PV Array Update: SAP Target Met

[FB.]

Despite a very poor summer, my solar array has just met its SAP2009 target - not that we place much weight on the SAP estimates, but at least it's a marker.

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System comissioned: 16-17th January 2012.
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(3.75kW) 15x 250W Kinve KV250-60M - two strings; 7+8.
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(3.6kW) PowerOne Aurora PVI-3600-UK (indoor model).
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Roof slope: 40 degrees.
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Panels facing: East-South-East - both strings.
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Negligible shading from nearby buildings or trees.
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SAP2009 target: 2991kWh per annum.
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Target met: lunchtime 14th October 2012 (two days short of nine months after installation).
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Seasonally-adjusted outperformance relative to SAP: 14% despite very poor summer.

 

[FB.]

System was peaking around 2.5kW output this morning, so with it having been a cold night and having no immediate use for the power, I absorbed quite a lot of it via an electric radiator which lives in the lounge and serves as a booster to the central heating system in really cold weather.

Not the most eco-friendly use of the solar array, but I only receive 3p per kWh exported and have to buy electricity back at 12p per kWh or gas at an average gas cost around 6p per kWh (plus gas heat losses from boiler exhaust gases and pipework, plus electricity for boiler fan and central heating pump making it more like 8p per kWh to heat with gas).

 

[FB.]

....and a simple bit of maths.....

If I spend £30 on a electric 1.5kW radiator (because it is safer than a fan heater, doesn't create air turbulence, doesn't smell from burning dust on the elements and holds its heat for some time after beng used), it would require 167 hours of constant use to pay for itself in "free" electricity.
Given that the heater may have a thermostat, and therefore be off one-third of the time because the heater is up to temperature, that means 250 hours of use to pay for itself - less than an hour a day for a year.

Then adjusting for gas being only about two-thirds the cost of electricity means a 1.5kW heater would need to be used for about 375 hours to pay for itself; about an hour's use, once per day, for year.

Not a bad payback - and arguably a more efficient use of the power than simply dumping all the power into the hot water immersion even when hot water isn't needed.

 

[sedgy34]

get an immersun fitted your export will heat your water in your tank for freeeeeeeeeeeeeeeeee lol

 

[FB.]

get an immersun fitted your export will heat your water in your tank for freeeeeeeeeeeeeeeeee lol

I think about getting one, but I have several reservations:

1. Expensive for what it is - wait a while and prices will come down a lot.
2. Not been around long enough to prove that they're built to last beyond the warranty period.
3. Not enough people giving real-world feedback that they are as effective as the claims.
4. There is a limit on just how much hot water can be usefully heated.

At this time of year, it's probably more efficient for me to dump the electrical power into daytime heating, and have the gas boiler heat the hot water at the same time as the gas-centrasl-heating comes on - just before we get up around 6-7am (no solar power at 6-7am; it's dark) and again around 6-7pm (no solar power; it's dark).
Being ESE-facing, heating the hot water at peak generation time (around 10-11am) means that it has cooled quite a lot by the time we come to use it for showers in the late evening.

So I reckon I'm better to dump spare electricity into heating the lounge during the daytime and let the gas boiler heat the hot water shortly before we actually need it.

If I'm running an electric heater instead of gas, it only needs to be drawing about half its power from the solar panels (with the remainder drawn from the grid), to be no more expensive than using the gas central heating.
An electrical heater also delivers heat instantly to the room that it's in, whereas a gas boiler takes some time to heat the water in the radiators before the room can start to heat up.

 

[Worcester]

Do both...

The immersun has a switch over relay when the hot water's up to temperatuire, put an extra jacket on the tank, irrespective of what you've already got there £15 from B&Q, £9.99 from wickes - it makes a big diiference, use the relay to dump the rest to heaters, it will still go back during the day and check to make sure that the water is up to temperature, so if there is any spare power, the water has the priority

We've installed a few like this already, i.e. additional circuits just for the excess power afterthe water is hot, and hard wired (flex outlets) the heaters, so that some *&^&* doesn't try to plug anything else into the circuit! Dimplex do flat panel 500W and 800 watt heaters, DXLWPxxx or better, the convection heaters PLXxxx range 500W - 3kW make sure you get the ones without the timers! Amazon offfer them at great prices.

As for pricing, well you could always build one yourself: Mk2 PV Controller, with triac | OpenEnergyMonitor

 

[Sunshine777]

The jacket's down to a fiver at Wickes - bargain at twice the price. Installed one a few weeks ago - quite surprised how much cooler the airing cupboard became.

 

[whinmoor]

The jacket's down to a fiver at Wickes - bargain at twice the price. Installed one a few Wickes ago - quite surprised how much cooler the airing cupboard became.

Did it already have a spray foam coating?

 

[Sunshine777]

Did it already have a spray foam coating?

Yes, that's why I'm surprised at the temperature change. It's now barely warmer than the hallway.

 

[bommels]

My 50 litre hot water tank has a thin spray foam coating and had a 180W standing loss in summer. After adding a jacket and some pipe lagging, it is now down to 100W. Modern 200 litre (!) heat stores claim losses as low as 85W....

 

[The Solar King]

My 50 litre hot water tank has a thin spray foam coating and had a 180W standing loss in summer. After adding a jacket and some pipe lagging, it is now down to 100W. Modern 200 litre (!) heat stores claim losses as low as 85W....

I take it by this you mean an hourly loss. Standing loss is normally quoted in kWh/24hrs. it gets proportionately less the larger the tank. The standard for minimum standing loss is now set in Part L (section 6 in Scotland) of the building regs. One thing to note is that the amount of insulation on a sprayed tank can be less for retrofit than new build. This is supposed to allow for the fact the tank would be bigger and may not fit in an existing cupboard. Cased tanks use a different type of insulation and are generally the same size for both new build and retrofit. I have seen unvented cylinders with losses as low as 1.41kwh/24hrs for a 150ltr and 1.8kwh/24hrs for a 210.