solar pv question please help me!

[openspaceman]

 

When the ratio between total generated & exported FIT rates was much higher (43p & 3p) the export portion was not significant. Now that its more like 15p & 4p getting paid accurately for your export is more important. That or ensuring you use more of it onsite.

 

Actually there is not much significance in the change for this device, a quick calculation on a 4kW array suggests that the income from the rates with deemed export at 50% is for early adopters:

 

FIT income 1419

Export income 49.5

own use 198

1666.5

 

Actual export 70%:

 

FIT income 1419

Export income 69.3

own use 118.8

1607.1

 

Late adopters at 50%:

 

FIT income 495

Export income 66

own use 198

759

 

Late adopters at 70%:

 

FIT income 495

Export income 92.4

own use 118.8

706.2

 

Not worth messing with IMO unless you are on a mission to become as self sufficient as possible.

 

 

Using it for jobs that can only be done my electricity is fine. However using it to displace other fuels for a heating function (space or water) is madness.

 

If maximum use is made by scheduling things like washing in the day then it makes sense to do as you say and use the pv output for electrical needs, battery charging would be one.

 

Whilst I wouldn't go as far as to say it's madness to use it to heat DHW there are other reasons it doesn't make sense, the use profile for DHW doesn't match the solar output and tanks are lossy. I heat DHW by gas and that only costs me 5p/kWh so the saving from using the excess electricity isn't the whole 12+3p.

[agg221]

Thats the whole point of the product this thread is about. It ensure that every unit is used onsite every day.

 

Agreed. That was the point I was trying to make

 

Using it for jobs that can only be done my electricity is fine. However using it to displace other fuels for a heating function (space or water) is madness.

 

Take the installation we're looking at - it's the maximum size installation allowed, and facing 190deg, at an angle of 40deg, not shaded, so should generate 3400kWh in a year. We live in a grade 2 listed house, which is currently band E so the FIT is only 6.85p/kWh. We can't improve this to band D to get the full FIT - the measures which are taken into account by the calculation method are things like installing insulated UPVC doors and windows, so even if we wanted to there is no way listed buildings would allow it!

 

We're out during the day, for about 11hrs on average. Over the year, during daylight hours the fridge freezer will use about 150kWh, the washing machine will use about 80kWh and the wireless router about 40kWh. In the daylight hours we are in the television will use about 8kWh and the kettle about 5kWh.

 

We don't have a dishwasher, don't use a tower computer, our cooking is gas and we don't use the lights when it's daylight As such, the total we will use of that which we generate would be under 300kWh, ie less than 10% of that which we generated, so we would need to do something to benefit from the power we were generating.

 

We could sell it to the grid at 4p/kWh, however if we do we will need to buy a different form of energy for heating. Gas is the cheapest at 4.3p/kWh (wood is about 7p/kWh). Also taking efficiency into account, gas systems are about 50% efficient, immersion heaters are about 85% efficient, so the 'real' cost equates to about 6.8p/kWh for gas, i.e. you save about 2.8p/kWh by running an immersion heater rather than buying in gas to do the same job (for comparison, wood is about 7p/kWh and about the same overall efficiency as gas-heated water, so the costs are comparable).

 

Note, I have ignored capital costs in the above - to get more accurate you would need to offset capital costs of the export meter against the capital cost of the immersion heating system, taking into account the depreciation period for both (for simplicity it's probably the same for each, and you might as well assume they last the lifetime of the installation). You would also need to factor in that the extra savings generated by the export meter would relate to the difference between 50% export (assumed) and actual, i.e. not all the electricity generated, while the immersion heating system cost should also factor in only the proportion not already being used, since this is the 'extra' saving you get from installing it.

 

Anyway, that's why if we do go ahead with the installation it will include a unit of this type.

 

Alec

Edited July 14, 2013 by agg221

[carpenter1]

thanks for all the help

 

i still do not understand:confused1: how if the hot water tank is a 3kw, and i am only got 500w spare, does it still only use that? or buy in more to power it?

 

it seems to make sence, as we are not at home in the day.

no dishwasher

or tumble dryer

 

 

also we have only got electric, so got to use it for every thing,

apart from the wood burner:thumbup1:

 

non of this modern gas and oil stuff, we are in the old days here in deep devon

 

thanks

[slasherscot]

if u have all this extra electricity during the day u would be better using Accumulator Buffer Tank Thermal Store linked to our radiators, heat ur home at night

[openspaceman]

i still do not understand:confused1: how if the hot water tank is a 3kw, and i am only got 500w spare, does it still only use that? or buy in more to power it?

 

Just because the immersion is rated at 3 kW if you connect 230V across it it can still work at a lower power if you connect a lower voltage across it. So the device will figure out what you have to spare and only switch the immersion on for part of each half cycle of the alternating current. This effectively modulates the voltage and thus the power delivered to the immersion. In your situation it does seem to make sense but do look at the figures first as you still need to get a return on the investment.

[carpenter1]

is the Immersun the same thing?

any preferences?