An Anniversary!

Today is the anniversary of the installation of solar panels at Montoya Mansions!

In my first year, I have generated 1636 kWh. This is comfortably more than the predicted 1400 kWh for my first year's production, and alters the payback threshhold in my favour: if the price of electricity exceeds 14.042 p per unit, my solar setup has cost less than the electricity it will generate over 25 years (accounting for deterioration).

The timing of my feed-in tariff payments has fallen nicely, such that each payment is due almost exactly halfway between an equinox and a solstice; thus, they correspond to the seasons as counted by duration of daylight. My first payment was £117.75 on 3 August; then £73.88 on 3 November. The sun could barely be bothered to rise in Winter, leading to a dire £29.12 on 3 February (although it still more than covered the £1.82 per week standing charge). Come 3 May, I expect to receive another £70 or 80 for the Spring (this payment and the Autumn one should be fairly similar, by symmetry: the graph of day length vs. day of the year is sinusoidal).

When I get my storage batteries and UPS plumbed in, I should be able to save even more, as I won't need to pay for all the electricity I will be using in the evening .....

You can't run that from batteries!

Recently, I have managed to acquire a used, APC 3000 VA uninterruptible power supply – minus batteries.  (APC branded battery packs cost almost as much as a new UPS.  Generic sealed lead-acid batteries of the same capacity can be bought from the likes of http://www.tayna.co.uk/ for a fraction of that.)  The UPS is basically a self-contained battery pack, charger and inverter.  It converts DC from a bank of batteries, which are ordinarily kept charged from the mains, to AC when the mains fails.  I plan to use this, in conjunction with a bank of large batteries, to implement a solar energy storage system.

Now I have managed to pick up some batteries.  Although they are not the right ones for this UPS, they are "just about" compatible – the right voltage, but the wrong capacity  (there would normally be two series chains of four 12 V, 5.5 Ah batteries, in parallel for 48 V / 11 Ah; I have just one series chain of four 12 V, 7 Ah batteries, for 48 V / 7 Ah).

These batteries are rather used, and have a remaining usable capacity somewhat lower than advertised – but they cost nothing, which is always a point in favour.

And of course, having some batteries, we can test out the UPS!

You can see clearly that these aren't the right batteries -- I have had to stand the battery tray on top of the UPS because these are too tall.  The lamp was from an earlier test; look out for the black extension lead heading off the bottom left corner.  The 4-way extension lead is fitted with a "C20" plug for the UPS output (which can be up to 3000 VA, which is more than the usual "C14" / kettle-type can handle.)  The other end goes to .....

This microwave oven!  It's cooking just the burger from a microwave cheeseburger.  I toasted the cob separately, and added my own special tomato and herb sauce.

I was worried that the microwave would pull down the battery voltage far enough to trip the undervoltage cut-out in the UPS –this was what happened with a 2 kW kettle.  Fortunately, the slow-start action of the magnetron filament heating up was enough to allow the UPS batteries to recover.

This is a good sign.  And the nice people at http://www.tayna.co.uk/ are very helpful.  They certainly know their batteries.

POWER!

My Asterisk server packed up two weeks ago and I've only just got round to installing its replacement.  (By the way, telephonistas: If you install a version of Dahdi that is too new for your Asterisk version, you'll need to rebuild Asterisk.  The clue is to rerun ./configure and make menuselect.  If chan_dahdi is XXX'ed out, you need a new Asterisk.)  Of course, it did more than Asterisk; it also published the telemetry data from my solar panels, so I've been unsure of how much I've been generating at any given time for a fortnight.  The generation meter next to the fusebox has still been clocking up the units, of course, but I've been too slack to read that.

This is actually low-carbon cooking!  The small burner uses 850 watts.  At the time of cooking, the inverter output was of the order of 1.5 kW.  All the electricity needed to run the hotplate was coming from the sun; therefore, the process of cooking generated no CO₂.  Using the gas cooker would have generated some CO₂, but less than generating electricity plus waste heat in a power station, then sending it over a lossy transmission network to heat the electric hotplate.

But also while the sun has been shining, my thoughts have been turning to .....  POWER!  While I'm doing nine to life, selling my brain to The Company, I'm doing nothing with several kilowatt-hours of energy.  Now, I get paid for them; but, due to the way the installation is carried out, I would still get paid for them even if I used them myself instead of electricity I was paying for.  Which is equivalent to getting paid double!

What I am on the lookout for now, is a 3 kVA UPS  (the biggest thing it has to be able to run is the washing machine, which asks for 2.2 kW when heating the water.  I can do laundry in the dark if I have to)  and four nice big leisure batteries  (this size UPS takes a 48 volt battery pack), plus a suitable charging arrangement.  Now here it gets interesting.  A small leisure battery is 50 Ah.  At 48 volts, that's 2400 Wh.  Even with a conversion efficiency of just 85%, which is almost certainly a pessmistic estimate, that's still just over 2 kWh.  Enough for 2 loads of laundry on the trot, anyway.

It's the Big Day!

My solar installation team have arrived and now they are getting stuff ready.

(I should have posted this just after 09:00 yesterday, but events sort of conspired against me.)

Anyway, all was up and running by 16:00; and the last couple of hours of daylight produced 0.45 kWh of electricity.

I have also learned that the human eye is utterly lousy for measuring light intensity. But I guess that's why cameras have exposure meters .....

Solar Payback Calculator

The "important solar calculation" below has been turned into a handy online calculator.  You can access it here.

Once you have had your site survey, you will receive a quotation for the installation and an estimated annual generation figure.  The brochures for your panels will include figures for degradation in performance due to ageing.  With these figures, you can determine the system output over its lifetime; and thence the equivalent cost per kWh treating the purchase of the generating system as a single bulk purchase of electricity.

Latest Developments on Solar Project

I now have my Energy Performance Certificate.  Montoya Mansions has earned a "D", 59 points.  Things like "energy saving light bulbs throughout"  (since 1996, for the record -- Ed.)  and "biomass secondary heating"  (my gorgeous log burner in the living room)  helped.  Solid walls, and only 100 mm. of loft insulation under the boards, did not.  Also, not having a room thermostat  (which I could leave cranked up to 30 all the time anyway)  on the  (non-condensing, but pilotless)  combi boiler counts against me, despite there being no suitable location for a room thermostat and all radiators having thermostatic valves -- but this is what happens when you prioritise box-ticking above thinking.

I also have my application forms for the feed-in tariff  (which I will need to send off as soon as I have the installation certificate),  a confirmed installation date for the solar panels, and a mini-statement from the cash machine shows that the cheque with which I paid the deposit has been cashed.  Things are moving forward .....

Solar Power: The Important Calculations

When deciding whether installing solar panels is worth it financially, you need to consider the system as a bulk purchase of electricity:  for the up-front price of the system, you are effectively getting all the electricity that it will generate over its lifetime.

The panels are reckoned to last for 25 years; after which time they will still be producing 0.8 of their rated capacity.  The inverter has no moving parts, so that should also last the 25 years.  Meaning, I will have paid just £5049 for all the electricity I am going to be producing over those 25 years.

Is that going to be worth it, compared to the price of electricity from my supplier?

My installer's  (pessimistic)  estimate is for 1400 kWh per year -- it probably will be more than that, in real life.  So over 25 years, that is a total of 35 000 kWh.  For £5049.  That works out at £0.144257143 = 14.43 p per kWh, which is less than I'm paying right now.  (I could do the calculation accounting for reduction in output, but I know that the installers' estimates are on the low side anyway.  Oh, all right.  At 25 years, the output will be 0.8 of what it is now; 1120 kWh/year.  £5049/25 for 1120 units is £0.180321429 = 18.03 p per kWh.  Due to the way this is decreasing, the most accurate average is the geometric mean -- the square root of the product.  So 16.12p.)

Even if the price of electricity doesn't go up, I am still going to come off better out of this deal :)

Montoya Mansions is going Solar Powered

Montoya Mansions is to become solar-powered!

I've had a very reasonable quotation to install solar panels on my roof.  They will be able to fit a 2kW system  (eight 250W panels)  in the clear space available  (the space immediately next to the chimney is unusable, as it would be in shadow in the afternoon; and the chimney is very much in use, for disposal of combustion products from my wood-burning stove).

Although the amount I am going to be able to generate is  (I hate to admit)  rather less than the amount I use, it is still worth it.  Electricity isn't getting any cheaper.  Even if the price per kilowatt-hour stays the same, the system should have paid for itself within 11 years.  And sooner if it goes up; since I'm effectively paying in advance for as much electricity as can I generate.  Whatever I generate and use, I won't have to pay for.

And if I can somehow reduce my consumption to the level of what I can generate, then I'm going to be up on the deal, since the rebate is paid on the assumption that you use half yourself and export the rest.

Anyway, having paid my deposit, there is now a statutory cooling-off period of 7 working days before they are allowed to begin the installation work; during which time, I am free to change my mind and ask for my money back.  The clock is already beginning to seem to take a long time between ticks .....

Watch this space for news.