PV Installation Considerations

[FrancisJeffries]

Just had a quote for £8k for a 10 panel 3kw system. Includes 10 year warranty on bits and 20 year on the panels. Inclusive device for switching output to immersion.
Seems like a bit much. [/color]

It does seem a lot. I had 3.25kW (13 panels) fitted last September and they cost £6.5k. the installers reckoned I'd get nearly 3000kWh/year, and that looks likely. The retun on the investment will almost certainly be above 10%, tax free with the FIT at 14.9p/kWh.
You might be interested to know that the initial quotes I got were for around £12k, so it's definitely worth bargaining! I didn't think the switching to the immersion heater (£500 extra) was a good idea because we heat our water with gas, and don't use much hot water during the day when the sun's shining anyway.
My roof is only a couple of degrees off south, and has a 35degree (from horizontal) slope. I didn't go for 4kW because if I did, the end panels would have suffered severely from shading in the morning and afternoon.
Shading is a BIG issue with PV. Even the shadow of a TV aerial mast is enough to really kill the whole array off. It's because a small shadow cuts off many cells (not just the ones the shadow falls on), and the way they have to be connected with by-pass diodes can almost switch off a complete panel!
Installers don't like to admit it, but one I got quotes from said NASA had done tests, and proved it wasn't a problem. They gave me the reference, and so I looked it up, and it did in fact show the bad effects of shading. I'm damned if I can find it for you to see for yourself. I'll keep looking for it.

 

[MikeS]

Quote "I didn't think the switching to the immersion heater (£500 extra) was a good idea because we heat our water with gas, and don't use much hot water during the day when the sun's shining anyway.”

Not sure that makes a lot of sense. Better to use the excess power to heat the water than return it to the grid. Moreover, if you have a well lagged tank and it is heated during the day from the PV then the water should stay plenty hot enough for the evening. I manually switch my immersion on when i am producing too much power and I don’t need to use my gas to heat the water in the evening.

 

[I33t]

Seems the use of immersion heater as loadbank is a result of poor feed in tariffs?

Here in Australia, the immersion heaters are basically outlawed due to their poor efficiency. I think it varies from state to state, but the only way you can have one here is if your old one has died. New installations are a no-no. When ours died (pre PV installation) we swapped from immersion to heatpump: The hot water bill and power consumption dropped to less than 30% of the immersion heater. Our water is quite hard so the immersion heaters used to corrode away pretty quickly. The heatpump does not suffer corrosion problems.

Even if the feed in was low, I'd go heatpump again. Why waste power? I'd pump it to the grid or put in a battery system for lighting etc.

 

[MikeS]

Seems the use of immersion heater as loadbank is a result of poor feed in tariffs?

Here in Australia, the immersion heaters are basically outlawed due to their poor efficiency. I think it varies from state to state, but the only way you can have one here is if your old one has died. New installations are a no-no. When ours died (pre PV installation) we swapped from immersion to heatpump: The hot water bill and power consumption dropped to less than 30% of the immersion heater. Our water is quite hard so the immersion heaters used to corrode away pretty quickly. The heatpump does not suffer corrosion problems.

Even if the feed in was low, I'd go heatpump again. Why waste power? I'd pump it to the grid or put in a battery system for lighting etc.

Different countries, different ways and payments! In the UK we only get 0.03 pence/kw/h for power exported so far better to use if. Also, we get a nominal 50% counted as export whether we export or not as we don’t normally, at this stage, have export meters! Immersion heaters are fairly standard in the UK as an emergency back up (I use a gas boiler to heat my water and house which is still cheaper than a heat pump), so it makes sense to use n existing system to ‘store’ the power. Furthermore, our systems don’t generally have any batteries associated with them.

 

[bishbosh]

We have had pv for a couple of years now and think it's superb. I would absolutely recommend the immersion heater switc, we have now turned or gas off yet still even with the poor weather get nice hot water for free on excess electricity from our solar panels.

We have this installed albeit an older version... http://www.immersun.co.uk/

 

[I33t]

Different countries, different ways and payments! In the UK we only get 0.03 pence/kw/h for power exported so far better to use if. Also, we get a nominal 50% counted as export whether we export or not as we don’t normally, at this stage, have export meters! Immersion heaters are fairly standard in the UK as an emergency back up (I use a gas boiler to heat my water and house which is still cheaper than a heat pump), so it makes sense to use n existing system to ‘store’ the power. Furthermore, our systems don’t generally have any batteries associated with them.

You get 50% assumption of export with no metering? :shock:

I guess it then depends on the possible uses for your excess power, to make the best use of it, you'd want to use it in the most efficient way. Houshold systems don't have batteries associated with them here either, but the more dollar and energy concious here use excess daytime power to feed a small battery system to run lighting and low power devices overnight. You can buy packaged systems for these purposes here now, here is one example: http://www.aussiebatteries.com.au/complete-power-kits/solar-powerhouse/280ah-complete-solar-battery-powerhouse

These systems have sprung up since the feed in tariffs have dropped to 8c here, not a lot more than yours unless you really mean 3/100 of a pence? If they pay a feed in so vastly short of the price charged per kwh then people will always be looking for ways to timeshift excess power into a time period when the PV is not outputting. Hot water is a good solution, so are the battery solutions.

 

[Bunter]

Mike's post was slightly wrong. In the UK we get 3.3 pence (approx) per kWh not 0.03 pence. This part is calculated on 50% of the energy produced and is in addition to the FIT we receive per kWh of energy produced. The later is paid regardless of where the energy goes. The rate people receive for this varies depending on installation date, older install receive maybe 3-4 x the rate that new installs get.

Regards

Bill

 

[I33t]

Ok, that all sounds confusing!

What happens to your meter, does it spin backwards? When our PV was first installed, we had to wait for the import/export meter to be installed for a couple of months. It was amusing to watch it going backwards, and the look on the meter reader's face when he came to read it in the middle of a sunny day was hilarious. I think he was going to report it faulty until we pointed out the large red PV notice on the meter board.

The meter was read about 6 weeks after the PV was installed, so we effectively 'unbought' all of the power used since the last bill. The calculation between that read and the read when the new meter was installed wasn't as beneficial (they created a pro rata bill) but the time period was very short and we didn't feel the need to fight the bureaucracy on that one.

 

[MikeS]

Yes correct the export rate is 3.3 pence per kw hour. My bad typing when I transferred the info from my spreadsheet. In general we don’t have export meters in the UK so we get a nominal export rate of 50% of production. Given the set export rate and the minuscule 3.3p then there is no benefit is returning the power to the grid. Using it to heat water is probably the most efficient option as it costs a lost of power to heat it and the heat (and hence the energy) can be easily stored in a suitably insulated tank.

P.S. No our meters should not go backwards unless you have avery old one….