Power Update

I’ve had several folks ask about our solar power system and so decided to add to what I’ve already posted

We are learning more and more about our Solar Power System. And with the longer daylight hours as we work into spring the system is working very well. June and July were a bit “dark” and we had to run the backup generator a few times, I think around 6 times each month for 2 or occasionally 3 hours per day. The generator is rated at 4.5 kw, but we were unable to get more than 2.3 kw into the batteries, although when I added a separate load the engine seemed to carry an extra 2 kw without issue.  The inverter that runs the batteries is programable, and I had it set up to allow an import of around 3.9 kw, but as mentioned we were only getting a bit over 2kw. Then I noticed that the generator frequency drooped to 47cps when connected. It should be 50 cps. And I found the engine governor was just a simple spring, and un-adjustable. So a bit of fiddling and a second over-ride adjustable spring, and voila, we had 52 cps and a steady import into the batteries of 4 kw.

We have run the engine for 110 hrs since 1st December. However had it been running as it should been then that would be actually been around 75 hrs or somewhere about 6 minutes per day. And since 2nd August we haven’t run the generator at all. So all in all the system is performing better than my initial research indicated.

Today is quite grey. No sun at all with high overcast. We were at 65% state of charge (SoC) at 0830 this morning, and just stating to show a charge. Batteries were full at just after 1230. On fine sunny days at this time of year we are getting positive charge over and above basic usage at around 0745. Battery SoC of 75% by 1130 with the panels putting out 9kw.  6kw going into the batteries, and 3kw being diverted into our hot water cylinder.

We have discovered that our little voltage sensitive relay which I set up to divert power when battery voltage reached 54.4v which sort of correlated to a  SoC of 98% on fine sunny days was actually diverting  sometimes at 75% SoC.   With a high rate of charge the battery voltage is significantly higher than with a low rate. And that allows better use of solar generation on fine days.

A  retro fit is never the best way to go Solar. Much much easier to design and do as a complete new build. And I’ve been asked about with what we know now how I would go about starting from scratch.

1.  I would align the roof east/west, with an asymmetrical pitch optimised for mid winter
2. The roof itself would possibly be Tesla Tiles, but would be as large an area with panels as possible. A house the size of Sails Ashore would fit at least 30 kw. This is way over what we would need for summer, but with what we’ve learned this winter would allow us even on the darkest days some 30 kw hours of usable energy over our current daily needs.
3. I would install at least 36 hrs of battery storage …. we have just over 24 hrs storage.
4. In the cellar I would install a very large, heavily insulated water tank. Perhaps as large as 15,000 litres. This would be heated by heat pumps using the “extra” energy. As heat pumps will produce around 2.5 times the amount of heat that a conventional electric element does the system would have a potential of at least 60 kw storage generation, and thus become a heat sink storage system for domestic hot water and central heating.
5. And really into the dream department. For a vehicle I would look for a plug in hybrid with the ability to act as a back up power source for the house (V2H or Vehicle to Home). A suitable hybrid seems to have around 30 to 40 k battery range, and we only very seldom would travel that far in a day, and in addition the vehicle could act as an auxiliary generator if all else failed.

Expensive. Of course it all is. But having cut our heating and hot water diesel consumption in half the return on investment for us looks  to be around 12%. Spending nothing at all on energy would certainly make it well worth a very close look at the above suggestions.

I’m always happy to answer any questions readers might have

We have links to all our Solar Power Posts etc on our “Solar Power & Environment” page