If you have sufficient roof space or area within your garden for PV, preferably South facing and little shade, PV will generate electrical energy from the sun for use in and around the home. This will provide some energy all year round, for hot water, lighting, heating and comfort cooling with heat pumps.
Reduce your carbon footprint dramatically
Using PV with heat pumps offsets some of the running costs
Use passive cooling with heat pumps in the summer using renewable energy
Reduce your electricity bills
Generates electricity 365 days of the year
Couple to batteries to increase the amount of self-consumption
In roof, on roof or ground mount systems available
Solar Photovoltaic Systems
Solar photovoltaic systems, commonly known as PV panels, work by producing electricity to help run your heat pump, household appliances and lighting, through a process called 'photovoltaic streaming'.
The electricity is produced via cells, which are made up into panels attached to your roof, walls or ground mounted. Multiple panels are known as an 'array' and an array may have several “strings” which are multiple panels cabled together. The cells are made up of semi conducting material, usually silicon. When light hits the panel a Direct Current (DC) electrical field is created across the layers when light shines through them.
The stronger the sunlight, the more electricity is produced. Photons (light) can penetrate clouds, so energy can be collected even on an overcast day. In full sunlight the cells' strength is measured in kWp (kilowatt peak).
The collected DC power is converted into Alternating Current (AC) via a power inverter. It is then the same standard power provided to your home by the National Grid. The electricity is connected to your home via the inverter and is linked to your electric meter and fuse box. An energy meter will monitor how much energy you are using, and how much is going out to the grid.
Feed in Tariff & Export Tariff – Is PV still worth it?
The Feed in Tariff (FIT) was introduced to stimulate the PV market. It has been very successful in achieving that. The market has grown, albeit with several bumps in the road, and costs for the technology have fallen. In many respects, the FIT has done what it set out to achieve. However, the FIT is coming to an end as of 31st March 2019. At the same time, the export tariff, which is the tariff people get for exporting their power to the grid (even if they don’t) may be also coming to an end (watch this space).
So, is there still any point in having PV installed? Will the industry be better for it? At Hex Energy we certainly believe there is still a reason for having PV and we believe that only the well run and reliable installation contractors have survived the bumps in the road. The cost of the installation has tumbled and with the advent of battery storage and the uptake of heat pumps increasing and let’s not forget electric vehicles, we believe that PV is now in fact even more relevant to today’s energy mix than ever before. PV is now being installed for the genuine reason of using the power and not simply as a return on investment (as nice as that was for some). While a standard residential system won’t send you “off grid” it will contribute to all of your electrical running costs. Using battery storage and also thermal storage with Ground Source Heat Pumps, the power no longer needs to be used at the exact same time it is generated. Time of generation can now be shifted towards the time of use.
Getting the Most from PV
There are also different inverters on the market with different performance and functions. The inverters we use are able to fully optimise the PV system. A standard system of perhaps 16 PV panels for example, may have one or two “strings” of 16 or 8 panels each string. Should just one panel per string be affected by shade such as a TV dish, chimney or tree, reducing that panels power output to 50% then the whole string is impacted by the same amount. The optimisers we use at Hex Energy are arranged per panel generally and so that is like having 16 strings. If one panel has 50% reduction due to shade then the other 15 are still able to operate at 100%. To compliment this, we also fit as standard a Modbus Meter. This enables consumption and generation to be monitored and also enables export power sent to the grid to be limited. This becomes important when Electric Vehicles are part of the household energy mix as there could be opportunities to have a larger PV array on a single-phase supply and so we can generate more power for self-consumption but remain within the limitations of the grid at the same time. This is also an important consideration when looking to implement battery storage.
With any PV system, the peak instantaneous power is important to consider. For example, if a PV system is generating 2 kW, the aim would be to try and manage the house appliances in particular high load appliances such as dishwashers and tumble driers to come on in stages as opposed to the same time. Each one of these appliances could require 2 kW each and so coming on together means they are drawing 4 kW when the PV is providing 2 kW. Only half of the power being consumed is covered by the PV generation if they both run at the same time. If these same two appliances were staged one after the other then 100% of their power requirement would have been covered by the PV.
PV and Heat Pumps
There are several excellent reasons for considering PV panels regardless of the heating system you might have. However, if you have a heat pump, the argument is even more compelling to introduce PV in to your energy provision for your property.
When opting for a heat pump over an oil, LPG or Gas boiler, you are swapping your main energy use of the house (Your space heating and hot water) from fossil fuel to being powered by electricity. Even though a GSHP is extremely efficient, it still requires power to run it. It therefore makes perfect sense to add PV to your property to generate as much PV as possible to contribute towards the power needed to run your heat pump and other electrical appliances.
While PV panels sized sensibly will not power your heat pump entirely due to the main heating season being in winter and PV maximum power generation in the summer, PV will still certainly contribute and the aim for any PV system ideally is to self-consume all that is generated as closely as possible.
It is then even more important to consider the heat pumps instantaneous load, as the heating will be operating for longer than dishwashers and tumble dryers. Again, as an example and using simple maths, if we have a 4 kW heating load in the house for an hour, a 16 kW fixed speed heat pump with a COP of 4 will require 4 kW of compressor input when it runs and will run for 15minutes in the hour to provide the 4 kW of heating energy. An inverter heat pump however can modulate down to 4 kW of heat output and assuming the same COP will have just 1 kW of input power for the full hour. The two graphs explain how the inverter heat pump will use all of the generated power if the PV array is providing 1.5 kW for that same hour whereas the fixed speed set up won’t use all of the power and requires additional grid power.
It’s all about spreading the loads and reducing the peak kW requirement to better match the PV power generated and if needed the battery storage available.
PV and Batteries
Batteries are not new. They have been in small appliances and vehicles for years. What is relatively new is a battery pack of sensible size and cost to store PV power for the home. These “system” sized batteries are now available and becoming ever more mainstream and if correctly sized and applied to residential systems are a cost-effective means of ensuring that your PV system powers as much of your house as possible and not somebody else’s via export to the national grid.
Not all PV systems suit a battery storage system. Smaller PV systems could well generate power that is already consumed in the house anyway and so adding a battery simply adds cost for no real benefit. The aim for us is to identify a suitable PV array and assess how much if any excess power is generated which could be used at a different time and whether it can be stored cost effectively. Furthermore, going for the “standard” PV array and no batteries might prove to be less cost effective than upsizing the array and using storage, by the time installation costs and scaffolding etc are considered. If the power can be collected and used at other times and with management of the peak power using inverter heat pumps and staging of high load appliances it is possible that considerably more of the PV generated can be self-consumed, in excess of 85 – 90% of the power generated. The devil is in the detail and it is the detail that Hex Energy will focus on.
Of course, batteries don’t just have to be charged by PV. With off peak power tariff’s batteries can be charged at night as well on certain tariffs and so even when PV power is low in the day, the battery can still be charged by cheaper electricity from the grid at night enabling overall household electricity costs to be reduced as far as possible to the lowest tariff.
PV Sizing & Modelling
Until now, the tools available for modelling the power generated by PV systems and the amount the property consumes were very basic and to be frank little more than a best guess as to how much self-generated power would be used. People did quickly cotton on to the fact that staging electrical appliances during the day can improve the amount of self-consumption but it was all still a bit of hit and miss guess work.
At Hex Energy we aim to use bespoke specialist software to model the general electrical use based on the living arrangements, i.e. family home, single mum or dad with kids or a working couple out all day. We add in the heat pump’s operation, even car charging times etc to arrive at the hour by hour energy profile of the house. We then apply a PV system to the profile that is created and assess the optimum size of the array to get as close to full self-consumption as possible. We can amend the profile and include battery storage in to the mix too and model the impact to see if batteries are a sensible option based upon your current circumstances.
Clearly, the way the home is used is key to maximising use of PV power but everything we do at Hex Energy including heat pumps underfloor heating and PV is done by design and not rules of thumb.