lesson #4: keep your mandatory loads separate from your discretionary loads.
The only thing we absolutely need to have electricity for is the well pump. Our new AC system is going to run off a separate bank of batteries and panels, but some of the solar panels will be switchable to the DC system to increase the charging rate on that system. If things get really bad, we can switch battery banks.
The AC system is now almost complete, the batteries are on the way.
Lesson #5: you can buy local (at least here in Nova Scotia).
My batteries are made by Surette in Springhill and actually cost less than alternatives I’ve priced. When it’s operational I’ll publish the designs.