Off grid solar

[deuce22]

Hi.

 

I am just about to start framing the roof and up until now, the plan was to install a gas boiler for heating the property and also the hot water cylinder.

 

I am now thinking of installing solar and I'm wondering if it's actually possible to use solar without mains electric to run everything in the property.

 

Can somebody tell me if this can be achieved?

 

Thanks.

[SteamyTea]

First thing is to go to PVGIS and work out what yield you can expect.

[kommando]

As Steamy says go to PVGIS, look at the Dec/Jan daily yields and see if they will supply all your needs every 24 hrs, assuming you are going to have batteries to retain some of the daytime production for overnight requirements.   

[billt]

Probably not, but it depends where you are, what your electrical consumption is and how good the site is. If you are thinking of replacing a gas boiler with a heat pump you definitely won't be able to do it.

 

I have a sort of off-grid system which is well over sized and it won't cover our winter usage.

 

 

This shows our monthly generation which varies from 115kWhr in December (3.7 kWhr per day) to 1352 kWhr in May (44kWhr per day). That's a 12:1 variation through the year; in fact it would be more than that but quite a lot of potential generation in the summer is lost as it can't be used.

 

This site isn't ideal and you could get more winter power with a site on the south coast with ideal orientation and no shading.

 

The other issue is how long you need autonomy for, IOW how much battery storage you will need. You tend to get several days together with no usable solar in the winter. You will need enough storage to cope with this and hope that you get a good sunny day at the end!

 

For instance, our big array averaged 2.2kWhr per day in late December and didn't get to a reasonable 11.2kWhr until the 9th of January. If you are very frugal and only use 8kWhr per day you would need at least 10 days of storage or 80kWhr and it would probably still not be enough.

 

People who seriously go off grid have a generator to cover winter/dull day shortfall.

[SteamyTea]

Module orientation and altitude is important, especially for winter generation.

Module power is proportional to the product of both the altitude and the azimuth.

Energy is the product of the mean power and the hours of daylight.

 

So two extreme examples, with a south facing, 1 kW_p array.  First is laying flat to the ground, second is 90° to the ground.

Very big difference in winter generation.

 

[deuce22]

Ok, thanks.

 

So it's probably not going to give enough energy for year round living. I was also planning on installing an ASHP and underfloor heating. Would solar be good enough to run the ASHP for heating and hot water? I would then have mains electric for everything else. 

[JohnMo]

Really depends on.

 

How much heat you require.

How much solar you are willing or able to install.

 

If you needed an average of 20kWh a day for heating, in Dec/Jan you would need 620kWh/month. For that around 7kW array assuming your heat pump gives you a CoP of 3.  

 

You would also need additional for hot water.  You would also need UFH so you can bulk charge the floor while you are generating.  Although some days you output will be close to zero, so will need an alternative power source.

 

 

[SteamyTea]

Building on what @JohnMo has said, to run a heat pump, and just about everything else, you need a minimum power.  Just knowing the energy (the kWh) needed a day is of little use.

The usual way around this for off gridders is to store as much as you can/need thermally, then what you need for the rest as electrical storage in batteries.

This runs the risk of double counting usage i.e. need 6 kWh for DHW which can be supplied purely from a resistance heater, so 6 kWh, or purely from a heat pump, so 2 to 3 kWh, what you don't do is say your DHW takes between 6 and 9 kWh.  It takes 6 kWh.

Resistance heaters can be designed to have different resistance, so can be used to take small amounts of power when it is deliverable, rather than only when there is enough power generated i.e. 3 kW.

 

I am not sure what the minimum power input is for any individual make of inverter, but there will be a minimum input.  Worth looking into that as it will set the minimum array size.

Edited July 17, 2022 by SteamyTea

[Temp]

1 hour ago, deuce22 said:

Ok, thanks.

 

So it's probably not going to give enough energy for year round living. I was also planning on installing an ASHP and underfloor heating. Would solar be good enough to run the ASHP for heating and hot water? I would then have mains electric for everything else. 

 

I think its unlikely unless you set out from the start to minimise consumption. If you take off the shelf figures...

 

https://www.mesh-energy.com/insights/thinking-about-installing-a-heat-pump-dont-forget-this-critical-service

 

Quote

Taking an average 200 square metre floor area home built to decent energy efficient standards, the likely heat pump size might be 9-10kW. This results in a 3kW load on the building electrics as well as likely 3kW immersion heater for the hot water.

 

https://www.deegesolar.co.uk/do_solar_panels_work_in_the_winter/#:~:text=According to the Energy Saving,to generate electricity for you!

 

Quote

According to the Energy Saving Trust, solar panels will generate around a 5th of their usual energy production in the winter months.

 

So does that suggest a 6kW load needs at least a 30kW solar array? And battery storage to smooth out supply and demand?

 

I know its possible to do better but isn't going to be something you can just throw together. Might need to start with more insulation.

[SteamyTea]

35 minutes ago, Temp said:

So does that suggest a 6kW load needs at least a 30kW solar array

Depends on the angles.

If, down here, a 1 kW array can produce 38 kWh a day in December, that implies a 6 kW, south facing, vertical array will do.

 

My current usage is 3 kWh a day at the moment.

That will go up to about 20 in December and January.

[Solarexploits]

I would say that unless your home is exceptionally well insulated &/or your energy demands are exceptionally low, then you would be better to accept that connection to the grid is a requirement, but go for something like Octopus's GO tariff, which gives VERY cheap (currently 5p/kWh, expecting that to go up to 7.5p in Oct) overnight leccy for 4 hours (00.30 to 4.30am). If you happen to be on the Siouth coast & have room for a huge array then that would help, but Dec/Jan are always going to be particularly problematic, particularly if panels are covered in snow!

 

I have a 4kW MCS array, installed back in 2011 which has a Solic immersion diverter giving us free hot water for around 8 months & a reduction in gas costs for the other 4 months, obviously associated reduction in all round leccy usage.

I've recently installed 10 x SH 310W solar panels with lead acid solar battery backup & I have more panels arriving soon (240W Renusola). The panels/batteries & inverter are providing almost all my summer usage requirements last bill for gas & leccy combined was £36 & most of that was standing charges!. The rest is mainly cooking costs as I don't have the oven/hob/microwave on the battery system as the inverter won't cope with those loads & charging my EV (of course done on the 5p overnight) During lower solar output months I can use the cheap overnight leccy to charge the batteries, further reducing consumption of grid power when it's expensive

 

I reckon it will defo pay for itself within a couple of years, maybe less given the way energy prices are going!

[Dillsue]

On 17/07/2022 at 12:47, deuce22 said:

I am now thinking of installing solar and I'm wondering if it's actually possible to use solar without mains electric to run everything in the property.

You probably need to get your head round whats involved in running off grid and get the buy in of everyone whos going to use the house. Have a good think about all the things you do over winter and consider if youd be able to do those if youd had a cold dull week when the ASHP has taken virtually everything out of the batteries and PV has put nothing back in. Obviously if youve got your own solar farm and a container of batteries, going off grid is reliably feasible,  but more likely the 50p/day electric standing charge is a bargain for the backup of a grid connection. 

[SteamyTea]

52 minutes ago, Dillsue said:

but more likely the 50p/day electric standing charge

About an extra 300W module every year.

Or, 750 kWh of diesel.

 

I would try and design to be off grid, then do some costings.

Edited July 18, 2022 by SteamyTea

[Carrerahill]

On 17/07/2022 at 12:47, deuce22 said:

Hi.

 

I am just about to start framing the roof and up until now, the plan was to install a gas boiler for heating the property and also the hot water cylinder.

 

I am now thinking of installing solar and I'm wondering if it's actually possible to use solar without mains electric to run everything in the property.

 

Can somebody tell me if this can be achieved?

 

Thanks.

I am in the process of doing this actually, I am grid connected now, but am working towards all loads going off grid by end of 2024, in short, the answer is yes. However, there are lots of caveats but I have worked it all out - just need to find all the kit and start the process. I am going to start with 2 consumer units, 1 will be mains loads, 1 will be off-grid. The first circuits to move over will be lighting etc. with the last loads moving over being the high consumers like kitchen appliances. 

 

The plan is to have have inverters with a backup AC input which can be grid or generator, at first it will be grid until I have a proven track record over a winter, then look at telling the utility where to go.