Robert Clark Posted July 21, 2019 Share Posted July 21, 2019 Hi Guys Wondering if solar PV is really worth installing in a Passivhause? Our heating requirement is likely to only be about 3kw, so UFH with an immersion heater should cope with that A Sunamp for hot water could be fed from economy 10 electric We do have two electric vehicles, but only do very low milage (guessing 7k combined per year) We travel a lot and are often away from home for a month at a time, maybe 4 times a year Is it worth investing thousands in solar PV and/or a battery system when our energy requirement is likely to be so low? Would apppreciate any comments / feedback Link to comment Share on other sites More sharing options...
scottishjohn Posted July 21, 2019 Share Posted July 21, 2019 7 minutes ago, Robert Clark said: Hi Guys Wondering if solar PV is really worth installing in a Passivhause? Our heating requirement is likely to only be about 3kw, so UFH with an immersion heater should cope with that A Sunamp for hot water could be fed from economy 10 electric We do have two electric vehicles, but only do very low milage (guessing 7k combined per year) We travel a lot and are often away from home for a month at a time, maybe 4 times a year Is it worth investing thousands in solar PV and/or a battery system when our energy requirement is likely to be so low? Would apppreciate any comments / feedback instead of mains connection or as well? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 21, 2019 Share Posted July 21, 2019 32 minutes ago, Robert Clark said: Hi Guys Wondering if solar PV is really worth installing in a Passivhause? Our heating requirement is likely to only be about 3kw, so UFH with an immersion heater should cope with that A Sunamp for hot water could be fed from economy 10 electric We do have two electric vehicles, but only do very low milage (guessing 7k combined per year) We travel a lot and are often away from home for a month at a time, maybe 4 times a year Is it worth investing thousands in solar PV and/or a battery system when our energy requirement is likely to be so low? Would apppreciate any comments / feedback We generate around 6 MWh/year from an array that, if installed new today, would have a net cost of around £5k to £6k (allowing for the saving in roofing cost from having roof-integrated panels). With no FiT, just export payments, and assuming these would be metered and paid at about 5p/kWh, then we would generate a direct income of around £120/year from exported energy. The remainder would be self-consumption, used to charge the car, provide hot water, run the house during the day, etc, during the useful generation months. We often have "zero import" days during the summer, with the whole house running for 12 hours or more from self-generated power, all of which offsets electricity use at peak rate. Without PV we would shift some loads, like charging the car, running the washing machine, etc to the off-peak rate. The value of our self-generated energy is around £540/year, but if we were to load shift some stuff to E7, because we didn't have PV, then that would shift to maybe £450/year. Total saving for us from having PV (ignoring FiT) is therefore around £660/year, but if we didn't have it and shifted some stuff to E7 that would reduce to about £570/year. It still looks as if a PV system could have a payback time of around 10 years or so, which seems to stack up reasonably well, given that the panels should last 20 to 30 years. The investment in a battery system is far less clear cut. At best it might break even in terms of whole life cost, but most probably there would be no saving at all. Still worth doing if you place a value on having standby power in the event of a power cut, though, assuming the battery system supports this (not all do). 1 Link to comment Share on other sites More sharing options...
Stones Posted July 21, 2019 Share Posted July 21, 2019 In terms of payback, it really depends on how much of what you generate you can use. Without diverting excess to DHW or car charging, my experience (and others) of a 3.68 kWp system is that you would use around 25% of what you generate and export the rest. If you can change behaviour and only use appliances throught the day you can push this up. Divert excess generation to heating DHW and you will use more / offset other energy use. Whether it's worth paying for an MCS install vs a DIY install is debatable. The only real benefit to the former will be the ability to claim an export payment when the revised payment scheme is rolled out. That will be a simple calculation - is it worth paying an extra £1K - £2K to get back £100 a year. A smaller DIY system, say up to 2 kWp may well be the optimum size. Don't discount buying second hand PV panels. @ProDave and I did this, and for us, has worked well / brought down the cost of our systems quite considerably. 1 Link to comment Share on other sites More sharing options...
nod Posted July 21, 2019 Share Posted July 21, 2019 This question seems to pop up every now and again I think Dave and Declan answered the question best If you can get the panels cheap and fit yourself It’s worth it But the figures don’t stack up if you use a company to supply and install Our sap producers 7 to 9k install £255 per year saving It would also add 3 points to our final sap rating 88-91 With electric vehicles perhaps a better option 1 Link to comment Share on other sites More sharing options...
Robert Clark Posted July 21, 2019 Author Share Posted July 21, 2019 53 minutes ago, scottishjohn said: instead of mains connection or as well? As well Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 21, 2019 Share Posted July 21, 2019 Another variable to add in to the mix is if your house has a need for active cooling. For the past few weeks some of our PV generation has been powering both the MVHR cooling heat pump and the ASHP in cooling mode. These two combined would cost around £0.18 to £0.20 per hour to run if we didn't have PV. 1 Link to comment Share on other sites More sharing options...
ProDave Posted July 21, 2019 Share Posted July 21, 2019 See my thread here As you will see from that I am on course to see £250 of savings per year so should have a payback of about 6 years. A few points: My system is smaller than Jeremy's and we have some serious shading issues from trees at the moment, something I will start addressing this winter with the start of a pruning and thinning regime. Because I DIY installed it I won't be eligible to claim the new export payment, but at the last count I had only exported less than £10 worth, so in my case it really would not have been worth paying extra for an MCS install just to claim such a tiny amount. @Robert Clark You mention the PV helping your heating. Sadly it won't. At the time you most need heating in the middle of winter, the PV will be producing very little. Our house has a worst case heat input a little over 2Kw provided by a 5KW Air Source Heat Pump. Most of our self usage comes from using the washing machine, dish washer and tumble dryer in the daytime (one at a time) the house base load, timing the ASHP to only heat hot water after 10AM when PV generation is reasonable, and lastly dumping any excess to the immersion heater to further heat the hot water. 1 Link to comment Share on other sites More sharing options...
nod Posted July 21, 2019 Share Posted July 21, 2019 41 minutes ago, ProDave said: See my thread here As you will see from that I am on course to see £250 of savings per year so should have a payback of about 6 years. A few points: My system is smaller than Jeremy's and we have some serious shading issues from trees at the moment, something I will start addressing this winter with the start of a pruning and thinning regime. Because I DIY installed it I won't be eligible to claim the new export payment, but at the last count I had only exported less than £10 worth, so in my case it really would not have been worth paying extra for an MCS install just to claim such a tiny amount. @Robert Clark You mention the PV helping your heating. Sadly it won't. At the time you most need heating in the middle of winter, the PV will be producing very little. Our house has a worst case heat input a little over 2Kw provided by a 5KW Air Source Heat Pump. Most of our self usage comes from using the washing machine, dish washer and tumble dryer in the daytime (one at a time) the house base load, timing the ASHP to only heat hot water after 10AM when PV generation is reasonable, and lastly dumping any excess to the immersion heater to further heat the hot water. Great point This was exactly the point that the Sap guy made he said Nov To Feb forget it Link to comment Share on other sites More sharing options...
SteamyTea Posted July 21, 2019 Share Posted July 21, 2019 (edited) 54 minutes ago, ProDave said: @Robert Clark You mention the PV helping your heating. Sadly it won't. Except you could store the PV energy as thermal energy, then just draw on it when needed. A lot of the time you would not be pulling the maximum 3kW. Remember that you only start importing energy once the load is greater than your PV is supplying. It is not 'either or ' Edited July 21, 2019 by SteamyTea Frigging autocorrect on my kindle. Tiny, useless touchscreen 1 Link to comment Share on other sites More sharing options...
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